Starting with Lavoisier in the 17805, then Jöns Jakob Berzelius, and Justus von Liebig from 1830, substances found in the plant and animal kingdoms, hence known as organic compounds, were analysed. Lavoisier had established that carbon was always present and usually hydrogen and oxygen. Later the presence of other elements such as nitrogen or sulphur was recognized. By the middle of the century the formulae of many organic substances had been ascertained, that is, the numbers of the different kinds of atoms contained in the molecules. It was found that compounds could have the same ‘molecular formula’ but possess different properties because their atoms were combined in a different way. This was expressed in structural formulae or diagrams showing how the atoms were imagined to be combined. Certain groups of atoms, like a carbon atom linked to three hydrogen atoms (CH3 ), were found to be present in many different compounds, producing a particular effect on its properties.
At the same time as progress was being made on the theoretical side, many of the constituent compounds were being extracted from natural substances. One of the most important of these was benzene, found to be present in coal tar in 1842, which became a subject of research by the brilliant group of chemists which August Wilhelm von Hofmann gathered round him at the Royal College of Chemistry, founded in 1845. Prince Albert had been instrumental in securing Hofmann’s appointment as the first professor there. Benzene was the starting point for many compounds, including an oil called aniline (first prepared from the indigo plant for which the Portuguese name is anil). One of Hofmann’s keenest and brightest students was the eighteen yearold William Henry (later Sir William) Perkin. In 1856, in a laboratory fitted up at his home, he was trying to prepare quinine from aniline and its derivatives, as they appeared to be related structurally.
The result, not unfamiliar to chemists, was an unpromising black sludge. On boiling it in water he obtained a purple solution from which purple crystals were formed. He tried dyeing a piece of silk with this substance and found it produced a brilliant mauve colour, resistant to washing and fast to light. It was the first synthetic, aniline dye. Perkin sent a specimen to the dyers Pullars of Perth, who reported favourably. He then set about exploiting the discovery, first on a back-garden scale, and then in a factory opened the following year at Greenford Green near Harrow, from family capital. The new ‘aniline purple’ swept the board in England and abroad—the French seized on it, naming it ‘mauve’. Queen Victoria wore a mauve dress at the opening of the International Exhibition of 1862; penny postage stamps were dyed mauve. Perkin’s commercial success was such that he was able to retire from business at the ripe old age of 35 and devote his time to chemical research. Other chemists followed in his wake with other dyestuffs derived from aniline. It was found that aniline could be subjected to the diazo reaction, lately discovered by Peter Griess and so named because two nitrogen atoms were involved. When the product of this reaction is treated with phenol, highly coloured substances are formed, many yielding satisfactory dyes. The first azo dye was Bismarck brown, prepared by Carl Alexander Martius in 1863.
The next nut to crack was the synthesis of the red colouring matter in madder, alizarin. The elucidation of its structure had to await further progress on the theoretical side and this was forthcoming when August Kekulé realized that benzene had a cyclic structure, that is, the six carbon atoms in the benzene molecule were joined up in a ring, visualized as the famous hexagonal benzene ring. Following on this, Graebe and Liebermann were able to work out the structure of alizarin and then to devise a way of synthesizing it on a laboratory scale. It was however Heinrich Caro, a chemist responsible for many advances in this field, who worked out a manufacturing process for synthetic alizarin, involving sulphonation of anthraquinone with concentrated sulphuric acid, while working for the firm Badische Anilin- und Soda-Fabrik. Perkin was working along the same lines and was granted a patent for his process on 26 June 1869—one day after Caro received his. A friendly settlement was reached, allowing Perkin to manufacture alizarin in Britain under licence from BASF. The synthetic dye was much cheaper than the natural version, so the maddergrowing industry fell into rapid decline and expired.
Success with alizarin stimulated chemists to turn their attention to indigotin. After many years of research, in which Adolf van Baeyer figured prominently, the molecular structure was found and in 1880 a method of synthesizing indigotin described. Again, the transition to manufacturing scale proved difficult; it was only in 1897 that success was achieved, after long and expensive research supported by BASF. By 1900 and beyond, the industry had not only achieved cheaper and more consistent production of the dyes previously found in nature, but at an everincreasing rate added enormously to the range of dyestuffs and colours available. In this great advance Britain had been given a head start by Perkin’s discovery, but the initiative was let slip and passed to Germany. The British industry lagged behind to such an extent that by the outbreak of the First World War, Britain had to import all but 20 per cent of her dyestuffs, mainly from Germany. The sudden removal of German competition had a tonic effect on the home industry, which rose to the occasion to meet the need. British, and also American, industry soon matched the Germans in this field. Two main factors contributed to the German pre-war pre-eminence in this and other areas: one was the sound education offered in school, university and polytechnic, heavily subsidized by the state, to ensure a good supply of welltrained chemists, and the other was the willingness of industrial concerns to employ chemists and fund research on a quite lavish scale. The synthetic aniline dye industry was the first really science-based industry and demonstrated the spectacular progress that could be achieved by the direct and deliberate application of scientific knowledge to industry.
Burhan-ud-din Kermani
