The Tragic Story of a Great Chemist: Archibald Scott Couper (1831-1892)

by Roberto Poeti
Carbon Chemistry

In the history of Organic Chemistry, to the German chemist Friedrich August Kekulé von Stradonitz (1829 – 1896) is reserved for a pre-eminent place. In 1858 he wrote an article listing two fundamental properties of the carbon atom: valence four and the ability of carbon atoms to bind together. In 1865 he published another paper in which he defined the hexagonal structure of the benzene molecule. These discoveries gave an extraordinary boost to the chemistry of the nineteenth century.  Today they constitute the axioms of organic chemistry.

But there’s another chemist

But in the same year 1858, a few weeks after the publication of Kekulè and in a completely independent way, another Scottish chemist Archibald Scott Couper (1831-1892) at only twenty-seven years old published an article “On a new chemical theory ” with the same conclusions to which Kekulè had arrived. The life of this chemist is as interesting as it is tragic. He was born in a small village a few miles from Glasgow in 1831. He was the only surviving son of Archibald Couper, a large cotton weaving plant owner that employed more than 600 workers. Of unsteady health, he had a good and scrupulous upbringing at home. In 1851 he began his undergraduate studies at Glascow in Latin and Greek, traveled to Germany, then continued his studies at the University of Edinburgh in philosophy, logic, metaphysics and moral philosophy. So far there are no references in his notes to chemistry studies.

 

.……………………………………………………………………………………………………………………………………

His passion for chemistry was born

He was facilitated in his studies by his father who did not force him to follow his own path in the world of industry.  After travelling in the south of Germany and northern Italy he returned to Scotland. In 1855 he was in Berlin and after a period spent in Paris he was back in Berlin where he took courses in analytical chemistry. There is no word on the reasons for the change in the direction of the studies and his new interest in chemistry. With incredible speed, after only three or four chemistry study sessions, Couper had acquired the knowledge and skills necessary to enable him to conduct experimental chemistry investigations independently. In 1856 he went to Paris where he found a place in the laboratory of Charles-Adolphe Wurtz (1817-1884).

 

Charles-Adolphe Wurtz (1817-1884). He was an influential and important chemist French. Convinced supporter of atomic theory, made great contributions to the development of organic chemistry, we remember Wurtz’s reaction.

 

 

 

 

 

 

………………………………………………………………………………………………………………………………………….

Writes his essay on carbon compounds

Publishes the first article on benzene properties and he was the first to synthesize bromobenzene and dibromobenzene. This will be followed by a major investigation into salicylic acid that we will talk about later. A short time later, he hands Wurtz his essay on a new theory of carbon compounds to present him at the French Academy. But Wurtz hesitates, wasting time and it will instead be Kekulè’s essay that will be first presented in Liebig’s Annalen. Couper’s essay will be presented shortly thereafter by Jean Baptiste André Dumas (1800-1884) at the French Academy and the account appeared in Comptes rendu’s. The priority of the discovery is attributed to Kekulè. Couper does not forgive Wurtz for his behaviour in this affair, reproaches him for his lightness and expresses it harshly. Wurtz reacts by moving Couper away from his lab.

The crisis and the disease

The clash with Wurtz will mark the life of the young chemist. He returned to Edinburgh in Scotland at the end of 1858 and found an assistant job at Professor Lyon Playfair’s laboratory (1818-1898). His academic position seemed to offer security, but soon after his tenure he suffered a severe form of nervous breakdown

The comfortable house in Kirlintilloch in Scotland that his mother had built for him, where Couper lived his last years

 

 

 

 

 

 

…………………………………………………………………………………………………………………………..

He spent the rest of his life until his death in 1892 at the age of sixty-one, unmarried, in the house that his mother had built for him, assisted by his mother who survived him, no longer able to engage in study and research, alternating short periods of tranquility at long periods of mental suffering.  After his essay ” On a New Chemical Theory ” of 1858 he no longer made any contribution, nor perhaps he became more interested in chemistry until his death.

A forgotten chemist

With his estrangement from the activity of chemist, his figure fell into oblivion. His tracks were lost. His essay, initially criticized and misunderstood by academic chemists, was overshadowed by the success that instead met Kekulè’s work. The merit of having rediscovered and valued Couper’s work and wrote his biography (from which I drew the information of my article) owes it to the organic chemist Richard Anschutz (1852-1937) who wrote a beautiful essay ” The life and work of the chemist Archibald Scott Couper “from 1909. So fifty years after the publication of his “On a New Chemical Theory ” Couper’s name gets his place in the history of chemistry. Anschutz tells us about the difficulties he encountered in obtaining news of Couper’s biography, and as he says ” I was unable to find his name in any dictionary of biographies of scientists. ”

 

Richard Anschutz (1852-1937)

 

 

 

 

 

 

 

Why Anschutz cares about Couper

Richard Anschutz was a valuable organic chemist who started working in the same Institute of Chemistry as the University of Bonn where Kekulè was head. On his death, he became an ordinary professor, and took Kekulè’s place.  But we see from an excerpt from his book on Couper how he rediscovers him: “Beyond the theoretical article, Couper published a communication “On some derivatives of Benzene” and, later, a very excellent experimental work “Research on salicylic acid”. But just as Couper, not his fault, came too late with his theoretical work, so even with his work on salicylic acid, in which he studied the action of phosphorus pentachloride on salicylic acid, he had the misfortune that two of the most illustrious German chemists, August Kekulè and Hermann Kolbe, as well as some others, repeated his experiments, but were unable to confirm his results.  Here Couper’s appearance in chemistry comes to an end.

