The apparent first and second dissociation constants of p-hydroxybenzoic acid, the constants for the phenol group of methyl, ethyl, n-butyl, a nd benzyl p-hydroxybenzoate, and potassium p-phenolsulfonate have been determined from ultraviolet spectral data. The compounds have wide absorption bands located in the region of 200 to 400 mIl, and the differences between the transmittancy curves for their ionic and molecular forms are great enough to p ermit the measurement of several intermediate steps in the transformation at various pH values. The buffers used to · control the dissociation were acetate/3, phosphates, and borate's, all of low ionic strengths. Esterification of t he carboxyl group of p-hydroxybenzoic acid apparently increases the dissociation of the phenol, and pK* decreases from 9.3 for the second dissociation of the acid to 8.3 for the esters. The thermodynamic dissociation constants are estimated.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.