Hydroxytriphenylmethane dyes

Aldehyde Method. This method is generally used for the preparation of diaminotriphenylniethane dyes or hydroxytriphenylmethane dyes. The central carbon atom is derived from an aromatic aldehyde or a substance capable of generating an aldehyde during the course of the condensation. For example. Malachite green is prepared by heating benzaldehyde under reflux with a slight excess of dimethylaniline in aqueous acid. 

Aldehyde Method. This method is generally used for the preparation of diaminotriphenylmethane dyes or hydroxytriphenylmethane dyes. 

Corresponding to this viewpoint, all hydroxytriphenylmethane dyes containing the group A react in the same fashion as Chrome Fast Pure Blue B when they come into contact with aluminum salts. To these color reactions the general formulation can be given ... 

The color reaction with the hydroxytriphenylmethane dye Chrome Fast Pure Blue B (see page 100) can be used for the detection of alumina in samples that have been decomposed by fusion with alkali bisulfate or persulfate. A much faster method is to allow an ether solution of this dye to act on the pulverized sample a red-violet tinting occurs almost at once. Beryllium oxide is made deep blue. These colored products, which are probably adsorption complexes, differ characteristically in that the alumina adsorbate is resistant to dilute acids. 

Hydroxytriphenylmethane derivatives give rise to anionic charge-resonance systems that are isoconjugate with the corresponding amino-substituted dyes. Thus, for example, the oxonol analogue of malachite green is benzaurine (Scheme 6.33). The quinonoid neutral form (6.184), which is pale yellow, produces a violet anion (6.185) on the addition of alkali in... 

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