TRIPHENYLMETHANE, a hydrocarbon, which gives its name to an important group of synthetic colouring matters which includes magenta, paramagenta (rosanilines), mala chite green, brilliant green, patent blue, aurin and rosolic acid. (See DYES, SYNTHETIC.) It is a white crystalline solid melting at 92° C and boiling at 358° C/76o mm. Its preparation is best effected by adding anhydrous aluminium chloride to a mixture of dry ben zene and dry carbontetrachloride; after 24 hours anhydrous ether is slowly added and the mixture then treated with acidified ice water. The hydrocarbon is extracted with benzene and obtained from this extract by a distillation under reduced pressure, being purified by crystallisation from ethyl alcohol (0. Kamm and J. F. Norris, Organic Syntheses, Vol. iv., J. Riley and Sons, 1925). Other modes of formation are as follows: (I) Condensation of benzal (benzylidene) chloride, with mercury di phenyl; (2) condensation of benzene with chloroform in presence of aluminium chloride; (3) from paramagenta (pararosaniline chloride) by successive reduction, diazotisation and replacement of diazo-groups by hydrogen. The third process is of historical interest as it served to establish the connection between the hydrocarbon and the rosaniline colouring matters (0. and E. Fischer, i881). Conversely, triphenylmethane can be nitrated and its trinitro-compound can be reduced to paraleucaniline, CH(C6H4.NH2)3, which on oxidation in acid solution yields para rosaniline chloride or paramagenta, Triphenylmethane on oxidation is found to give triphenylcarbinol, a feebly basic hydroxide which on treatment with hydrogen chloride is converted into colourless triphenylmethyl chloride, melting at 1I1° C. This chloride is the
primary product of the foregoing condensation of benzene and carbon tetrachloride (v. supra).
By the action of various metals (zinc, silver, copper or mer cury) on triphenylmethyl chloride, M. Gomberg in the year I900 isolated a very remarkable unsaturated hydrocarbon, triphenyl methyl, and he showed that the reaction was general by removing chlorine from other triarylmethyl chlorides.
Triphenylmethyl is colourless in the solid state but yields yellow solutions. Cryoscopic determinations show that the dissolved hydrocarbon is chiefly in the bimolecular state, which is in equilibrium with the coloured unimolecular form. With increasing complexity of the aryl groups there is a greater tendency for the triarylmethyls to exist in the unimolecular con dition, so that the successive replacement of phenyl by diphenyl is accompanied by an increase in depth of colour until trisdi phenylmethyl, (C6H5.C6H4)3C, which occurs only in the coloured unimolecular condition, is obtained as a green crystalline powder melting at 186° C (W. Schlenk, T. Weickel and A. Herzenstein, 191o). On the other hand diphenyldiphenylenemethyl, exists only in the colourless bimolecular condition. (See J. Schmid lin, Das Triphenylmet/tyl, F. Enke, 1914.) (G. T. M.)