Nitrate Induced Photooxidation of Phenol and o-Substituted Phenolic Compounds in Aqueous Solution

Abstract

The excitation of nitrate ions at 313 nm in the presence of phenol, 2-chlorophenol or 2-methylphenol in aqueous solution produced a complex mixture of compounds. The photoproducts were identified by LC-MS. Nitration, hydroxylation and coupling reactions were found to be the principal chemical processes. Cl/OH, CH₃/OH substituted and hydroxylated phenolic derivatives are formed in very small amount. In contrast with phenol, no nitroso derivative was detected by 2-chlorophenol and 2-methylphenol under the same reaction conditions. Both nitrosation and nitration are attributed to reactions of nitrogen oxides NO₂^• and N₂O₄. Nitration and nitrosation are favoured in acidic medium. Kinetic studies were compared by varying environmental parameters including substrate and NO₃^– concentrations, oxygen content, pH and ethanol. The influence of substituted phenols is investigated by comparing their initial rates of degradation. Degradation pathways involving ^•OH and NO₂^• radicals as reactive species are proposed.