Rate coefficients and products for gas‐phase reactions of chlorine atoms with cyclic unsaturated hydrocarbons at 298 K

Abstract

Rate coefficients for the reaction of Cl atoms with cycloalkenes have been determined using the relative rate method, at 298 K and atmospheric pressure of N 2 . Reference molecule was n-hexane, and the concentrations of the organics were followed by gas chromatographic analysis. Cl atoms were prepared by photolysis of trichloroacetyl chloride at 254 nm. The relative rates of reactions of Cl atoms with cycloalkenes, with respect to n-hexane, are measured as 1.12 ± 0.38, 1.31 ± 0.14, and 1.69 ± 0.18 for cyclopentene, cyclohexene, and cycloheptene, respectively. Considering the absolute value of the rate coefficient of the reaction of Cl atom with n-hexane as 3.03 ± 0.06 × 10 −10 cm 3 molecule −1 s −1 , the rate coefficient values for cyclopentene, cyclohexene, and cycloheptene are calculated to be (3.39 ± 1.08) × 10 −10 , (3.97 ± 0.43) × 10 −10 , and (5.12 ± 0.55) × 10 −10 cm 3 molecule −1 s −1 , respectively. The experiments for each molecule were repeated six to eight times, and the slopes and the rate coefficients given above are the average values of these measurements, and the quoted error includes 2σ as well as all other uncertainties in the measurement and calculations. The rate coefficient increases linearly with the number of carbon atoms, with an increment per additional CH 2 group being (8.7 ± 1.6) × 10 −12 cm 3 molecule −1 s −1 . Chloroketones and chloroalcohols, along with unsaturated ketones and alcohols, were found to be the major products of Cl-atom-initiated oxidation of cycloalkenes in the presence of air. The atmospheric implications of these results are discussed, along with a comparison with the reported structure activity relationships.

Rate Coefficients for the Gas‐Phase Reactions of Chlorine Atoms with Cyclic Ethers at 298 K

“…The rate of reaction of 2,3-DHF with CH 3 COCl was found to be lower than that with CCl 3 COCl and hence photolysis of CH 3 COCl at 254 nm was used as the source molecule for the Cl atom. The utility of this molecule as the source of the Cl atom was tested with butane, 1-butene, and cycloheptene with n-hexane as the reference molecule, and the measured relative ratios and rate coefficients were found to match with the reported values [12,18,19]. 1-Butene and n-hexane could not be used as reference molecules for determining the rate coefficient of 2,3-DHF, since their depletion rate due to the reaction with the Cl atom was found to be slower than the rate of depletion of 2,3-DHF due to the dark reaction with CH 3 COCl.…”

“…The rate coefficient is estimated assuming no interference from other radical reactions. The rate coefficient of the reaction of the Cl atom with cycloheptene is (5.32 ± 0.57) × 10 −10 cm 3 molecule −1 s −1 [12]. Although the absence of heterogeneous chemistry cannot be completely ruled out in the present experimental conditions, the major products observed here match very well with those reported for THP in a 200 L Teflon bag [16], namely tetrahydro-4H-pyran-4-ol, tetrahydro-4H-pyran-4-one, tetrahydro-2H-pyran-2-one, 2-methyl tetrahydrofuran, tetrahydro-2-furanone, and ring-opened product 3-chloropropyl formate.…”

“…The reactivity of both OH and Cl toward unsaturated molecules is generally higher than that of the saturated ones, due to the higher rate coefficients of addition reactions [6,11]. However, our recent measurement of rate coefficients of reactions of Cl atoms with unsaturated cyclic hydrocarbons at room temperature [12,13] showed that their rate coefficients increase with the number of carbon atoms (from 5 to 8), but do not change significantly with unsaturation. Considering the importance of Cl atom reactions in the troposphere, it is desirable to understand these trends in their rate coefficients as compared to that of OH radicals, which requires measurement of rate coefficients of more molecules with different functional groups.…”

“…All the experiments were performed at 298 ± 2 K. The details of the experimental setup are given elsewhere [12,13]. The reaction mixture, consisting of CE (200-250 ppm), reference molecule (200-300 ppm), the source molecule for Cl generation (Cl 2 /CCl 3 COCl), and buffer gas (N 2 /air), was prepared in a Pyrex/quartz reactor cell of volume 3 L, having a sealed port for taking out samples for concentration measurement.…”

Photoisomerization and Photoinduced Reactions in Liquid CCl4 and CHCl3

“…However, reactions of Cl atoms with unsaturated hydrocarbons exhibit addition pathways that compete with, or can dominate the direct abstraction pathway. [3][4][5][6][7][8][9] The energized adduct may eliminate HCl under low pressure…”