Wednesday, May 31, 2006

Get lucky

William Perkin did 150 years ago, when he discovered the first aniline dye. (Luck had little to do, however, with the commercial success that he had from it.) In an article in Chemistry World I explore this and other serendipitous discoveries in chemistry. Perkin’s wonderful dye is shown in all its glory on the magazine’s cover, and here is the article and the leader that I wrote for Nature to celebrate the anniversary:

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Perkin, the mauve maker

150 years ago this week, a teenager experimenting in his makeshift home laboratory made a discovery that can be said without exaggeration to have launched the modern chemicals industry. William Perkin was an 18-year-old student of August Wilhelm Hofmann at the Royal College of Chemistry in London, where he worked on the chemical synthesis of natural products. In one of the classic cases of serendipity for which chemistry is renowned, the young Perkin chanced upon his famous ‘aniline mauve’ dye while attempting to synthesize something else entirely: quinine, the only known cure for malaria.

As a student of Justus von Liebig, Hofmann made a name for himself by showing that the basic compound called aniline that could be obtained from coal tar was the same as that which could be distilled from raw indigo. Coal tar was the residue of gas production, and the interest in finding uses for this substance led to the discovery of many other aromatic compounds. At his parents’ home in Shadwell, east London, Perkin tried to make quinine from an aniline derivative by oxidation, based only on the similarity of their chemical formulae (the molecular structures are quite different). The reaction produced only a reddish sludge; but when the inquisitive Perkin tried it with aniline instead, he got a black precipitate which dissolved in methylated spirits to give a purple solution. Textiles and dyeing being big business at that time, Perkin was astute enough to test the coloured compound on silk, which it dyed richly.

Boldly, Perkin resigned from the college that autumn and persuaded his father and brother to set up a small factory with him in Harrow to manufacture the dye, called mauve after the French for ‘mallow’. The Perkins and others (including Hofmann) soon discovered a whole rainbow of aniline dyes, and by the mid-1860s aniline dye companies already included the nascent giants of today’s chemicals industry.

(From Nature 440, p.429; 23 March 2006)

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A colourful past

The 150th anniversary of William Perkin’s synthesis of aniline mauve dye (see page 429) is more than just an excuse to retell a favourite story from chemistry’s history. It’s true enough that there is still plenty to delight at in that story – Perkin’s extraordinary youth and good fortune, the audacity of his gamble in setting up business to mass-produce the dye, and the chromatic riches that so quickly flowed from the unpromising black residue of coal gas production. As a study in entrepreneurship it could hardly be bettered, for all that Perkin himself was a rather shy and retiring man.

But perhaps the most telling aspect of the story is the relationship that it engendered between pure and applied science. The demand for new, brighter and more colourfast synthetic dyes, along with means of mordanting them to fabrics, stimulated manufacturing companies to set up their own research divisions, and cemented the growing interactions between industry and academia.

Traditionally, dye-making was a practical craft, a combination of trial-and-error experimentation and the rote repetition of time-honoured recipes. This is not to say that the more ‘scholarly’ sciences failed sometimes to benefit from such empiricism – an interest in colour production led Robert Boyle to propose colour-change acidity indicators, for instance. But the idea that chemicals production required real chemical expertise did not surface until the eighteenth century, when the complexities of mordanting and multi-colour fabric printing began to seem beyond the ken of recipe-followers.

That was when the Scottish chemist William Cullen announced that if the mason wants cement, the dyer a dye and the bleacher a bleach, “it is the chemical philosopher who must supply these.” Making inorganic pigments preoccupied some of the greatest chemists of the early nineteenth century, among them Nicolas-Louis Vauquelin and Louis-Jacques Thénard and Humphry Davy. Perkin’s mauve was, however, an organic compound, and thus, in the mid-nineteenth century, rather more mysterious than metal salts. While the drive to understand the molecular structure of carbon compounds during this time is typically presented now as a challenge for pure chemistry, it owed as much to the profits that might ensue if the molecular secrets of organic colour were unlocked.

August Hofmann, Perkin’s one-time mentor, articulated the ambition in 1863: “Chemistry may ultimately teach us systematically to build up colouring molecules, the particular tint of which we may predict with the same certainty with which we at present anticipate the boiling point.” Both the need to understand molecular structure and the demand for synthetic methods were sharpened by chemists’ attempts to synthesize alizarin (the natural colourant of madder) and indigo. When Carl Graebe and Carl Liebermann found a route to the former in 1868, they quickly sold the rights to the Badische dye company, soon to become BASF. One of those who found a better route in 1869 was Ferdinand Riese, who was already working for Hoechst. (Another was Perkin.) These and other dye companies, including Bayer, Ciba and Geigy, had already seen the value of having highly skilled chemists on their payroll – something that was even more evident when they began to branch into pharmaceuticals in the early twentieth century. Then, at least, there was no doubt that good business needs good scientists.

(From Nature 440, p.384; 23 March 2006)

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