24 августа, 2015 
Pokraskin Indigoid dyes represent one of the oldest known class of organic dyes. For 5000 years they have been used for dyeing textiles such as wool, linen, and cotton. For example, 6,6′-dibromoindigo is Tyrian Purple, the dye made famous by the Romans. Tyrian Purple was so expensive that only the very wealthy were able to afford garments dyed with it. Indeed, the phrase “born to the purple” is still used today to denote wealth. Although many indigoid dyes have been synthesized, only indigo itself (1) is of any major importance today. Indigo is the blue used almost exclusively for dyeing denim jeans and jackets and is held in high esteem because it fades to give progressively paler blue shades.
Adolf von Baeyer reported the chemical structure of indigo in 1883, having already prepared the first synthetic indigo from isatin (2) in 1870. Until then, isa- tin had only been obtainable by oxidation of indigo. It was not until 1878 that von Baeyer first synthesized it from phenylacetic acid, making a complete synthesis of indigo possible [1].
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