Gas-Phase Reaction of Hydroxyl Radical with p-Cymene over an Extended Temperature Range

The kinetics of the reaction of OH radicals with p-cymene has been studied in the temperature range of 243-898 K using a flow reactor combined with a quadrupole mass spectrometer: OH + p-cymene -> products. The reaction rate constant was determined as a result of absolute measurements, from OH decay kinetics in excess of p-cymene and employing the relative rate method with OH reactions with n-pentane, n-heptane,1,3-dioxane, HBr, and Br-2 as the reference ones. For the rate coefficient of the H atom abstraction channel, the expression k(1b) = (3.70 +/- 0.42) x 10(-11) exp[-(772 +/- 72)/T] was obtained over the temperature range of 381-898 K. The total rate constant (addition + abstraction) determined at T = 243-320 K was k(1) = (1.82 +/- 0.48) X 10(-12) exp[(607 +/- 70)/T] or, in a biexponential form, k(1) = k(1a) + k(1b) = 3.7 X 10(-11) exp(-772/T) + 6.3 X 10(-13) exp(856/T), independent of the pressure between 1 and S Ton of helium. In addition, our results indicate that the reaction pathway involving alkyl radical elimination upon initial addition of OH to p-cymene is most probably unimportant.