29 No. 5
Friedrich Wöhler (1800–1882), one of the most important German chemists of the 19th century, is best known for his serendipitous preparation of urea from ammonium cyanate in 1828. This momentous discovery happened at a time when most scientists believed that naturally occurring organic compounds such as urea, which was first isolated from urine by the French chemist Hilaire Marin Rouelle in 1773, could only be produced by living organisms. Thus, Wöhler’s synthesis of urea not only helped to bridge the gap between organic and inorganic chemistry that prevailed then, but also played a key role in the demise of the vitalistic theory. It is also worth noting that Wöhler was a man of many talents: He discovered organic radicals with his lifelong friend and collaborator Justus von Liebig, he worked with Berzelius on the isolation of beryllium and silicon, he prepared the first (impure) sample of metallic aluminum, and he was a prolific writer and a dedicated teacher at the University of Göttingen for more than 45 years.
The 100th anniversary of Wöhler’s death was commemorated with the stamp that illustrates this note, issued in Germany on 12 August 1982. It displays a beautiful ball-and-stick diagram of urea, clearly showing a carbon–oxygen double bond for the carbonyl group, and a balanced chemical equation for its synthesis from ammonium cyanate. Interestingly, the latter is a relatively unstable species that can be generated from the reaction of silver cyanate with ammonium chloride or the treatment of lead cyanate with aqueous ammonia, two of the methods originally reported by Wöhler. However, urea is nowadays obtained industrially on a massive scale from ammonia and carbon dioxide (i.e., the Bosch–Meiser process), and some 90 percent of the world production (more than
100 megatonne per year!) is used as a fertilizer.
Written by Daniel Rabinovich <firstname.lastname@example.org>.
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