On a novel class of organic radicals
by Adolphe Wurtz.
Originally published as "Sur une nouvelle classe de radicaux organiques." in Annales de chimie et de physique, 44, pp. 275-312. 1855.
The organic groups that are agreed upon by chemists to exist in their alcohol and ester forms were isolated, as we know, by Kolbe and Frankland. Methyl, ethyl, butyl, and amyl are not purely hypothetical radicals, as we have for so long believed, but they can be separated from their mixtures by different processes. Frankland [1] has prepared methyl, ethyl, and amyl by using zinc to decompose the iodides—that is to say, the hydriodic esters—of methyl, ethyl, and amyl. These radicals form in other quite remarkable reactions which have been described by Kolbe [2]: that is, by electrolysis of volatile fatty acids CnHnO4. If one passes an electric current through a concentrated solution of potassium acetate, acetic acid is essentially split into carbonic acid and methyl.
Butyl C8H9 has been obtained in the same manner by electrolysis of potassium valerate. Using these reactions, Kolbe and Frankland have made a series of composite hydrocarbons that they have named alcoholic radicals, whose compositions they have expressed by the following formulas:
Of late, caproyl (C12H13) [3] and--even more recently--capryl (C16H17) [4] have been added to this series.
One sees from the work of these chemists, that the alcoholic radicals in their free state will display the same atomic weight and molecular form that they do in mixtures. If their alcohols display the following formulas:
then they will be isolated with the same formulas, and in this state, their equivalent will correspond to 2 volumes of gas.
This opinion has not been accepted by all chemists. Laurent and Gerhardt were the first to propose a doubling of the formulas for the alcoholic radicals, such that their equivalent corresponds to 4 volumes of gas, as is the case in all other hydrocarbons. The comparison of boiling points of these radicals has driven Hofmann to a similar conclusion. According to him, one is driven to adopt doubled formulas, considering the large differences in boiling points between two neighboring terms in this series. Butyl, for example, boils at 108°C and amyl at 158°C; the difference between these two boiling points—that is to say, 50°C—will be at least double that which one normally observed between the boiling points of two composite homologs which only differ by units of C2H2. If therefore the true equivalents of butyl and amyl were represented by the formulas:
the boiling points of these hydrocarbons would present an anomaly that would not disappear upon doubling their formulas. This argument rests, as we will see, on purely physical principles. It has not been accepted by Kolbe, who has made the remark that the boiling points rule does not appear to him to be applicable to composites of which an equivalent does not correspond to 2 volumes of gas.
Be that as it may, it has appeared to me useful in this discussion to formulate new fundamental arguments about incontrovertible chemical facts. Let us first pose the question and clarify what is necessary about the double formulas in question: Would they simply represent the hydrocarbons:
that is to say, the homologs of the swamp gas C2H4, as proposed first by Laurent and Gerhardt? No, because these homologs have since been prepared by Kolbe and Frankland and they form, under the name "hydrides," a distinct series of radicals properly state. They represent double molecules, isomeric to hydrides and form true binary groups of which their constitution is made evident by the following formulas:
If we therefore double the formulas of the radicals isolated by Frankland and Kolbe, we thereby express that at the moment they are liberated, the alcoholic groups combine in some way with themselves. Thus posed, the question of radicals touches on the most fundamental points of the new chemical doctrines. We understand its importance and the interest attached to facts that can shed some light on this discussion. Here is the argument that I put forth: If the radicals constitute, in their free state, double molecules, it must be possible to replace an alcoholic group in these molecules with another and obtain therefore a series of mixed radicals. If ethyl is
it must be possible to substitute a radical from butyl alcohol or amyl alcohol for one of the ethyl groups and therefore obtain the compositions:
These mixed radicals do, in fact, exist. I have obtained them in two different circumstances: First, in decomposing a mixture of hydriodic esters with sodium; Second, by electrolysis of a mixture of fatty acids.—Before describing these experiments and in order to have some terms of comparison in the study of these novel combinations, I will report some experiences that I have had with the normal radicals butyl and amyl.
Butyl. — Kolbe has obtained this hydrocarbon by electrolysis of potassium valerate; I have prepared it, as I have indicated in my paper on butyl alcohol, by decomposing butyl iodide with potassium.
It is advantageous to replace potassium with sodium, and not only because sodium is less expensive, but also because it reacts in a less energetic manner with hydriodic esters. When one decomposes butyl hydriodic ester with potassium in a closed tube, as I did at first, explosions often occur; in addition to potassium iodide and butyl, it produces butene and butyl hydride which are gaseous, and which sometimes cause such a sudden and forceful expansion that the tube does not remain intact. With sodium, the reaction is calmer, and it forms fewer gaseous products which are the result of a secondary decomposition of butyl iodide with sodium:
The following procedure allows one to experiment with a considerable quantity of material.
Butyl iodide is placed with a small excess of sodium [5] into a round-bottom flask which has been equipped with a glass cooling coil. In the mantle of the coil, whose weight is supported, ice or water is introduced to maintain a low temperature for the duration of the experiment. The reaction begins in the cold and gives off heat. The sodium is observed to blister and turn blue little by little, resulting in a strange composition first discovered by Bouis. Once this effect is produced, the decomposition typically slows and it is necessary to activate the reaction by heating it with an alcohol lamp. The liquid is held at boiling until the aforementioned blue color has completely disappeared and the flask contains a white mass of sodium iodide impregnated with butyl. Thus marks the end of the experiment, provided that the cooling coil has remained sufficiently cold that the butyl vapors have condensed continuously and have flowed back into the flask. As for the butene and butyl hydride, they are lost via the opening in the coil; nothing prevents one from condensing them if so desired.
To extract the butyl from the mass of iodide which it impregnates, the flask is immersed in an oil bath at 150°C; the butyl is collected via distillation and is dried over sodium. It is observed that there is no longer a trace of iodine as long as the liquid metal remains brilliant and polished like a silver ball. When its surface tarnishes, this is proof that the butyl contains iodine and it is necessary to boil with sodium for a longer period of time. As soon as this product is pure, it is purified a second time and the fraction that distills at between 105°C and 108°C is collected. This is pure butyl.
As a result of my experiments, this hydrocarbon boils at 106°C. At 0°C, its density is 7.057; its vapor density is found to be 4.070. This number is calculated from the following values:
The theoretical density is 3.939, the equivalent corresponding to 4 volumes of gas.
I have tried a number of times to regenerate butyl alcohol from butyl. Up to now, all attempts have been unsuccessful. Chlorine and bromine do indeed attack butyl, but they form substitution products and hydrochloric and hydrobromic acid. It is the same with perchlorides of antimony and phosphorus; the first attacks butyl with formation of hydrochloric acid and chlorinated products of which I have not made an analysis. As for phosphorus perchloride, it is only decomposed by butyl after boiling for an extended period, and it is transformed into phosphorus protochloride at the same time that it forms butyl chloride and hydrochloric acid. Having failed in my attempts to reconstitute a butyl derivative from butyl radical with chlorine and bromine, I have wanted to repeat them with iodine, which, as one knows, has a lesser tendency to form substitution products than other halogens. I have therefore passed iodine and butyl vapor into a tube containing platinum sponge, heated to around 300°C; abundant vapors of hydriodic acid were evolved and a fraction of butyl was transformed into an iodide: I cannot obtain this product in a large enough quantity to be able to decide if it is a substitution product (which is likely) or a butyl iodide.
One can hope that butyl will be cleaved in the presence of hydrochloric acid in butyl chloride and butyl hydride, as shown in the following equation:
but the experiment did not confirm this expectation. Hydrochloric acid did not react with butyl either at room temperature or at temperatures raised to nearly the boiling point of the oil bath.
Amyl. — I have prepared this radical using the same procedure I used to isolate butyl. Amyl iodide is less easily attacked by sodium than butyl iodide. I have not seen the reaction begin spontaneously and without the aid of applied heat. When it is heated, it displays the phenomena which have been previously described. The reaction is ended when the sodium has transformed into a white mass of iodide: after having separated the amyl which impregnates this mass by distillation with an oil bath, the material is purified over sodium and the material that distills over at 158°C is collected.
Amyl is a clean and mobile liquid with an aromatic odor which does not resemble the penetrating odor of amyl alcohol. Its density at 0°C is 0.7413. It expands greatly in heating from 0 to 20°C; such that, at 20°C, its density is only 0.7282. Its vapor density has been found as 4.956 from the following values:
Its theoretical density is 4.907, the equivalent corresponding to 4 volumes of gas.
Here are the results from its analysis:
0.285 grams of material gave 0.880 grams of carbonic acid and 0.402 grams of water.
These values, in percent:
Amyl boils at 158°C. Among the most curious of its properties, one must mention its considerable optical rotatory power. It rotates the plane of polarization to the right, but with a variable intensity; different samples that I examined did not give the same results at all. One can judge by the following numbers, calculated using the well-known formula from Biot:
$$[\alpha]=\frac{a}{l\delta}$$
These variations are observed in amyl alcohol itself, which possesses different rotatory powers depending on the examined sample. Here are the observations that I have made in that regard:
Amyl dissolves neither in sulfuric acid monohydrate nor in fuming sulfuric acid. When it is left in contact for some time with such an energetic acid, it darkens and gives off sulfurous acidic products. Upon contacting anhydrous sulfuric acid vapors with amyl in a cooling bath, I noted that this hydrocarbon was slowly attacked with formation of a black mass and emission of sulfur-containing acidic products. It did not form the conjugate acid under these conditions, as I had hoped; the product of the reaction having been mixed with water and saturated with barium carbonate, the neutral solution thus obtained contained hardly any trace of dissolved barium. Nitric acid monohydrate attacks amyl slowly, with the reagent disappearing entirely over several days of boiling, if one takes care to condense and recapture the vapors which escape the flask. Upon saturation with potassium carbonate and concentration by evaporation, the liquid deposits a yellow material with neutral pH that is only slightly soluble in water and which I have not analyzed. Finally, it becomes a mass formed by crystals of potassium nitrate from which a small quantity of yellow deliquescent potassium salt can be extracted with absolute alcohol. I have not been able to discover valeric acid among the products of oxidation of amyl, but it is not impossible that the yellow salt that I just mentioned is potassium nitrovalerate. I have obtained too little of it to be able to submit it to analysis.
Antimony perchloride attacks amyl, giving off hydrochloric acid and forming substitution products. When one heats this hydrocarbon in an oil bath with the corrosive powdered sublimate , it is reduced at a temperature around 250°C; however, in this circumstance it again does not form amyl chloride, but gives off hydrochloric acid. I am sure, hence, that neither hydrochloric nor hydriodic acid are attacked by amyl, which remains perfectly intact in these gases even at 300°C.
