Kinetic studies of the self-reaction and reaction with HO2 of a tertiary ?-brominated peroxy radical between 298 and 393 K

Abstract

The kinetics of reactions of the tertiary β-brominated peroxy radical BrC(CH3)2C(CH3)2O2 (2-bromo-1,1,2-trimethylpropylperoxy) have been studied using the laser flash photolysis technique, photolysing HBr at 248 nm in the presence of O2 and 2,3-dimethylbut-2-ene. At room temperature, a rate constant of (2.0 ± 0.8) × 10−14 cm3 molecule−1 s−1 was determined for the BrC(CH3)2C(CH3)2O2 self-reaction. The reaction of BrC(CH3)2C(CH3)2O2 with HO2 was investigated in the temperature range 306–393 K, yielding the following Arrhenius expression: k(BrC(CH3)2C(CH3)2O2 + HO2) = (2.04 ± 0.25) × 10−12 exp[(501 ± 36)K/T] cm3 molecule−1 s−1, giving by extrapolation (1.10 ± 0.13) × 10−11 cm3 molecule−1 s−1 at 298 K. These results confirm the enhancement of the peroxy radical self-reaction reactivity upon β-substitution, which is similar for Br and OH substituents. In contrast, no significant effect of substituent has been observed on the rate constant for the reactions of peroxy radicals with HO2. The global uncertainty factors on rate constants are equal to nearly 2 for the self-reaction and to 1.35 for the reaction with HO2. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 33: 41–48, 2001