Stability and reactions of the tetrachloroethyl radical

At temperatures above 410°K, the photochlorination of trichloroethylene involves a succession of competitive reactions. These have been studied in detail both by a conventional and by a mass-spectrometric technique. The results are interpreted in terms of a mechanism derived from the study of simpler systems. The rate constant of formation (k2) and decomposition (k4) of the C2HCl4 radical and the rate of the radical-atom chain-breaking step (k7) have been measured and the reverse (k5) of the chain propagating step (k3) has been calculated using thermodynamic data: C2HCl3+Cl→C 2HCl4 log10 k2 = 9.75±0.3, C2HCl4→C2HCl3+Cl log 10 k4 = (13.7±0.5)-(20,400±1,000)/4.576 T. C2HCl4+Cl→C2HCl5, or log 10 k7 = 10.85±1, C2Cl4+HCl, or C2HCl3+Cl2. C2HCl 5+Cl→C2HCl4+Cl2 logi 10 k5 = (10.8±0.5)-(17,9000±1,000)/4.576 T. The possibility of observing the atom-atom (Cl+Cl) chain-breaking step and the primarily formed activated C2HCl4* radical is discussed.SCOPUS: ar.j