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Pierre Eugene Marcellin Berthelot: an illustrious pioneering French chemist.

This article highlights the numerous achievements of o highly versatile scientist and public servant of the nineteenth century.

Pierre Eugene Marcellin Berthelot was born in Paris on October 25, 1827 and died there on March 18, 1907. He followed courses at Collage Henri IV in Paris and entered the College de France to study medicine, perhaps because his father was a physician. However, he did not continue in medicine after coming tinder the influence of Jean-Baptiste Andre Dumas and other professors, his interest having turned to chemistry. In 1851, he was named assistant to Antoine Balard (1802-1876), titular professor of chemistry in the Collage de France, and only eight years later was appointed professor of organic chemistry in the Ecole Superieure de Pharmacie. Later on, a special chair of studies was created for Berthelot at the Collage de France [1], which he held until the end of this life. Through his extensive original and fundamental research and exceptionally broad interests he was to become "one of the most distinguished chemists of the 19th century" [2]. In addition, Berthelot was a philosopher and in later life embarked, like the famous chemist Dumas [3], upon a successful parallel career as a politician!

Bertholot's impressive scientific contributions were duly recognized. In 1863, he was elected a member of the Academy of Medicine and ten years later was admitted to the important Academy of Sciences. Ultimately, he was elected a member of the prestigious Academie francaise. in 1889, Berthelot was appointed Permanent Secretary of the Academy of Sciences, a most influential post that had been held 21 years earlier by Dumas [3].

Contributions to Organic Chemistry

During his early career, Marcellin Berthelot developed general methods for the synthesis of alcohols and hydrocarbons. In the 1850s, he systematically synthesized many organic compounds such as ethyl alcohol and methane. In 1856, Berthelot prepared methane by reacting carbon disulphide with hydrogen sulphide over healed copper [2]. In 1862, he obtained acetylene in the electric arc between carbon electrodes in a hydrogen atmosphere [4], while using an apparatus that became known as "l'oeuf de Berthelot". He showed that it was possible to create organic substances from their constituent elements, i.e., hydrogen, carbon, nitrogen and oxygen. He had realized that in 1828 Friedrich Wohler (1800-1882) had brought about a total synthesis of urea (an organic compound) from only inorganic materials, and without the intervention of "vital force" (life). Thus, he set out to achieve similar complete syntheses of other types of organic compounds, and succeeded brilliantly. Some of Berthelot's achievements in organic synthesis are listed in chronological order in Table 1.

By 1860, Berthelot's monumental researches on synthesis [5] had introduced fundamental change into organic chemistry, and had led to the demise of the "doctrine of vitalism". In fact, he recommended that life be banned from all explanations concerning organic chemistry! Berthelot, along with his contemporaries Hermann Kolbe (1818-1884) and Edward Frankland (1825-1899), is justly considered to be a great pioneer in the field of synthetic organic chemistry [6].

Berthelot's contributions to organic chemistry were not limited to his synthesis work for he did other significant research on glycerine, sugars and terpenes. For instance, in 1853, he found that glycerine combined with three equivalents of acetic acid and concluded that it was a three-basic alcohol [4]. Soon thereafter, he showed that this was also the case with other acids [2]. In 1854, Berthelot reacted glycerine with stearic acid and obtained tristearin which proved to be identical to the triglyceride present in natural fats [7].

After much work on sugars, Berthelot correctly concluded that they were both polyatomic alcohols and aldehydes. He classified the carbohydrates into three groups. In 1855, he showed that erythrite was a tetratomic alcohol rather than a sugar [8], and five years later recognized that mannit was a hexabasic alcohol [4]. For cane sugar, Berthelot proposed the name "saccharose" which is still used in the French-language chemical literature of today. Because of his research on sugars he became interested in fermentation, and found that the conversion of cane sugar into invert sugar during fermentation was brought about by a "ferment" (enzyme) present in yeast. He precipitated said enzyme by addition of alcohol to a yeast extract, and named it "ferment glucosique" [8]. The idea that both intra- and extracellular enzymes could exist was accepted by Berthelot and others in 1856 [9].

