Laurent, Auguste (or Augustin)

Laurent, Auguste (or Augustin)

(b. St.-Maurice, near Langres, Haute-Marne, France, 14 November 1807; d. Paris, France, 15 April 1853),

chemistry.

Jean Baptiste Laurent, who owned a small farm, married Marie-Jeanne Maistre, the daughter of a merchant from Burgundy. Augustin Laurent (who always signed his name as Auguste in later life) was the second of their four children. He received the traditional classical education at local collège in Gray. He passed the entrance examination for the prestigious École des Mines in Paris, as an external student, on 9 December 1826, and received his engineering degree in June 1830. His first publication (1830), written jointly with Arrault, was a thesis submitted in partial fulfillment of the requirements for obtaining a degree; it was written on some of the techniques used in cobalt mines in Germany, which he had visited during his vacation the previous year.

At the beginning of the academic year 1830-1831 he was employed as a laboratory assistant at the École Centrale des Arts et Manufactures by J. B. Dumas. From 1832 to 1834 Laurent worked as chemist for the royal porcelain works at Sèvres, under the direction of Alexandre Brongniart, Dumas’s father-in-law. There Laurent developed a method of analyzing silicates by the action of hydrofluoric acid that is still used by chemists.

In 1835 Laurent opened a private school in Paris where he taught chemistry to fee-paying adults. The school was closed after about a year, and its furnishings were sold to pay for the publication of Laurent’s doctoral dissertation at the Sorbonne’s Faculty of Sciences.

In December 1837 Laurent passed his oral examination and obtained the degree of docteur-ès-sciences. His main doctoral thesis developed the principal ideas of his theory of fundamental and derived radicals in organic chemistry.

In 1836-1837 Laurent worked as an analyst for a Paris perfumery owned by a certain Laugier, who regarded him as a partner and associated him with the firm’s profits. Laurent received 10,000 francs when he left the perfumery, as his share of the profits.

Laurent was of a very sensitive and nervous disposition, easily discouraged and readily provoked into a quarrel over real or imagined insults. He was also generous and frank and had radical political commitments. A firm adherent of the left-wing republican tradition in France, he was impatient and suspicious of authority. Dumas, who epitomized conventional virtues of the authoritarian and traditionalist kind, was a natural target for Laurent’s hostility. Although there is no positive evidence that Dumas tried to harm him, Laurent was persuaded of his senior’s malevolence and bad faith. After receiving his doctorate, Laurent became persuaded that Dumas and other university authorities were opposed to the novelty of his ideas in organic chemistry and that he stood no chance of a university appointment in France. Consequently he contemplated abandoning a research career and in 1838 accepted a post as industrial chemist at a ceramics works in Luxembourg. The same year he married Anne-Françoise Schrobilgen, the daughter of an important Luxembourg dignitary.

Laurent’s ideas were in fact so easily assimilated by French chemists that by 1839 both the younger chemists as well as their seniors active in research in organic chemistry, including Dumas, had accepted the essentials. Notwithstanding Liebig’s exacerbated vanity and nationalism, by 1845 a large group of Germany chemists had also adopted Laurent’s views. The same was true of England. Even Berzelius in Sweden, against whose views in organic chemistry Laurent directed most of his work, rendered homage to his genius for experimental work, while dismissing his theoretical assumptions. In his annual report on the development of chemistry during 1843, Berzelius devoted nearly half his account of organic chemistry to a highly complimentary account of Laurent’s work; the previous year he had said that Laurent’s work on indigo was the best piece of experimental research in vegetable chemistry since Liebig and Wöhler had discovered the benzoyl radical in 1832.

On 30 November 1838 Laurent was appointed to the newly created chair of chemistry at Bordeaux, in his native region. He returned from Luxembourg in early 1839 and occupied this post for the next six years. This was the most productive period of his life, during which he published nearly 100 papers.

During his annual summer vacation visit to his in-laws in 1843, Laurent went to see Liebig in Giessen, where he was well received and established important contacts with the younger German chemists, especially von Hofmann. In the fall of that year he met Gerhardt; by 1844 they were in close contact and their lifelong collaboration had started. Laurent became a chevalier of the Légion d’Honneur in 1844.

