The aqueous phase nitration of phenol and benzoic acid studied through flow-gated capillary electrophoresis

The aqueous phase nitration of benzoic acid and phenol was investigated via on-line capillary electrophoresis (CE). The presence of nitrated benzoic acid and phenol was supported through appearance of corresponding molecular ion peaks in ESI-MS measurements, and speciation of the nitrated isomers is achieved via the on-line CE method. The nitrated isomers produced in both reactions were successfully separated in <4 min by addition of 15 mM β-cyclodextrin to the electrophoresis buffer. Sequential separations (on-line analysis) allowed the reaction kinetics to be described. For benzoic acid, reaction yields were low (2-3%) however, results suggest both 3- and 2-nitrobenzoic acid form in a 1-1.4 concentration ratio. In addition, 3-hydroxybenzoic acid also forms in significant quantity under our reaction conditions. For the nitration of phenol, the reaction occurred more rapidly with observed yields between ≈10-30% for individual isomers. The yield of 2-nitrophenol was higher than 4-nitrophenol by a ratio of ≈ 1.7-2, but 3-nitrophenol was not detected. For both reactions, nitrated and hydroxylated aromatics were the major products and formation of higher molecular weight oligomers was not observed.