August Wilhelm von Hofmann

August Wilhelm von Hofmann (April 8, 1818 – May 5, 1892) was a German chemist.

Biography
Hofmann was born at Gießen, Grand Duchy of Hesse. Not intending originally to devote himself to physical science, he first took up the study of law and philology at Göttingen. But he then turned to chemistry, and studied under Justus von Liebig at University of Giessen. When, in 1845, a school of practical chemistry was started in London, under the style of the Royal College of Chemistry, Hofmann, largely through the influence of the Prince Consort, was appointed its first director. It was with some hesitation that he, then a Privatdozent at Bonn, accepted the position, which may well have seemed rather a precarious one; but the difficulty was removed by his appointment as extraordinary professor at Bonn, with leave of absence for two years, so that he could resume his career in Germany if his English one proved unsatisfactory. Fortunately the college was more or less successful, owing largely to his enthusiasm and energy, and many of the men who were trained there subsequently made their mark in chemical history. In 1864 he returned to Bonn, and in the succeeding year he was selected to succeed Eilhard Mitscherlich as professor of chemistry and director of the laboratory in Berlin University.

Hofmann's work covered a wide range of organic chemistry. His first research, carried out in Liebig's laboratory at Giessen, was on coal-tar and his investigation of the organic bases in coal-gas naphtha established the nature of aniline. This substance he used to refer to as his first love, and it was a love to which he remained faithful throughout his life. His perception of the analogy between it and ammonia led to his famous work on the amines and ammonium bases and the allied organic phosphorus compounds while his researches on rosaniline, which he first prepared, formed the first of a series of investigations on coloring matter which only ended with quinoline red in 1887.

The Hofmann rearrangement and Hofmann elimination reaction bear his namesake. Hofmann was also the first to introduce molecular models into his public lectures around 1860, following the earlier (1855) suggestion by his colleague William Odling that carbon is tetravalent. This legacy is still remembered nowadays by continuing use of  Hofmann's colour scheme: (carbon = black, hydrogen = white, nitrogen = blue, oxygen = red, chlorine = green,  sulfur = yellow, as cited by  W. D. Ollis,  "Models and molecules",    Proceedings of the Royal Institution of Great Britain,  (1972),  45,  1-31). The models look rather odd nowadays, primarily because Hofmann had them built so that the carbon was planar, and smaller in size than the hydrogen! (it was Loschmidt in 1861 who probably first appreciated the differing sizes of different atoms). It was not until 1874, when Jacobus Henricus van't Hoff and (independently) Joseph Achille Le Bel suggested carbon can be tetrahedral, that molecular models assumed their modern appearance.

William Henry Perkin was a student of his at the Royal College of Chemistry in London, when he discovered the first aniline dye, mauveine.