The inertness of alcoholic radicals, and of amyl in particular, is well demonstrated by the manner in which they behave with phosphorus perchloride. This energetic reagent produces no action on amyl at room temperature. When heated, it dissolves in considerable quantity in the liquid, and is deposited by cooling without notable alteration. It is only after prolonged boiling that it attacks amyl, giving off hydrochloric acid and phosphorus protochloride continuously and forming substitution products. I have obtained two chlorinated products derived from amyl, having reacted 2 or 4 equivalents of phosphorus perchloride with 1 equivalent of this hydrocarbon.
1. Seven grams of amyl were submitted to a prolonged boiling with 21 grams of phosphorus perchloride, until the liquid had begun to change color in the flask. The residue was washed with water, dried over calcium chloride, then distilled; the thermometer rose rapidly to 210°C. The fractions that passed between 210-215°C and 215-220°C were collected separately. These two portions were submitted for analysis.
These number give, in percent:
and result in the formula:
The substance analyzed was therefore amyl dichloride, which forms according to the following reaction:
2. Five grams of amyl were submitted to boiling for several days with 30 grams of phosphorus perchloride in an apparatus which permitted less volatile vapors to reflux continuously. The perchloride disappeared little by little, and it gave off hydrochloric acid and phosphorus protochloride. The reaction was interrupted as soon as the liquid began to change color. The product was purified by washing with water and distilling after having dried the product. The fraction that distilled at above 270°C was colleted. It was a neutral colorless liquid, denser than water, insoluble in water, soluble in alcohol, and containing C20H18Cl4. This formula was derived by the following analysis:
0.5835 grams of material gave 0.3605 grams of water and 0.8945 grams of carbonic acid.
Which gives:
The difference that one sees between the calculated and observed values is on the order of what one would expect to encounter for a chlorinated species whose extremely high boiling point was not, as a matter of fact, constant.
It is possible that the constitution of this chloride derived from amyl is expressed by the formula:
and one can hope to obtain the oxygenated radical of valeric acid
by substituting oxygen with chlorine in the preceding synthesis. I have tried to perform this transformation from radical chloride to radical oxide by heating the former in a closed tube with an alcohol solution of potassium. In fact, potassium chloride formed, along with an oleaginous liquid which was separated by adding water to the alcoholic solution. This liquid distilled at around 220°C, but its boiling point was not constant. Nevertheless, it gave upon analysis results that were near enough to those implied by the preceding formula, but which are not correct enough for me to believe that it is necessary to report them.
Ethyl-butyl. — This mixed radical was obtained by the following procedure:
40 grams of butyl iodide and 34 grams of ethyl iodide were decomposed with 11 grams of sodium in the apparatus described above. The reaction began by itself, but soon it was necessary to add heat. At the end of three days of boiling, the sodium was transformed into a white mass in which could still be seen a number of blue points. Upon distillation with an oil bath, it was noted that the thermometer remained for some time between 60 and 70°C. The part that distilled below 100 degrees was collected. From 100 to 110°C, a large quantity of butyl was distilled. The most volatile part was heated with sodium in a closed tube and while the melted sodium remained brilliant, it was distilled again. While the thermometer remained for some time between 60 and 65°C, the liquid that distilled between these temperatures was collected; it formed the largest fraction of the product. After several purifications, a liquid was obtained with a reasonably constant boiling point.
The ethyl-butyl thus obtained is a light and mobile liquid. It boils at 62°C. At 0°C, its density is 0.7011. Its vapor density was found to be 3.053.
Here are the results of the experiment:
The theoretical density of the vapor of ethyl-butyl is 2.972, the equivalent corresponding to 4 volumes of gas. Here are the results of the analysis:
0.316 grams of material gave 0.470 grams of water and 0.9675 grams of carbonic acid.
These numbers give, in percent:
One sees that the analysis and the density of the vapor, as well as the boiling point and the method of formation of ethyl-butyl, leave no doubt about its constitution which must be expressed by the formula:
Ethyl-amyl. — 70 grams of amyl iodide and 60 grams of ethyl iodide were decomposed with 14 grams of sodium; simultaneously in another apparatus, 34 grams of amyl iodide and 27 grams of ethyl iodide were decomposed with 8 grams of sodium. When the reaction was almost finished I added an additional 50 grams of amyl iodide, 40 grams of ethyl iodide and 12 grams of sodium and continued heating while employing the precautions indicated above. By dividing the procedure therefore into three parts, I could carry out a reaction of 154 grams of amyl iodide and 127 grams of ethyl iodide with 34 grams of sodium while avoiding a reaction that was too violent. Having terminated the reaction, the volatile products were separated with distillation using an oil bath. The fraction that distilled below 120°C was collected in part and heated to 120°C in a closed tube, and then very strongly with an excess of sodium. After thus having removed the last traces of iodine, the liquid was distilled into multiple fractions, and a notable quantity of product was obtained which boiled between 87.5 and 89.5°C, with the largest part distilled at 88°C. This was ethyl-amyl.
At 0°C, the density of this hydrocarbon is 0.7069, its vapor density was found to be 3.522. Here is the experimental data:
The theoretical vapor density of ethyl-amyl is 3.455, the equivalent corresponding to 4 volumes of gas. Its composition was determined by the following analysis:
These numbers give, in percent:
We represent the constitution of ethyl-amyl with the formula:
which seems sufficiently justified by the circumstances under which the hydrocarbon is formed. An interesting physical property is found in corroborating this formula. Ethyl-amyl exhibits optical rotation. Like amyl and all amyl derivatives (except for the alcohol), ethyl-amyl rotates the plane of polarization to the right. The deviation effected by a path length of 100 millimeters was found = +0.920°.
This physical circumstance seems to indicate that the complex molecule C12H14 contains the amyl group C10H11. The derivatives of amyl alcohol in which this group is destroyed, such as amylene, valeric acid, etc., are optically inactive. We must therefore admit that the amyl alcohol radical is contained without alteration in ethyl-amyl, and to express the constitution of this hydrocarbon we can only choose between the formulas:
No known fact, no analog supports the last two; as a consequence, we adopt the first as being the simplest and the most accurate.
Ethyl-amyl, which boils at 88°C, is only very weakly attacked by phosphorus perchloride at its boiling point. It gives off hardly any hydrochloric acid, and the perchloride which dissolves in the liquid when heated redeposits upon cooling again. This energetic reagent only significantly attacks ethyl-amyl at a temperature above 100°C, when the two are heated together in a closed tube and placed in an oil bath. I have not been able to study the chlorinated products that form under these conditions, because the experiment terminated with an explosion.
Butyl-amyl. — 160 grams of a mixture of butyl iodide and amyl iodide were decomposed by 20 grams of sodium. At the end of the reaction after several days of boiling, the product was distilled. The largest part of the liquid distilled between 130 and 140°C. But upon reaching the three boiling points of the three radicals (butyl, butyl-amyl, and amyl), a large number of fractional distillations were necessary to yield a product with a constant boiling point. Nonetheless, a certain quantity of liquid was finally obtained which distilled entirely between 132 and 135°C.
This liquid was the mixed radical butyl-amyl, as proven by its analysis and its vapor density. It boils at roughly 132°C with the thermometer immersed in the liquid, and roughly 130°C with the thermometer immersed in the vapor. At 0°C, its density is 0.7247.
Its vapor density was found to be 4.465. Here is the experimental data:
The theoretical vapor density of butyl-amyl is 4.423, the equivalent corresponding to 4 volumes of vapor. The composition of this hydrocarbon is established by the following analysis:
0.297 grams of material gave 0.422 grams of water and 0.919 grams of carbonic acid.
These numbers give, in percent:
and imply the formula
Butyl-caproyl. — I have obtained this mixed radical by electrolysis of a mixture of potassium valerate and potassium oenanthylate. 100 grams of pure oenanthylic acid were mixed with 120 grams of valeric acid, and this mixture was saturated with pure potassium carbonate. The concentrated solution was placed in a test tube and decomposed with a current from a pile of six Bunsen elements. As recommended by M. Kolbe, the electrolysis liquid was carefully maintained at a temperature of 0°C. It is necessary that it be slightly alkaline, for if it is neutral it froths considerably at the beginning of the experiment. The reaction is finished when the evolution of gas has almost entirely ceased: one finds an abundance of crystallization of potassium bicarbonate at the bottom of the test tube, and at the surface of the alkaline solution rests an oily liquid possessing a penetrating odor. This liquid, dried over calcium chloride, was purified. A small part distilled at less than 100°C, another part between 100-140°C, the largest part between 140-180°C, and the final part between 180-220°C.
The part which distilled between 140 and 180°C was boiled with potassium which attacked and retained a small quantity of oxygenated product. Upon fractional distillation, a notable portion of product distilled between 150 and 160°C, where the thermometer increased only slowly between these temperature limits. After a series of purifications two portions of liquid were recovered: one distilling between 150 and 155°C, and the other between 155 and 160°C.
The density of the vapor was determined for these two portions:
The vapor density of the portion distilling between 150 and 155°C was found from this data to be 4.866, and the vapor density of the potion distilling between 155 and 160°C was found to be 4.917. The theoretical density calculated from the formula
was 4.907. One sees from this that the first fraction gives a value somewhat too low and the second fraction gives a value somewhat too high; this seems to indicate that the boiling point of the compound C20H22 is situated around 155°C. [7]
The indications made by the vapor density relative to the composition of the product are corroborated by the results of the analysis itself, which shows that the carbon and hydrogen are in a ratio of 10:11. Here are the numerical results of these analyses:
These numbers give, in percent:
These numbers confirm the formula
indicated by the vapor density; from one angle, if one considers the mode of formation and the boiling point of this hydrocarbon, one is compelled to envision it as a mixed radical, and to express its constitution by the formula
In fact, if butyl is formed from the electrolysis of valeric acid and caproyl is formed from the electrolysis of oenanthylic acid, why can butyl-caproyl not form from the electrolysis of a mixture of the two acids? In the reaction which produces the mixed radical, events occur as if butyl and caproyl had combined in a nascent state. It is not probable that a current with the given intensity decomposes valeric and oenanthylic acid with equal facility; one can suppose that the complex oenanthylic acid molecule is cleaved more easily, all other things being equal, than the simpler and more stable valeric acid. Such is the reason that valeric acid is found predominantly in the electrolysed mixture.
In any case, other products form in the reaction which produces the mixed radical butyl-caproyl. The fraction of liquid which distills at below 100°C, contained a very volatile substance which was probably caproene C12H12. Between 100 and 120°C, a notable quantity of butyl passed, and the less volatile products contained caproyl. I have analyzed the liquid which passed between 202 and 210°C, and I have found the vapor density after having boiled it with potassium. Here are the results of these experiments:
From this data, one finds the value 5.983 for the vapor density of caproyl. The theoretical value is 5.874. The small quantity of liquid which remained in the flask was distilled and submitted to analysis:
0.212 grams of material gave 0.296 grams of water and 0.655 grams of carbonic acid.
These numbers give, in percent:
The caproyl prepared by electrolysis of oenanthylic acid is optically inactive, and I regard it as probable that the amyl formed by electrolysis of caproic acid will itself be inactive.
