Diphenylmethane dyes

Diphenylmethane Dyes. The diphenyhnethane dyes aie usually classed with the tiiaiyhnethane dyes. The dyes of this subclass are ketoimine derivatives, and only three such dyes are registered in the Colour Index. They ate Auramine O [2465-27-2J Cl Basic Yellow 2 (Cl 41000) (21, R = CHg), Auramine G [2151 -60-2] Cl Basic Yellow 3 (Cl 41005) (22), and Cl Basic Yellow 37 [6358-36-7] (Cl 41001) (21, R = C2H5). These dyes are still used extensively for the coloration of paper and in the preparation of pigment lakes. 

Although treated as separate classes in the Colour Index, these structural types are closely related and the few diphenylmethane dyes such as auramine (1.28 Cl Basic Yellow 2) are now of little practical interest. Commercial usage of the triarylmethane dyes and pigments has also declined considerably in favour of the major chemical classes. They were formerly noteworthy contributors to the acid, basic, mordant and solvent ranges, primarily in the violet, blue and green sectors. Numerous structural examples are recorded in the Colour Index. The terminal groupings can be amine/quinonimine, as in auramine and crystal violet (1.29 Cl Basic Violet 3), hydroxy/quinone, or both. The aryl nuclei are not always benzenoid (section 6.5). 

The substituted diphenylmethane dye, auramine O, is weakly fluorescent in fluid solvents but highly fluorescent in viscous or rigid media. It was originally used to probe the viscosity of viscous polymeric samples. Such a strong dependence on solvent viscosity can be explained in the same way as for triphenylmethane dyes. 

A representative diphenylmethane dye. It melts at 250 C and begins to vaporize, boils at 290 C and is partly carbonized. This material on the market is generally hygroscopic. 

Tetrabase, which is tetramethyl-/)-diaminodiphenylmethane with the cation (I), may be regarded as a stable leuco form of a diphenylmethane dye with the cation (II), whose intense blue color is due to the development of... 

Closely related to the triphenylmethane dyes are the diphenylmethane dyes. One of these, Basic Yellow 37, is used for coloring the yellow pages of telephone books. 

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