Kinetic isotope effects and rate constants for the gas‐phase reactions of three deuterated toluenes with OH from 298 to 353 K

The rate constants for the gas‐phase reactions of three deuterated toluenes with hydroxyl radicals were measured using the relative rate technique over the temperature range 298–353 K at about 1 atm total pressure. The OH radicals were generated by photolysis of H 2 O 2 , and helium was used as the diluent gas. The disappearance of reactants was followed by online mass spectrometry, which resulted in high time resolution, allowing for a large amount of data to be collected and used in the determination of the Arrhenius parameters. The following Arrhenius expressions have been determined for these reactions (in units of cm 3 molecule −1 s −1 ): k =(6.42 −0.99 +1.17 )×10 −13 exp [(661±54)/ T ] for toluene‐ d 3 , k =(2.11 −0.69 +1.03 )×10 −12 exp [(287±128)/ T ]for toluene‐ d 5 , and k =(1.40 +0.44 −0.33 )×10 −12 exp [(404±88)/ T ]for toluene‐ d 8 . The kinetic isotope effects (KIEs, k H / k D ) of these reactions were 1.003 ± 0.042 for all three compounds at 298 K. The KIE for toluene‐ d 3 was temperature dependent; at 350 K, its KIE was 1.122 +0.048 −0.046 . The KIE of toluene‐ d 5 and toluene‐ d 8 did not vary significantly with temperature. These KIE results suggest that methyl H‐atom abstraction is more important than aromatic OH addition at higher temperatures. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 821–827, 2012