RATE CONSTANTS FOR THE GAS-PHASE REACTION OF THE HYDROXYL RADICAL WITH A SERIES OF DIMETHYLBENZALDEHYDES AND TRIMETHYLPHENOLS AT ATMOSPHERIC-PRESSURE

Rate constants for three dimethylbenzaldehydes and two trimethylphenol s have been determined for the OH reactions at 298 +/- 2 K and atmosph eric pressure using a relative rate method. The OH reaction rate const ants were placed on an absolute basis using the literature rate consta nt for 1,2,4-trimethylbenzene of (3.25 +/- 0.5) x 10(-11) cm(3) molecu le(-1) s(-1). The measured rate constants were (in units of cm(3) mole cule(-1) s(-1)) 2,4-dimethyl-benzaldehyde, (4.32 +/- 0.67) x 10(-11); 2,5-dimethylbenzaldehyde. (4.37 +/- 0.68) x 10(-11); 3,4-dimethylbenza ldehyde, (2.14 +/- 0.34) x 10(-11); and 2,3,5-trimethylphenol, (12.5 /- 1.9) x 10(-11), 2,3,6-trimethylphenol, (11.8 +/- 1.8) x 10(-11). Us ing an average OH concentration of 8.7 x 10(5) molecule cm(-3), the es timated atmospheric lifetimes are ca. 7.5 h for 2,4- and 2,5-dimethylb enzaldehydes, ca. 15 h for 3,4-dimethylbenzaldehyde, ca. 2.5 h for 2,3 ,5- and 2,3,6-trimethylphenols. The reactivities of the trimethylpheno ls exceed those of the dimethyl-benzaldehydes by more than a factor of 3. (C) 1997 John Wiley and Sons, Inc.