According to the results above, electrolysis of a mixture of potassium valerate and oenanthylate forms butyl, butyl-caproyl, and caproyl. However, it is evident that the analysis of a mixture of butyl and caproyl must give the same results as the mixed radical butyl-caproyl. To give my experiments on this subject a degree of certitude that this possibility is not allowed, it has been necessary for me, as a result, to take great care in determining the vapor density of butyl-caproyl. It is not evident that if I had used a mixture of butyl and caproyl, that I would have necessarily obtained a value much to large for the vapor density; the butyl boiling at 108°C would have necessarily evaporated and separated for the most part before the caproyl began to boil at around 200°C. Wishing to convince myself of this point by direct experiment, I found the vapor density of a mixture of butyl and caproyl. Here are the results that I obtained:
From this one finds the value 5.420 for the vapor density, which differs notably from the value 4.917 that was found for the vapor density of butyl-caproyl.
Methyl-caproyl. — I have tried to prepare this mixed radical by electrolysis of a mixture of potassium acetate and oenanthylate. As the acetic acid molecule is much more stable than the complex oenanthylic acid molecule, it must be the case that passing a current through the mixture decomposes the latter acid more easily than the former. This is, it seems to me, the reason why the mixed radical only forms in small quantities under the conditions indicated, even when a large excess of potassium acetate is used. I electrolysed over 150 grams of oenanthylic acid with a corresponding quantity of acetic acid, and I only obtained a very small quantity of a liquid that I could regard as methyl-caproyl, but analysis of which did not give very clean results. Upon purification, the oily and odorous liquid resulting from the decomposition of the mixture was recovered from a fraction distilling at below 100°C. This product was treated with potassium and submitted to fractional distillation. The portions of liquid boiling around 60°C and again around 85°C were collected. The first was made up of a very volatile hydrocarbon, containing 85.7% carbon and 14.7% hydrogen. [8] Caproene (C12H12) contains, by comparison, 85.7% carbon and 14.3% hydrogen. Analysis of the second gives the following results:
These numbers give, in percent:
These numbers are much closer to the formula:
than the formula:
The first is confirmed by the vapor density of the analyzed product, which was found to be 3.426
The theoretical density of the compound C14H16 is 3.455.
These experiments prove that the analyzed compound contains the hydrocarbon C14H16, but they show at the same time that this compound has not been obtained in a pure state. In any case, its constitution must be expressed by the formula
The facts exhibited in this paper seem to have put beyond doubt the existence of a novel class of organic radicals, which we call mixed radicals because they contain two alcohol groups at the same time. These radicals are
The conditions under which these radicals form, and their physical properties, among which we note principally the optical rotation of ethyl-amyl, shed new light on their constitution. Moreover, the comparison of their properties with those of normal radicals leaves no doubt about the place that the latter occupy in the series, and as a consequence, about their true equivalent. One can assess them using the following table.
One sees by this table that the values which express the composition, vapor densities, and boiling points of the normal and mixed radicals follow an almost regular progression and establish a sort of harmony between their composition on one side and their physical properties on the other. Though, this harmony is quite natural and is easily explained if one admits double formulas for butyl, amyl, and caproyl
It is evident that one would have trouble attributing the simple formulas C8H9, C10H11, and C12H13 to these radicals.
We arrive at the same conclusion if we compare the modes of formation of normal and mixed radicals. The reactions which produce butyl and ethyl-butyl, for example, do not perfectly agree with the condition for doubling the formula of butyl:
The argument that one can make from the existence, the mode of formation, and the physical properties of mixed radicals relative to the constitution of normal radicals therefore seems to me to be decisive. It is of the same order and as conclusive as the proof that Williamson has furnished in support of double formulas by which we represent the constitution of ethers today, and which is founded, as we know, on the existence of mixed ethers.
We will admit as a consequence, that the normal alcoholic radicals, from the moment they are liberated, double their molecule by combining in some fashion with themselves. This idea of a group which combines with itself does not make sense, if one wishes to attach the old chemical theories to it. One will see from the following developments what novelties it is necessary to attribute to them.
Everyone agrees that the radicals of alcohols can be represented in a manner similar to hydrogen in organic chemistry, and that they play the role of this simple radical perfectly. This analogy which exists between hydrogen and alcoholic radicals permits us—moreover, obliges us—to apply firstly the ideas that we have adopted for their organic congeners. Consequently, if the groups which replace and represent 1 equivalent of hydrogen are doubled at the moment when they are liberated, one can draw from this natural consequence that the equivalent of hydrogen itself is doubled when it is given off from these combinations, and that if the molecule of the liberated radicals is formed by two groups or 2 equivalents, the free hydrogen molecule is equally represented by 2 equivalents. One experiment that I performed over ten years ago seems to me to give a direct proof in favor of this opinion, that free hydrogen constitutes the molecule H2. I noted that copper hydride is decomposed instantaneously by hydrochloric acid with a lively effervescence of hydrogen. As the copper itself was not attacked by this acid, the decomposition of copper hydride would be an inexplicable fact by the ordinary laws of affinity if one admitted that free hydrogen is represented by its equivalent H. In fact, if the affinity of hydrogen for chlorine cannot be overpowered by copper, it should not be overpowered, a fortiori, by copper combined with hydrogen. Since in the first reaction there is an affinity to overcome, there are two to overcome in the second, which seems more difficult. Nevertheless, the decomposition of copper hydride with hydrochloric acid happens with such facility that it should be attributed to a contact force, if one wishes to remain faithful to the old ideas relative to the constitution of simple bodies. If, on the contrary, one views hydrogen as formed from 2 equivalents, nothing is more simple than explaining the reaction in question. It is a double decomposition between hydrogen chloride and copper hydride which forms copper chloride and hydrogen hydride
The idea of representing hydrogen as a double molecule is not novel in science. Nearly 30 years ago, Dumas made the remark in his Traité de Chimie [10] that the atoms of hydrogen and of chlorine were divisible and could be cut in two to form atoms of hydrochloric acid. Ampère had already admitted the divisibility of atoms and had explained the combination of hydrogen and chlorine as a double decomposition. Later, these ingenious views were adopted and developed at length by Laurent in his beautiful Mémoire sur les combinaisons azotées [11]. In any case, it is evident that the idea that hydrogen and chlorine represent double molecules in their free state—hydrogen hydride and chlorine chloride—can be applied to bromine, iodine, potassium, sodium, silver, and other simple bodies. It forms, without a doubt, one of the fundamental points of the new chemical doctrines that can be summarized as:
Simple bodies are constituted, just as composite bodies, by groups of equivalents, and they combine, not by addition, but by an exchange of elements between each other. The state of combination is characterized, not by a union of elements which add to themselves and leave with a more complicated molecular structure, but by substitution of a given group with an equivalent of another. As a result, hydrogen, chlorine, potassium, etc., constitute in their free state molecular groups with a complexity—I will say as compounds—on the order of hydrochloric acid and potassium chloride. This point of view has already been applied to salts themselves. For many chemists, these combinations do not results from the immediate union of the acidic and basic elements, but rather from an exchange which occurs between them.
Truly, this idea that a host of compounds form by way of substitution has been issued and accepted for a long time: it serves as the basis of a theory of types to which science is beholden to Dumas. The preceding propositions therefore only generalize a theory which only at appeared to apply to the origin of a certain class of compounds.
One knows what important developments the discoveries of these last few years have added to the theory of types. They have demonstrated that one can reintroduce organic combinations, and without a doubt also mineral compounds, as a small number of general types represented by substances which are very simple in their constitution, such as hydrogen, water, and ammonia. [12] The substances belonging to the hydrogen type, for example, can be envisioned as deriving by substitution from the double molecule HH in which 1 or 2 equivalents of hydrogen can be replaced by another simple body or by a group. These replacements can happen equally with the more complex molecules water or ammonia. This poses no difficulty: but how must we conceive of the mode of generation of the molecular groups which constitute water and ammonia themselves? Must we envision them as the result of an addition of elements, in the sense of the old ideas, or instead as generated by an exchange of elements, conforming to the principles developed above? The choice between these two hypotheses is unequivocal: since if we adopt the second for combinations in general, the most important of all combinations (water and ammonia) would not be an exception to the rule in this system. We will admit therefore that from the theoretical point of view of their modes of generation both of these compounds are products of substitution: water derives by substitution of oxygen and ammonia by substitution of nitrogen. The following developments leave no doubt about the sense of these propositions.
The necessity of comparing bodies of the same volume has often been insisted, when postulating them to be in the gaseous or vapor state. [13] Since molecular hydrogen H2 corresponds to 4 volumes, it is evident that free molecular oxygen, necessarily corresponding to the same 4 volumes, will be represented by the group O4 of equivalents. If now in the group [O2O2] half of the oxygen is replaced with an equivalent quantity of hydrogen, it results in the group H2O2, that is to say, a molecule of water corresponding to 4 volumes of vapor. In this group H2O2, the two equivalents of hydrogen (forming 4 volumes) occupy exactly the same place that 2 volumes of oxygen occupy in the group [O2O2]. This point of view leads to a powerful and simple interpretation of the phenomenon of condensation that oxygen and hydrogen undergo at the moment when water is formed. One can allow that the 4 volumes of hydrogen which must be substituted (combined) with 2 volumes of oxygen condense to half and that, in this new condensed state, 1 volume of hydrogen is equivalent to 1 volume of oxygen. Therefore, this contraction only consumes the hydrogen which condenses to water, being double that of its free state. That being said, it is understood that water, being connected with oxygen, is itself derived by substitution of the type O2O2, or more generally, M2M2, whereas free hydrogen corresponds to HH, of type MM.
In ammonia, hydrogen finds itself in a more condensed state than that of water; whereas 4 volumes of water vapor contain 4 volumes of hydrogen, 4 volumes of ammonia contain 6 volumes of hydrogen. Now, to explain the mode of ammonia generation, if we allow that this body is derived by substitution of nitrogen NN = 4 volumes, as water is derived from oxygen, we must also allow that in ammonia, nitrogen conserves its condensation state and that the contraction consumes hydrogen, wherein 6 volumes takes the place of 2 volumes of nitrogen in the group NN.
As a result of this, hydrogen is condensed into ammonia three times more than in its free state, and one can also express the mode of generation of this combination in allowing that it is derived via triply condensed hydrogen H3H3 = 4 volumes, in which 3 equivalents of hydrogen would be replaced by the tribasic radical nitrogen = N‴. [14] Ammonia therefore appears as the type M3M3.
As a result of the preceding arguments, hydrogen, water, and ammonia appear as three types MM, M2M2, and M3M3, which have the same general form and only differ in the condensation state of the reacted material. If we represent the condensation state of free hydrogen as 1, it is necessary to represent the condensation state of hydrogen in water as 2 and the state of hydrogen in ammonia as 3. These relations are expressed by the following figures which indicate the mode of generation of hydrochloric acid, water, and ammonia and only represent—for the sake of simplicity—2 volumes of gas or vapor.
