1911 Encyclopædia Britannica/Triphenylmethane

TRIPHENYLMETHANE, (C₆H₅)₃CH, a hydrocarbon, important as being the parent substance of several series of exceedingly valuable dyestuffs, e.g. rosanilines and malachite greens derived from aminotriphenylmethanes, and aurins and phthaleins derived from oxytriphenylmethanes. It is obtained by condensing benzal chloride with mercury diphenyl (Kekulé and Franchimont, Ber., 1872, 5, p. 907); from benzal chloride or benzotrichloride and zinc dust or aluminium chloride; from chloroform or carbon tetrachloride and benzene in the presence of aluminium chloride; and deamidating di- and tri-aminotriphenylmethane with nitrous acid and alcohol (O. and E. Fischer, Ann., 1881, 206, p. 152). The last reaction is most important, for it established the connexion between this hydrocarbon and the rosanilines. Triphenylmethane is a white crystalline solid, melting at 92° and boiling at 358°. It separates from benzene and thiophene with one molecule of the “ solvent of crystallization.” On oxidation it gives triphenylcarbinol, (C₆H₅)₃C·OH, and reduction with hydriodic acid and red phosphorus gives benzene and toluene. It combines with potassium to give (C₆H₅)₃CK, which with carbon dioxide gives potassium triphenylacetate, (C₆H₅)₃C·CO₂K. Fuming nitric acid gives a paratrinitro substitution derivative which on reduction gives paraleucaniline; the salt of the carbinol formed on oxidizing this substance is the valuable dye rosaniline.

Considerable interest is attached to the remarkable series of hydrocarbons obtained by Gomberg (Ber., 1900, 33, p. 3150, et seq.) by acting on triphenylmethane chloride (from triphenylmethane carbinol and phosphorus pentachloride, or from carbon tetrachloride and benzene in the presence of aluminium chloride) and its homologues with zinc, silver or mercury. Triphenylmethane chloride yields triphenylmethyl; ditolylphenylmethyl and tritolylmethyl have also been prepared. They behave as unsaturated compounds, combining with oxygen to form peroxides and with the halogens to form triarylmethane halides. Triphenylmethyl also combines with ethers and esters, but the compounds so formed are unsaturated. In the solid state triphenyl is colourless, crystalline and bi molecular. It was thought that it might be identical with hexaphenylethane, but the supposed synthesis of this substance by Ullmann and Borsum (Ber., 1902, 35, p. 2877) appeared to disprove this, although it showed that triphenylmethyl readily isomerized into their product, under the influence of catalysts. A.E. Tschitschibabin (Ber., 1908, 41, p. 2421), however, has shown that Ullmann and Borsum's preparation was para-benzhydroltetraphenylmethane (C₆H₅)₂CH·C₆H₄·C(C₆H₅)₃; and the view that solid triphenylrnethyl is hexaphenylethane has much in its favour. Another remarkable fact is that these substances yield coloured solutions in organic solvents; triphenylmethyl gives a yellow solution, whilst ditolylphenyl and tritolylmethyls give orange solutions which on warming turn to a violet and to a magenta, the changes being reversed on cooling. Several views have been published to explain this fact. A summary is given by Tschitschibabin (Journ. prak. Chem., 1907 (ii.), 74, p. 340). It ap ears probable that the solutions contain a quinonoid modification (see Gomberg and Cone, Ann., 1909, 370, p. 142).