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

Abstract

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.

Keywords:

• nitration reactions
• aqueous organic aerosol
• secondary organic aerosol
• capillary electrophoresis
• chemical kinetics

Acknowledgements

The authors would like to thank the State of Texas/Texas Tech University for financial support of this project through new faculty start-up funding. The University of Illinois MS facility provided rapid analysis of the samples and helpful discussions. The authors would also recognize the contributions of the late Professor Dennis Shelly whose laboratory provided capillary tubing for completion of this work. Hao Tang performed most experiments, analyzed and reported data, and contributed to authoring the manuscript. Yiyi Wei performed UV-VIS experiments. Jon Thompson provided guidance and assisted authoring and editing the manuscript.