The first number of the journal jointly edited by Gerhardt and Laurent, Comptes-rendus mensuels des travaux chimiques, appeared in February 1845. On 11 August 1845, he was elected a corresponding member of the Académie des Sciences and later that month left Bordeaux for good; he was granted leave of absence with pay until his appointment in 1848 to the post he had long desired, assayer at the Paris Mint. In the meantime he worked at various laboratories at the Collège de France, École Normale, and École des Mines. In 1847 he published his book on crystallography.

Laurent presented his candidature for the chair of chemistry at the Collège de France left vacant by the resignation of Pelouze in November 1850. He was elected by thirteen votes to nine for his rival Balard. But the election had to be ratified by the Académie des Sciences, which preferred Balard (35 to 11). Presumably the hostility of the Academy was dictated by the political disturbances in France in 1851, which aggravated the antagonism of political moderates toward radicals such as Laurent. Having fallen seriously ill, in 1852 he went to recuperate in the south of France but died in Paris of consumption the following year. His family was awarded a state pension. He left the manuscript of Méthode de chimie, which was edited by J. Nicklés and published in 1854. Odling published an English version in 1855, and Kekulé offered to translate it into German.

Laurent’s career coincided with the attempt to establish organic chemistry as a precise science, clearly distinguishable in its methods and fundamental principles from inorganic chemistry, which had been the main preoccupation of chemists during the previous half century. He was a central figure in the emergence of organic chemistry as a mature science.

A “philosophical” chemist, Laurent realized the need to pass beyond the narrow ad hoc theories of limited application adopted by his contemporaries, in order to establish a set of general theoretical principles valid for the whole domain of phenomena studied by organic chemistry. He insisted that an adequate scientific theory had to fulfill three requirements: explanation of all phenomena within the range of the theory; prediction of new and hitherto untested phenomena with its help; and enlargement of the scope of the scientific discipline by the imaginative application of theoretical principles to areas outside its original domain or subject matter.

His earlier contributions to organic chemistry were his thorough and meticulous experimental investigations of naphthalene and its derivatives. The subject had been chosen for him by Dumas, who was studying the reactions of the halogens upon various hydrocarbons (1832). Laurent adapted the existing method for the preparation of naphthalene (developed by Kidd) and succeeded in obtaining a very pure product, at low cost, by the fractional distillation of coal tar. By an extension of this early procedure, he became a major figure in the development of this branch of organic chemistry, the preparation and isolation of compounds by the distillation of coal tar. Using the same method, he and Dumas discovered anthracene (paranaphthalene) in 1832. Upon analysis both naphthalene and anthracene were found to be hydrocarbons containing the same relative proportions of carbon to hydrogen, namely 5:2 (C = 6).

The preparation of naphthalene was followed by a study of its reactions with chlorine, bromine, and nitric-and sulfuric-acid anhydries. Laurent’s practice of exhaustively investigating the compounds that a substance formed with each of a small number of reagents—rather than superficially spreading his researches over a very extensive range—was already formed and he never abandoned it. His most striking experimental discoveries were due to this method, such as the eventual preparation of nearly 100 new derivatives of naphthalene with the four reagents mentioned above.

While studying the reactions of naphthalene and its compounds with the halogens and nitric acid, Laurent was from the start characteristically concerned with the construction of an explanatory theory that would account for these phenomena. Like most creative scientists, he generalized his solution to a specific problem through the imaginative use of analogy, leading to the elaboration of the first comprehensive theory adequate for dealing with the whole domain of contemporaneous organic chemistry.

Several factors can be singled out in Laurent’s earliest attempt to construct such a theory:

1. Analogy. Laurent based his theory upon at least four kinds of analogy drawn from the work of his contemporaries.

a) Hydrocarbons : Dumas had affirmed that a hydrocarbon such as ethylene (C₂H₄) acted as an organic radical and gave rise to a whole series of derivative compounds such as alcohol (C₂H₄ + H₂O), ether (2C₂H₄ + H₂O), and Dutch liquid (C₂H₄ + Cl₂). Laurent’s study of naphthalene and anthracene, which appeared to contain the same relative proportions of carbon and hydrogen as ethylene and benzene, led him to generalize that all compounds could be understood as derivatives of hydrocarbons analogous to Dumas’s series for ethylene.

b) Substitutions and Additions: Dumas had also shown that, in a large number of organic reactions, hydrogen was replaced by an equivalent amount of halogens, oxygen, etc. Laurent interpreted the action of the halogens upon naphthalene by applying Dumas’s law of substitutions. But the most important demonstration of the truth of this law came from his study of naphthalic acid (C₄₀H₈O₄ + O₄; 4-volume formula, C = 6). This was formed by treating the following halogen derivative of naphthalene with nitric acid: C₄₀H₁₂Cl₄ + H₄Cl₄ (in modern notation C₁₀H₈Cl₂).

