COLOR CHANGES AMONG DYES OF THE TRIPHENYLMETHANE SERIES AS INFLUENCED BY THE HYDROGEN ION CONCENTRATION OF ACIDS OF DIFFERENT DISSOCIATION CONSTANTS. (ON CATALYSES WITH WEAK ACIDS, III.1)
Journal of the American Chemical Society
SERIES AS INFLUENCED BY THE HYDROGEN ION CON- As is well known, the commonly accepted interpretation of .the production of color in derivatives of triphenylmethane is the formation of a quinoid complex. Thus, colorless pararosaniline, the carbinol form (NH,C,HJ,C(OH), in the presence of an acid, is transformed to the dye, the quinoid form (NH,C,H,),C = (==> __ = NHHX ~ In like manner colorless phenolphthalein, the benzenoid form in the presence of an alkali yields the colored quinoid form \CO,K
... In this molecular readjustment there is a certain resemblance to the rearrangement occurring in the transformation of the cinchona alkaloids, such as cinchonine, into their corresponding toxins, In the latter case there is a change from the carbinol to the ketone form with the shifting of hydrogen to.a nitrogen atom;2 in the former case there is a change from the carbinol to the quinoid form with a preliminary shifting of hydroxyl or acid radical to an amide group. In view of the peculiar catalyzing influence of the slightly dissociated organic acids in accelerating the speed of the conversion of cinchonine into cinchotoxine, it becomes of interest to determin whether relations in any way similar to these obtain among the derivatives of triphenylmethane in the conversion of the benzenoid into the quinoid form. From the nature of the change it seemed not unreasonable to suppose that phenomena o€ a somewhat similar character would be found among these derivatives, although probably modified by other reactions which do not obtain among the cinchona alkaloids. Some months ago I began a study of a number of the dyes of the triphenylmethane series with reference t o determining the influence of 5 0 0 ( 1 9 ' 2 ) . Biddle, Science, 32, 486 (1910); B e y . , 45, 5 2 6 , 2 8 3 2 ( 1 9 1 2 ) ; THIS JOURNAL, 34, Biddle, THIS JOURNAL, 34, 5 0 0 ( 1 9 1 2 ) .