Indigo – Development of chemical synthesis procedures

The dye Indigo, since the end of the 19th century produced synthetically through various chemical reactions, is widely known as the blue color used for coloring blue jeans trousers. Originally, in Europe the color was produced from dyer´s woad (the “European Indigo” Isatis tinctoria) and later also from the imported “Indian Indigo” Indigofera tinctoria. As the obtaining of the color from the plants was very time intensive, it was one of the expensive dyes and was used for special purposes. One very popular usage started, when in the last quarter of the 19th century, Levi Strauss invented the jeans fabric for very hardwearing clothes – using the blue Indigo color for their coloration. From the usage of the blue dye from Genua, the word “Jeans” was derived from “Bleu de Gênes”. The cotton used for the sturdy trousers came from the place “Nimes” in the South of France from which the designation “Denim” comes from.
With the possibility for producing Indigo on an industrial scale via chemical synthesis procedures, its usage increased very fast. In the presentation, a historic overview of the traditional blue coloring with the dyer´s woad Isatis tinctoria and the Indian Indigo Indigofera tinctoria will be given as well as the development of the chemical synthesis starting with the history of the determination of the chemical
structure of the Indigo molecule and the first steps to reproduce Indigo from its parts. In the following, 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.