Photo-Oxidation Reaction Kinetics and Mechanistics of 4‑Hydroxy-2-butanone with Cl Atoms and OH Radicals in the Gas Phase

The temperature-dependent rate coefficients for the gas-phase reaction of 4-hydroxy-2-butanone (4H2BN) with Cl atoms and OH radicals were explored experimentally using relative rate technique and computational methods. The concentrations of the reactants as well as products were followed using gas chromatography (GC) with the flame ionization detector, GC/mass spectrometry, and GC/infrared spectroscopy as analytical techniques. Formaldehyde was obtained as the major product during the title reaction. The kinetics of 4H2BN with Cl atoms and OH radicals were measured over the temperature range of 298–363 K at 760 Torr in the N2 atmosphere using C3H8, C2H4, isopropanol, and n-propanol as reference compounds. The temperature-dependent rate coefficients for the reaction of 4H2BN with Cl atoms and OH radicals were obtained as k Expt(T) = [(1.52 ± 0.86) × 10–26]T 5 exp[(2474 ± 450)/T] cm3 molecule–1 s–1 and k expt(T) = [(2.09 ± 0.24) × 10–12] exp­[−(409 ± 15)/T] cm3 molecule–1 s–1, respectively. Theoretical calculations were carried out at the M062X/6-31G­(d,p) and M06-2X/6-31+G­(d,p) level of theories, and the rate coefficients for H abstraction reactions were evaluated using the canonical variational transition state theory with the inclusion of small-curvature tunneling correction over the temperature range of 200–400 K. The rate coefficients obtained over the studied temperature range were used to fit the data, and the Arrhenius expression was obtained to be k Cl(Theory) (200–400 K) = (6.10 × 10–25)T 4.42 exp­(2397/T) cm3 molecule–1 s–1, k OH(Theory) (200–400 K) = (1.13 × 10–19)T 2.27 exp­(1505/T) cm3 molecule–1 s–1, respectively, for the reactions of Cl atoms and OH radicals with 4H2BN. The possible reaction mechanism proposed based on the obtained products for the title reaction, thermochemistry, branching ratios, and atmospheric implications and cumulative lifetime of 4H2BN were also explored in this study.