Blue is the typical of all colors to denim or jeans. Form day one, this blue color to denim is developed form indigo dye.
Indigo powder is a dark blue crystalline compound which is insoloable to water. The chemical formula of the compound is C16H10N2O2. it is insoluable to water as well as ether or alcohol but soluble in nitrobenzene, concentrated sulfuric acid or chloroform.
The strong relation of denim to indigo is for the reason that natural indigo was the only major source of dye till the beginning of 19th century. It is among the oldest of the dyes used in textile. About all over the world the use of indigo was known to old civilizations. However in Europe, the use of indigo was rare in middle ages. Where as a similar dye known as Woada was used instead of indigo.
In German chemist Adolf von Baeyer began working with indigo. His work culminated in the first synthesis of indigo in 1878 from Istatine, a second synthesis in 1880 from o-nitrobenzaldehyde and acetone upon addition of dilute sodium hydroxide, barium hydroxide, or ammonia and the announcement of its chemical structure three years later.
The production of o-nitrobenzaldehyde was too complicated for a commercial product so the search for alter
native starting materials was crucial. The synthesis of N-(2-Carboxyphenyl) glycine starting from the easy to obtain anthracene gave the development of a synthesis a boost. By 1913 natural indigo had been almost entirely replaced by synthetic indigo. The manufacturing process finalized in the late 1800s is still in use throughout the world. In this process, indoxyl is synthesized by the fusion of sodium phenylglycinate in a mixture of sodium hydroxide and sodamide. The modern synthesis of indigo is slightly different from that route originally used. In this process, N-phenylglycine is treated with an alkaline melt of sodium and potassium hydroxides containing sodamide. This produces indoxyl, which is subsequently oxidised in air to form indigo.
Indigo is a challenging dye to use because it is not soluble in water; to be dissolved, it must undergo a chemical change (reduction). When a submerged fabric is removed from the dye-bath, the indigo quickly combines with oxygen in the air and reverts to its insoluble form.