The dye that revolutionised chemistry: Perkin and the discovery of mauveine

Fig. 1: Chemical structure of Tyrian purple.

Historically, the colour purple has always been linked to nobility. The first purple dye was Tyrian purple (Fig. 1), a natural dye obtained from the mollusc Murex brandaris by the Phoenicians. In Greek and Roman times, this prestigious and expensive colour was an exclusive of the rich and an indication of social status. This changed in the 1800s, when an English chemist, William Perkin, synthesised the first synthetic dye: Mauveine.

Sir William Henry Perkin was born in London on 12th March 1838, just three months before the coronation of Queen Victoria. Growing up, Perkin wasn’t sure of what he wanted to do, until he observed a friend carrying out experiments with crystals in solution and was captivated by chemistry. In the late 1800, the subject was still very mysterious and seen as alchemy, rather than a real science. Although Perkin’s father wanted him to become an architect, Perkin enrolled at the Royal College of Chemistry in London. In the Easter of 1856, at the age of 18 and only three years after he joined the college, William Perkin was working in his laboratory at home, trying to synthesise quinine. The compound was an expensive plant-based drug used to treat malaria, a very serious condition, especially during Victorian times. Since Perkin’s knowledge was limited to the empirical formula of quinine (C₂₀H₂₄N₂O₂), the reaction failed and he obtained a black precipitate. He added some methanol to what he believed to be yet another ‘waste product’, probably to wash it, and noticed it gave a purple solution. Since the colour looked attractive, Perkin decided to use it to stain a silk cloth: the first synthetic dye was born.

Fig. 2: Piece of silk dyed with Perkin’s mauveine in 1860.

He noticed the colour was both bright and fast to light, qualities that were rarely found in dyes derived from nature. Perkin could not imagine that the dye would soon revolutionise the manufacture of colourants and the entire chemical industry. Because of the deep purple colour obtained from mauveine, the chemist first called the dye ‘Tyrian purple’ from the name of the iconic purple used in the Ancient world, then ‘Aniline purple’ from the starting material used to produce it, and, finally, ‘Mauve’ or mauveine from the French name for the mallow flower. In 1857 Perkin patented the dye and managed to open his first factory in the north of London. Most importantly, the chemist understood that he needed to invest in research and development in order to produce more colours. It is important to remember that, at this point in the history of dyes, the aromatic structure of benzene was still undetermined. This was in fact theorised in 1865 by Kekulé, almost ten years after Perkin discovered mauveine. It is remarkable how the young chemist was able to carry out the manufacture of mauveine and other synthetic dyes without fully knowing their chemical structures and properties! The discovery of mauveine, the first synthetic dye, paved the way to the creation of many more synthetic dyes in a range of colours. Soon, nearly all the colours of the rainbow could be obtained, and it was even possible to predict the colour of a compound before its production. As aniline dyes were cheaper, easier to source and more resistant than natural dyes, the natural dyes market eventually collapsed, with the result that with very few dyes sourced from nature are used today.

Fig 3: Glass bottles containing mauveine

salts.

The famous shade of purple became very fashionable and highly desired, especially by Royals and the nobility, after Queen Victoria wore a purple dress for her daughter’s wedding in 1858. Empress Eugenie, wife of Napoleon III, also enjoyed wearing dresses of the same colour or dyed with other aniline-based colours. The dye industry was founded on scientific discovery: when mauveine was first introduced, its chemistry was still a mystery to many. The aniline employed by Perkin during the first synthesis of mauveine was not pure but consisted of a mixture of anilines and toluidines. Although Perkin was aware of this, the mixture in the starting materials was only identified in 1994 by advanced analytical techniques. Interestingly, Perkin also made a dye from pure aniline, and called it pseudo-mauveine. However, its colour was not as bright nor as attractive as that of the original mauveine.

Fig. 4: Victorian stamp 

dyed with Perkin’s mauveine.

Recent attempts aimed at recreating Perkin’s original synthetic method have led to different results concerning the composition of the dye. If Perkin’s patented method is followed, this always leads to different mixes of mauveine’s chromophores. After comparison of original samples of the dye from museums (patented method) and commercial mauveine (industrial manufacture) found in Victorian stamps from 1867-1880 (Fig. 4), the existence of different synthetic pathways and different formulations was suggested. Perkin might have deliberately chosen to omit details of his synthesis to fight back his competition or he might have adapted the synthesis due to the need of a more efficient industrial manufacture. Despite the wide popularity of Mauve, no analytical investigation was carried out by Perkin or other chemists of the time. The English chemist reported several empirical formulae, which often resulted in contradictions. In fact, although affirming that mauveine followed the formula C₂₇H₂₄N₄ in 1863 and then again in 1879, he went back and forth between a C₂₇ and a C₂₆ structure (respectively, with 27 and 26 carbon atoms) during these years. Mauveine has been studied and analysed since the 1960’s for its historical interest, however the definitive structures of its chromophores were only determined with NMR for the first time in 1994. The study led to the determination of a mixture of two major chromophores in the commercial dye, named mauveine A and mauveine B (Fig. 5).

Fig. 5: Chemical structures of Mauveine A and Mauveine B.

Very recent studies conducted in 2007, revealed the presence of four main chromophores: the already known mauveine A and B, and mauveine B2 and C, over a mixture of at least thirteen methyl derivatives (C24 to C28) (Fig. 6).

Fig. 6: Chemical structures of Mauveine B2 and Mauveine C.

Adriana Iuliano

Bibliografia

• S. Garfield, in Mauve: how one man invented a colour that changed the world, Faber and Faber, London, 2001. 
• M. M. Sousa, M. J. Melo, A. J. Parola, P. J. T. Morris, H. S. Rzepa and J. S. S. De Melo, Chemistry - A European Journal, 2008, 14, 8507–8513. 
• O. Meth-Cohn and M. Smith, Perkin Transactions 1, Journal of the Chemical Society, 1994, 5–7. 
• A. Filarowski, Resonance, 2010, 15, 850–855. 
• P. Ball, Chemistry World, 2017, https://www.chemistryworld.com/news/dye-detective-work-uncovers-perkins-chemistry-secrets/2500193.article, (accessed 26/10/2018). 
• T. F. G. G. Cova, A. A. C. C. Pais and J. S. S. D. Melo, Scientific Reports, 2017, 7.