A provincial scientist

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Throughout his prolific career in chemistry, Paul Sabatier remained faithful to his roots in provincial France. Mary Jo Nye introduces us to the Nobel laureate and investigates the chemistry that made him such an important figure in organic chemistry

Just over 150 years ago, on 5 November 1854, Paul Sabatier was born at Carcassonne in southern France. He shared the Nobel prize in chemistry with Victor Grignard in 1912, each chemist being recognised for innovation in organic chemistry that revolutionised both academic chemical research and industrial chemical production.

Grignard received recognition for discovering the organometallic compounds known as the Grignard reagents and Sabatier for his method of directly hydrogenating organic compounds using a finely-divided metal catalyst. Along with Henri Moissan in 1906 and Marie Curie in 1911, Grignard and Sabatier became the only French scientists to receive the Nobel prize in chemistry until Fr?d?ric and Ir?ne Joliot-Curie were awarded the prize in 1935.

At the time of the 1912 Nobel award, both were scientists in provincial France rather than in the French capital - Grignard was teaching at the University of Nancy, and Sabatier was teaching at the University of Toulouse. Nor were they members of the French Academy of Sciences, because membership then required residence in Paris.

For Sabatier, the Nobel award was not only a personal triumph, but a vindication of his dedication as an administrator in the science faculty at Toulouse and his decision to stay in Toulouse even when he was offered opportunities in 1907 to succeed Moissan at the Sorbonne or Marcellin Berthelot at the Coll?ge de France in Paris.

Sabatier began teaching at Toulouse in 1882, and he was dean of the sciences faculty from 1905 to 1929. He worked hard to forge university ties with local industrial and agricultural interests in the Midi region of France, and he successfully presided over the establishment of new institutes for applied science in chemistry, electrotechnology, and agriculture that were funded largely from regional resources. The fact that his scientific work not only brought Toulouse a Nobel prize, but that it had immediate applications in industry, also vindicated his devotion there to both fundamental and applied science.

Sabatier’s loyalty to Toulouse, only 100 kilometres from his birthplace in Carcassonne, wasn’t because he was unfamiliar with Paris. Sabatier, along with his older brother Th?odore, had initially studied mathematics and science at the Carcassonne lyc?e, where their uncle was a professor and where later Th?odore would become a physics professor.

When their uncle moved to Toulouse, Paul Sabatier followed him there as a boarding student. He took entrance examinations for the Ecole Polytechnique and Ecole Normale Sup?rieure (ENS) in Paris, choosing the latter after being fortunate enough to be admitted to both schools.

Following his studies at the ENS, Sabatier won first place in the competitive national physics agr?gation examination. He then taught for a year at the lyc?e in N?mes until in 1878 Berthelot offered him a position as assistant in his organic chemistry laboratory at the Coll?ge de France.

Sabatier completed a doctoral thesis under Berthelot in 1880 on the thermochemistry of sulfides, taught at Bordeaux, and then got a post at Toulouse in 1882, where he became a professor in 1884, at the age of 30.

On the face of it, Sabatier was a lucky young scientist, although this was not quite the way he saw the matter.

Sabatier was convinced that Berthelot would never support him for a prestigious position in Paris because the master and student differed significantly on matters of politics and science. Berthelot was strongly anti-clerical and anti-religious, while Sabatier was a pious Catholic whom one university administrator described as distant from the liberal, republican side of the political spectrum.

Despite these differences, Sabatier conformed in his dissertation to Berthelot’s old-fashioned preference for a chemical notation expressed in terms of chemical equivalents rather than chemical atoms. However, he soon adopted the contemporary system of chemical atomic weights and the new periodic table of the elements that chemists were routinely using outside France. In his teaching at Toulouse, Sabatier used these new ideas and spearheaded reforms in the chemistry curriculum.

