Temperature Effects on the Kinetics of Carbonate Radical Reactions in Near-Critical and Supercritical Water

Abstract

Pulse radiolysis was used to generate the carbonate radical (CO3-•) in subcritical and supercritical water. The effect of the charge of the reaction partner on the kinetics of the reaction with aqueous carbonate radical was examined over the temperature range 30−400 °C, at 4150 ± 75 psia, pH 10.55. The rate constant for oxide transfer between two CO3-• radicals was insensitive to temperature below 200 °C, but increased by a factor of 300 from 1.61 × 107 to 2.90 × 109 M-1 s-1 between 200 and 400 °C. The rate constants for the one-electron oxidation of aniline, p-aminobenzoate, N,N-dimethylaniline, and p-N,N-dimethylaminobenzoate by CO3-• under the same conditions all displayed a negative temperature dependence at temperatures below 320 °C. Above 320 °C, the rate constants for the oxidation of the anionic aminobenzoates by CO3-• increased sharply, whereas those for the oxidations of the corresponding neutral anilines did not increase until 360 °C.