Determination of toluene's degradation products under simulated atmospheric conditions

Abstract

Previous work on toluene includes both product studies and proposed mechanisms. In all previous studies, the oombined product yields are half or less of the initially reacted toluene. A major reason for the poor carbon balances found in these studies is the precipitation of interrrediate reaction products fran the gas phase to the reaction walls. We have studied the oxidation process by blacklight irradiation of 1-10 ppm each of toluene and oxides of nitrogen in 22-liter pyrex flasks, in zero-air at 50% relative hmnidity. The flasks were pre-cleaned by baking at 350 C and the products were recovered from the walls by extraction with methanol or dichloromethane. Some gas-phase products were recovered in the solvent as well. The extracts were analyzed on a Finnigan MAT triple stage quadrllp)le mass spectraneter/ data systen by direct probe injection. Methane chemical ionization converted the products to Mf-l parent ions. The molecular weights of the products were determined fram the cr nass spectrmn, and also by the general survey methods of neutral loss and puent ion spectra. Once their molecular weights were determined, the products were fragmented by collision-induced-dissociation (CID) in the middle quadrupole to produce characteristic daughter ions. To assist in the spectral interpretation, toluene in three isomeric forms was subjected to simulated atmospheric reaction. In addition to normal (HS) toluene, methyl-deuterated (03) and per-deuterated (08) toluene were used. J This study confiDIled the existence of a number of products identified in past studies, confirmed the formation of same products which have been hyp:>thesized in several proposed mechaniSl"s for toluene oxidation, identified a nwnber of previously unidentified and unproposed products. In sane cases the fragmentation patterns didn' tallow cooice among several methylor hydroxyl-positional isaners, and undoubtedly rore than one isomer was often present, as would be expected. Detailed mechanistic steps have been outlined for all reaction products' fornation and destruction. other analytical techniques including GC, GC/MS, and HPLC, have supplanented the MS/MS analysis. These results and the further study of the types of compounds identified should nake a significant contribution to the understanding of atmostileric aranatic systens.