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

HCl elimination from chloroform is shown to be the lowest energy channel for initiation in the thermal conversion of chloroform to CCl4, 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(CHCl3 --> (CCl2)-C-1 + HCl) = 5.84 x 10(40) x T-8.7 exp(-63.9 kcal/mol/RT) s(-1), which is in good agreement with literature values. The reactions of (CCl2)-C-1 with itself, with CCl3, and with CHCl3 are incorporated in a detailed mechanistic analysis for the CHCl3 + 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, CHCl3, C2Cl6 species profiles are significantly different at elevated temperatures- Inclusion of the (CCl2)-C-1 + Cl-2 --> CCl3 + 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) 2003 Wiley Periodicals, Inc.