PULSE-RADIOLYSIS STUDIES OF P-HYDROXYPHENYLPROPIONIC ACID

The pulse radiolysis technique has been used to investigate the initial radiolysis products of aqueous p-hydroxyphenylpropionic acid (S). The transient absorption spectra show that OH and H adducts are formed initially in acidic and near-neutral solutions while in alkaline solutions both addition products and phenoxyl radicals are formed simultaneously. The decay of the addition products in acidic and near-neutral solutions is accompanied by a parallel formation of phenoxyl radicals by a process obeying first-order kinetics with k = (2.7 ± 0.3) × 103 sec-1. Both the OH and H adducts have overlapping intense uv absorptions. Their molar extinction coefficients at 320 and 330 mμ are 5.0 × 103, 3.5 × 103 and 3.4 × 103, 4.1 × 103 M-1 cm-1, respectively. The reaction rate constants of H atoms with p-hydoxyphenylpropionic acid is (1.5 ± 0.3) × 109 M-1 sec-1. Evidence was obtained for reactions of O2 with the phenoxyl type radicals in alkaline solutions of p-hydroxyphenylpropionic acid and L(-)-tyrosine, and with the OH adduct of DL-phenylalanine.