In the terpene field, Berthelot discovered several new compounds and characterized the pinenes using the hydrochlorides. He obtained camphol and camphor from turpentine in 1859 [2]. His researches were important for the classification of the terpenes [8], and it was Berthelot who first put forward the isoprene rule [4].
Table 1. Some of Berthelot's Achievements in Organic Synthesis.

Year Achievement

1850 Prepared ethylene iodide from ethylene

1854 Converted ethylene into ethyl alcohol

1855 Made potassium formate by reacting carbon monoxide with
 caustic potash

1856 Prepared formic acid from oxalic acid and glycerine

1856 Obtained hexyne by reacting allyl iodide with sodium

1860 Prepared acetylene by passing electric sparks through a
 mixture of cyanogen and hydrogen

1866 Polymerized acetylene into benzene by heat treatment

1867 Obtained hydrocarbons by dry distillation of benzoates with
 salts of fatty acids

1869 Oxidized camphene to camphor

1881 Synthesized ethyl peroxide from ethyl ether by reaction with
 ozone


A Precursor to Physical Chemistry

In the early 1860s, Berthelot became interested in reaction velocities, mechanisms, and chemical affinity; aspects which were later to be included in the field of physical chemistry. In 1861, he investigated the relationship between reaction rate and affinity, and later defined affinity as "the resultant of the actions that held the elements of the compound bodies together" [1]. Berthelot and his collaborators noticed that reactions of gases, as compared to liquids, took place very slowly, an observation that was subsequently confirmed by others.

Together with Leon Pean de Saint-Gilles (1832-1863), Berthelot studied the kinetics of the esterification of acetic acid with ethyl alcohol, and the influence of time and certain equilibrium conditions (new chemical mechanics). In this work, which has been described as "an important milestone in the development of the concept of chemical equilibrium" [10], they found that the rate of formation of the ester was proportional to the amounts of reacting substances.

In the same decade, Berthelot also carried out a great deal of research in the new field of thermochemistry [11]. Using a bomb calorimeter of his own making, he determined the heats of combustion of a large number of compounds, and concluded that heats of reaction were a quantitative measure of affinity [12]. Berthelot proposed three fundamental thermochemical principles, namely: the principle of molecular work, the principle of the calorific equivalence of chemical transformations, and the principle of maximum work [13]. The latter principle: "that every chemical reaction leads to the production of those substances that develop the maximum amount of heat" led to considerable debate, and in 1893, Walter Nernst (1864-1941) announced that it could only be true if the heat of reaction was independent of the temperature [14]. It is perhaps not widely known that Bertheot coined the words "endothermic" and "exothermic", which are still in general use to this day.

In 1887, Berthelot was appointed a member of the editorial board of the important journal Zeitschrift fur physikalische chemie, and due to his pioneering efforts in the field has rightly been called "un des precurseurs de la chimie physique" [15]. He has also been referred to as the "fondateur de la thermochimie" [16]; however, that honour must be shared with the Danish chemist Julius Thomsen (1826-1908) who carried out early and extensive calorimetric work [17].

Researches in Other Areas

Berthelot did important work in other fields, for example, on explosives [13]. He devised an ozonizer baring liquid armatures, and studied reactions initiated by silent electric discharge; and thus discovered persulphuric anhydride in 1878. He investigated the various allotropes of arsenic, sulphur, and phosphorus, and in 1891 discovered iron pentacarbonyl [8]. In addition, Berthelot carried out numerous experiments using voltaic cells. His researches on photochemical reactions were published in the journal Annales de Chimie between 1898 and 1905.

Another area where Berthelot left his mark was animal and plant chemistry. In 1865, he carried out experiments on animal heat and some 24 years later studied the heat given off by the action of oxygen on blood [8]. He also devised methods for the measurement of the heats of combustion of proteins, fats and sugars [9]. In 1876, Berthelot showed that plants absorb atmospheric nitrogen under the influence of a silent electric discharge, and later on found that nitrogen assimilation occurs via microorganisms in the soil.

