Abstract
The two phenol ionizations of 3, 4-dihydroxyphenylbutyric acid and 3, 4-dihydroxybenzoic acid were studied by detailed potentiometric titration and complementary tristimulus colorimetric method (CTS method). The thermodynamic parameters were calculated from the dissociation constants. From a comparison of the related compounds of 3, 4-dihydroxyphenylbutyric acid, it was indicated that the effect of carboxylate group on the dissociations of two phenol groups was not present when more than two methylene groups were introduced between benzene ring and carboxylate group. The microscopic acid dissociation constants of 3, 4-dihydroxyphenylbutyric acid and 3, 4-dihydroxybenzoic acid were calculated by two different methods. In Method A, the dissociation constants of 3-methoxy-4-hydroxyphenyl derivatives were used as substituted values. Method B is a modification of Edsall method. There were no effect of carboxylate group on the tautomeric constants when more than one methylene group are introduced between benzene ring and carboxylate group.
