Rate Coefficient and Mechanism of the OH-Initiated Degradation of 1-Chlorobutane: Atmospheric Implications.

Abstract

In this work, we investigate the degradation process of 1-chlorobutane, initiated by OH radicals, under atmospheric conditions (air pressure of 750 Torr and 296 K) from both experimental and theoretical approaches. In the first one, a relative kinetic method was used to obtain the rate coefficient for this reaction, while the products were identified for the first time (1-chloro-2-butanone, 1-chloro-2-butanol, 4-chloro-2-butanone, 3-hydroxy-butanaldehyde, and 3-chloro-2-butanol) using mass spectrometry, allowing suggesting a reaction mechanism. The theoretical calculations, for the reactive process, were computed using the BHandHLYP/6-311++G(d,p) level of theory, and the energies for all of the stationary points were refined at the CCSD(T) level. Five conformers for 1-chlorobutane and 33 reactive channels with OH radicals were found, which were considered to calculate the thermal rate coefficient (as the sum of the site-specific rate coefficients using canonical transition state theory). The theoretical rate coefficient (1.8 × 10-12 cm3 molecule-1 s-1) is in good agreement with the experimental value (2.22 ± 0.50) × 10-12 cm3 molecule-1 s-1 determined in this work. Finally, environmental impact indexes were calculated and a discussion on the atmospheric implications due to the emissions of this compound into the troposphere was given.