In the last 20 years of his life, Berthelot became involved in the history of chemistry and alchemy. He translated many Greek and Arabic manuscripts into French [17], and, thus, was able to make available a "nearly complete and critical edition of the writings of the oldest chemists of the Alexandrian period" [2]. His efforts resulted in a series of publications, including les Origines de l'Alchimie (1885) and Collection des anciens Alchimistes Grecs (three volumes, 1887-1888). In his book Science et Morale, published in 1897, Berthelot wrote: "j'ai reconstitue toute true science, l'alchimie antique; jusque-la meconnue et incomprise". His pioneering work on the analysis of very old objects originating in the Middle East constituted the beginnings of chemical archaeology [8]. One year before his death, Berthelot's book Archeologie et Histoire des Sciences was published.

Berthelot's last researches were devoted to studies on the elements argon, helium and radium. He claimed to have produced an argon compound by sparking benzene vapour, but it was later shown that no reaction had actually taken place [17].

Publications and Students

Berthelot was the author or co-author of at least 1600 papers in fields as varied as "inorganic, organic, physical, analytical, technical, agricultural, physiological, and historical chemistry" [8]. He also found the time to write some 25 books, a number of which became well-known, particularly: Chimie Organique fondee sur Ia Synthese (two volumes, 1860); Essai de Mecanique Chimique fondee sur la Thermochimie (two volumes, 1879); La Revolution Chimique, Lavoisier(1890); and Les Carbures d'Hydrogene, 1851-1901, Recherches Experimentales (three volumes, 1901).

Some brilliant students were attracted to the College de France due, in part, to Berthelot's reputation. Four of these, all of whom were to become notable professors of chemistry, were: Francois Marie Raoult (1830-1901), Philippe Antoine Barbier (1848-1922); Paul Sabatier (1854-1941), and Alfred Werner (1866-1919). Barbier and Sabatier were both appointed assistants to Berthelot. In 1912, Sabatier was awarded the Nobel Prize for Chemistry, which he shared with his fellow countryman Victor Grignard. Alfred Werner undertook advanced studies for one year (1890-1891) with Berthelot, during which he developed his theory of inorganic compounds for which he was to receive the Nobel Prize for Chemistry in 1913.

Politics and Statesmanship

In middle age and while still very actively involved in research and lecturing, Berthelot entered the world of national politics where he was to occupy a series of increasingly important governmental posts. He became inspector of higher eduction in 1876 and ten years later was named Minister of Public Instruction. Then, in 1895, he was appointed to the key post of Foreign Minister [16]. Berthelot had been elected a Senator in 1881. It is nothing short of incredible that he was able to handle all of these responsibilities and yet remain productive in science throughout his long lifetime. Interestingly, the famous German chemist Adolf von Baeyer (1835-1917) while visiting Berthelot in Paris is said to have told hint that he was "a great chemist", whereupon Berthelot replied: "Non, je ne suis pas grand chimiste, je suisun homme d'etat." [8].

Conclusion

The output of Berthelot, who has been called "France's elder statesman of chemistry" (17), was aptly described as "astonishing in its volume, originality, and importance" [8]. However, although he always kept himself up-to-date on scientific advances, Berthelot was surprisingly resistant to some developments that were generally accepted by others. For instance, he was a sceptic when it came to the atomic theory, and he used the old atomic weights and even HO for the formula of water until as late as 1891! When Jacobus van't Hoff (1852-1911) and Joseph-Achille Le Bel (1847-1930) independently proposed in 1874, as an explanation for the phenomenon of optical activity, that the valences of the carbon atom were oriented towards the corners of a tetrahedron, Berthelot rejected the idea.

One annoying trait possessed by Berthelot was his frequent use of the published results of others with hardly any or no acknowledgement of their source! This inevitably brought forth disapproval from those concerned. One notable victim of this untoward treatment was the German chemist Friedrich Wilhelm Ostwald (1853-1932) who complained bitterly [18]. Berthelot shared this unfortunate behaviourial flaw with his great predecessor Antoine Laurent Lavoisier (1743-1794) who was also criticized for it.