For the first 10 years or so of his research, Sabatier focused on thermochemistry and physical chemistry, including studying how fast metaphosphoric acid was transformed, partition coefficients, and absorption spectra. He received the Paris Academy’s Prix La Caze in 1897 for his work in inorganic chemistry, amounting to some 90 articles.

His interest in chemical affinity led him to a collaboration with Jean-Baptiste Senderens, who was teaching chemistry at the Institut Catholique in Toulouse. Senderens completed his doctoral thesis in Sabatier’s laboratory in 1892, following earlier work with Sabatier’s more senior colleague Edouard Filhol, whose lectures at Toulouse had originally inspired Sabatier in the early 1870s to become a university scientist.

Sabatier and Senderens followed up some independent work by Ludwig Mond and by Berthelot, who had recently synthesised the metal carbonyl compounds Ni(CO)₄ and Fe(CO)₅ by fixing the unsaturated gas molecule nitrogen dioxide on the metals copper, cobalt, nickel, and iron.

After failing to get similar results with nitric oxide and nitrous oxide, Sabatier and Senderens decided instead to try ethylene with finely-divided metal, knowing that Moissan and Charles Moureu had recently failed in similar experiments with acetylene and platinum black, a well-known inorganic catalyst.

Experimenting with ethylene and finely-divided nickel at around 300 ?C produced a carbon deposit and hydrogen gas, as in Moissan and Moureu’s results, but also produced methane. Sabatier and Senderens hypothesised that they had formed an unstable intermediary between nickel and ethylene, similar to nickel carbonyl, and this led to carbon, methane, and nickel being produced.

After experimenting with lower temperatures and different methods of cooling and washing the gases, Sabatier and Senderens discovered that directing equal volumes of ethylene and hydrogen on freshly reduced nickel, with heating to only 30-45?C, resulted in a gas mixture that was practically all ethane.

Cold acetylene with nickel likewise produced ethane; and cobalt, iron, copper, and platinum black gave similar, but less intense, results.

In 1901 they prepared cyclohexane by using reduced nickel and hydrogen at 180?C in a vertical U-tube cooled by melting ice. They noticed the tube becoming clogged by colourless crystals that they assumed was benzene solidifying at 5?C. Cyclohexane had previously been reported to crystallise at -110?C. However, when they opened the tube, they were hit by a smell of roses. It was coming from cyclohexane which, in fact, crystallises at 6.5?C. Sabatier later said that this was one of the greatest joys of his life.

Sabatier and Senderens continued working together until 1905, when they shared the Academy’s Prix Jecker. From 1901 to 1905, they went from one type of reaction to another, transforming unsaturated ethylenic and acetylenic carbides into saturated carbides; nitrate derivatives and nitriles into amines; aldehydes and ketones into alcohols; carbon monoxide and carbon dioxide into methanol; phenol into cyclohexanol; and aniline into cyclohexane.

They produced major types of natural petroleum by modifying conditions for hydrogenating acetylene.

Sabatier also began collaborating with Alphonse Mailhe, and with other students and co-workers: Marcel Murat (1912-1914); L?o Espil (1914); Georges Gaudion; (1918-1919); Itizo Kasiwagi (1918); and Bonasuke Kubota and Antonio Fernandez (in the 1920s).

Sabatier and Mailhe found that powdered metallic oxides like thoria, silica, and alumina were catalysts for both hydration and dehydration. Sabatier also discovered that hydrogen could be removed from one part of a molecule and then introduced into another.

From 1905, Senderens worked exclusively at the Institut Catholique, collaborating with Jean Aboulenc on metalloids and their catalytic action on metals, also investigating how metallic oxides, salts, and mineral acids acted on alcohols and organic acids. Senderens also worked as a consultant to the large industrial firm Poulenc Fr?res.

The mechanism for catalytic hydrogenation and hydration interested Sabatier considerably, as he discussed at some length in his Nobel lecture of 1912. Gustav Robert Kirchhoff had discovered in 1811 that mineral acids play a role in changing starch into dextrine and sugar without themselves undergoing any changes.

