Protonation kinetics of acrylate radical anions
The radical anions of acrylamide, methacrylamide and 2-hydroxypropyl acrylate were produced by pulse radiolysis of moderately acidic aqueous solutions well below the pKa of the radical anion. The rate coefficients of protonation were determined by UV kinetic spectroscopy at wavelengths where the protonated and ionic forms have considerably different absorbances. The rate coefficients of protonation were measured as (6.0±0.9)×1010, (6.6±1.0)×1010 and (5.0±1.0)×1010 mol−1 dm3 s−1. Using these rate coefficients and the pKa values of the radical anion, 7.9, 8.0 and 5.5, the rate coefficients of deprotonation were determined as 7.5×102, 6.6×102 and 1.6×105 s−1. The results clearly showed that in acidic solution the protonation occurred with H3O+ and not with H2O. The rate coefficients determined were discussed and compared with relevant data in the literature.