Triphenylmethanes and Carbinol Bases

Hydroxy leuco bases can be converted into the corresponding amino leuco bases by allowing the leuco compound to react with a secondary amine in the presence of acetic acid.78 Examples, 54, of amine bases utilized in this manner are imidazole, 1,2,4-triazine, aryl amine, and cyclohexayl amine. 

Experimental Procedure19 for 3-[a-(4-dimethylaminophenyl)benzyl]indole (45). To a solution of 4-A(A7-dimethylaminobenzhydrol (0.45 g, 2 mmol) in MeOH (25 ml) under reflux, was added a solution of indole and concentrated hydrochloric acid (0.8 ml) in water (25 ml). The mixture was heated under reflux for 90 min, followed by the addition of KOH solution (5%, 30ml). After the reaction was allowed to cool, the product was isolated by filtration (0.63 g, 97%). 

The reaction of an aromatic aldehyde with an aromatic nucleophile containing hydroxy or amino groups gives products with at least two identical phenyl groups79 83 e.g., 55, 56. Use of two different nucleophiles generally results in lower yield. 

Benzene and naphthalene compounds can be formylated under Vil-smeir conditions. The formyl compounds, with or without isolating, can be condensed with amino arenes to give leuco compounds. In this reaction, the benzhydrol intermediate is not isolated.21,79,84 86 The reaction is generally carried out in an alcohol solvent such as isopropanol, butanol, or pentanol and an acid catalyst such as hydrochloric acid, sulfuric acid, or methanesul-fonic acid.87 Acetic acid can also be used both as catalyst and as the solvent. Urea sometimes is added as catalyst.84,88 Terephthaldehyde reacts with W-diethyl-3-methylaniline89 and substituted azulenes to give a bis-triphenylmethane21 57 and 58, respectively. 

Experimental Procedure19 for 4-bis(4-dimethylaminophenyl)methyl-2,6 dimethoxyphenol (55a). A mixture of syringaldehyde (5.46 g, 30 mmol, A.A-dimethylaniline (7.26 g, 60 mmol), urea (2.7 g), and concentrated sulfur ic acid (4.41 g) in isopropanol (100ml) was heated at 90°C under a nitrogen atmosphere for 24h. The reaction was cooled to room temperature and 40ml of water added followed by 50% NaOH until alkaline. The mixture was filtered and the residue washed with 200ml of cold water. The solid was recrystallized from ethanol and yielded 12.0g (97%), mp 136-138°C. 

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