Indigo - The history of its synthesis

The dye Indigo is nowadays especially popular as it is widely used for the colouring of blue jeans trousers. Its intensive use started in the last quarter of the 19th century as Levi Strauss invented the jeans fabric for very hardwearing clothes – using the blue Indigo colour for their coloration. At this time also first chemical synthesis ways for the blue colour originally derived in Europe from dyer´s woad (a very time-consuming and long during process) and later imported from Asia - have been developed. The work will give an historic overview of the traditional blue colouring with the dyer´s woad (the “European Indigo” Isatis tinctoria) and the Indian Indigo Indigofera tinctoria. Then it will present the experimental ways for the determination of the chemical structure of the Indigo molecule and the first steps to reproduce Indigo from its parts. An overview of different approaches for chemical synthesis will be described. Important researchers and companies in this synthesis process will be presented, chemical reaction equations will give explanations for the development of finally the best synthesis way at the beginning of the 20th century.