The reaction was explained by saying that H₄Cl₄ was removed from the radical directly derived from naphthalene (that is, C₄₀H₁₂Cl₄, where Cl₄ had replaced H₄ in the hydrocarbon: C₄₀H₁₆). But hydrochloric acid had further been added to the halogen derivative of naphthalene (C₄₀H₁₂Cl₄ + H₄Cl₄). This additional acid was shown by the reactions of naphthalene acid to remain outside the main radical corresponding to the hydrocarbon. Two analogies were thus involved: one with Dumas’s theory of substitution and another based upon the explanation of the additional acid which remained outside of the substituted derivative of naphthalene. Laurent generalized from both and concluded that similar considerations applied to all organic reactions.

c)Crystallography : Laurent was greatly influenced by the work of Haüumly in crystallography. Haüy had shown that the vast multiplicity of crystalline forms to be discovered in nature were in fact derived from five or six fundamental types of geometrical structure. By the application of a set of mathematical laws it was possible to reconstruct the basic form from which any given crystal was derived. Apart from the essential structure that could be discovered within a crystal, there were external accretions added to the crystal during its growth. A crystal was a unitary structure and it was only by a feat of abstraction that different parts could be discovered within it. While developing his theory, Laurent closely followed an analogy with Haöy: the basic hydrocarbons from which all organic compounds were derived corresponded to the fundamental crystalline structure; the essential part of a crystal was like that portion of an organic molecule in which substitution occurred, while the additional parts, outside of the main radical, were assimilated to the accidental accretions to the crystal. Even more important than these detailed analogies was Laurent’s general supposition, adopted from Haüy(via Baudrimont), that an organic molecule was a unitary structure that could not be interpreted in terms of the predominant dualistic theories of contemporary chemistry.

d)Isomorphism : Mitscherlich’s law of isomorphism had shown that several substances which crystallized identically possessed similar properties, even though their elementary components were different. From this Laurent concluded that in organic compounds an analogous situation was to be found: it was the position and arrangement of the atoms in a molecule that determined their properties—not their intrinsic natures. Likewise, the properties of organic compounds were dependent upon their position within a “series” into witch all such substances were to be naturally classified.

2. Models. Laurent wanted to construct a model that would be both a visual aid in understanding his theory and an account of some of the more obvious features of the crystalline forms of the substances studied. There were two kinds of current chemical models upon which he wished to draw, although both were recognized as unsatisfactory in certain important respects. In the first model it was assumed that when two chemical compounds reacted with each other, their molecules retained their original forms and were simply juxtaposed in the resulting combination. The other model was based on the contrary assumption that the original molecules disintegrated completely during the reaction and gave rise to a completely new type of structure. Laurent recognized the force of reasoning behind this second position, especially since it could not be denied that during a reaction there was an internal movement of all the constituents. He suggested however that reactions would be more intelligible if a certain deformation rather than a destruction of the molecular structures of the reactants were assumed.

For organic substances he suggested a pyramidal model that functioned like Haüy’s fundamental and derived crystalline structures. Since all organic compounds were ultimately derived from hydrocarbons, Laurent imagined that there was a right-angled pyramid at the center, having as many solid angles and edges as there were atoms of carbon and hydrogen composing the hydrocarbon. The carbon atoms were represented at the angles while the hydrogen atoms occupied the centers of the edges. Attached to the sides of this central structure, although not an integral part of it, there would be other pyramids representing additions to the hydrocarbon, such as water, in Dumas’s account of the composition of alcohol or ether (C₂H₄ + H₂O or 2C₂H₄ + H₂O).