One sees that it is easy to account for the contractions observed in experiments with the formation of water and ammonia by supposing that these species are generated by substitution: that 2 volumes of hydrogen take the place of 1 volume of oxygen, and that 3 volumes of hydrogen take the place of 1 volume of nitrogen.
The remarks that we have just made on the condensation state of hydrogen can be applied to other elements. As we know for certain, nitrogen is found in another condensation state: in nitrous oxide, in nitrogen dioxide, and in ammonia. It seems to me to be impossible to account for this fact and not conclude that nitrogen differs in these three combinations, from a molecular point of view. In general, it appears to me that the moment has come to abandon this opinion that simple bodies all come in the same form, the same molecular state, the same equivalent in all their combinations. This idea is accredited to the spirit of an era where neither dimorphism nor isomerism were known phenomena. Today, we know that simple species are not always identical when they are free; can we still allow that they are identical in combination?
That being said, this fact, that only one and the same material can possess different condensation states, is demonstrated for us by examples familiar to everyone. Do we not observe that sulfur vapor at 400°C is observed with a condensation state triple that which is observed at 1000°C, [16] that the vapors of free phosphorus and arsenic have condensation states double that which we assign them in their nitrogen analogs, that liquid cyanogen chloride and methylcyanic ester condense before our eyes into solid cyanogen chloride and methylcyanuric ester And who knows if the remarkable differences of appearance and properties that appear in the modifications of sulfur and phosphorus are a result of different molecular condensations, as we can affirm for the cyanogen chlorides? In all cases, when cyanogen chloride CyCl becomes Cy3Cl3, it changes from type MM which represents the first degree of condensation into the type M3M3, and when the hydride of bitter almonds C14H6O2 transforms into benzoin 2[C14H6O2], it changes from type MM to type M2M2.
As a result of the preceding developments, we can allow the three types
to which, without a doubt, it is still necessary to add others expressing even greater condensations of material. Thus, the second and third type can double and triple to constitute the types
Thus these molecular types, which can describe so many different materials, are linked to each other in the most natural manner by this principle of successive condensations which we have tried to develop.
The following table offers an overview of these ideas. The examples which are cited here show relationships of generation and derivation of a certain number of inorganic and organic species. The second differ from the first only in the complexity of the substituted groups. [17]
Now, if we seek to define the molecular constitution and the form of combination that affects all simple or composite matter belonging to these different types, we recognize that this form is essentially binary, and that it can be expressed by the general symbol or type MnMn. The values that the coefficient n can take express successive condensations of matter. We propose that the condensation state of free hydrogen be taken as unity. [20]
Thus we arrive at a generalization of the idea of double molecules which was at first applied only to a small number of compounds and which I regard as one of the fundamental points of the new chemical theories. Basically, this idea reproduces, rejuvenates in some fashion, this principle of dualism which has been discussed so frequently in the last few years. Binary constitution and combination by the addition of antagonistic elements were at the heart of the old dualism; binary constitution and combination by substitution of elements describes the type of dualism that one can still accept today.
One sees, where some would believe them to be separated by an abyss, that the old chemical theories and the new are not absolutely mutually exclusive. One or another scientist attaches himself to theories which it is customary to represent as at odds with one another, but which are not so in reality. These are the theory of radicals and that of substitutions: the first, freed from incidental ideas, deals principally with groups which one must allow in organic compounds; the second considers the mode of combination. They express, as we see, two different points, and far from contradicting each other, they in fact complete one another.
In closing, I must say that I do not attach any importance to the necessity of the ideas that I have tried to develop and that I am far from considering them as the absolute expression of the truth. In the physical sciences, theories must never aim so high. The best theory is that which embraces the largest number of facts, which accounts for them in the most satisfying manner, and which permits prediction of new observations. The chemical theories which tend to prevail today appear to me to do so: they will be good only insofar as they remain fertile.
Notes
Originally published as "Sur une nouvelle classe de radicaux organiques." in Annales de chimie et de physique, 44, pp. 275-312. 1855.
The organic groups that are agreed upon by chemists to exist in their alcohol and ester forms were isolated, as we know, by Kolbe and Frankland. Methyl, ethyl, butyl, and amyl are not purely hypothetical radicals, as we have for so long believed, but they can be separated from their mixtures by different processes. Frankland [1] has prepared methyl, ethyl, and amyl by using zinc to decompose the iodides—that is to say, the hydriodic esters—of methyl, ethyl, and amyl. These radicals form in other quite remarkable reactions which have been described by Kolbe [2]: that is, by electrolysis of volatile fatty acids CnHnO4. If one passes an electric current through a concentrated solution of potassium acetate, acetic acid is essentially split into carbonic acid and methyl.
Butyl C8H9 has been obtained in the same manner by electrolysis of potassium valerate. Using these reactions, Kolbe and Frankland have made a series of composite hydrocarbons that they have named alcoholic radicals, whose compositions they have expressed by the following formulas:
| Methyl | C2H3 |
| Ethyl | C4H5 |
| Butyl (Kolbe's valyl) | C8H9 |
| Amyl | C10H11 |
Of late, caproyl (C12H13) [3] and--even more recently--capryl (C16H17) [4] have been added to this series.
One sees from the work of these chemists, that the alcoholic radicals in their free state will display the same atomic weight and molecular form that they do in mixtures. If their alcohols display the following formulas:
| Methyl |  |
| Ethyl |  |
| Butyl |  |
| Amyl |  |
then they will be isolated with the same formulas, and in this state, their equivalent will correspond to 2 volumes of gas.
This opinion has not been accepted by all chemists. Laurent and Gerhardt were the first to propose a doubling of the formulas for the alcoholic radicals, such that their equivalent corresponds to 4 volumes of gas, as is the case in all other hydrocarbons. The comparison of boiling points of these radicals has driven Hofmann to a similar conclusion. According to him, one is driven to adopt doubled formulas, considering the large differences in boiling points between two neighboring terms in this series. Butyl, for example, boils at 108°C and amyl at 158°C; the difference between these two boiling points—that is to say, 50°C—will be at least double that which one normally observed between the boiling points of two composite homologs which only differ by units of C2H2. If therefore the true equivalents of butyl and amyl were represented by the formulas:
C8H9 and C10H11,
the boiling points of these hydrocarbons would present an anomaly that would not disappear upon doubling their formulas. This argument rests, as we will see, on purely physical principles. It has not been accepted by Kolbe, who has made the remark that the boiling points rule does not appear to him to be applicable to composites of which an equivalent does not correspond to 2 volumes of gas.
Be that as it may, it has appeared to me useful in this discussion to formulate new fundamental arguments about incontrovertible chemical facts. Let us first pose the question and clarify what is necessary about the double formulas in question: Would they simply represent the hydrocarbons:
C4H6,
C8H10,
C16H18,
C20H22,
C8H10,
C16H18,
C20H22,
that is to say, the homologs of the swamp gas C2H4, as proposed first by Laurent and Gerhardt? No, because these homologs have since been prepared by Kolbe and Frankland and they form, under the name "hydrides," a distinct series of radicals properly state. They represent double molecules, isomeric to hydrides and form true binary groups of which their constitution is made evident by the following formulas:
 |
Methyl |
|
Ethyl |
 |
Butyl |
 |
Amyl |
If we therefore double the formulas of the radicals isolated by Frankland and Kolbe, we thereby express that at the moment they are liberated, the alcoholic groups combine in some way with themselves. Thus posed, the question of radicals touches on the most fundamental points of the new chemical doctrines. We understand its importance and the interest attached to facts that can shed some light on this discussion. Here is the argument that I put forth: If the radicals constitute, in their free state, double molecules, it must be possible to replace an alcoholic group in these molecules with another and obtain therefore a series of mixed radicals. If ethyl is
it must be possible to substitute a radical from butyl alcohol or amyl alcohol for one of the ethyl groups and therefore obtain the compositions:
 |
and |  |
These mixed radicals do, in fact, exist. I have obtained them in two different circumstances: First, in decomposing a mixture of hydriodic esters with sodium; Second, by electrolysis of a mixture of fatty acids.—Before describing these experiments and in order to have some terms of comparison in the study of these novel combinations, I will report some experiences that I have had with the normal radicals butyl and amyl.
Butyl. — Kolbe has obtained this hydrocarbon by electrolysis of potassium valerate; I have prepared it, as I have indicated in my paper on butyl alcohol, by decomposing butyl iodide with potassium.
It is advantageous to replace potassium with sodium, and not only because sodium is less expensive, but also because it reacts in a less energetic manner with hydriodic esters. When one decomposes butyl hydriodic ester with potassium in a closed tube, as I did at first, explosions often occur; in addition to potassium iodide and butyl, it produces butene and butyl hydride which are gaseous, and which sometimes cause such a sudden and forceful expansion that the tube does not remain intact. With sodium, the reaction is calmer, and it forms fewer gaseous products which are the result of a secondary decomposition of butyl iodide with sodium:
2 C8H9I + 2 Na = C8H8 + C8H10 + NaI
The following procedure allows one to experiment with a considerable quantity of material.
Butyl iodide is placed with a small excess of sodium [5] into a round-bottom flask which has been equipped with a glass cooling coil. In the mantle of the coil, whose weight is supported, ice or water is introduced to maintain a low temperature for the duration of the experiment. The reaction begins in the cold and gives off heat. The sodium is observed to blister and turn blue little by little, resulting in a strange composition first discovered by Bouis. Once this effect is produced, the decomposition typically slows and it is necessary to activate the reaction by heating it with an alcohol lamp. The liquid is held at boiling until the aforementioned blue color has completely disappeared and the flask contains a white mass of sodium iodide impregnated with butyl. Thus marks the end of the experiment, provided that the cooling coil has remained sufficiently cold that the butyl vapors have condensed continuously and have flowed back into the flask. As for the butene and butyl hydride, they are lost via the opening in the coil; nothing prevents one from condensing them if so desired.
To extract the butyl from the mass of iodide which it impregnates, the flask is immersed in an oil bath at 150°C; the butyl is collected via distillation and is dried over sodium. It is observed that there is no longer a trace of iodine as long as the liquid metal remains brilliant and polished like a silver ball. When its surface tarnishes, this is proof that the butyl contains iodine and it is necessary to boil with sodium for a longer period of time. As soon as this product is pure, it is purified a second time and the fraction that distills at between 105°C and 108°C is collected. This is pure butyl.
As a result of my experiments, this hydrocarbon boils at 106°C. At 0°C, its density is 7.057; its vapor density is found to be 4.070. This number is calculated from the following values:
| Excess weight of flask | 0.3265 g |
| Bath temperature | 202°C |
| Air temperature | 13.5°C |
| Barometer | 748.8 mmHg |
| Flask volume | 199 |
| Remaining air | 1.3 cc |
The theoretical density is 3.939, the equivalent corresponding to 4 volumes of gas.
