Reaction of OH Radical with C₂H₃Cl:  Rate Constant and Reaction Pathway Analysis

Abstract

There are two different carbon sites in C2H3Cl where OH addition or abstraction reactions can occur, α and β to the Cl atom, with several dissociation and isomerization products of each addition adduct. Thirteen elementary reactions and 18 species are included in the analysis of this reaction system. Thermochemical kinetic parameters are developed for each elementary reaction process. Chemical activation kinetic analysis with multifrequency QRRK theory for k(E) and master equation for falloff are used to estimate overall rate constants as functions of temperature and pressure. Thermodynamic parameters, including ΔH f°298, S°298, and C p°(T) (300 ≤ T/K ≤ 1500), of stable species are from the literature when available or estimated by the group additivity method. Values for CHClOHĊH2 are determined by density functional calculation and isodesmic reactions. Results are compared with the experimental data. Rate constants (300∼2000 K, in cm3 mol-1 s-1, E a in cal/mol) for the important addition and abstraction channels at 760 Torr are as follows: k = 1.22 × 1084 T -25.5 exp(−15000/RT) for C2H3Cl + OH → CHClOHĊH2; k = 1.77 × 1040 T -9.08 exp(−7240/RT) for C2H3Cl + OH → ĊHClCH2OH; k = 9.72 × 106 T 2 exp(−3800/RT) for C2H3Cl + OH → CH2ĊCl + H2O; k = 1.69 × 107 T 2 exp(−4390/RT) for C2H3Cl + OH → ĊHCHCl + H2O.

Kinetics and thermochemistry of the addition of atomic chlorine to acetylene

“…As an example of an application of these results, we note that at above about 800 K abstraction is faster than addition for the reaction of OH with chloroethene at 1 atm pressure [13]. At for example 1000 K the total abstraction rate constant is predicted to be 5 × 10 -12 cm 3 molecule -1 s -1 , with an α:β chlorovinyl product ratio of about 0.4:0.6 [13].…”

“…At for example 1000 K the total abstraction rate constant is predicted to be 5 × 10 -12 cm 3 molecule -1 s -1 , with an α:β chlorovinyl product ratio of about 0.4:0.6 [13].…”

“…Chlorovinyl radicals in general are intermediates in the incineration of chlorinated waste, and C 2 H 2 Cl is a product of the oxidation of vinyl chloride, for example by OH [13]. Although needed for reliable combustion modeling, no experimental data are available for the enthalpies of formation of any chlorovinyl radicals.…”

Rate Coefficients and Mechanistic Analysis for Reaction of OH with Vinyl Chloride between 293 and 730 K

“…These combined experimental and modeling observations suggest that (1,-1) and (2) are dominant at room temperature and moderate pressures and that Cl elimination plays a minor role. Two possible mechanisms for explaining this behavior were suggested by Perry et al 7 and Atkinson 9 and subsequently evaluated by Zhu et al 11 The first is that the OH radical addition only occurs at the -carbon and the 1,2-migration of OH is ratedetermining. The second is that the addition occurs at both the R and -position, but mainly at the -position, and the 1,2-migration is sufficiently slow as to be negligible.…”

“…In addition, a refined QRRK analysis of the OH addition reaction mechanism is performed by combining the recent analyses of Zhu et al 11 with variational transition state theory calculations of the rate of formation of the OH-vinyl chloride adducts. An evaluation of the temperature-dependent rate of H atom abstraction is also performed by utilizing G3 (MP2) ab initio calculations in conjunction with thermochemical transition state theory.…”