Substitution reactions were represented in this model by the replacement of a hydrogen atom from one of the edges by an equivalent atom, such as chlorine. This obviously meant that for Laurent an electronegative element like a halogen could play a role identical to that of an electropositive element like hydrogen. This idea led to serious personal difficulties with Berzelius. For in explaining a reaction such as the formation of naphthalic acid, where both substitution and addition occurred in Laurent’s model, he assumed that two simultaneous modifications were involved: replacement of the atoms on the edges by their equivalents and attachment of new prisms to the bases. For instance, if four atoms of chlorine acted on the hydrocarbon C₁₂H₁₂, two chlorine atoms would replace two of the hydrogen atoms, while the latter combined with the other two chlorine atoms and formed hydrochloric acid, H₂Cl₂, which would attach itself to the bases.

When an equal number of equivalents replaced the atoms of a fundamental radical, the new substance formed had to have a similar formula and composition and the same fundamental properties as the original. In all these reactions it was emphasized that the central nucleus or pyramid retained its structure only as long as the carbon atoms were unaffected. If any of these were removed, the pyramid was destroyed and a wholly different type of product was formed having no relationship to the initial hydrocarbon. As long as the central pyramid was unaffected, the series of compounds belonged to the same family, of which the father was called the fundamental radical and the members to which it gave birth by substitution and addition were called derived radicals.

3. Rationalism: The third important influence on Laurent was his unquestioning faith in the rationality of nature. It found expression both in the assumption that nature always follows the simplest means to accomplish the most complicated ends and in the belief that natural phenomena embody mathematical principles. Thus, in his assertion that atoms always combine in simple numerical ratios to form organic compounds Laurent was also influenced by his belief in the uniformity of chemical principles that had to be equally valid both for organic and inorganic chemistry. Now if the laws of multiple proportions and of combining volumes in the latter were to be extended to organic chemistry then all combinations—and not only inorganic ones—occurred in simple numerical ratios. Concretely this meant that the fundamental hydrocarbons from which all organic substances were derived contained carbon and hydrogen in proportions of 1:1, 1:2, 1:3, 2:3, 3:5,…. Another consequence of this rationalistic thinking was Laurent’s attempt to give a quasi-mathematical form to his theory, which was stated as a set of formal propositions, an idiosyncrasy that has often occurred in the history of chemistry.

Due to its analogy with Haüy’s crystallography, the formal theory was called the theory of fundamental and derived radicals, the former being a hydrocarbon and the latter its substitution and addition products. Among the theory’s main tenets was the characterization of the hydrocarbons as neutral substances. The acidity was due to the existence of oxygen as a pyramid suspended outside the nucleus. Laurent maintained that alongside Dumans’s law of substitution, the action of the halogens, oxygen, and nitric acid resulted in the formation of the corresponding halogen acid, or water, or nitrous acid, which were sometimes given out and sometimes combined with the new radical that was formed. He based this idea upon his view of acids as being hydrates. Laurent was also concerned to show why compounds containing large proportions of oxygen, such as sugar, gums, and carbon monoxide, were not acidic, surprising as this appeared to those who held that acidity was dependent upon the quantity of oxygen in a substance. This was even more difficult to reconcile with the fact that substances like stearic acid and margaric acids were distinctly acidic in their properties despite the tiny proportion of oxygen that they contained. The explanation Laurent offered was that in the former cases all the oxygen was contained within the fundamental nuclei, while in the latter cases the small quantity of this element was outside them. Thus, these acids were to be written as follows:

C70H66O2 + O (margaric acid)

C140H134O3 + O2 (stearic acid)

Both were derived from the hydrocarbon C₃₅H₃₅ Similar reasons led to the assertion that when the halogens or hydrogen were located outside the nucleus, the former generated acidic halogen compounds and the latter hydracids or hydrobases. These elements could be removed by the action of alkalis, heat, and other similar agents if they were outside the nucleus, but not when they were part of it. This furnished a simple experimental test for determining their positions.

Organic substances were classified into series defined by the relative numerical proportions of carbon and hydrogen. Given any such compound, it was possible to discover the series to which it belonged by imaginatively reconstructing the fundamental hydrocarbon from which it was derived. Examples of such series were:

a) C:H :: 1:1 which included cetene, tetrene, etherin, methylene, and their respective derivatives.

b) C:H :: 5:2 which included anthracene, naphthalene, and their derivatives.

c) C:H :: 2:1 which included cinnamene, benzogine, benzene, and their derivatives.

d) C:H :: 3:2 which included acetone, metacetone, and chloracetone.

e) C:H :: 5:4 which included pinic and silvic acids, camphene, citrene, and their derivatives.

f) C:H :: 10:7 which included camphor and its derivatives.