I have tried a number of times to regenerate butyl alcohol from butyl. Up to now, all attempts have been unsuccessful. Chlorine and bromine do indeed attack butyl, but they form substitution products and hydrochloric and hydrobromic acid. It is the same with perchlorides of antimony and phosphorus; the first attacks butyl with formation of hydrochloric acid and chlorinated products of which I have not made an analysis. As for phosphorus perchloride, it is only decomposed by butyl after boiling for an extended period, and it is transformed into phosphorus protochloride at the same time that it forms butyl chloride and hydrochloric acid. Having failed in my attempts to reconstitute a butyl derivative from butyl radical with chlorine and bromine, I have wanted to repeat them with iodine, which, as one knows, has a lesser tendency to form substitution products than other halogens. I have therefore passed iodine and butyl vapor into a tube containing platinum sponge, heated to around 300°C; abundant vapors of hydriodic acid were evolved and a fraction of butyl was transformed into an iodide: I cannot obtain this product in a large enough quantity to be able to decide if it is a substitution product (which is likely) or a butyl iodide.
One can hope that butyl will be cleaved in the presence of hydrochloric acid in butyl chloride and butyl hydride, as shown in the following equation:
but the experiment did not confirm this expectation. Hydrochloric acid did not react with butyl either at room temperature or at temperatures raised to nearly the boiling point of the oil bath.
Amyl. — I have prepared this radical using the same procedure I used to isolate butyl. Amyl iodide is less easily attacked by sodium than butyl iodide. I have not seen the reaction begin spontaneously and without the aid of applied heat. When it is heated, it displays the phenomena which have been previously described. The reaction is ended when the sodium has transformed into a white mass of iodide: after having separated the amyl which impregnates this mass by distillation with an oil bath, the material is purified over sodium and the material that distills over at 158°C is collected.
Amyl is a clean and mobile liquid with an aromatic odor which does not resemble the penetrating odor of amyl alcohol. Its density at 0°C is 0.7413. It expands greatly in heating from 0 to 20°C; such that, at 20°C, its density is only 0.7282. Its vapor density has been found as 4.956 from the following values:
| Excess weight of flask | 0.6045 g |
| Bath temperature | 260°C |
| Air temperature | 14°C |
| Barometer | 764.2 mmHg |
| Flask volume | 291.5 cc |
| Remaining air | 0.2 cc |
Its theoretical density is 4.907, the equivalent corresponding to 4 volumes of gas.
Here are the results from its analysis:
0.285 grams of material gave 0.880 grams of carbonic acid and 0.402 grams of water.
These values, in percent:
| Experiment | Theory | ||
|---|---|---|---|
| Carbon | 84.20 | C20 | 84.50 |
| Hydrogen | 15.65 | H22 | 15.50 |
| 99.85 | 100.00 |
Amyl boils at 158°C. Among the most curious of its properties, one must mention its considerable optical rotatory power. It rotates the plane of polarization to the right, but with a variable intensity; different samples that I examined did not give the same results at all. One can judge by the following numbers, calculated using the well-known formula from Biot:
$$[\alpha]=\frac{a}{l\delta}$$
| 1st sample * [6] | +9.109° |
| 2nd sample † | +8.496° (Observed by Biot.) |
| 3rd sample | +7.908° |
| 4th sample †† | +2.785° |
These variations are observed in amyl alcohol itself, which possesses different rotatory powers depending on the examined sample. Here are the observations that I have made in that regard:
| 1st sample * | -3.509° |
| 2nd sample † | -3.028° (Observed by Biot.) |
| 3rd sample | -3.134° |
| 4th sample †† | -1.204° |
Amyl dissolves neither in sulfuric acid monohydrate nor in fuming sulfuric acid. When it is left in contact for some time with such an energetic acid, it darkens and gives off sulfurous acidic products. Upon contacting anhydrous sulfuric acid vapors with amyl in a cooling bath, I noted that this hydrocarbon was slowly attacked with formation of a black mass and emission of sulfur-containing acidic products. It did not form the conjugate acid under these conditions, as I had hoped; the product of the reaction having been mixed with water and saturated with barium carbonate, the neutral solution thus obtained contained hardly any trace of dissolved barium. Nitric acid monohydrate attacks amyl slowly, with the reagent disappearing entirely over several days of boiling, if one takes care to condense and recapture the vapors which escape the flask. Upon saturation with potassium carbonate and concentration by evaporation, the liquid deposits a yellow material with neutral pH that is only slightly soluble in water and which I have not analyzed. Finally, it becomes a mass formed by crystals of potassium nitrate from which a small quantity of yellow deliquescent potassium salt can be extracted with absolute alcohol. I have not been able to discover valeric acid among the products of oxidation of amyl, but it is not impossible that the yellow salt that I just mentioned is potassium nitrovalerate. I have obtained too little of it to be able to submit it to analysis.
Antimony perchloride attacks amyl, giving off hydrochloric acid and forming substitution products. When one heats this hydrocarbon in an oil bath with the corrosive powdered sublimate , it is reduced at a temperature around 250°C; however, in this circumstance it again does not form amyl chloride, but gives off hydrochloric acid. I am sure, hence, that neither hydrochloric nor hydriodic acid are attacked by amyl, which remains perfectly intact in these gases even at 300°C.
The inertness of alcoholic radicals, and of amyl in particular, is well demonstrated by the manner in which they behave with phosphorus perchloride. This energetic reagent produces no action on amyl at room temperature. When heated, it dissolves in considerable quantity in the liquid, and is deposited by cooling without notable alteration. It is only after prolonged boiling that it attacks amyl, giving off hydrochloric acid and phosphorus protochloride continuously and forming substitution products. I have obtained two chlorinated products derived from amyl, having reacted 2 or 4 equivalents of phosphorus perchloride with 1 equivalent of this hydrocarbon.
1. Seven grams of amyl were submitted to a prolonged boiling with 21 grams of phosphorus perchloride, until the liquid had begun to change color in the flask. The residue was washed with water, dried over calcium chloride, then distilled; the thermometer rose rapidly to 210°C. The fractions that passed between 210-215°C and 215-220°C were collected separately. These two portions were submitted for analysis.
- Fraction boiling from 210-215°C. 0.311 grams of material gave 0.2975 grams of water and 0.6645 grams of carbonic acid.
- Fraction boiling around 220°C. 0.436 grams of material gave 0.385 grams of water and 0.912 grams of carbonic acid.
These number give, in percent:
| Trial I | Trial II | Theory | ||
|---|---|---|---|---|
| Carbon | 58.26 | 57.04 | C20 | 56.92 |
| Hydrogen | 10.61 | 9.80 | H20 | 9.48 |
| Chlorine | — | — | Cl2 | 33.60 |
and result in the formula:
C20H20Cl2
The substance analyzed was therefore amyl dichloride, which forms according to the following reaction:
2 PCl5 + C20H22 = 2 HCl + 2 PCl3 + C20H20Cl2
2. Five grams of amyl were submitted to boiling for several days with 30 grams of phosphorus perchloride in an apparatus which permitted less volatile vapors to reflux continuously. The perchloride disappeared little by little, and it gave off hydrochloric acid and phosphorus protochloride. The reaction was interrupted as soon as the liquid began to change color. The product was purified by washing with water and distilling after having dried the product. The fraction that distilled at above 270°C was colleted. It was a neutral colorless liquid, denser than water, insoluble in water, soluble in alcohol, and containing C20H18Cl4. This formula was derived by the following analysis:
0.5835 grams of material gave 0.3605 grams of water and 0.8945 grams of carbonic acid.
Which gives:
| Experiment | Theory | ||
|---|---|---|---|
| Carbon | 41.80 | C20 | 42.85 |
| Hydrogen | 6.86 | H18 | 6.42 |
| Chlorine | — | Cl2 | 50.73 |
The difference that one sees between the calculated and observed values is on the order of what one would expect to encounter for a chlorinated species whose extremely high boiling point was not, as a matter of fact, constant.
It is possible that the constitution of this chloride derived from amyl is expressed by the formula:
and one can hope to obtain the oxygenated radical of valeric acid
by substituting oxygen with chlorine in the preceding synthesis. I have tried to perform this transformation from radical chloride to radical oxide by heating the former in a closed tube with an alcohol solution of potassium. In fact, potassium chloride formed, along with an oleaginous liquid which was separated by adding water to the alcoholic solution. This liquid distilled at around 220°C, but its boiling point was not constant. Nevertheless, it gave upon analysis results that were near enough to those implied by the preceding formula, but which are not correct enough for me to believe that it is necessary to report them.
Ethyl-butyl. — This mixed radical was obtained by the following procedure:
40 grams of butyl iodide and 34 grams of ethyl iodide were decomposed with 11 grams of sodium in the apparatus described above. The reaction began by itself, but soon it was necessary to add heat. At the end of three days of boiling, the sodium was transformed into a white mass in which could still be seen a number of blue points. Upon distillation with an oil bath, it was noted that the thermometer remained for some time between 60 and 70°C. The part that distilled below 100 degrees was collected. From 100 to 110°C, a large quantity of butyl was distilled. The most volatile part was heated with sodium in a closed tube and while the melted sodium remained brilliant, it was distilled again. While the thermometer remained for some time between 60 and 65°C, the liquid that distilled between these temperatures was collected; it formed the largest fraction of the product. After several purifications, a liquid was obtained with a reasonably constant boiling point.
The ethyl-butyl thus obtained is a light and mobile liquid. It boils at 62°C. At 0°C, its density is 0.7011. Its vapor density was found to be 3.053.
Here are the results of the experiment:
| Excess weight of flask | 0.305 g |
| Bath temperature | 165.5°C |
| Air temperature | 9°C |
| Barometer | 758.9 mmHg |
| Flask volume | 263.5 cc |
| Remaining air | 5.5 cc |
The theoretical density of the vapor of ethyl-butyl is 2.972, the equivalent corresponding to 4 volumes of gas. Here are the results of the analysis:
0.316 grams of material gave 0.470 grams of water and 0.9675 grams of carbonic acid.
These numbers give, in percent:
| Experiment | Theory | ||
|---|---|---|---|
| Carbon | 83.48 | C12 | 83.72 |
| Hydrogen | 16.50 | H14 | 16.28 |
| 99.98 | 100.00 |
One sees that the analysis and the density of the vapor, as well as the boiling point and the method of formation of ethyl-butyl, leave no doubt about its constitution which must be expressed by the formula:
Ethyl-amyl. — 70 grams of amyl iodide and 60 grams of ethyl iodide were decomposed with 14 grams of sodium; simultaneously in another apparatus, 34 grams of amyl iodide and 27 grams of ethyl iodide were decomposed with 8 grams of sodium. When the reaction was almost finished I added an additional 50 grams of amyl iodide, 40 grams of ethyl iodide and 12 grams of sodium and continued heating while employing the precautions indicated above. By dividing the procedure therefore into three parts, I could carry out a reaction of 154 grams of amyl iodide and 127 grams of ethyl iodide with 34 grams of sodium while avoiding a reaction that was too violent. Having terminated the reaction, the volatile products were separated with distillation using an oil bath. The fraction that distilled below 120°C was collected in part and heated to 120°C in a closed tube, and then very strongly with an excess of sodium. After thus having removed the last traces of iodine, the liquid was distilled into multiple fractions, and a notable quantity of product was obtained which boiled between 87.5 and 89.5°C, with the largest part distilled at 88°C. This was ethyl-amyl.
