Methyl violet 6B

Methyl violet 6B (Pentamethylparosanilinium chloride, 4-[ [4-(dimethylamino)phenyl]-(4-methyliminocyclohexa-2,5-dien-1-ylidene)methyl]-N,N-dimethylaniline·hydrochloride) is a violet triarylmethane dye from the group of cationic dyes and an essential component of C.I. Basic Violet 1 (trivial name methyl violet). The compound is sometimes equated with methyl violet in the literature.

Methyl violets are mixtures of tetramethyl (2B), pentamethyl (6B) and hexamethyl (10B) pararosanilins.

Synthesis
To produce methyl violet 6B, N,N-dimethylaniline is oxidized with atmospheric oxygen and copper sulfate as a catalyst, using phenol and large amounts of salt as a diluent. The central carbon atom of the dye is provided by the oxidation of a methyl group of N,N-dimethylaniline to formaldehyde. In this process, a reaction product is obtained that contains the tetra- to hexamethylated compounds in addition to the pentamethylated compound.