Kinetics and mechanism of the thermal chlorination of chloroform in the gas phase

The gas-phase thermal chlorination of CHCl3 has been studied up to high conversions by photometry and gas chromatography in a conditioned static quartz reaction vessel between 573 and 635 K. The initial pressures of both CHCl3 and Cl-2 ranged from about 10-100 Torr, and the initial total pressure was varied between about 30-190 Torr. The reaction is rather complex because the produced CCl4 is not stable. The rate of consumption of Cl-2 therefore increases in the course of time. This acceleration is explained quantitatively in terms of a radical mechanism and its kinetic and thermodynamic parameters. This reaction model is based on a known model for the pyrolysis of CCl4 to which only one reaction couple involving CHCl3 has been added. Analyses of the rates of the homogeneous elementary steps show that the primary source of Cl atoms is the second-order dissociation of Cl-2, which is rapidly superseded by a secondary source, the first-order dissociation of the CCl4 primary product. (C) 2000 John Wiley & Sons, Inc.