At 0°C, the density of this hydrocarbon is 0.7069, its vapor density was found to be 3.522. Here is the experimental data:
| Excess weight of flask | 0.424 g |
| Bath temperature | 190.5°C |
| Air temperature | 12.5°C |
| Barometer | 755.5 mmHg |
| Flask volume | 308 cc |
| Remaining air | 7.1 cc |
The theoretical vapor density of ethyl-amyl is 3.455, the equivalent corresponding to 4 volumes of gas. Its composition was determined by the following analysis:
- 0.285 grams of material gave 0.4155 grams of water and 0.878 grams of carbonic acid.
- 0.2915 grams of material gave 0.416 grams of water and 0.8985 grams of carbonic acid.
- 0.2675 grams of material gave 0.3955 grams of water and 0.824 grams of carbonic acid.
These numbers give, in percent:
| Trial I | Trial II | Trial III | Theory | ||
|---|---|---|---|---|---|
| Carbon | 84.01 | 84.04 | 84.00 | C14 | 84.00 |
| Hydrogen | 16.18 | 15.83 | 16.41 | H16 | 16.00 |
| 100.19 | 99.87 | 100.41 | 100.00 |
We represent the constitution of ethyl-amyl with the formula:
which seems sufficiently justified by the circumstances under which the hydrocarbon is formed. An interesting physical property is found in corroborating this formula. Ethyl-amyl exhibits optical rotation. Like amyl and all amyl derivatives (except for the alcohol), ethyl-amyl rotates the plane of polarization to the right. The deviation effected by a path length of 100 millimeters was found = +0.920°.
This physical circumstance seems to indicate that the complex molecule C12H14 contains the amyl group C10H11. The derivatives of amyl alcohol in which this group is destroyed, such as amylene, valeric acid, etc., are optically inactive. We must therefore admit that the amyl alcohol radical is contained without alteration in ethyl-amyl, and to express the constitution of this hydrocarbon we can only choose between the formulas:
 |
 |
or |  |
No known fact, no analog supports the last two; as a consequence, we adopt the first as being the simplest and the most accurate.
Ethyl-amyl, which boils at 88°C, is only very weakly attacked by phosphorus perchloride at its boiling point. It gives off hardly any hydrochloric acid, and the perchloride which dissolves in the liquid when heated redeposits upon cooling again. This energetic reagent only significantly attacks ethyl-amyl at a temperature above 100°C, when the two are heated together in a closed tube and placed in an oil bath. I have not been able to study the chlorinated products that form under these conditions, because the experiment terminated with an explosion.
Butyl-amyl. — 160 grams of a mixture of butyl iodide and amyl iodide were decomposed by 20 grams of sodium. At the end of the reaction after several days of boiling, the product was distilled. The largest part of the liquid distilled between 130 and 140°C. But upon reaching the three boiling points of the three radicals (butyl, butyl-amyl, and amyl), a large number of fractional distillations were necessary to yield a product with a constant boiling point. Nonetheless, a certain quantity of liquid was finally obtained which distilled entirely between 132 and 135°C.
This liquid was the mixed radical butyl-amyl, as proven by its analysis and its vapor density. It boils at roughly 132°C with the thermometer immersed in the liquid, and roughly 130°C with the thermometer immersed in the vapor. At 0°C, its density is 0.7247.
Its vapor density was found to be 4.465. Here is the experimental data:
| Excess weight of flask | 0.375 g |
| Bath temperature | 232°C |
| Air temperature | 10°C |
| Barometer | 759.4 mmHg |
| Flask volume | 200.5 cc |
| Remaining air | 0.9 cc |
The theoretical vapor density of butyl-amyl is 4.423, the equivalent corresponding to 4 volumes of vapor. The composition of this hydrocarbon is established by the following analysis:
0.297 grams of material gave 0.422 grams of water and 0.919 grams of carbonic acid.
These numbers give, in percent:
| Experiment | Theory | ||
|---|---|---|---|
| Carbon | 84.38 | C18 | 84.37 |
| Hydrogen | 15.77 | H20 | 15.63 |
| 100.15 | 100.00 |
and imply the formula
Butyl-caproyl. — I have obtained this mixed radical by electrolysis of a mixture of potassium valerate and potassium oenanthylate. 100 grams of pure oenanthylic acid were mixed with 120 grams of valeric acid, and this mixture was saturated with pure potassium carbonate. The concentrated solution was placed in a test tube and decomposed with a current from a pile of six Bunsen elements. As recommended by M. Kolbe, the electrolysis liquid was carefully maintained at a temperature of 0°C. It is necessary that it be slightly alkaline, for if it is neutral it froths considerably at the beginning of the experiment. The reaction is finished when the evolution of gas has almost entirely ceased: one finds an abundance of crystallization of potassium bicarbonate at the bottom of the test tube, and at the surface of the alkaline solution rests an oily liquid possessing a penetrating odor. This liquid, dried over calcium chloride, was purified. A small part distilled at less than 100°C, another part between 100-140°C, the largest part between 140-180°C, and the final part between 180-220°C.
The part which distilled between 140 and 180°C was boiled with potassium which attacked and retained a small quantity of oxygenated product. Upon fractional distillation, a notable portion of product distilled between 150 and 160°C, where the thermometer increased only slowly between these temperature limits. After a series of purifications two portions of liquid were recovered: one distilling between 150 and 155°C, and the other between 155 and 160°C.
The density of the vapor was determined for these two portions:
| Fraction distilling at 150-155° | Fraction distilling at 155-160° | |
|---|---|---|
| Excess weight of flask | 0.315 g | 0.314 g |
| Bath temperature | 227°C | 228°C |
| Air temperature | 12°C | 11°C |
| Barometer | 747 mmHg | 762.5 mmHg |
| Flask volume | 144.5 cc | 141 cc |
| Remaining air | 0 cc | 0.2 cc |
The vapor density of the portion distilling between 150 and 155°C was found from this data to be 4.866, and the vapor density of the potion distilling between 155 and 160°C was found to be 4.917. The theoretical density calculated from the formula
C20H22
was 4.907. One sees from this that the first fraction gives a value somewhat too low and the second fraction gives a value somewhat too high; this seems to indicate that the boiling point of the compound C20H22 is situated around 155°C. [7]
The indications made by the vapor density relative to the composition of the product are corroborated by the results of the analysis itself, which shows that the carbon and hydrogen are in a ratio of 10:11. Here are the numerical results of these analyses:
- 0.218 grams of material gave 0.305 grams of water and 0.679 grams of carbonic acid.
- 0.2295 grams of material gave 0.322 grams of water and the carbonic acid was lost.
- 0.233 grams of material gave 0.3215 grams of water and 0.7215 grams of carbonic acid.
These numbers give, in percent:
| Trial I | Trial II | Trial III | Theory | ||
|---|---|---|---|---|---|
| Carbon | 84.93 | — | 84.44 | C20 | 84.50 |
| Hydrogen | 15.54 | 15.50 | 15.35 | H22 | 15.50 |
These numbers confirm the formula
C20H22
indicated by the vapor density; from one angle, if one considers the mode of formation and the boiling point of this hydrocarbon, one is compelled to envision it as a mixed radical, and to express its constitution by the formula
In fact, if butyl is formed from the electrolysis of valeric acid and caproyl is formed from the electrolysis of oenanthylic acid, why can butyl-caproyl not form from the electrolysis of a mixture of the two acids? In the reaction which produces the mixed radical, events occur as if butyl and caproyl had combined in a nascent state. It is not probable that a current with the given intensity decomposes valeric and oenanthylic acid with equal facility; one can suppose that the complex oenanthylic acid molecule is cleaved more easily, all other things being equal, than the simpler and more stable valeric acid. Such is the reason that valeric acid is found predominantly in the electrolysed mixture.
In any case, other products form in the reaction which produces the mixed radical butyl-caproyl. The fraction of liquid which distills at below 100°C, contained a very volatile substance which was probably caproene C12H12. Between 100 and 120°C, a notable quantity of butyl passed, and the less volatile products contained caproyl. I have analyzed the liquid which passed between 202 and 210°C, and I have found the vapor density after having boiled it with potassium. Here are the results of these experiments:
| Excess weight of flask | 0.381 g |
| Bath temperature | 256°C |
| Air temperature | 16.5°C |
| Barometer | 767.5 mmHg |
| Flask volume | 138 cc |
| Remaining air | 1.2 cc |
From this data, one finds the value 5.983 for the vapor density of caproyl. The theoretical value is 5.874. The small quantity of liquid which remained in the flask was distilled and submitted to analysis:
0.212 grams of material gave 0.296 grams of water and 0.655 grams of carbonic acid.
These numbers give, in percent:
| Experiment | Theory | ||
|---|---|---|---|
| Carbon | 84.25 | C24 | 84.70 |
| Hydrogen | 15.49 | H26 | 15.30 |
| 99.74 | 100.00 |
The caproyl prepared by electrolysis of oenanthylic acid is optically inactive, and I regard it as probable that the amyl formed by electrolysis of caproic acid will itself be inactive.
According to the results above, electrolysis of a mixture of potassium valerate and oenanthylate forms butyl, butyl-caproyl, and caproyl. However, it is evident that the analysis of a mixture of butyl and caproyl must give the same results as the mixed radical butyl-caproyl. To give my experiments on this subject a degree of certitude that this possibility is not allowed, it has been necessary for me, as a result, to take great care in determining the vapor density of butyl-caproyl. It is not evident that if I had used a mixture of butyl and caproyl, that I would have necessarily obtained a value much to large for the vapor density; the butyl boiling at 108°C would have necessarily evaporated and separated for the most part before the caproyl began to boil at around 200°C. Wishing to convince myself of this point by direct experiment, I found the vapor density of a mixture of butyl and caproyl. Here are the results that I obtained:
| Excess weight of flask | 0.353 g |
| Bath temperature | 249°C |
| Air temperature | 11.5°C |
| Barometer | 764.7 mmHg |
| Flask volume | 146.5 cc |
| Remaining air | 1.5 cc |
From this one finds the value 5.420 for the vapor density, which differs notably from the value 4.917 that was found for the vapor density of butyl-caproyl.