If a substance lost a carbon atom during its reactions, then it ceased to belong to the original series and gave rise to one or more compounds in other series.

Laurent’s theory, formulated in 1835-1837, had thus succeeded not only in constructing an explanatory model and a set of general rules from which the formation of new organic compounds could be predicted by considering the numerous derivatives of a fundamental hydrocarbon nucleus but he had also furnished the first example of a comprehensive classification of organic compounds. The immediate experimental result that helped to test and confirm this theory was Laurent’s discovery of two new hydrocarbons, pyrene and chrysene. Investigating the reactions of these and other similar hydrocarbons with nitric acid, Laurent also succeeded in preparing a new compound with anthracene, anthracenose (anthraquinone). In 1837 he investigated the preparation and properties of fatty acids and showed that the results coincided with those predicted on the basis of his theory.

In 1842 Laurent investigated the action of bromine on camphor and discovered that a compound was formed having a remarkable property: when this compound was heated or treated with an alkali it directly gave off bromine and not hydrobromic acid. Laurent had previously asserted that the theory of hydracids was correct in that when a halogen or oxygen acted upon a hydrocarbon, half of the element replaced an equivalent amount of hydrogen in the hydrocarbon nucleus. The other half united with the hydrogen given off during substitution, forming the corresponding acid or water; and this could combine with the derivative radical as an addition product located outside the central radical. It followed that, upon heating or reacting with potash, this acid or water was given off, a fact Laurent thought had been confirmed by all his previous work. But the behavior of the compound formed by camphor and bromine had disproved this, since bromine and not hydrobromic acid was given off. This observation was of special importance to him, for it involved modifying his theory in several important respects. First, he had to admit the correctness of the hydrogen theory of acids, due to Davy and Dulong, rather than the theory that the acids were hydrates, which he had hitherto maintained. Second, he had to abandon Dumans’s theory of ethers and their halogen products. An ether did not contain water, nor did its halogen compounds contain a halogen acid; in both cases the fundamental radical was directly combined to oxygen or a halogen.

This result was of such importance to Laurent, involving, as it did, a modification of some of his essential ideas, that he had to obtain further experimental confirmation. The new experiments upon naphthalene and its compounds fully confirmed the predictions based on the view that in superchlorates or superbromides the additional chlorine and bromine existed outside the central nucleus as halogens and not as hydracids. There was still the need to prove that oxygen existed as such and not as water in similar cases. The proof was furnished by experiments upon the benzoyl series.

Ammonium sulfide was made to react with bitter almond oil, and the new compound obtained corresponded to the sulfide of the oil (hydrure de sulfobenzoile):

bitter almond oil C²⁸H¹² + O²

new sulfide formed C²⁸H¹² + S².

Various products were obtained upon distillation of this sulfide of benzoyl, including a new hydrocarbon, first discoverd by Laurent, which he named stilbene. It resembled naphthalene in its properties, and its composition was represented by bitter almond oil minus oxygen, C²⁸H¹²,or in four volumes C⁵⁶H²⁴. On reacting with chromic acid, this substence gave the desired addition product in which the hydrocarbon nucleus combined directly with water; bitter almond oil or benzoic acid were the oxidation products of stilbene. (C⁵⁶H²⁴ had thus formed C²⁸H¹² + O², an oxide—not a hydrate.)

Alongside this discovery another important influence led Laurent to modify his original theory. This was his work on crystallography in which he attempted to prove that the compounds derived by substitution from a fundamental radical were all isomorphic. He had already suggested this for the naphthalene series in 1837 and had continued to collect experimental evidence for it. The influnce of the arrangment and order of the atoms in on orgonic molecule thus appeared to be of far greater importance in determining its properties than Laurent had previously realized. He thus insisted that the substitution derivatives of a fundamental hydrocarbon radical were distinguishable not onely by their composition but also by the order in which the elements were introduced into them. For instance, if the fundamental radical were C³²H³², and four of its hydrogen atoms were replaced by two chlorine and two bromine atoms, the resulting products would then be two different derived radicals, C³²H²⁸Br²Cl² and C³²H²⁸Cl²Br².

