Ultraviolet spectra and dissociation constants of p-hydroxybenzoic acid, methyl, ethyl, n-butyl, and benzyl p-hydroxybenzoate and potassium p-phenolsulfonate

Abstract

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.

Supramolecular Self-assembly Formed from Cucurbit[8]uril and p-Hydroxybenzoic Acid

“…The free host Q [8] exhibits no absorbance at λ > 210 nm. The UV-vis spectra obtained for the p-HBA aqueous solutions showed a strong absorption at 248 nm, attributed to the absorption peak of dissociated phenol hydroxyl group [28]. Upon addition of variable concentrations of Q [8] to the p-HBA aqueous solution, the absorption peak of the p-HBA gradually increased and red shifted to 253 nm, with a red shift of 5 nm (Figure 3a).…”

Dissociation Constants of Certain γ-Pyrone Dicarboxylic Acids

“…Spectrophotometric Method.-The results obtained by the titration method were checked by a spectrophotometric procedure (3). Meconic acid and chelidonic acid were found to obey Beer's law in the range of 230 to 315 mp in both acidic, neutral, and basic solutions.…”