GENERAL ARTICLE Sir William Henry Perkin: The Man and his ‘Mauve’ G Nagendrappa Today we cannot imagine our lives without a variety of colours. Every colour we see, consume, enjoy, apply and use wherever we need has a dye associated with it. More than 90% of the thousands of dyes used now are synthetic. A little more than 150 years ago a handful of dyes of only natural origin were available. In 1856 the era of synthetic dyes was ushered in by a spirited young chemist, William Henry Perkin, when G Nagendrappa was a professor of Organic he was trying to synthesize quinine, but obtained a coloured Chemistry at Bangalore substance instead. It was a much desired colour and therefore University, Bangalore, and became an instant hit. The following is an account of Perkin’s Professor and Head of the life as a chemist and an industrialist par excellence. Department of Medicinal Chemistry, Sri Ramachandra (Medical) Eighteen hundred and fifty six was the year when one of the most University, Chennai, from celebrated accidental discoveries in chemistry was made. It im- where he recently retired. pacted not just chemistry or science in general, but many other He is currently in Jain areas of human activity. It provided stimulus to the economy, and University, Bangalore. He continues to teach and do became an instrument of social, cultural and political change. research. His work is in Textiles and printing became more colourful and cheaper; artists the area of organosilicon K.V.Rashmiis currentlyan M.E.student atthe IndianInstitute ofScience.Shereceived herB.Tech. chemistry, synthetic and had moredegree choices from of the shades National to paint Institute with; ofstaining Technology of biological Karnataka, Surathkal. Her current research mechanistic organic specimensinterests revolutionized are in coding biology theory, and error-correction medicine. The in discovery networks and wireless communication.“ chemistry, and clay- kindled a rapid growth in research activity that went directly into catalysed organic reactions industrial manufacturing. (Green Chemistry). It was not only the momentous happening, but the vigorous pursuit to exploit it by an enthusiastic teenage youth that led to the developments that followed. The young man was William Henry Perkin, who is credited with the preparation of the first synthetic dye called mauve or mauveine or aniline purple. It became the basis on which a new chemical industry was built, which became a model for others to follow. Early Life Keywords Perkin, mauve, mauveine, qui- William Henry Perkin was born in London on 2nd March 1838, nine, dye. RESONANCE September 2010 779 GENERAL ARTICLE The changes in forms three months before Queen Victoria was crowned (28th June and colours, 1838). He was the seventh child and second son of George Fowler appearance and Perkin (1802–1862) and Sarah Perkin. George Perkin was a disappearance of the builder and carpenter. ThePerkin’s family was oneof thewealthiest crystals in solution in Shadwell, the locality where they were living in London. had a magical effect William’s first schooling was at Private Arbour Terrace School on the young Perkin’s situated a few hundred yards from his home. He was an intelligent mind. student endowed with musical talent, and skills in drawing, painting and photography. His first photograph was a self-portrait taken when he was 14 years. He was proficient in playing several musical instruments, and music was a part of his regular activity throughout his life. Senior Perkin used to get copies of building plans made by William with the intention, in addition to using his drawing skill, to influenceWilliam to takeup architectureas career. But destiny’s design was different. Just before he turned thirteen, William observed a friend performing some chemistry experiments with crystals and crystallization. The changes in forms and colours, appearance and disappearance of the crystals in solution had a magical effect on the young mind. He thought that the magnifi- cence of chemistry was far greater than any other subject he knew. So he wanted to study chemistry. However, chemistry was not a popular subject in those days and it was taught in very few schools. But destiny was in Perkin’s favour, for he at 13 was sent to the City of London School by Cheapside near St. Paul’s Cathedral, as it was closer to his house; the school had chemistry as a subject of study, and Thomas Hall taught it. Hall, who had learnt chemistry from A W Hofmann, was an inspiring teacher and encouraged Perkin to do safe experiments at home and to attend Letheby’s (a well-known analytical chemist) chemistry lectures at the London Hospital. This deepened Perkin’s interest in chemistry further. At 14, he obtained permission from Faraday to attend his lectures at the Royal Institution, during his spare time. The exposure to the great master of experimental science was a thrilling experience to the young