Laurent also pointed out (a factor that was to have an important development under the designation “mixed types” in the theories of Williamson and others) that complicated fundamental radicals were in fact due to additions of simpler ones; conversely, simpler fundamental radicals could be obtained by successive subtractions from a more complicated one. In fact it was possible to discover the intenal arrange- ment of simpler radicals that were combined to form a complex one. Here a change from Laurent’s original model was involved; instead of a single pyramid at the center, the nucleus was a complicated structure of several pyramids. For example, the following series all contained the last fundamental radical (C²⁴H¹²) or one of its derivatives as a constituent part:

coumalic series	C40	benzoic series	C28
anisic series	C32	salicylic series	C28
phthalic series	C32	anthracenic series	C28
cinnamic series	C32	aniline series	C28
hippuric series	C32	chloranilic series	C24
indigo series	C32	benzic series	C29
estragon oil	C40	phenic series	C29

It was possible to transform these series into simpler ones and thereby to discover the simpler radicals of which their fundamental radicals were formed. Estragon oil, for example (derived radical C⁴⁰H²⁴O²), was composed of three simpler radicals: C⁸H⁸,C²⁴H¹², C⁸H⁴O².

The modified theory was accompanied by a new method of classification. Laurent criticized (1844) the prevalent schemes in organic chemistry, derived as they were mainly from the dualistic classification of compounds into acids, bases, and the salts they engendered. He said that the same organic substance, for example, the same vegetable oils, could in fact be simultaneously considered as an essence or a fatty body, and a base or a salt, depending upon the characteristics singled out. The best classification for him would have been one in which the only substances grouped together were those that could be mutually transformed into each other, for instance, acetic and chloracetic acids. Unfortunately, this principle of mutual generation could not be applied in the vast majority of cases, so that another, more indirect, set of criteria had to be sought.

Laurent suggested two such criteria that could serve as mutual checks upon the position of an organic compound within a classificatory scheme (constancy in the number of carbon atoms in all members of the same group) and the existence of a fundamental radical from which all compounds in the same group were to be derived. Likening his classificatory principles to those of botany, he predicted that while external characteristics were of no help in taxonomy, the need to classify plants according to their generating principles—from seed to tree, flower, fruit—would eventually lead to the discovery of an embryonic cell or a nucleus that was reduplicated within each member of a botanical family. Fundamental radicals were similar to such nuclei, since they were reduplicated as a stable structure in all the members of a series in organic chemistry. This analogy has led to Laurent’s theory being referred to as the “nucleus” theory.

In this later classification Laurent pointed out that the fundamental nuclei in organic chemistry did not necessarily have to be hydrocarbons but could contain any number of primary constituents and carbon.

Organic chemistry for Laurent comprised five types of structures.

1. Fundamental radicals. These were groups of atoms which fulfilled the same functions as the nonmetallic elements. From these, by equivalent substitution, derived radicals were formed which also played the same role as nonmetallic elements. For example:

fundamental radical C₃₂H₃₂ = R

derived radical C₃₂H₃₀Cl₂ = R′

derived radical C₃₂H₂₈Cl₄ = R″

derived radical C₃₂H₂₀Cl₁₂ = R‴.

2. Derived and fundamental radicals combined with elements to form chlorides, oxides, sulfides, etc. represented by: aR, bR, cR, … ; aR′, bR′, cR′, … ; aR″ , bR″ , cR″ , ….

3. An excess of oxygen transformed the radical into an acid, that is, under the influence of oxygen in excess, an equivalent of hydrogen underwent a modification of properties that made it easy for a metal to replace it. Depending upon the quantity of oxygen, various kinds of weak organic acids were formed when this element combined with the radical:

oxides OR, OR′, OR″ , OR‴, …;

monobasic acids O₂R, O₄R, O₄R′, …;

polybasic acids O₆R, O₆R′, O₈R, ….

4. Organic metals. Hydrogen played the same role as a metal in organic chemistry, because the addition of hydrogen to a radical resulted in the formation of compounds that behaved identically to metals in inorganic chemistry.

