The mechanism of reaction of sulfate radical anion with some derivatives of benzoic acid

Abstract

The products of the reactions of SO/sub 4//sup -/ with some benzoic acid derivatives have been examined by ESR using steady-state radiolysis and photolysis to produce SO/sub 4//sup -/ and by optical absorption spectrophotometry in pulse radiolysis experiments. The optical absorption spectrum of the hydroxycyclohexadienyl radical following reaction of benzene with SO/sub 4//sup -/ is shown to be formed with <0.1 ..mu..s delay. Thus it appears that a cation is formed which reacts very rapidly with water. Similarly, pulse ESR methods have been used to show that the p-carboxyphenyl radical is formed within <1 ..mu..s of the reaction of SO/sub 4//sup -/ with terephthalate. With benzoate, most of the reaction leads to the phenyl radical but about 30% gives hydroxycyclohexadienyl radicals. The three isomeric toluates give different products. The ortho isomer gives mainly the o-carboxybenzyl radical while the para isomer gives approximately equal amounts of p-carboxybenzyl, p-methylphenyl, and a mixture of hydroxycyclohexadienyl radicals. The meta isomer gives mainly a mixture of hydroxycyclohexadienyl radical isomers. Several carboxyphenols were studied by ESR and all gave phenoxyl radicals. All reactions observed are consistent with the oxidation of the benzene ring to a cationic species which then reacts in parallel reactions by either hydroxylation,more » loss of a proton (from OH or CH/sub 3/ groups), or loss of CO/sub 2/.« less