Purple – Pride Comes Before the Fall

chemistry of Pleasure This is the first article in a series of seven in which the theme is the chemistry of the seven cardinal sins: pride, greed, lust, envy, gluttony, wrath and sloth. The writer Ulf Ellervik uses his next book about the Chemistry of Pleasure as a springboard. Purple – pride comes before the fall (By Ulf Ellervik, Professor of Bioorganic Chemistry, Lund University) Genuine purple is a very dark, almost black colour. It was the colour of kings and emperors until a curious chemist stumbled on a synthetic variant. ost probably, it a beautiful purple by the sun. forms the colourless substances the boil continued. To be first- was the Phoeni- The snails produce a colourless in the secretion into purple di- rate, the pigment should inclu- cians who first secretion whose purpose is to bromo-indigo. One of the steps de an element of black. Textiles discovered that capture small unwanted partic- in this transformation is a pho- were soaked in the solution for Msome snails, for instance the les picked up by the molluscs tochemical reaction requiring five hours before they were re- murex snail, Bolinus branda- whilst feeding. strong sunlight. moved and left to dry. ris, change colour when expo- The secretion is probably also sed to sunlight. Murex snails a defence mechanism since it were commonly used in food contains a few relatively weak There was a certain rich man, which and it is likely that someone spilt nerve toxins. When a snail is » a crushed snail onto their clo- crushed, the enzyme purpurase was clothed in purple and fine linen, thes – which were then dyed is released which quickly trans- and fared sumptuously every day. The Phoenicians soon learnt to In the strong Mediterranean sun- utilise the murex snails and es- light, the rest of the process only tablished, as early as 1300 BC, takes ten minutes. In the pho- an industry for dyeing fabric tochemical reaction, sulfur-con- near the ancient city of Tyre taining substances are also rele- and the dye became known ased which give the dyestuff an as Tyrian purple. Producing unpleasant smell, similar to gar- dyestuff from snails is a labour lic – those wanting to dress well intensive process, and through had to put up with the smell. the ages purple dye has always Gradually, purple became so been at least ten times as ex- exclusive that the Roman empe- pensive as gold, per unit of ror Nero issued a decree stating weight. In his Naturalis His- that the colour was to be worn toria, written around 77 AD, by emperors only – and so pur- Pliny the Elder described the ple became a colour for royalty. process used to dye fabric with Due to its high cost, purple la- Tyrian purple. ter caught the attention of many First, the snails had to be so- scientists. aked in salt water for three days, In 1879, the English chemist after which the stinking sludge Edward Schunk managed to iso- of semi-fermented snails was late 7 milligrams of the pigment boiled in a cauldron of tin or lead. from 400 snails, and he was All protein was skimmed off and also able to show that the same In 1561, the coronation mantle of Erik XIV was made by the tailor then the witches’ brew was left to pigment was present in purple- Claes Bertilsson. The oldest piece of clothing remaining from a boil for a further couple of days. coloured fabric. Unfortunately, Swedish coronation, the mantle was later worn in turn by Johan III (1568), Karl IX (1604) and Gustav II Adolf (1611). Following the battle At regular intervals, the quality the amount was not enough to of Lützen in1632, Sweden was in a tumultuous state and Gustav’s of the dye was tested on a piece determine the structure of the daughter probably never wore the mantle of beautifully purple velvet. of cloth, and if not satisfactory, substance. 32 Kemivärlden Biotech med Kemisk Tidskrift. Nr 3. March 2013 The German chemist Paul Fried- called, which quickly gained po- aniline länder showed considerably pularity not least because it was more patience when he dis- much loved by Napoleon III’s NH2 sected and sun-dried 12,000 wife, the Empress Eugénie. It snails, from which he success- spurred a literal epidemic of fully purified 1.4 grams of the mauve-coloured clothes in Fran- exclusive dye, enough to enable ce, a fashion that quickly spread him to establish its molecular to England, where Perkin beca- structure in a series of clever me a rich man thanks to his dis- anilin experiments. The pigment of covery. Meanwhile, many other the murex snail, 6,6’-dibromo- similar pigments were develo- a mauve-coloured pigment indigo, is one of very few natu- Unfortunately it is not pos- ped and in 1881 the mauve dye ral compounds that contain the sible to chemically produce pur- was used for the very last time N element bromine. However, its ple dye by letting indigo react to print the mauve 1 penny po- colour is purple only when the with bromine. That is because stage stamp. H2N N NH bromine atoms are in precisely the bromine atoms will end up the right position. in all sorts of positions except The development of aniline dye If the bromine atoms are mo- the right ones. However, the- continued, mainly in Germa- ved around within the molecule, re are other ways of producing ny. Through their names, many ett malvafärgämne the colour changes to blue. The beautiful shades of purple. German industries known to- same molecule without bromi- day can be traced back to the 6,6’-dibromo-indigo ne is called indigo, one of the In the spring of 1856, the young production of aniline dye, for world’s most important pig- and very promising chemist example AGFA (Aktiengesell- O ments. Indigo is found, for in- William Henry Perkin was busy schaft für Anilinfabrikation) H N Br stance, in a close relative of the in the laboratory. He had just and BASF (Badische Anilin- Br N purple murex snail, Murex trun- turned 18 and his idea was to & Sodafabrik). After the First H culus; but the most common try to make the malaria drug World War, the six largest Ger- O source of indigo is the plant In- quinine by the oxidation of allyl man chemical industries ini- 6,6'-dibromoindigo digo tinctoria, a herb that grows toluidine with potassium dich- tiated a tentative collaboration just over a metre high. romate. His experiments failed, supervised by Carl Duisberg. In order to produce the pig- but Perkin did not give up. In- All the companies had suffe- indigo ment, harvested plants are so- stead, he tested the same met- red badly following the Treaty O aked in water over night and hod but with a simpler starting of Versailles and established In- H then a yellow liquid can be tap- material, aniline. This did not teressen-Gemeinschaft Farben- N ped off. The liquid contains a result in quinine either; instead industrie AG, IG. water soluble form of the pig- a black blob was left in the bot- IG would come to play a par- N H ment called indigo white. tom of the flask. ticularly unpleasant role during O The miracle occurred when the Second World War, but that indigo Textiles and yarn to be dyed are Perkin was washing up. The is a completely different story. KB submerged in the yellow solu- black blob dissolved in metha- tion and then hung up to dry in nol and displayed a beautiful the sun. The oxygen in the air mauve colour, not dissimilar to then oxidizes indigo white into that of the herb mallow. Cont- a blue form which is insoluble rary to most of his colleagues, in water. Consequently the co- Perkin, who at one point had lour will remain in the fabric contemplated a career as an ar- even after it has been washed tist and therefore had good in- many times. sight into all sorts of pigments, Today, indigo is produced realised that he had discovered synthetically, and one of its a gold mine. most important applications is Perkin decided to concentrate the dyeing of jeans. Between on the pigment, and within a 3 and 12 grams of pigment is few months he produced large used for each pair of jeans. quantities of aniline dye, as the Adolf von Baeyer, one of the new substance became known. late 19th century’s most famous Due to a minor mistake when chemists, was awarded the No- Perkin applied for a patent, the bel Prize in 1905 for his work on pigment was never patented in chemical synthesis and in par- France. Hence, the French were The murex snail, Bolinus brandaris, changes colour when exposed ticular the synthesis of indigo. able to produce mauve, as it was to sunlight. Kemivärlden Biotech med Kemisk Tidskrift. Nr 3. March 2013 33.

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