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Hofmann, August Wilhelm von

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(1818–92) German organic chemist: major discoverer of new organic compounds of nitrogen.

Hofmann began his studies in Giessen as a law student, but attendance at some of chemistry lectures changed his interests and Liebig welcomed this, perhaps because Hofmann’s father, an architect, was overseeing the building of the new chemical laboratory. Young Hofmann’s first research was on coal tar aniline (C6H5NH2 ) and began the interest in organic amines which was to prove so important. He won prizes, became engaged to Liebig’s wife’s niece and came to London as the first head of the new Royal College of Chemistry in Oxford Street in 1845. He stayed for 20 years, and he and his students created organic chemistry in England. One of these students, , made the first synthetic dye produced on any scale (mauve, from aniline) and founded the British organic chemical industry. Other students, and Hofmann himself, made a variety of new organic dyes. From them, in turn, medicinal chemicals were developed.

In 1850 Hofmann showed that ammonia can be progressively alkylated by a reactive alkyl halide to give a mixture of amines. Thus ethyl iodide with ammonia in a sealed container (he was a large-scale user of champagne bottles from Windsor) gives the ethylamines, which he represented as follows, basing them on the ‘ammonia type’ in a way which advanced the ‘Type Theory’:

He made similar compounds from phosphine (PH3 ) in 1855. He moved to a professorship in chemistry in Berlin in 1865. Hofmann was not a theorist, but he had excellent instincts as an experimentalist and this, combined with his use of the theory available to him, led to his high output of new results. The Hofmann rearrangement (1881) gives a primary amine as the organic product (via an isosyanate) when an amide is heated with bromine (or chlorine) and alkali:

Also named after him is the Hofmann exhaustive methylation reaction, which allows a complex nitrogen-containing organic compound to be degraded to simpler, identifiable, products; its early use was to determine structures but later it became a subject for the study of reaction mechanism. Hofmann produced hundreds of research papers; he had many assistants and a large number of friends; he was married four times and had 11 children.

Four different atoms or groups (A, B, D, E) attached to a central carbon atom can be arranged in two different ways, which are non-superposable mirror images. The tetrahedra are imaginary: the double lines represent bonds with the carbon atom.

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