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any of several basic and acidic dyes that are derivatives of triarylmethane, HC(Ar)3. Of the greatest importance are basic triarylmethane dyes, with the general formula
The effect of substituents on the color of triarylmethane dyes is shown in Table 1.
|Table 1. Effect of substituents on the color of triarylmethane dyes|
Triarylmethane dyes yield colorless leuco compounds under the action of reducing agents and colorless carbinol compounds under the action of bases.
Basic triarylmethane dyes are used for dyeing paper, leather, and plastics, as well as in the manufacture of writing, printing, and stamping inks. Some triarylmethane dyes are used for dyeing polyacrylonitrile fibers. Acidic triarylmethane dyes containing at least two S03H groups are used to a limited extent in dyeing wool and silk. Dyes that contain hydroxyl groups—for example, phe-nolphthalein and fuchsin—instead of amino groups are used as chemical indicators.
Triarylmethane dyes are prepared by the condensation of aldehydes, ketones, acid anhydrides, or acid chlorides with aromatic amines or phenols (naphthols).