ORGANIC CHEMISTRY

"Science is well-off and comfortable only where it is sur- rounded by the complete sympathy of society" -- A.M. Butlerov.

150th ANNIVERSARY OF THE BIRTH OF A. M. BUTLEROV

B~ A. Arbuzov

September, 1978, marks the 150th anniversary of the birth of the great Russian scien- tist Aleksandr Mikhailovich Butlerov, the founder of the theory of the structure of organic compounds, who was the driving force behind the development of organic chemistry and indus- trial organic synthesis over the course of more than a century. The ideas behind Butlerov's structural theory have had a productive influence on many areas of physical and inorganic chemistry. The structural theory of organic compounds has not lost its importance even at the present time.

Aleksandr Butlerov was born in the city of Chistopol' in the Kazanskaya Province. Four days after his birth, his mother died. His childhood passed in the village of Podlesnaya Shantala with his grandmother and grandfather, the Strelkovs. At the age of 16 he graduated the Kazan' High School and entered the nature department of the physicomathematical division of Kazan' University. In high school Aleksandr Butlerov was enthusiastic about chemistry, but in the university he was attracted to zoology and botany. However, under the influence of K. K. Klaus and N. N. Zinin, Butlerov became seriously interested in chemistry, and this determined his future. In 1849 he graduated from the university, and the ideas of Klaus were left with him. In 1851 Butlerov defended his first dissertation "Oxidation of Organic Compounds." In 1852 Klaus moved to Derpt [Tartu], and at the age of 23 Butlerov placed all his efforts into the teaching of chemistry. Despite his great educational work, in 1854 Butlerov passed his doctoral examination and defended a dissertation entitled "Essential Oils '~ for the degree of Doctor of Chemical Sciences at Moscow University. After the defense of his dissertation, he went to Petersburg for a meeting with his teacher N. N. Zinin, who was an ardent supporter of the ideas of Laurent and Gerhardt. This prompted Aieksandr Butlerov to make a thorough investigation of the theoretical problems of chemistry at that time.

In 1857 Butlerov was sent abroad for a year, during which he visited all the foremost laboratories of Europe, met the most prominent chemists, and became acquainted with the most important problems of theoretical organic chemistry. However, there were many such problems

Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2035- 2039, September, 1978.

0568-5230/78/2709-1791507.50 �9 1979 Plenum Publishing Corporation 1791

facing organic chemistry. On the theoretical level, organic chemistry was at the crossroads. The theory of radicals was being dropped, and the theory of types, which was superceding it, made it possible to classify Organic compounds and to indicate the characteristic types of reactions for them according to analogies to inorganic compounds.

However, it soon became clear that numerous organic compounds that had been synthesized do not fit into the types adopted. It became necessary to introduce additional mixed types, which, in turn, also failed to encompass the existing synthetic material and were associated with considerable arbitrariness in the writing of the formulas. The situation was further complicated by the fact that, according to the view of Gerhardt, it is possible to evaluate organic substances only at the time of their conversions, and hence different formulas could be written for one particular substance according to its conversion products. Thus, Berthe- lot wrote ii formulas for acetic acid. The practical experimentation was far ahead of the theoretical ideas of that time, and this situation slowed the further development of organic chemistry.

After Butlerov returned to Kazan', he carried out a number of important experiments with methylene iodide, which he had synthesized in WHrtz's laboratory. He synthesized the for- maldehyde polymer "dioxymethylene" from it and used the latter to synthesize the sugary sub- stance "methylenitan." By reacting methylene iodide with sodium he obtained ethylene instead of the expected methylene. This was of great importance for understanding the nature of unsaturated compounds. In parallel with his experimental work A. M. Butlerov analyzed the theoretical aspects of organic chemistry and recognized that they were unsatisfactory. But- lerov's theoretical thoughts evolved to their final form as the theory of the chemical struc- ture of organic compounds.

Butlerov advanced the ideas behind his structural theory in his lectures at Kazan' University back in 1860. He presented it in a complete form in his famous paper in Speyer in September, 1861. Although the basic ideas for the structural theory were in the form of a theory of valence and the concept of chemical bonding, Butlerov's paper was received coldly. It was difficult to abandon the customary concepts at once. Butlerov returned to Kazan' and soon carried out the synthesis of tertiary alcohols, which was a heavy argument in favor of the validity of the structural theory. In this paper there is no need to present the essence of the theory. We cite only its main points: i) The chemical properties of molecules are determined by their own atoms, their number, and the chemical structure. 2) When combined to form a molecule, atoms influence one another directly or indirectly. The second point, whose significance we wish to stress, was developed to an especially great extent in the works of V. V. Markovnikov and is one of the most important problems in modern organic chemi- stry. Butlerov's famous work entitled Introduction to the Complete Study of Organic Chemis- try, which was based completely on the ideas of chemical structure, was published in Kazan' in 1864-1866. The "Introduction" was published in German in 1867-1868 in Leipzig and promo- ted the spread of the structural theory in the West.

