Cl-initiated photo-oxidation reaction of methyl propionate was investigated experimentally using relative rate method. Gas chromatography/mass spectrometry (GC-MS) and GC/infrared spectroscopy (GC-IR) were used as analytical tools to follow the concentrations of reactants and products during reaction. The gas-phase kinetics of methyl propionate with Cl atoms was measured over the temperature range of 263-363 K at 760 Torr in N atmosphere using CH and CH as reference compounds. The temperature-dependent rate coefficient for the reaction of methyl propionate with Cl atom was obtained as k(T) = [(3.25 ± 1.23) × 10] T exp [- (33 ± 4) / T] cm molecule s. Theoretical calculations were also performed at CCSD(T)/cc-pVDZ//B3LYP/6-31G(d,p) level of theory, and the rate coefficients for H abstraction reactions were evaluated using canonical variational transition state theory (CVT/SCT) with interpolated single point energy (ISPE) method over the temperature range of 200-400 K. The rate coefficients over the studied temperature range yielded the Arrhenius expression k(T) = (7.22 × 10) T exp (466 / T) cm molecule s. The reaction mechanism based on product analysis, thermochemistry, branching ratios, atmospheric implications, degradation pathways, and cumulative lifetime of methyl propionate is also presented in this manuscript. Graphical abstract ᅟ.
Temperature-dependent rate coefficients for the photo oxidation reaction of ethyl propionate with Cl atom were investigated experimentally using the relative rate technique. Gas chromatography with flame ionization detector (GC-FID), gas chromatography–mass spectrometry (GC–MS), and GC-infrared spectroscopy (GC-IR) were used to follow the concentrations and identification of reactants and products. The kinetics of ethyl propionate with Cl atoms was investigated over the temperature range of 263–363 K at atmospheric pressure, relative to C2H6 and C2H4. Theoretical calculations were also performed at CCSD(T)/6-311++G(d,p)//BHandHLYP/6-311G(d,p) level of theory, and the rate coefficients for H-abstraction reactions were calculated using canonical variational transition state theory (CVT) with interpolated single point energies (ISPE) method over the temperature range of 200–800 K. The temperature-dependent rate coefficients for the reaction of ethyl propionate with Cl atom were obtained both experimentally as well as theoretically and are k Expt(T) = [(6.88 ± 1.65) × 10–24]T 4.5 exp[(1108 ± 87)/T] cm3 molecule–1 s–1 and k Theory(T) = (6.73 × 10–19)T 2.74 exp[(571)/T] cm3 molecule–1 s–1, respectively. On the basis of product analysis on the title reaction and the computational studies, we have proposed the atmospheric degradation mechanism and various pathways for Cl atom-initiated photo oxidation of EP. Propionic acid is identified as the major product in the degradation of ethyl propionate on reaction with Cl atom. The thermochemistry, branching ratios, and cumulative lifetime of ethyl propionate are calculated and presented in this Article.
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.
The temperature-dependent reaction kinetics of methyl cyclohexane (MCH) and methyl cyclopentane (MCP) with Cl atoms were experimentally explored via the relative rate technique. Gas chromatography coupled with a flame ionization detector was employed to follow the reactant as well as the reference compound concentrations during the course of reaction. Gas chromatography coupled with mass spectrometry and gas chromatography coupled with infrared spectroscopy were used as the diagnostic tools for the detection and identification of the products in the title reaction. The rate coefficients for the reaction of Cl atoms with methyl cyclohexane and methyl cyclopentane were measured in the temperature range of 283–363 K at 760 Torr using isoprene and propylene as reference compounds. To support the experimental results, computational calculations were performed over the temperature range of 200–400 K using canonical variational transition state theory coupled with small curvature tunneling (CVT/SCT), conventional transition state theory (CTST) coupled with Wigner tunneling corrections, and CVT coupled with Wigner tunneling methods using the MP2 level of theory with 6-31G(d,p) as the basis set. The temperature-dependent rate coefficients were measured for the reaction of methyl cyclohexane and methyl cyclopentane with Cl atoms to be k (MCH) = [(4.48 ± 0.75) × 10–11]exp[(604 ± 25)/T] cm3 molecule–1 s–1 and k (MCP) = [(5.71 ± 0.66) × 10–12]exp[(1819 ± 669)/T] cm3 molecule–1 s–1, respectively. The measured rate coefficients at 298 K for the reactions of Cl atoms with methyl cyclohexane and methyl cyclopentane are k 298 K MCH = (3.36 ± 0.34) × 10–10 cm3 molecule–1 s–1 and k 298 K MCP = (2.25 ± 0.24) × 10–10 cm3 molecule–1 s–1, respectively. The conceivable atmospheric degradation mechanism for the reaction of methyl cyclohexane as well as methyl cyclopentane with Cl atoms was projected based on the products obtained during the reaction. Atmospheric implications, cumulative atmospheric lifetimes, thermochemistry, ozone formation potentials, and branching ratios of these molecules were also calculated and have been reported in this article.
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