(644f) 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.