Methyl-caproyl. — I have tried to prepare this mixed radical by electrolysis of a mixture of potassium acetate and oenanthylate. As the acetic acid molecule is much more stable than the complex oenanthylic acid molecule, it must be the case that passing a current through the mixture decomposes the latter acid more easily than the former. This is, it seems to me, the reason why the mixed radical only forms in small quantities under the conditions indicated, even when a large excess of potassium acetate is used. I electrolysed over 150 grams of oenanthylic acid with a corresponding quantity of acetic acid, and I only obtained a very small quantity of a liquid that I could regard as methyl-caproyl, but analysis of which did not give very clean results. Upon purification, the oily and odorous liquid resulting from the decomposition of the mixture was recovered from a fraction distilling at below 100°C. This product was treated with potassium and submitted to fractional distillation. The portions of liquid boiling around 60°C and again around 85°C were collected. The first was made up of a very volatile hydrocarbon, containing 85.7% carbon and 14.7% hydrogen. [8] Caproene (C12H12) contains, by comparison, 85.7% carbon and 14.3% hydrogen. Analysis of the second gives the following results:
- Less volatile portion: 0.242 grams of material gave 0.3395 grams of water and 0.749 grams of carbonic acid.
- More volatile portion: 0.203 grams of material gave 0.2825 grams of water and 0.630 grams of carbonic acid.
These numbers give, in percent:
| Trial I | Trial II | Theory | Theory | |||
|---|---|---|---|---|---|---|
| Carbon | 84.40 | 84.63 | C14 | 84.00 | C12 | 84.50 |
| Hydrogen | 15.57 | 15.44 | H16 | 16.00 | H12 | 14.29 |
| 99.97 | 100.07 | 100.00 | 100.00 |
These numbers are much closer to the formula:
C14H16
than the formula:
C14H16
The first is confirmed by the vapor density of the analyzed product, which was found to be 3.426
| Excess weight of flask | 0.191 g |
| Bath temperature | 179°C |
| Air temperature | 9°C |
| Barometer | 751.8 mmHg |
| Flask volume | 164 cc |
| Remaining air | 9.7 cc |
The theoretical density of the compound C14H16 is 3.455.
These experiments prove that the analyzed compound contains the hydrocarbon C14H16, but they show at the same time that this compound has not been obtained in a pure state. In any case, its constitution must be expressed by the formula
The facts exhibited in this paper seem to have put beyond doubt the existence of a novel class of organic radicals, which we call mixed radicals because they contain two alcohol groups at the same time. These radicals are
| Ethyl-butyl |  |
| Ethyl-amyl |  |
| Butyl-amyl |  |
| Butyl-caproyl |  |
The conditions under which these radicals form, and their physical properties, among which we note principally the optical rotation of ethyl-amyl, shed new light on their constitution. Moreover, the comparison of their properties with those of normal radicals leaves no doubt about the place that the latter occupy in the series, and as a consequence, about their true equivalent. One can assess them using the following table.
| Radicals | Composition | Density at 0°C | Observed vapor density | Theoretical vapor density | Boiling point | Difference from previous boiling point |
|---|---|---|---|---|---|---|
| Ethyl-Butyl |  |
0.7011 | 3.053 | 2.972 | 62°C | — |
| Ethyl-Amyl |  |
0.7069 | 3.522 | 3.455 | 88°C | 26°C |
| Methyl-Caproyl(?) |  |
— | 3.426 | 3.455 | 82°C(?) | 18-24°C from Ethyl-Butyl |
| Butyl |  |
0.7057 | 4.070 | 3.939 | 106°C | 24°C |
| Butyl-Amyl |  |
0.7247 | 4.465 | 4.423 | 132°C | 26°C |
| Amyl |  |
0.7413 | 4.956 | 4.907 | 158°C | 23°C |
| Butyl-Caproyl |  |
— | 4.917 | 4.907 | 155°C | — |
| Caproyl |  |
0.7574 | 5.983 | 5.874 | 202°C(?) | 2×22°C |
One sees by this table that the values which express the composition, vapor densities, and boiling points of the normal and mixed radicals follow an almost regular progression and establish a sort of harmony between their composition on one side and their physical properties on the other. Though, this harmony is quite natural and is easily explained if one admits double formulas for butyl, amyl, and caproyl
|
|
 |
It is evident that one would have trouble attributing the simple formulas C8H9, C10H11, and C12H13 to these radicals.
We arrive at the same conclusion if we compare the modes of formation of normal and mixed radicals. The reactions which produce butyl and ethyl-butyl, for example, do not perfectly agree with the condition for doubling the formula of butyl:
The argument that one can make from the existence, the mode of formation, and the physical properties of mixed radicals relative to the constitution of normal radicals therefore seems to me to be decisive. It is of the same order and as conclusive as the proof that Williamson has furnished in support of double formulas by which we represent the constitution of ethers today, and which is founded, as we know, on the existence of mixed ethers.
We will admit as a consequence, that the normal alcoholic radicals, from the moment they are liberated, double their molecule by combining in some fashion with themselves. This idea of a group which combines with itself does not make sense, if one wishes to attach the old chemical theories to it. One will see from the following developments what novelties it is necessary to attribute to them.
Everyone agrees that the radicals of alcohols can be represented in a manner similar to hydrogen in organic chemistry, and that they play the role of this simple radical perfectly. This analogy which exists between hydrogen and alcoholic radicals permits us—moreover, obliges us—to apply firstly the ideas that we have adopted for their organic congeners. Consequently, if the groups which replace and represent 1 equivalent of hydrogen are doubled at the moment when they are liberated, one can draw from this natural consequence that the equivalent of hydrogen itself is doubled when it is given off from these combinations, and that if the molecule of the liberated radicals is formed by two groups or 2 equivalents, the free hydrogen molecule is equally represented by 2 equivalents. One experiment that I performed over ten years ago seems to me to give a direct proof in favor of this opinion, that free hydrogen constitutes the molecule H2. I noted that copper hydride is decomposed instantaneously by hydrochloric acid with a lively effervescence of hydrogen. As the copper itself was not attacked by this acid, the decomposition of copper hydride would be an inexplicable fact by the ordinary laws of affinity if one admitted that free hydrogen is represented by its equivalent H. In fact, if the affinity of hydrogen for chlorine cannot be overpowered by copper, it should not be overpowered, a fortiori, by copper combined with hydrogen. Since in the first reaction there is an affinity to overcome, there are two to overcome in the second, which seems more difficult. Nevertheless, the decomposition of copper hydride with hydrochloric acid happens with such facility that it should be attributed to a contact force, if one wishes to remain faithful to the old ideas relative to the constitution of simple bodies. If, on the contrary, one views hydrogen as formed from 2 equivalents, nothing is more simple than explaining the reaction in question. It is a double decomposition between hydrogen chloride and copper hydride which forms copper chloride and hydrogen hydride
Cu2H + HCl = Cu2Cl + HH [9]
The idea of representing hydrogen as a double molecule is not novel in science. Nearly 30 years ago, Dumas made the remark in his Traité de Chimie [10] that the atoms of hydrogen and of chlorine were divisible and could be cut in two to form atoms of hydrochloric acid. Ampère had already admitted the divisibility of atoms and had explained the combination of hydrogen and chlorine as a double decomposition. Later, these ingenious views were adopted and developed at length by Laurent in his beautiful Mémoire sur les combinaisons azotées [11]. In any case, it is evident that the idea that hydrogen and chlorine represent double molecules in their free state—hydrogen hydride and chlorine chloride—can be applied to bromine, iodine, potassium, sodium, silver, and other simple bodies. It forms, without a doubt, one of the fundamental points of the new chemical doctrines that can be summarized as:
Simple bodies are constituted, just as composite bodies, by groups of equivalents, and they combine, not by addition, but by an exchange of elements between each other. The state of combination is characterized, not by a union of elements which add to themselves and leave with a more complicated molecular structure, but by substitution of a given group with an equivalent of another. As a result, hydrogen, chlorine, potassium, etc., constitute in their free state molecular groups with a complexity—I will say as compounds—on the order of hydrochloric acid and potassium chloride. This point of view has already been applied to salts themselves. For many chemists, these combinations do not results from the immediate union of the acidic and basic elements, but rather from an exchange which occurs between them.
Truly, this idea that a host of compounds form by way of substitution has been issued and accepted for a long time: it serves as the basis of a theory of types to which science is beholden to Dumas. The preceding propositions therefore only generalize a theory which only at appeared to apply to the origin of a certain class of compounds.
One knows what important developments the discoveries of these last few years have added to the theory of types. They have demonstrated that one can reintroduce organic combinations, and without a doubt also mineral compounds, as a small number of general types represented by substances which are very simple in their constitution, such as hydrogen, water, and ammonia. [12] The substances belonging to the hydrogen type, for example, can be envisioned as deriving by substitution from the double molecule HH in which 1 or 2 equivalents of hydrogen can be replaced by another simple body or by a group. These replacements can happen equally with the more complex molecules water or ammonia. This poses no difficulty: but how must we conceive of the mode of generation of the molecular groups which constitute water and ammonia themselves? Must we envision them as the result of an addition of elements, in the sense of the old ideas, or instead as generated by an exchange of elements, conforming to the principles developed above? The choice between these two hypotheses is unequivocal: since if we adopt the second for combinations in general, the most important of all combinations (water and ammonia) would not be an exception to the rule in this system. We will admit therefore that from the theoretical point of view of their modes of generation both of these compounds are products of substitution: water derives by substitution of oxygen and ammonia by substitution of nitrogen. The following developments leave no doubt about the sense of these propositions.
The necessity of comparing bodies of the same volume has often been insisted, when postulating them to be in the gaseous or vapor state. [13] Since molecular hydrogen H2 corresponds to 4 volumes, it is evident that free molecular oxygen, necessarily corresponding to the same 4 volumes, will be represented by the group O4 of equivalents. If now in the group [O2O2] half of the oxygen is replaced with an equivalent quantity of hydrogen, it results in the group H2O2, that is to say, a molecule of water corresponding to 4 volumes of vapor. In this group H2O2, the two equivalents of hydrogen (forming 4 volumes) occupy exactly the same place that 2 volumes of oxygen occupy in the group [O2O2]. This point of view leads to a powerful and simple interpretation of the phenomenon of condensation that oxygen and hydrogen undergo at the moment when water is formed. One can allow that the 4 volumes of hydrogen which must be substituted (combined) with 2 volumes of oxygen condense to half and that, in this new condensed state, 1 volume of hydrogen is equivalent to 1 volume of oxygen. Therefore, this contraction only consumes the hydrogen which condenses to water, being double that of its free state. That being said, it is understood that water, being connected with oxygen, is itself derived by substitution of the type O2O2, or more generally, M2M2, whereas free hydrogen corresponds to HH, of type MM.
In ammonia, hydrogen finds itself in a more condensed state than that of water; whereas 4 volumes of water vapor contain 4 volumes of hydrogen, 4 volumes of ammonia contain 6 volumes of hydrogen. Now, to explain the mode of ammonia generation, if we allow that this body is derived by substitution of nitrogen NN = 4 volumes, as water is derived from oxygen, we must also allow that in ammonia, nitrogen conserves its condensation state and that the contraction consumes hydrogen, wherein 6 volumes takes the place of 2 volumes of nitrogen in the group NN.
