Gas-Phase Kinetics of a Series of cis -3-Hexenyl Esters with OH Radicals under Simulated Atmospheric Conditions.

The present relative kinetic study reports on the experimentally determined gas-phase reaction rate coefficients of OH radicals with a series of seven cis- 3-hexenyl esters. The experiments were carried out in the environmental simulation chamber made of quartz from the "Alexandru Ioan Cuza" University of Iasi (ESC-Q-UAIC), Romania, at a temperature of (298 ± 2) K and a total air pressure of (1000 ± 10) mbar. In situ long-path Fourier transform infrared (FTIR) spectroscopy was used to monitor cis- 3-hexenyl formate ( Z 3HF, ( Z )-CH 3 CH 2 CH═CH(CH 2 ) 2 OC(O)H), cis- 3-hexenyl acetate ( Z 3HAc, ( Z )-CH 3 CH 2 CH═CH(CH 2 ) 2 OC(O)CH 3 ), cis- 3-hexenyl isobutyrate ( Z 3HiB, ( Z )-CH 3 CH 2 CH═CH(CH 2 ) 2 OC(O)CH(CH 3 ) 2 ), cis- 3-hexenyl 3-methylbutanoate ( Z 3H3MeB, ( Z )-CH 3 CH 2 CH═CH(CH 2 ) 2 OC(O)CH 2 CH(CH 3 ) 2 ), cis- 3-hexenyl hexanoate ( Z 3HH, ( Z )-CH 3 CH 2 CH═CH(CH 2 ) 2 OC(O)(CH 2 ) 4 CH 3 ), cis -3-hexenyl cis -3-hexenoate ( Z 3H Z 3H, ( Z,Z )-CH 3 CH 2 CH═CH(CH 2 ) 2 OC(O)CH 2 CH═CHCH 2 CH 3 ), cis- 3-hexenyl benzoate ( Z 3HBz, ( Z )-CH 3 CH 2 CH═CH(CH 2 ) 2 OC(O)C 6 H 5 ), and the reference compounds. The following reaction rate coefficients (in 10 -11 cm 3 molecule -1 s -1 ) were obtained for the OH radical-initiated gas-phase oxidation of cis -3-hexenyl esters: (4.13 ± 0.45) for Z 3HF, (4.19 ± 0.38) for Z 3HAc, (4.84 ± 0.39) for Z 3HiB, (5.39 ± 0.61) for Z 3H3MeB, (7.00 ± 0.56) for Z 3HH, (10.58 ± 1.40) for Z 3H Z 3H, and (3.41 ± 0.28) for Z 3HBz. The results are discussed in terms of hexenyl ester reactivity and compared with the available literature data and structure-activity relationship (SAR) estimates. The atmospheric implications based on the average lifetimes of the investigated cis -3-hexenyl esters are discussed in the present study. The gas-phase rate coefficients for OH radical reactions are given herein for the first time for cis -3-hexenyl isobutyrate, cis -3-hexenyl 3-methylbutanoate, cis -3-hexenyl hexanoate cis -3-hexenyl cis -3-hexenoate, and cis -3-hexenyl benzoate. The newly determined gas-phase reaction rate coefficients provide new information for existing kinetic databases and contribute to the further development of SAR methodologies useful for predicting the reactivity of oxygenated volatile organic compounds.