J?ns Jacob Berzelius had coined the term catalyst ( roughly translated as ’I destroy’) in 1836, arguing that the effect was to raise the temperature. Most chemists assumed that compression and local heating of gases in porous surfaces accounted for reactions that otherwise would require a much higher temperature.

In contrast, Sabatier argued that because the different catalysts and their effects were so specific, the assumption must be made that unstable intermediary compounds formed during the reaction, and that one of them had to be a nickel hydride. By the 1920s, Irving Langmuir’s ’chemisorption’ theory became a rival hypothesis to Sabatier’s, allowing the intermediary compounds to be more varied than Sabatier wanted to allow.

It was immediately apparent that the work on hydrogenation would have numerous commercial applications. These included: transforming nitrobenzene into aniline, acetone into isopropyl alcohol, carbon monoxide into methanol; making cyclohexanes; and eventually, producing liquid fuels by coal hydrogenation. Sabatier filed eight patent applications, including one for converting liquid fatty acid (oleic acid) into solid acid (stearic acid).

After the first world war, hydrogenating oils into solid fats became big business, especially for making and marketing popular products like margarine. (More recently, the trans-fats, made by hydrogenating vegetable oils, have fallen under scrutiny for raising the level of low-density lipoproteins, or ’bad’ cholesterol, and lowering high-density lipoproteins, or ’good’ cholesterol.)

Sabatier was a reserved man, who was devastated by his wife’s death in 1898, which left him widowed with four daughters, the youngest only a year old. He was an avid amateur artist, and his family still have all the watercolours that he painted.

In Sabatier’s lifetime, the new catalytic hydrogenation method gained nothing but praise. Occasionally, however, Sabatier was criticised as scientific administrator and Nobel prize winner. Some colleagues at Toulouse regarded him as overly committed to the applied science institutes and insufficiently sympathetic with the needs of scientists in mathematics, astronomy, and other fields that didn’t have direct ties to industry and agriculture. Some younger colleagues also complained that Sabatier and his allies ran the sciences faculty in a hierarchical and autocratic fashion, rather than agreeing to more democratic governance processes, a criticism that is not uncommon in universities the world over.

Perhaps it isn’t very surprising that some scientists argued that the Swedish Academy of Sciences should have made the Nobel award jointly to Senderens and Sabatier. Sabatier was also criticised for failing to give his former collaborator proper credit. Indeed, in a letter to the Berlin Chemical Society in 1911, Sabatier apologised for referring to Senderens in a recent lecture as his student and for neglecting to state clearly Senderens’ crucial role in discovering the method of catalytic hydrogenation and dehydrogenation.

In his 1912 Nobel lecture, Sabatier did not make this mistake again, referring to Senderens six times and speaking of him as a collaborator, while also referring to his work with his pupils Mailhe and Murat.

However, Sabatier’s reference to Senderens as his ’pupil’ reappeared again in later years. Clearly, Sabatier’s perception of his relationship with Senderens was very different to that held by Senderens himself and Senderens’ proponents.

In 1913 Sabatier became the first scientist elected to a newly created section of six members of the French Academy of Sciences for members not living in Paris. Grignard, almost 20 years younger than Sabatier, was elected to the section in 1926.

The award of the Nobel prize to these two provincial scientists put French organic chemistry in the limelight at a time when German chemists had been dominating the field for several decades.

Grignard and Sabatier also demonstrated the powerful roles that French universities outside Paris could play in French science. By the end of the 20th century Sabatier’s name was given to the Universit? Paul Sabatier in suburban Toulouse, which is the science and engineering campus for the University of Toulouse.

It now numbers some 28 000 students and 2500 teachers and researchers working in over 100 laboratories, a notable expansion in scope beyond the 15 teachers and 340 students in the sciences faculty when Sabatier began his deanship about a century ago.

Sabatier would doubtless regard the success of science and engineering in Toulouse as one of his great achievements along with his benchmark achievements in organic catalysis.