Kinetic and Product Study of the Gas-Phase Reactions of OH Radicals with Trans-2-Hexenal, Trans-2-Octenal and Trans-2-Nonenal

 

Abstract

        The rate constants of the gas-phase reaction of OH radicals with trans-2-hexenal, trans-2-octenal and trans-2-nonenal were determined at 298±2 K and atmospheric pressure using the relative rate technique. Two reference compounds were selected for each rate constant determination. The relative rates of OH + trans-2-hexenal versus OH + 2-methyl-2-butene and b-pinene were 0.452±0.054 and 0.530±0.036, respectively. These results yielded an average rate constant for OH + trans-2-hexenal of (39.3±1.7) °Á10^-12 cm³molecule^-1s^-1. The relative rates of OH+ trans-2-octenal versus  the OH reaction with butanal and b-pinene were 1.65±0.08 and 0.527±0.032, yielding an average rate constant for OH + trans-2-octenal of (40.5±2.5) °Á10^-12 cm³molecule^-1s^-1. The relative rates of OH+ trans-2-nonenal versus OH+ butanal and OH + trans-2-hexenal were 1.77±0.08 and 1.09±0.06, resulting in an average rate constant for OH + trans-2-nonenal of  (43.5±3.0) °Á10^-12 cm³molecule^-1s^-1. In all cases, the errors represent 2¦" (95% confidential level) and the calculated rate constants do not include the error associated with the rate constant of the OH reaction with the reference compounds. The rate constants for the hydroxyl radical reactions of a series of trans-2-aldehydes were compared with the values estimated using the structure activity relationship. The mechanism of hydroxyl radial reaction with trans-2-hexenal was also investigated experimentally. The major product of the OH+ trans-2-hexenal reaction was butanal. Additional work is underway to identify other products.