Tyrian purple

(2E )-6- bromo-2- (6 -bromo -3-oxo -1H-indole -2-ylidene )-1H -indol- 3-one

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The or purple ( Old High German [ Female] purple [ a] purpura from Latin, it borrowed from Greek πορφύρα, porphyra, dye from shellfish ) is called a dye (preferably Murex trunculus ) was originally derived from living in the Mediterranean Sea Snails. His luminous color is called purple. Chemically it is 6,6 '- dibromoindigo, which is related closely to the Indigo.

History

The discovery of the coloring of purple was attributed to the inhabitants of the Phoenician city of Tyre in ancient times. But it could be shown that has already been established around 1600 BC in Minoan Crete purple.

According to legend, equated with the Phoenician Melkarth Heracles is said to have recreated a nymph named Tyros. When the dog of Hercules took a bite of a person sitting on a cliff by the sea purple snail and his lips be stained with a beautiful red, told the nymph wanting to receive Heracles again until he gives her a dress with this color.

After Achilles Tatius the dog of a fisherman is said to have bitten a discarded purple snail. When the fishermen wanted to wash out the supposed wound, he discovered the resistance of the color.

The manufacturing process is described by Pliny and Aristotle. The snails were caught between autumn and spring. The surviving animals were opened, the color- containing Hypobranchialdrüse removed and placed three days in salt. The mass was purified and concentrated by boiling in urine to one sixteenth of the original amount. The dyed fabric had to be exposed to light during drying so that capsized by an enzyme reaction, the originally pale yellow coloring to the desired shade of red. The staining was supposedly fixed by the addition of honey. To produce one gram of pure purple about 10,000 snails are required.

In ancient Rome, the dye was the Senators ( who were allowed to wear a purple stripe on their clothes ) reserved. Later, the emperor wore a toga, which was quite stained with purple. In fact, the private people operated with purple dresses luxury has no decree can contain ever. There was in Rome guilds ( collegia or familiae ) the Purpuraii in whose hands lay the production of purple fabric. Livy describes similar to the smell of the raw dye as offensive, and its color than that of the stormy sea.

In late antiquity, a certain purple color was privilege and insignia of the Byzantine emperors. Later this privilege was transferred to the pope and papal legate.

The color was also a status symbol for the German emperors, and from 1468 she was the official color of the Catholic cardinals. Remarkably, these garments were, however, usually dyed with kermes as a substitute for the original purple.

Purple is now only used at traditional church- or government - official occasions, but no longer carried the staining with the juice of the purple snail.

Chemistry

The structure of the purple was determined in 1909 by Paul Friedlander as dibromoindigo.

The dye 6,6 '- dibromoindigo was first chemically synthesized in 1903. The total synthesis of purple required after the structure determination for some time yet. The installation of the bromine is directed by the other substituents in the benzene ring to the substitution site. The CRO group is the amino group -NHR ortho-para directing group, meta- directing group, and thus the bromine substitution thermodynamically not favored. In direct bromination of indigo therefore 5,5 '- dibromoindigo or 5,5', 7,7 ' - tetrabromoindigo formed. These are due to the π -electron ratios are not the desired color characteristics.

Use

Today the expensive original ink is only very rarely in use. Mostly it is used for religious purposes, such as for dyeing garments for the Jewish Rabbinate. Field of application is the restoration of original stained with purple fabrics. To date, this dye is the most expensive. The company offers Kremer Pigments purple at a price of about 2450 Euros per gram.

The purple snail

The marine biologist Félix Joseph Henri de Lacaze - Duthiers 1858 found that three snails in the Mediterranean produce purple blue dyes. One way of Murex trunculus (now Haustellum trunculus ), was of him as the source of the blue purple in the Bible determined (2 Mos 26 EU). In his book Mémoire sur le pourpre (Paris 1859) he treated the ancient purple dyeing. The gastropod Purpura lapillus, which is found in the Atlantic, provides the dye.

Purple oxides

Iron oxide pigments, which are obtained as by-product in the roasting of pyrite for the production of sulfuric acid are called Purple oxides. They, too, are added in order to increase their opacity often brown organic pigments.

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