Reaction of the 2-hydroxy-2-propyl radical with acrylate type molecules in aqueous solution: Radical addition or electron transfer

摘要

The reaction of 2-hydroxy-2-propyl (IP) radical with 12 acrylate type monomers in aqueous solutions was investigated by means of pulse radiolysis: the molecular structure effects and the mechanisms were evaluated. Radicals were generated either in the reaction of hydrated electron with acetone and subsequent protonation or in the H abstraction reaction by OH radicals from i-propanol. IP radical reacts with acrylamides and acrylic acid esters in radical addition reaction of the type: (CH3)(2)(OH)C+ CH2=CH-C(O)R -> (CH3)(2)(OH)C-CH2-C'H-C(O)R with rate coefficients between 3.2 x 10(7) and 1.9 x 10(8) mol(-1) dm(3) s(-1). Rate coefficients of the reaction with maleic acid (neutral), dimethyl- and diethyl maleate are between 1.3 x 10(8) and 4.7 x 10(8) mol(-1) dm(3) s(-1). The values for dimethyl- and diethyl fumarate are ca. one order of magnitude. higher. However with maleates and fumarates there is also a few percent contribution from the electron transfer reaction of the type (CH3)(2)(OH)C + ROOC-CH=CH-COOR + H2O -> ROOC-CH=CH-CO-OR + (CH3)(2)CO + H3O+. In neutral solutions and at pH similar to 3 and similar to 9, the same rate coefficients were measured. However, in dialkyl maleate and -fumarate solutions between pH 9.5 and 10.5, a base catalyzed decomposition of the IP radical adduct was observed forming electron adduct: ROOC-C((CH3)(2)(OH)C)H-CH-COOR + OH- -> ROOC-CH=CH-CO-OR + (CH3)(2)CO + H2O. Molecular structure effects were evaluated using logk-sigma(p) and log k-LUMO plots. (c) 2006 Elsevier B.V. All rights reserved.