Abstract
As the mechanism for the color reaction between phenol and xanthydrol, formation of 9-(p-hydroxyphenyl)xanthylium salt (II), through the intermediate 9-(p-hydroxyphenyl)xanthene (I) was presumed and, in order to prove this reaction, II was synthesized by the known process and II was found to be identical with the pigment formed by the color reaction between phenol and xanthydrol. Measurement of the reaction rate showed that the formation of I followed the second-order reaction formula and the formation of II, in which I and xanthylium ion took part, followed the second-order reaction formula. Formation reaction of I was slower than that of II, so that the former is the rate determining step in the color reaction between phenol and xanthydrol. Decomposition of I, i.e. reverse reaction of the formation of I, also takes place but the rate is much slower than the formation reaction of I and II, and can therefore be neglected.