boy. By now Perkin’s interest in chemistry was unshakable. But in his father’s view the 780 RESONANCE September 2010 GENERAL ARTICLE subject had no good future and he wanted William to become an architect. Hall who was aware of William’s passionate love for chemistry stepped in and convinced the reluctant father to allow William to pursue a career in chemistry. William, at 15, joined the Royal College of Chemistry, London, where AW Hofmann, one of the great organic chemists of the time, was Professor of Chemistry. Perkin took some analytical courses and worked on the reactions of anthracene. He oxidized anthracene to anthraquionone by nitric acid and carried out chlorination and bromination of an- thracene. Impressed by his work, Hofmann made him an honorary assistant. Further, Perkin conducted experiments on the reaction of anthracene with cyanogen chloride. The work was published in the Journal of Chemical Society in 1856, which helped him get a promotion as staff assistant. Quinine Inspires, Mauveine Arrives Starting from Wöhler’s accidental synthesis of urea in 1828, synthesizing organic compounds had gained much favour with chemists of the day. Quinine, the only important medicine for malaria, was high in the mind of Hofmann as a synthetic target, because the medicine obtained from the bark of cinchona tree, grown mainly in South America, was in short supply. Hofmann had suggested that it would be nice if someone could synthesize quinine. The challenge was taken by Perkin in 1856, and he started the work on quinine in the laboratory he set up at home. The most basic requirement for synthesizing a compound is the knowledge of its molecular structure, i.e., how its atoms are Starting from connected. In 1856, knowledge of chemical structures was just Wöhler’s accidental then emerging, though fairly correct molecular formulae could be synthesis of urea in determined. The structures of only small molecules could be 1828, synthesizing written. The ring structures were still unknown. Perkin was organic compounds therefore completely ignorant of the quinine structure (Box 1). It had gained much was indeed presumptuous on the part of Perkin to have under- favour with chemists taken quinine synthesis, which must be attributed to his irrepress- of the day. ible enthusiasm and confidence. It seems that he had no doubt RESONANCE September 2010 781 GENERAL ARTICLE Box 1. Quinine was identified as the active constituent of cinchona in 1820 by Pelletier and Coventou. Pasteur determined its optical activity as leavo-rotatory and carried out some reactions in 1852. The molecular formula was found to be C20H24N2O2 by Liebig in 1831 and later in 1854 by Strecker. The correct molecular structure was established in 1907 by Rabe. A partial synthesis of quinine was announced by Rabe and Kindler in 1918. The correct stereochemistry was settled by the early 1940s. In 1944, Woodward and Doering published a formal synthesis of quinine with the required stereochemistry, which is considered to be a milestone in organic synthesis, but also a subject of criticism and controversy. A fully stereocontrolled total synthesis was achieved only in 2001 by Stork and his coworkers. Between 1944 and 2001 and thereafter also, several other notable papers on quinine C H synthesis have appeared. OH C H N Quinine has four stereogenic centres (marked with red C, Bridgehead red N is C OH also chiral, but its chirality merges with bridgehead red C). As a result, there are C H sixteen stereoisomers, of which the natural quinine is just one. So, one can N imagine the formidable problem ahead of a synthetic chemist who ventures into Quinine quinine synthesis. about the outcome. His reasoning was simple. The empirical formula of quinine was known to be C20H24N2O2. Therefore it is quite logical to assume that one can combine two molecules of a compound with molecular formula C10H13N to get C20H26N2, at the same time adding two oxygen atoms and removing two hydrogen atoms. And it would be perfectly understandable if one thought, in 1856, of oxidizing a compound with formula C10H13N to get a compound of formula C20H24N2O2: 2 - Cr2O7 , H2SO4 C10H13N + 3 O C20H24N2O2 + H2O (1) (O) Allyl toluidine Quinine Marvellous Mauve from Muck Perkin chose allyltoluidine, which has the formula C10H13N, as the reactant and heated it with potassium dichromateand sulphuric acid as oxidizing agent. Of course, only a miracle would have produced quinine from such a concoction, and indeed what Perkin got was a reddish brown precipitate. However, he did not give up, but decided to investigate the reaction with aniline, a 782 RESONANCE September 2010 GENERAL ARTICLE simpler compound. He treated aniline sulphate with potassium dichromate. Now he obtained a black precipitate. When he added methanol, probably to wash it, he noticed that methanol became purple coloured. As the colour was attractive, young Perkin thought of using it as a dye.