Butlerov's structural theory explained the phenomenon of isomerism and subsequently accounted for geomeric isomerism and tautomerism. Having an enormous capacity for predic- tion, it caused the vigorous development of synthetic organic chemistry. After Pasteur, the idea of a carbon tetrahedron was advanced by Butlerov (1862) and later by Kekul~ (1867).

Butlerov's structural theory was not acknowledged at once. Among its opponents were such outstanding scientists as Kolbe, Berthelot, N. A. Menshutkin, and at first D. I. Mendeleev. After the structural theory was accepted, articles ascribing authorship to Kekul~ and Cooper began to appear outside of Russia. Butlerov and V. V. Markovnikov had to undertake an active struggle in defense of the Russian authorship of the structural theory of organic compounds. It should be stated that the ignoring of the real role of Butlerov both in the creation of the structural theory and in its further development has been obser- ved up to the present time.

The structural theory has withstood the test of time for more than a century. During this time, remarkable discoveries were made both in the physical sciences and in chemistry. Our ideas regarding the nature of material particles have been radically altered and compli- cated. Phenomena, which seemingly contradicted the structural theory, but helped to further its development and enrichment, were discovered. As examples we can point out the special properties of compounds with conjugated bonds, which gave rise to the theory of partial valen- ces and the oscillation formulas of aromatic compounds. The discovery first of free radicals of the triphenylmethyl series and then of the simplest aliphatic radicals with trivalent

1792

carbon and radicals of other elements subsequently created a new important field in organic chemistry. The discovery of the existence of free radicals led to the important concept of a homolytic type of reaction, and in the practical respect it led to the appearance of chain polymerization processes with the participation of free radicals. Free radicals play a great role in photochemical and oxidative reactions and in biochemical processes taking place in living organisms. Of the other discoveries, the existence of compounds with divalent carbon (isonitriles and carbenes) should be mentioned. Butlerov tried to synthesize the simplest compound of this type, i.e., methylene, from CH212. Butlerov was the initiator of investi- gations whose purpose was to synthesize polymers from the simplest unsaturated compounds. In 1873 he tried to pol)~erize ethylene. This attempt led him to the synthesis of ethanol. He also tried to polymerize propylene and isobutylene under the action of H2S04 or BF3, and in the latter case he obtained a dimer and a trimer of isobutylene. At the present time all these processes, which "result in the formation of polymeric compounds, are being carried out on enormous industrial scales under conditions which were unaccessible at the time of Butlerov.

In 1868 Butlerov moved from Kazan' to Petersburg, wherehe was elected to be a professor in the university. In 1870 he was elected to be an assistant, and in the following year he was elected to be an Extraordinary Academician of the Academy of Sciences, where he con- tinued his experimental work on unsaturated compounds and the development of the structural theory.

In this ~hort article it is impossible to provide a complete characterization of the in- fluence which the structural theory had on the development of organic chemistry and the rela- ted disciplines for more than a century or of the richness of the ideas which filled Butlerov's work. We should dwell on Butlerov's truly brilliant intuition, which helped pave the way for the development of a number of areas of organic chemistry for many decades. Regardless of the views of Kolbe, Butlerov believed it was possible to determine the atoms in space and represent their arrangement in planes. Butlerov thereby planned the development of stereochemistry.

The opponents of the structural theory reproached it over the fact that the structural formulas are rigid and immobile. Answering N. A. Menshutkin, Butlerov categorically denied such ideas. He wrote, "We look at a chemical compound not as something dead and immobile. On the contrary, we assume that it is giftedwith contlnualmotlon, which is confined to its tiniest particles." At that time, nothing was known about the nature of the chemical bond. Considering the possible nature of chemical bonding, Butlerov spoke about a vast store of motion, which is inherent to atoms and which we can call chemical energy, and he pointed out that this subject is familiar not only to chemists, but also, possibly, even more clearly to physicists. If we understand this continual motion, about which Butlerov spoke, in the stereochemical respect, it coincides with the contemporary idea of the conformation of mole- cules. If we understand the motion in a bond between two directly joined atoms in a mole- cule as the causative mutual influence of the atoms on one another and the resultant inequi- valence of single and multiple bonds, it has since been reflected and considered in elec- tronic theories in organic chemistry.

