A civil servant’s son with a love of art
Otto Wallach was born on March 27, 1847, in Königsberg, then the capital of East Prussia and today Kaliningrad in Russia. His father, Gerhard Wallach, was a senior Prussian civil servant who later became Auditor General at Potsdam; his mother, Otillie Thoma, came from a Protestant German family. His father’s postings took the family first to Stettin and then to Potsdam, where Otto went to the classical Gymnasium.
School gave him a deep and lasting love of history and art, interests that stayed with him for the rest of his life. Chemistry was hardly taught at secondary schools in those days, so the teenage Wallach carried out his own experiments at home, in his parents’ house. That mix of an artist’s eye and a chemist’s hands would later suit him perfectly for a field built around the scents of plants.
A fast start at Göttingen and Bonn
In 1867 Wallach went to the University of Göttingen to study chemistry with Friedrich Wöhler and his colleagues. After a semester in Berlin with August Wilhelm von Hofmann, he returned to Göttingen and worked so hard that he earned his doctorate in 1869 after only five semesters. Working hours in Wöhler’s laboratory ran from seven in the morning to five in the afternoon, after which the gas was turned off and students finished their experiments by the light of candles they bought themselves.
After a year as an assistant in Berlin he joined August Kekulé at the University of Bonn in 1870. Kekulé, himself an artist at heart, had written to him that in Bonn they led a scientific artist’s life. The Franco-Prussian War soon called Wallach away to military service, and afterwards he tried working in Berlin for the young dye company that later became Agfa. His health could not stand the factory fumes, and in 1872 he returned to Bonn, where he stayed for nineteen years. He became a lecturer, an associate professor in 1876 and, in 1879, was obliged to take over the chair of pharmacology, which pushed him toward the chemistry of natural medicines.
The Bonn years were productive even before terpenes. Wallach discovered the imino chlorides, made by treating acid amides with phosphorus pentachloride, and studied amidines, glyoxalines and azo dyes. He also converted chloral into dichloroacetic acid. This was solid, careful work of the kind that earned respect without fame, and it gave him a mastery of reactive organic compounds that he would soon need.
The forgotten cupboard
The turning point came almost by chance. Kekulé showed Wallach an old, forgotten cupboard full of bottles of essential oils, the fragrant liquids distilled from plants such as pine, lemon, peppermint, eucalyptus and lavender, and invited him to study them. Wallach became absorbed. It was the start of more than two decades of work that would become his life’s achievement.
The field was a mess. Essential oils contain families of closely related compounds called terpenes. Many have exactly the same chemical formula, ten carbon atoms and sixteen hydrogen atoms, and nearly the same boiling point, yet they smell and behave differently. Chemists had described nearly a hundred of them, usually named after the plant they came from, under names like camphene, citrene, carvene, cinene and hesperidine. They were unstable and changed into one another at the slightest provocation. As the Swedish Academy later put it, a thorough study of the field had seemed practically hopeless.
Bringing order to the scents of plants
Wallach published his first terpene paper in 1884. His key insight was practical. Most terpenes are liquids, which are hard to identify, so he used simple reagents such as hydrogen chloride and hydrogen bromide to turn them into solid crystalline compounds whose melting points could be compared. In this way he could tell terpenes apart and recognize them even in mixtures. Within a few years he showed that many of the supposedly different substances were in fact identical, cutting the confusing list of known terpenes down to a handful of genuine compounds.
He also learned how easily terpenes rearrange into one another, worked out the conditions that prevented those changes, and used the rearrangements to deduce the structures of unknown terpenes by converting them into known ones. He coined the names terpene and pinene, and he pointed out that terpenes appear to be built up from five-carbon units of isoprene, an observation later developed by Leopold Ruzicka into the isoprene rule that still organizes the field. After six years of this work he published a first summary of his results, and other chemists in many countries quickly took up the field he had opened. Wallach himself kept leading it, preparing and determining the structures of a very large number of compounds, among them alcohols and ketones related to the terpenes and larger molecules such as the sesquiterpenes. The Swedish Academy judged that, because of this work, the chemistry of ring-shaped alicyclic compounds had grown from a curiosity into one of the main branches of organic chemistry, and that Wallach had contributed more to it than anyone else. In 1909 he gathered his findings into a 600-page book, Terpene und Campher, which he dedicated to his students. Several reactions still carry his name, including the Leuckart–Wallach reaction, used to make amines, and the Wallach rearrangement.