5. Complex types. Radicals of two or more different types sometimes combined to form more complicated structures. For example, formiobenzoic acid, C₁₆H₈ + O₆, in spite of the six atoms of oxygen was monobasic, because it was formed by the combination of two different compounds: C₁₄H₆ + O₆ (bitter almond oil) + C₂H₂ + O₄ (monobasic formic acid). Laurent wanted to introduce a consistent nomenclature into organic chemistry, rather similar to Lavoisier’s reform of the nomenclature of inorganic chemistry. His attempt was eminently rational but came too soon to be effective. Although Laurent’s ideas were to be the basis—acknowledged or unacknowledged—of later structural organic chemistry, his views needed to be supplemented by a clear recognition of the idea of valence and chemical bond before a complete reform of the basis of organic chemistry was to be possible.

Laurent tried various types of nomenclatures; this was necessitated by the growing number of organic compounds discovered by him and his contemporaries. Some idea of a later version of his attempted reform can be gathered form the following:

Hydrocarbons. These were to have names ending in “ene” for the fundamental radicals: benzene, stilbene, etc.

Derived radicals. If oxygen replaced the hydrogen in a fundamental radical, then the progressive substitution products had names ending in the same order as the vowels:

palène C₄H₄

palase C₄H₂O

palèse C₄O₂.

If chlorine, bromine, …, were substituted then the prefixes chlo-, bro-, …, were to be added:

chlopalase C₄H₂Cl₂

chlopalèse C₄Cl₄.

Additional products. If the fundamental or derived radicals combined with an equivalent hydrogen, forming an organic metal, the ending “ene” was changed to “um” :

palène C₄H₄

chlopalase C₂H₂Cl₂

palum H₄(C₄H₄)

chlopalasum H₄(C₄H₂Cl₂)

If oxygen combined with the organic metals to give acids, the ending was changed to “ique” :

palène C₄H₄ acid

palase C₄H₂O

palique (C₄H₄) H₄ + O₄

acid palasique (C₄O) H₄ + O₄

In Mèthode de chimie Laurent gave a more detailed and systematic account of the ideas on theoretical chemistry and classification that he had been developing. Among other important discoveries the following two are especially noteworthy.

1. Reform of atomic weights. Laurent pointed out that the formulas of organic compounds needed to be reduced to half their accepted values, that is, two-volume formulas were to replace four-volume formulas. In arriving at this conclusion he had been influenced by Gerhardt. Laurent also recognized that the molecules of the elements hydrogen, chlorine, etc. were biatomic.

2. The benzene ring. Chemical compounds, represented on a geometrical model, were taken to form complete polyhedra. In a substitution reaction with a simple element, such as the replacement of hydrogen by chlorine in naphthalene, one of the edges of the original polyhedron occupied by a hydrogen atom was supposed to be removed; and the resulting complex could be stable only if the original polyhedron was immediately reformed by the substituted chlorine edge. When the substitution occurred in a complex radical the situation was even more complicated. Here two complete ployhedra were originally present, as, for example, in the action of ammonia upon benzoyl chloride (C₇H₅CIO). During the reaction both polyhedra lost an edge, respectively due to the removal of hydrogen in ammonia and chlorine in benzoyl chloride, the amide (NH₂) and benzoyl radical being left in the end product. These were two model taken by Laurent for these compounds was, significantly, a hexagon in each case and the substitution was represented thus: Bz = C₆H₅O; A = NH₂

The two-faced CI and H were removed during the reaction, and the polyhedron BzA was formed as a result.

Laurent constructed numerous other models of the same kind for different types of chemical reactions; but the fact that compounds of the benzene series were already envisaged as hexagonal, coupled with the view that the reinstatement of the edge was prompted by the requirement for chemical stability in the residual compounds, is especially significant for its obvious parallels with Kekulé’s later views on the structure of benzene.

BIBLIOGRAPHY

An excellent bibliography, listing 216 of Laurent’s publications, is J. Jacques, “Essai bibliographique sur l’oeuvre et la correspondance d’Auguste Laurent,” in Archives. Institut grandducal de Luxembourg. Section des sciences naturelles, physiques et mathématiques, 22 (1955), 11-35. Laurent’s doctoral diss. was published as Recherches diverses de chimie organique. Sur la densité des argiles cuites á diverses températures (Paris, 1837); a rare work, it may be consulted at the Faculté de Pharmacie and at the Bibliothéque de l’Institut, Paris. His two books are Précis de cristallographie suivi d’une méthode simple d’analyse au chalumeau (Paris, 1847) ; and Methode de chimie (Paris, 1854). There is no worthwhile secondary literature.

Sathis C. Kapoor