As a result of this, hydrogen is condensed into ammonia three times more than in its free state, and one can also express the mode of generation of this combination in allowing that it is derived via triply condensed hydrogen H3H3 = 4 volumes, in which 3 equivalents of hydrogen would be replaced by the tribasic radical nitrogen = N‴. [14] Ammonia therefore appears as the type M3M3.
As a result of the preceding arguments, hydrogen, water, and ammonia appear as three types MM, M2M2, and M3M3, which have the same general form and only differ in the condensation state of the reacted material. If we represent the condensation state of free hydrogen as 1, it is necessary to represent the condensation state of hydrogen in water as 2 and the state of hydrogen in ammonia as 3. These relations are expressed by the following figures which indicate the mode of generation of hydrochloric acid, water, and ammonia and only represent—for the sake of simplicity—2 volumes of gas or vapor.
2 vol.
|
2 vol.
|
2 vol. [15]
|
2 vol.
|
2 vol.
|
2 vol.
|
One sees that it is easy to account for the contractions observed in experiments with the formation of water and ammonia by supposing that these species are generated by substitution: that 2 volumes of hydrogen take the place of 1 volume of oxygen, and that 3 volumes of hydrogen take the place of 1 volume of nitrogen.
The remarks that we have just made on the condensation state of hydrogen can be applied to other elements. As we know for certain, nitrogen is found in another condensation state: in nitrous oxide, in nitrogen dioxide, and in ammonia. It seems to me to be impossible to account for this fact and not conclude that nitrogen differs in these three combinations, from a molecular point of view. In general, it appears to me that the moment has come to abandon this opinion that simple bodies all come in the same form, the same molecular state, the same equivalent in all their combinations. This idea is accredited to the spirit of an era where neither dimorphism nor isomerism were known phenomena. Today, we know that simple species are not always identical when they are free; can we still allow that they are identical in combination?
That being said, this fact, that only one and the same material can possess different condensation states, is demonstrated for us by examples familiar to everyone. Do we not observe that sulfur vapor at 400°C is observed with a condensation state triple that which is observed at 1000°C, [16] that the vapors of free phosphorus and arsenic have condensation states double that which we assign them in their nitrogen analogs, that liquid cyanogen chloride and methylcyanic ester condense before our eyes into solid cyanogen chloride and methylcyanuric ester And who knows if the remarkable differences of appearance and properties that appear in the modifications of sulfur and phosphorus are a result of different molecular condensations, as we can affirm for the cyanogen chlorides? In all cases, when cyanogen chloride CyCl becomes Cy3Cl3, it changes from type MM which represents the first degree of condensation into the type M3M3, and when the hydride of bitter almonds C14H6O2 transforms into benzoin 2[C14H6O2], it changes from type MM to type M2M2.
As a result of the preceding developments, we can allow the three types
| MM | M2M2 | M3M3 |
to which, without a doubt, it is still necessary to add others expressing even greater condensations of material. Thus, the second and third type can double and triple to constitute the types
| 2 M2M2 | 3 M2M2 | 3 M3M3 |
Thus these molecular types, which can describe so many different materials, are linked to each other in the most natural manner by this principle of successive condensations which we have tried to develop.
The following table offers an overview of these ideas. The examples which are cited here show relationships of generation and derivation of a certain number of inorganic and organic species. The second differ from the first only in the complexity of the substituted groups. [17]
| Type MM (hydrogen type) | |
|---|---|
| HH | free hydrogen |
| ClCl | free chlorine |
| KK | free potassium |
| PtPt | platinum |
| CyCy | cyanogen |
| (C4H5)(C4H5) | ethyl |
| alcoholic radicals, etc. | |
| ClH | hydrochloric acid |
| ClK | potassium chloride |
| ClPt | platinum protochloride |
| ClC4H5 | ethyl chloride |
| simple esters | |
| ClCy | cyanogen chloride |
| organic chlorides | |
| C4H5H | ethyl hydride |
| Many hydrocarbons, aldehydes, ketones (Gerhardt). | |
| Type M2M2 (water type) | Type 2M2M2 | Type 3M2M2 | |||
|---|---|---|---|---|---|
| O2O2 | free oxygen |  |
oxalic acid | S6S6 = 3(S2S2) | sulfur at 400°C |
| S2S2 | sulfur at 1000°C |  |
carbonic acid |  |
phosphorous acid |
| H2O2 | water | Bibasic acids in general |  |
cyanuric acid | |
| R2O2 | oxides | Tribasic acids in general | |||
 |
hydrates |  |
iron sesquioxide [18] | ||
 |
sulfates |  |
iron sulfate sesquioxide | ||
 |
acetates |  |
glycerin | ||
| salts and esters of monobasic acids | |||||
 |
alcohol and congeners | ||||
| Pt2Pt2 | platinum | ||||
| Pt2Cl2 | platinum bichloride | ||||
| Type M3M3 (ammonia type) | Type 2M3M3 [19] | Type 3M3M3 | |||
|---|---|---|---|---|---|
| N‴N‴ (n3n3) | nitrogen considered as a tribasic radical |  |
urea |  |
cyanuramide (melamine) |
| P‴P‴ | phosphorus considered as a tribasic radical |  |
Reiset's first base |  |
hydromelon (Gerhardt) |
| Sb‴Sb‴ | antimony considered as a tribasic radical | ||||
| N‴H3 | ammonia | ||||
| P‴Cl3 | phosphorus protochloride | ||||
| Sb‴(C4H5)3 | Ethylantimony | ||||
| Cy3Cl3 | solid cyanogen chloride | ||||
Now, if we seek to define the molecular constitution and the form of combination that affects all simple or composite matter belonging to these different types, we recognize that this form is essentially binary, and that it can be expressed by the general symbol or type MnMn. The values that the coefficient n can take express successive condensations of matter. We propose that the condensation state of free hydrogen be taken as unity. [20]
Thus we arrive at a generalization of the idea of double molecules which was at first applied only to a small number of compounds and which I regard as one of the fundamental points of the new chemical theories. Basically, this idea reproduces, rejuvenates in some fashion, this principle of dualism which has been discussed so frequently in the last few years. Binary constitution and combination by the addition of antagonistic elements were at the heart of the old dualism; binary constitution and combination by substitution of elements describes the type of dualism that one can still accept today.
One sees, where some would believe them to be separated by an abyss, that the old chemical theories and the new are not absolutely mutually exclusive. One or another scientist attaches himself to theories which it is customary to represent as at odds with one another, but which are not so in reality. These are the theory of radicals and that of substitutions: the first, freed from incidental ideas, deals principally with groups which one must allow in organic compounds; the second considers the mode of combination. They express, as we see, two different points, and far from contradicting each other, they in fact complete one another.
In closing, I must say that I do not attach any importance to the necessity of the ideas that I have tried to develop and that I am far from considering them as the absolute expression of the truth. In the physical sciences, theories must never aim so high. The best theory is that which embraces the largest number of facts, which accounts for them in the most satisfying manner, and which permits prediction of new observations. The chemical theories which tend to prevail today appear to me to do so: they will be good only insofar as they remain fertile.
Notes
- Ann. der Chem. und Pharm., v. LXXI, p. 171.
- Ann. der Chem. und Pharm., v. LXIX, p. 257.
- Gossleth and Bouis, Quarterly Journal of Chem. Society, v. III, p. 210.
- Bouis, Ann. de Chim. et de Phys., v. XLIV, p. 77.
- For 100 grams of butyl iodide, one should use 13 to 14 grams of sodium.
- These different amyl samples come from the alcoholic amyl samples characterized in the same manner.
- It must be pointed out that the boiling point of the amyl species which is isomeric to butyl-capryl was measured by Frankland to be 155°C. In my own experiments, it is a bit higher (158°C).
- Another analysis gave carbon 83.8 and hydrogen 15.5. It is thus possible that the most volatile part of the distilled product was a mixture of caproene C12H12 and caproyl hydride C12H14.
- It is my understanding that Brodie has repeated this experiment—decomposition of copper hydride with hydrochloric acid—and has suggested the same argument.
- Traité de Chimie appliquée aux arts, v. I. Introduction, p. xxxviii (1828).
- Recherches sur les combinaisons azotées. Annales de Chimie et de Physique, 3rd series, v. XVIII, p. 266.
- Gerhardt admits four general types: water, hydrogen, hydrochloric acid, and ammonia (Annales de Chimie et de Physique, 3rd series, volume XXXVIII, page 337). The hydrochloric acid type is actually a subset of the hydrogen type, in view of its generation and microscopic constitution. But if one wishes to make an account of the general properties of compounds, it is good to maintain the hydrochloric acid type as a sort of subdivision. It would perhaps be advantageous, and greatly facilitate studies in this field, to subdivide the general types into a number of particular types.
- See Gerhardt, Revue Scientifique, v. X, and Prècis de Chimie organique.
- This notation was used by Odling (Quarterly Journal of the Chemical Society, volume VII, page 1.)
- The notation N‴N‴ indicates that the nitrogen is a tribasic radical, capable of combining with 3 volumes of hydrogen from the group [H3H3]. We can explain this property of nitrogen by supposing that nitrogen itself is formed from 3 bonded and inseparable atoms. If this is the case, then what we call 1 equivalent of nitrogen in ammonia would represent a group of 3 atoms n3 = N‴, and the formula for ammonia would be H3n3 (type M3M3). Phosphorus chloride appears to be of the same type, and derives from the group Cl3Cl3 by substitution of three equivalents of chlorine with the tribasic radical P‴. If we represent P‴ by p3, the formula for phosphorus protochloride becomes Cl3p3, phosphorus hydride becomes H3p3, and the phosphorus acids:
etc.
But, as this notation rests on considerations which are not yet susceptible to rigorous demonstration, I will leave it for the moment. - Bineau, L'Institut, volume XVI, p. 246. See also Malaguti, Leçons élémentaires de Chimie, volume I, p. 113.
- If hydrogen bonded to carbon did not possess the property which we have here elucidated by the discovery of a series of homologous hydrocarbons, organic chemistry would not exist.
- It would be easier to write the formula for iron sesquioxide as fe2O2. But the composition of aluminates seems to indicate that this formula should be tripled. In fact, the quantity of iron sulfate which corresponds to (reacts with) one equivalent of potassium sulfate is:
- This type gives the same empirical formula as type 3M2M2.
- There is a small number of cases where the empirical formula is less than what is represented by free hydrogen, such as sal ammoniac, hydriodide of phosphuretted hydrogen, phosphorus perchloride, etc. Consider, for example, the quantity of sal ammoniac which corresponds to 4 volumes, represented by the formula \(\frac{NH_{4}Cl}{2}\). It must be allowed that the molecules of hydrochloric acid HCl and ammonia NH3 split in two just as they come together. In light of this circumstance, it would be suitable to represent the species as H2Cl2 and H6N2, and as a consequence adopt the following notation:
H4, H2Cl2, H6N2, H4O2, ClH4N = 4 vol.But as the compounds involved—those giving 8 equivalent volumes of vapor—comprise a very small number, it is better to continue the notation used herein or that of Gerhardt.