Rate constants for the gas-phase reaction of the hydroxyl radical with a series of dimethylbenzaldehydes and trimethylphenols at atmospheric pressure

Abstract

Rate constants for three dimethylbenzaldehydes and two trimethylphenols have been determined for the OH reactions at 298±2 K and atmospheric pressure using a relative rate method. The OH reaction rate constants were placed on an absolute basis using the literature rate constant for 1,2,4-trimethylbenzene of (3.25±0.5)×10⁻¹¹ cm³ molecule⁻¹s⁻¹). The measured rate constants were (in units of cm³ molecule⁻¹ s⁻¹) 2,4-dimethyl-benzaldehyde, (4.32±0.67)×10⁻¹¹; 2,5-dimethylbenzaldehyde, (4.37±0.68)×10⁻¹¹; 3,4-dimethylbenzaldehyde, (2.14±0.34)×10⁻¹¹; and 2,3,5- trimethylphenol, (12.5±1.9)×10⁻¹¹, 2,3,6-trimethylphenol, (11.8±1.8)×10⁻¹¹. Using an average OH concentration of 8.7×10⁵ molecule cm⁻³, the estimated atmospheric lifetimes are ca. 7.5 h for 2,4- and 2,5-dimethylbenzaldehydes, ca. 15 h for 3,4-dimethylbenzaldehyde, ca. 2.5 h for 2,3,5- and 2,3,6-trimethylphenols. The reactivities of the trimethylphenols exceed those of the dimethyl-benzaldehydes by more than a factor of 3.