Kinetics and mechanism for the thermal chlorination of chloroform in the gas phase: Inclusion of HCl elimination from CHCl₃

Abstract

HCl elimination from chloroform is shown to be the lowest energy channel for initiation in the thermal conversion of chloroform to CCl 4 , with chlorine gas in the temperature range of 573-635 K. Literature data on this reaction is surveyed and we further estimate its kinetic parameters using ab initio and density functional calculations at the G3//B3LYP/6-311G(d,p) level. Rate constants are estimated and reported as functions of pressure and temperature using quantum RRK theory for k(E) and master equation analysis for fall-off. The high-pressure limit rate constant of this channel is k(CHCl 3 → 1 CCl 2 + HCl) = 5.84 × 10 40 × T −8.7 exp(−63.9 kcal/mol/RT ) s −1 , which is in good agreement with literature values. The reactions of 1 CCl 2 with itself, with CCl 3 , and with CHCl 3 are incorporated in a detailed mechanistic analysis for the CHCl 3 + Cl 2 reaction system. Inclusion of these reactions does not significantly change the mechanism predictions of Cl 2 concentration profiles in previous studies (Huybrechts, Hubin, and Van Mele, Int J Chem Kinet 2000, 32, 466) over the temperature range of 573-635 K; but Cl 2 , CHCl 3 , C 2 Cl 6 species profiles are significantly different at elevated temperatures. Inclusion of the 1 CCl 2 + Cl 2 → CCl 3 + Cl reaction (abstraction and chain branching), which is found to have dramatic effects on the ability of the model to match to the experimental data, is discussed. C

Determination of the Rate Constant of the Reaction of CCl2 with HCl

“…Gas chromatographic analysis was used to determine the reactant and products concentrations as a function of temperature at different reaction times. In 2003, Zhu and Bozzelli analyzed previous literature results of the thermal conversion of CHCl 3 to CCl 4 in the presence of Cl 2 in the 846–908 K temperature range using a detailed mechanism. The following mechanisms were proposed for the insertion reaction CCl 2 + CHCl 3 : …”

“…The rate constants' temperature dependence of mechanisms – was studied by the authors obtaining values of 2.6 × 10 −21 and 3.1 × 10 −27 cm 3 molecule −1 s −1 for reaction at 300 K. For reaction the values obtained were 5.9 × 10 −29 and 1.7 × 10 −29 cm 3 molecule −1 s −1 , respectively. The rate constants derived for reaction were 1.7 × 10 −29 and 2.4 × 10 −17 cm 3 molecule −1 s −1 , respectively.…”

“…Mono‐ and dihalocarbenes were particularly well studied regarding the determination of kinetic rate constants. The determination of the steps that follow CHCl 3 pyrolysis has been the subject of numerous investigations . Flow and shock tube techniques have been employed using diverse detection methods to resolve the kinetics .…”

CANALES DE MINIMA ENERGIA PARA LAS REACCIONES DEL RADICAL CCl2 CON O2(1∑g) Y O2(1Δg)

“…Kumaran et al en su estudio de la descomposición térmica de CHCl 3 [13] , reportan la constante de velocidad de formación de C 2 Cl 4 en el régimen de baja presión, y de formación de C 2 Cl 2 . En los estudios de la descomposición térmica de CHCl 3 , Won et al [14] y Zhu et al [15] presentan valores para las constantes de velocidad de la reacción de recombinación entre radicales CCl 2 para formar C 2 Cl 4 y C 2 Cl 3 +Cl. En nuestro laboratorio hemos determinado la constante de velocidad de la reacción CCl 2 + CCl 2 → C 2 Cl 4 a 298 K y presiones entre 1 y 30 Torr [9] .…”

“…Zhu et al [15] y Kumaran et al [13] determinaron para la barrera de la reacción CCl 2 + HCl los valores 0,9 y 3,8 kcal mol -1 , respectivamente. Por otra parte, en nuestro laboratorio estudiamos por medio de la técnica de Fluorescencia Inducida por Láser (LIF) la cinética de dicha reacción y obtuvimos la constante de velocidad a 298 K, k HCl = (2,7 ± 0,1) x 10 -14 cm 3 molécula -1 s -1 [10] .…”