Nighttime tropospheric chemistry:: Kinetics and product studies in the reaction of 4-alkyl- and 4-alkoxytoluenes with NO3 in gas phase

Alkylbenzenes are important constituents of gasoline and industrial solvents and contribute to the formation of tropospheric ozone. The removal of these compounds from the troposphere is due to reaction with OH during the day and with NO(3) during the night. Five para-substituted toluenes are reacted with the nitrate radical in gas phase. Samples to be used for product analysis were preconcentrated and analyzed by GC-MSD analysis with the use of a reference curve. The yields of methanol, ethanol, and formaldehyde were determined by FTIR analysis of the reaction mixture in the chamber. Carbonyl compounds, benzyl alcohols, and nitroderivatives were formed. In the case of the alkoxytoluenes, products were also an alkanol, benzyl alcohols, and nitrophenols. Indirect rate constants measurements were performed by comparing by FTIR measurements the decay of the aromatic compound under investigation to that of a reference compound, with a known rate constant for the reaction with NO(3) added to the gas mixture. Wail loss constants were evaluated by FTIR. A Hammett correlation with rho = - 4.3 +/- 0.6; r(2) = 0.87 was obtained. This and the kinetic isotope effect of 1.5-1.8 suggest a reaction mechanism occurring via an addition-elimination pathway.