Kinetics and mechanism for the oxidation of 1,1,1-trichloroethane

The reaction mechanisms for oxidation of CH3CCl2 and CCl3CH2 radicals, formed in the atmospheric degradation of CH3CCl3 have been elucidated. The primary oxidation products from these radicals are CH3CClO and CCl3CHO, respectively. Absolute rate constants for the reaction of hydroxyl radicals with CH3CCl3 have been measured in 1 atm of Argon at 359, 376, and 402 K using pulse radiolysis combined with UV kinetic spectroscopy giving (OH + CH3CCl3) = (5.4 ± 3) 10−12 exp(−3570 ± 890/RT) cm3 molecule−1 s−1.

A value of this rate constant of 1.3 × 10−14 cm3 molecule−1 s−1 at 298 K was calculated using this Arrhenius expression. A relative rate technique was utilized to provide rate data for the OH + CH3 CCl3 reaction as well as the reaction of OH with the primary oxidation products. Values of the relative rate constants at 298 K are: (OH + CH3CCl3) = (1.09 ± 0.35) × 10−14, (OH + CH3CClO) = (0.91 ± 0.32) × 10−14, (OH + CCl3CHO) = (178 ± 31) × 10−14, (OH + CCl2O) < 0.1 × 10−14; all in units of cm3 molecule−1 s−1.

The effect of chlorine substitution on the reactivity of organic compounds towards OH radicals is discussed.