toluidine

Toluidine refers to any of three isomeric amino derivatives of toluene, with the chemical formula C₇H₉N. These compounds are analogous to aniline and are utilized as intermediates in the production of dyes.1

One specific type, toluidine blue, is a basic thiazine dye. It is structurally related to methylene blue and serves as a biological stain. Historically, toluidine has been found to be a necessary component in the synthesis of certain triphenylmethane dyes, such as fuchsine and aniline blue. These early synthetic dyes, developed in the mid-19th century, were crucial to the burgeoning synthetic dye industry.23