of the
Colour Purple

26 March 2018

This March, Google honoured Sir William Henry Perkin FRS (1838-1907), the discoverer of the first synthetic purple dye, with a Google doodle.

His accidental discovery and the dye he called mauveine made him incredibly wealthy, thanks to the booming textile industry and the hefty price tag already associated with the colour purple. This was because, until Perkin’s discovery in 1856, the only known purple dye was Tyrian Purple.

Tyrian Purple can be dated back to the Bronze Age, where it was farmed by exposing the juices of sun-dried murex shellfish, particularly Murex brandaris, to oxygen in the air. Unfortunately, around 10,000 shellfish were required to produce one gram of the dye, which was only enough to dye the hem of a garment. The scarcity of the dye meant it was worth more than its weight in gold.

It’s history is lavish: Cleopatra dyed the sails of her ship with it; Julius Caeser wore the first fully dyed purple toga, which he reserved for Roman emperors leading to the phrase “to don the purple” for “the assumption of imperial dignity”; If you were caught wearing purple in the era of Nero, he would have you killed.

Tyrian Purple is actually a cousin of indigo dye. Indigo is well-known and remains the most produced dye worldwide. Historically, indigo was farmed from the indigofera genus of plants, but now tonnes of it are produced synthetically each year.

Tyrian purple is indigo with two bromine atoms attached at the 6–positions (6,6’–dibromoindigo). Fatefully, a chemist trying to brominate indigo dye directly in the lab would succeed at adding bromine at the 4, 5 and 7 positions, but not the 6 position.

There are several synthetic preparations of Tyrian Purple, which is something I have been researching for a few upcoming publications (stay tuned!). However, despite my own efforts, the synthesis of Tyrian Purple is time consuming, a little expensive and not as industrially viable as the modern synthetic purples. Alas, I won’t be following in Sir William Henry Perkin’s footsteps, and this beautiful dye seems destined to remain in the history books.

For the time being at least.

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