Gas-Phase Oxidation Products of Biphenyl and Polychlorinated Biphenyls

Abstract

Our laboratory recently measured the gas-phase reaction rate constants of polychlorinated biphenyls (PCBs) with the hydroxyl radical (OH) and concluded that OH reactions are the primary removal pathway of PCBs from the atmosphere. With the reaction system previously employed for kinetics, we have now investigated the products of these PCB−OH reactions. Experiments were carried out in either air or He as the diluent gas at approximately 1 atm in a 160-mL quartz chamber. Temperatures ranged between 318 and 363 K in order to enhance the vapor pressures of these less volatile compounds. OH was produced in situ by the photolysis of ozone in the presence of H2O. Reaction products from biphenyl, the three monochlorobiphenyls, and five dichlorobiphenyls were extracted from the chamber, derivatized by diazomethane, and analyzed by gas chromatographic mass spectrometry (GC/MS). Experiments gave benzoic acid and the appropriate chlorinated benzoic acids in significant product yields (8−17%).