The striking versatility of Berthelot coupled with his remarkable drive brings to mind the earlier impressive exploits of his celebrated compatriot Joseph Louis Gay-Lussac (1778-1849) that were also characterized by wide variety and great quantity [19].

There is no doubt as to the immense prestige attained by Berthelot since both he and his wife, who died only one hour before him, were accorded, by a grateful nation, the unprecedented honour of a joint state funeral in the Pantheon in Paris. Berthelot's 1860 statement to the effect that "La chimie cree son objet. Cette faculte creatrice, semblable "a celle de l'art lui-meme, la distingue essentiellement des sciences naturelles et historiques" [5], will forever serve to emphasize the uniqueness of chemistry and its creative power.

References

1. Levere, T.H., Affinity and Matter: Elements of Chemical Philosophy 1800-1865, Clarendon Press, Oxford, pp. 205-209, 1971.

2. Partington, J.R., A Short History of Chemistry, 3rd. ed., Macmillan & Co., Ltd., New York, pp. 281, 283, 295, 1965.

3. Newbold, B.T, 'Jean Baptiste Andre Dumas: A Dominating Influence in Nineteenth Century French Chemistry', ACCN, 50(7): 17, 1998.

4. Father, E., The Evolution of Chemistry, 2nd. ed., The Ronald Press Co., New York, pp. 173, 194, 216, 380, 1969.

5. Berthelot, M. Chimie Organique fondee sur la Synthese, 2 vols., Paris, 1860.

6. Salzberg, H.W., From Caveman to Chemist, American Chemical Society, Washington, DC, p. 241, 1991.

7. Asimov, I., A Short History of Chemistry, Anchor Books, Doubleday & Co., Inc, Garden City, NY, p. 98, 1965.

8. Partington, J.R., A History of Chemistry, Vol. 4, Macmillan & Co., Ltd., New York, pp. 308, 399, 465-474, 1964.

9. Florkin, M., A History of Biochemistry, Part II, Comprehensive Biochemistry, Vol. 30, Elsevier Publishing Co., Amsterdam, pp. 238, 267, 1972.

10. Lindauer, M.W., 'The Evolution of the Concept of Chemical Equilibrium from 1775 to 1923', J. Chem. Educ., 39:386, 1962.

11. Berthelot, M, Essai de Mecanique Chimique fondee sur la Thermochimie, 2 Vols., Paris, 1879.

12. Leicester, H. M., The Historical Background of Chemistry, Dover Publications, Inc., New York, p. 205, 1956.

13. Leicester, HM, and H.S. Klickstein, A Source Book in Chemistry: 1400-1900, McGraw-Hill Book Co., Inc., New York, pp. 428-431, 1952.

14. Farber, E., Milestones of Modern Chemistry, Basic Books, Inc., New York, p. 185, 1966.

15. Lockemann, G, Histoire de la Chimie, Dunod, Paris, p. 199, 1962.

16. Dictionnaire Usuel, Editeurs Quillet-Flammarion, Paris, p. 163, 1960.

17. Brock, W.H., The Fontana History of Chemistry, Fontana Press, Harper Collins Publishers, New York, pp. 3, 337-338, 1992.

18. Wall, F.E., 'Wilhelm Ostwald - A Study in Mental Metamorphosis', J. Chem. Educ., 25:4, 1948.

19. Newbold, B.T., 'Joseph Louis Gay-Lussac: Polyvalence Personified', ACCN, 50(1):29, 1998.

Brian Newbold, FCIC recently retired from the Departement de chimie et biochimie at Universite de Moncton, Moncton, NB. Newbold won the Union Carbide Award for Chemical Education in 1977 and in 1997 was awarded the Meritorious Services Prize of the Chemical Software Society of Japan. He is currently engaged in research on the history of chemistry.
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Author:Newbold, Brian T.
Publication:Canadian Chemical News
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Geographic Code:1CANA
Date:Feb 1, 1999
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