Science given freely to industry
Wallach’s work did not stay in the laboratory. It transformed the industry that processes essential oils into perfumes, flavourings and medicines. Once the terpenes could be identified and measured, manufacturers could check the purity of their raw materials, which had often been adulterated, and could develop new ways of making and using these compounds. At the 1910 Nobel ceremony the Swedish Academy reported that annual production of such preparations in Germany alone had risen from 12 million marks in 1885 to 45 to 50 million marks.
Most strikingly, Wallach never patented his discoveries. According to the Swedish Academy, he always put his observations at the disposal of industry free of charge, and many of his students carried his exact methods into industrial laboratories. That choice mattered. In an age when chemical discoveries were becoming valuable property, Wallach treated his knowledge of the terpenes as something that belonged to everyone who could use it. Firms large and small could apply his methods without paying for them, and the analytical tests he devised became common ground for buyers and sellers of essential oils, helping honest producers compete with adulterated goods.
Among the doctoral students he trained was Walter Haworth, who later helped work out the structure of vitamin C and won the Nobel Prize himself in 1937.
What the terpenes give us today
Terpenes and their relatives, the terpenoids, are one of the largest families of natural molecules. They include menthol in mint, limonene in citrus peel, camphor, the pinene that gives pine forests their smell and the many compounds blended into perfumes, soaps, cleaning products and food flavourings. The modern fragrance and flavour industry rests on the ability to identify, purify and make these molecules, the very skills Wallach first worked out.
The same chemistry reaches into medicine and nutrition. Vitamin A and the carotenoids that colour carrots and tomatoes are terpenoids, as are important plant-derived medicines such as the anti-malaria drug artemisinin and the cancer drug paclitaxel. Natural rubber is a long chain of isoprene units. Wallach could not have foreseen most of these, but the systematic study of terpenes that he founded made them understandable and, in many cases, possible to produce.
Jewish heritage
Wallach’s Jewish heritage came through his father. Gerhard Wallach descended from a Jewish family that had converted to Lutheranism, a path taken by many Prussian Jewish families who sought careers in state service in the nineteenth century. Wallach himself was raised Protestant, and there is no record that he identified with Judaism.
He is nevertheless counted among Jewish Nobel laureates by the Jewish Virtual Library and other listings, on the strength of that paternal ancestry. His story is one of many in this period in which a family’s Jewish origins faded from view within a generation or two, yet remained part of who they were.
Göttingen, the war and final years
In 1889 Wallach was called back to Göttingen to succeed Victor Meyer in Wöhler’s old chair, which also made him director of the university’s Chemical Institute. He stayed there for the rest of his working life. Besides terpenes he made important contributions to the chemistry of amides, amidines and azo dyes, and his Nobel biography stresses that, like Baeyer and Emil Fischer, he trusted carefully performed experiments more than theoretical speculation.
The Nobel Prize in Chemistry came in 1910, for his pioneering work on alicyclic, or ring-shaped, compounds. Other honours followed, including the Davy Medal of the Royal Society in 1912 and honorary doctorates from Manchester, Leipzig and Braunschweig. The First World War brought his career to a sad close: in 1915, after six of his assistants were killed in action at the start of the war, he retired from his posts. Wallach never married. He died in Göttingen on February 26, 1931, and was buried there. His legacy is the orderly science of nature’s scents, built by a chemist who chose to share it rather than own it.
Sources & further reading
Otto Wallach, Biographical, NobelPrize.org · Award ceremony speech, Nobel Prize in Chemistry 1910, NobelPrize.org · Otto Wallach, Jewish Virtual Library · Otto Wallach, Wikipedia · Researched from the sources above and checked against them. Spotted an error? Tell us.
A life of tikkun olam. This is part of tikkun olam, the Jewish idea of repairing the world, and every one of us can add to it.