How did this happen?

Although his skills seemed to qualify him eminently for a distinguished scientific career, none of his further communication was found in any scientific journal.  How did this happen? What happened to Archibald Scott Couper?  My interest in Couper was first awakened by his work on the action of phosphorus pentachloruro on salicylic acid, a topic on which I too was particularly concerned [ Ndt. Anschutz repeating experiments on salicylic acid confirmed the results he had achieved couper, disassembling the criticisms of Kekulè and Kolbe ].  My sympathy with Couper grew when, in the course of studies that were required for the preparation of a full biography of Kekulè, it seemed necessary to deepen Couper’s article “On a new chemical theory.” This article by Couper must, in fact, always take place next to that of Kekulè “On the constitution and metamorphosis of chemical compounds”»

A portrait of Couper

Among the direct and indirect testimonies he managed to gather was that of a friend of Couper with whom he spent a lot of time in Berlin in the period that began his studies in chemistry:

«Couper was a very handsome man, tall and slender, of distinguished appearance, aristocratic. Her pretty face, with her bright complexion, was animated by the almost incredible brilliance of her deep black eyes. He had no appearance of weakness, but nevertheless his health was delicate, and I heard that his mother was always anxious for him. The basis of his character, as is often the case with the Scots, was deeply religious. He was very fond of music, classical, serious and lively, and rarely missed a good concert when he was in Berlin.» Richard Anschutz concludes his memoir: «In the history of organic chemistry Archibald Scott Couper so hard tried deserves a place of honour next to his luckiest colleague, Friedrich August Kekulè

 

 

 

…………………………………………………………………………………………………………………………………….

Further than Kekulè

 In his article Couper argues that the valence of carbon can be two and four. In the article that Kekulè writes at the same time the value of carbon assumes only the valence four. Kekulè firmly criticizes the double value of carbon hypothesized by Couper .

In the following three columns (taken from Anschutz’s book) three versions of the same formulas are listed: in the first column those that appeared in the note that Archibald Scott Couper presented to the French Academy, the column in the middle represents the version of the formulas that he adopted, shortly after the note, in the article published in the Philosophical Magazine in Edinburgh and in the third column formulas as they would appear by adopting the atomic weight 16 of oxygen, where an oxygen atom replaces the symbol O…..O with the consequent halving of oxygen atoms

The third column presents formulas in such a modern way that it is amazing, especially if we compare them with representations of the same substances in the same period.

A comparison of Couper and Kekulè formulas

 For example, Kekulè represented glycolic acid, referring to the double water type, according to Gerhardt’s Theory of Types, as follows.

 

Glycolic acid according to  Kekulè

 

 

…………………………………………………………………………………………………………………………

The two dashes above the hydrogen indicate the overall value of the group or radical. Valence is seen as the property of a group of atoms and the representation of its structures still remains within the theory of Types where groups or blocks of atoms take on almost the meaning of elements. (With the bar on the carbon and oxygen symbol Kekulè indicated that he was using the new atomic weights sixteen and twelve respectively for the two elements). Archibald Scott Couper, on the other hand, represented it by using dashed lines for the first time as a connection between two atoms. The version on the right is entirely equivalent to the modern formula if we report, as we have seen before, the atomic weight of oxygen to 16, thus halving the oxygen atoms.

Glycolic acid according to  Couper

 

 

 

…………………………………………………………………………………………………………………………..

The example of glycolic acid shows that although Kekulè speaks in his essay on the bonding between carbon atoms, this discovery unlike Couper is not represented in the language of his formulas. Kekulè is formed in the great rut of the tradition of European organic chemistry where it is believed that formulas do not correspond to a physical reality. Kekulè’s point of view is a development of the Theory of Types, then in force, for which in formulas the focus is on groups typical of atoms and not their internal relationships. Couper has a philosophical background and Anschutz argues that Couper was able to deal with the problem with his mind much freer from preconceived ideas. But the almost complete break he makes with the coded chemical knowledge of his time will not help him to accept his opinions.

Couper goes even further

 The version of Couper’s essay, which was published in Comptes rendus, eventually contains a reference to nitrogen to which he correctly attributes valence three and five. Makes examples of cyanide compounds

Cyanuric acid of couper 1858                                                                                                                    The modern formula

Archibald Scott Couper’s formula of cyanuric acid, although oxygen is carbon-related and not nitrogen, contains the ring structure, seven years before Kekulè devised a cyclical arrangement for benzene carbon atoms.

The material at your disposal in PDF

 Archibald Couper’s essay “On a New Chemistry Theory

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Articoli Correlati