The determination of the nature of covalent bonds, which had become possible owing to the development of physics, led to the appearance of the idea of the displacement of the electrons in a single bond and of their movement in multiple bonds both under the influence of internal and external factors. These ideas were a great step forward in the development of the structural theory and in learning about the mutual effects of atoms in a molecule and the relationship between the structure of a molecule and its reactivity. A new set of symbols to denote these effects was required.

In the fifties and sixties of the present century the state of the theory of the chemi- cal structural of organic compounds was discussed in connection with the mesomerism theory of the outstanding English scientist Ingold and his school, as well as the resonance theory of the outstanding American scientist Pauling and his students. Judgements were made regar- ding the need to replace the classic theory of structure with its symbols by another theory. However, it subsequently became clear that both the theory of mesomerism and the theory of resonance, if certain tenets of the latter, such as the possibility of the real existence of resonance forms are discarded, are ways of depicting the distribution of the electron den- sity in molecules of organic compounds. Even at the present time organic chemists generally use the classical symbol to denote a covalent bond, even though they have given it a far deeper meaning.

1793

The computational part of the theory of resonance was found to be a link between the classical qualitative structural theory and the quantum chemistry of organic compounds. Speaking about quantum chemistry, we must mention the remarkable words of Butlerov regarding the future role of mathematical analysis in the development of the structural theory. On the subject of the relationship between chemistry and the other manifestations of the activ- ity of matter, in his Introduction to the Complete Study of Organic Chemistry, Butlerov wrote, "Furthermore, those who call all the manifestations of chemistry motion are possibly not wrong. If a time when the causal relationships between all the forms of this motion will be understood does come, the phenomena of chemistry will have their own mechanical theory, i.e., a theory in the full sense of the word, and taking its place in science as a definite part of a unified whole, this theory together with other parts, i.e., theories of other kinds of motion, will be subjected to mathematical analysis." These words of Butlerov were writ- ten more than i00 years ago.

Contemporary organic chemistry with its methods for the synthesis of highly complicated compounds and the determination of the structure of natural compounds by chemical methods is inseparable from the use of various physical methods. The physical methods for the inves- tigation of the structure oforganic compounds have proved to be an invaluable aid in lear- ning about the nature of organic compounds. At Butlerov's time the known physical methods were very unimpressive, and yet he properly evaluated their use, In the Introduction to the Complete Study of Organic Chemistry, Butlerov showed what importance the physical properties of compounds under study have for comprehending the "interrelationships under which their component parts exist in the compounds" by stating that the chemical and physical properties have a "causal interrelationship." Butlerov thoroughly understood the full significance of the structural theory, but he did not consider it completely finished or unalterable. He thought that the structural theory should develop and be modified as science provides new facts. "The facts which cannot be explained by the existing theories are very precious to science, and its development in the future should be expected predominantly from their treat- ment," wrote Butlerov. The past i00 years from the time of the appearance of the struc- tural theoryhave been Elating support for these remarkable works of Butlerov. They were marked by tremendous advances in the understanding of the nature of matter, which have been directly reflected in the theoretical aspects of organic chemistry. The possibility of such disco- veries was predicted by Butlerov. In a paper entitled "Current significance of the theory of chemical structure" he wrote, "Of course, when we will be more closely familiar with the nature of chemical energy and the origin of atomic motion, then the laws of mechanics will also be applied to it and then our conception of chemical structure will decline, as the previous chemical theories have declined, but like most of those theories, it will decline not in order to disappear, but in order to enter the group of new and broader ideas in a modified form." "However perfect a theory is, it is only an approximation of the truth," wrote Butlerov. The structural theory did not decline, but it was expanded and modified, and its basic principles remain the basis for contemporary organic chemistry.

The public activity of Butlerov, to which he devoted a great deal of time throughout his life, must be mentioned. He was one of the founders of the Russian Physicochemical Society and its president from 1878 to 1882. Butlerov was an active advocate of higher education for women in Russia and played an important role in its realization. Butlerov had to carry on a persistent struggle with the reactionary groups of the Academy of Sciences, especially in connection with the blackballing of Academician D. I. Mendeleev.

Aleksandr Butlerov died on August 17, 1886, on his own estate Butlerovka at the height of his Creative powers and was buried not far from Butlerovka.

On the campus of Kazan' University there isan unimpressive two-story building, which was the old chemistry laboratory, i.e., the "cradle of Russian organic chemistry," where Butlerov studied, worked, and created and where he devised his theory of the structure of organic compounds. Everything in this building has been maintained as it was during the life of A. M. Butlerov: his study with his bookcases and personal library, the desk on which he worked, preparations of methylene iodide and trioxymethylene, which were personally pre- pared by Butlerov, with his signature, and the balance on which Butlerov worked with a note written by the hand of Aleksandr Butlerov.

We solemnly preserve these priceless relics left by Butlerov, who was a great chemist

and patriot.

1794