any of a group of basic dyes whose molecules contain the thiazine heterocycle.
Among the thiazine dyes, methylene blue is of the greatest industrial significance.
Methylene blue is synthesized in three stages. First, a mixture of p-amino-N, N-dimethylaniline and sodium thiosulfate are oxidized by means of sodium bichromate, which forms sodium o-amino-m-dimethylaminobenzolthiosulfate. Second, N, N-dimethylaniline is added and, continuing the oxidation, “inda-mine-thiosulfonic acid” (Bindschädler’s Green) is produced. Finally, the reaction mass is heated together with bichromate and copper sulfate. During this stage a sulfite ion is detached and the thiazine ring is closed, forming methylene blue. This is a brilliant, intense dye, which is widely used for coloring paper and for the production of colored pencils and printing inks. (For the use of methylene blue in medicine, seeMETHYLENE BLUE.)
The blue, green, and black sulfur dyes are sometimes regarded as thiazine dyes.
REFERENCEStepanov, B. I. Vvedenie v khimiiu i tekhnologiiu organicheskikh krasitelei [textbook]. Moscow, 1971.
M. A. CHEKALIN