Johann von Baeyer | Robert Bunsen | August Wilhelm von Hofmann
Johann FWA von Baeyer was born in Berlin, and studied chemistry under Bunsen and Kekulé at Heidelberg. He later followed Kekulé to Ghent. In 1860 he returned to Berlin where he taught chemistry for 12 years at the Technical Institute, the forerunner of the Charlottenburg Technical High School. In 1872 he was appointed Director of the newly-founded University of Strasbourg and, in 1875, succeeded Liebig at Munich. There, he built up a reputation as one of Germany's foremost organic chemists.
It was von Baeyer who devised the eponymous Baeyer test for unsaturation1, whereby potassium manganate (VII) is decolorised in the presence of an alkene or alkyne. In 1865 he began a series of researches that led to elucidation of the structure of the dye-stuff, indigo-tin (indigo-blue), thus preparing the way for its commercial production. En route to this structure, von Baeyer synthetised isatin from phenylethanoic acid, thereby confirming its formula, first proposed by Kekulé in 1869.
It was Professor von Baeyer who, in 1872, first observed that a resinous material is obtained when 'carbolic acid' (phenol) is mixed with formaldehyde (methanal). In 1908, industrial use was made of this material when the American chemist (but Belgian by birth) Leo H Baekeland showed that when this resinous material is heated in the presence of an alkaline catalyst, it first softens and then becomes quite hard. This artificial resin is now known as the thermosetting plastic, bakelite, and was the first really artificial plastic of any great importance.
Von Baeyer's work contributed greatly to the confirmation of Kekulé's theory of the constitution of benzene. Thus von Baeyer (1885) was the first to point out that the angle subtended by the corners and centre of a regular tetrahedron 109°28', lies between the values of the angles in a regular pentagon (108°) and a regular hexagon (120°). On the basis, therefore, of a tetrahedral carbon atom, von Baeyer advanced his 'strain theory' whereby the less the 'strain' between the valencies of the carbon atoms, the greater will be the ease of formation and the greater the stability of closed-ring compounds. Thus, according to von Baeyer, rings containing five or six carbon atoms form most readily, and are the most stable, because they involve the least strain (or distortion) from the natural valence angle.
Johann von Baeyer died on 20 August, 1917.