Diphenylmethane imine

The practical route for oxidizing leuco diphenylmethanes 15 demands inital conversion to an imine salt 16. The imine salt is obtained by heating a mixture of diphenylmethane, sulfur, ammonium chloride, and sodium chloride at 175°C in a current of ammonia or by heating a mixture of diphenylmethane, urea, sulfamic acid, sulfur, and ammonia at 175°C (Scheme 3). Dyes 16 can be represented as the quinonoid resonance structure 17. Dyes of this class, known as auramines, are all yellow, with the only commercial representative being auramine O 16a. Due to its poor lightfastness and instability to hot acids and bases, its use has been restricted to dyeing and printing cotton, paper, silk, leather, and jute. 

Fig. 8.7. Surface imprinting with a covalently coupled diimine template has been used to position two amines onto a flat silica surface in an effort to isolate the effect of functional group placement in molecular imprinting. The rectangular spacer between the imines represents either a phenyl or diphenylmethane. Adapted from [37].

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