Addition of a chlorine atom to tetrachloroethylene

Abstract

The gas-phase competitive photochlorination C1,-I-CzCI4-t-1 ,2-C2H4C12 has been studied at 310°K bctwccn 40 and 642 torr in the presence and absence of added CO, and SFs. The results are explained in terms of a mechanism in which the activated C2Cli radical initially formed by addition of a C1 atom to C2CI4 is deactivated by collision much more rapidly than it can react. The experimental data, combined with those from a parallel study of the competition C12-1 C2CI4+C2IIG at 348°K and those from previous studies at higher temperatures, lead to the new values and for the reactions log,,k2 (mole-' 1. scc-I) = 10.1 log, ,k, (sec-') = I 3.5 1 -16080/4*576T. c1+ C , C I , ~ C,ClS k 2 4 and C,CI,-+C,CI,+ c1, k4 where C2C15 is a thermalized radical. These results, combined with known therniochemical data, yield : D(C2C14-C1) = 16.9, D(CzC15-H) -95.8 and D(C2Cls-CI) -72-6 kcal mole-', (C2Cl5) = 8.4 kcal mole-' and SiQ8 (C2CI5) -96.4 cal mole-' deg.-l. The rate constant ka for the reaction CzClf -KzC14+CI is estimated to be less than 4 x lo7 sec-'. Existing data on additionsubstitution competitive photochlorinations of C2H4, 1,2-C2H2Cl2, C2HClJ and C,C14 are discussed.Competitive photochlorinations of the ethylenes CZH4-,$3n (n = 0,2,3,4) with saturated hydrocarbons have led to measurements of the rate constant k2 for the addition of a C1 atom to the double bond. The value of logIok, (mole-1 1. sec-l) is about 10.6 for C2H4,1 1,2-C2H2C12 and C2HC13,3 while for C2C14 it is reported to be 9.4. Moreover, the competitive chlorination of C2C14 has been explained by a mechanism involving reactions of thermalized pentachloroethyl radicals alone, while for C2H4, 1 ,2-C2H2C12 and C2HC13, reactions of chcmically activated radicals are observed. It therefore seemed intercsting to check the low value of k, for C2Cl4 and to investigate the effect of total pressure on its chlorination.

Kinetics and Thermochemistry of the Cl(2PJ) + C2Cl4 Association Reaction

“…Although this study represents the first systematic investigation of the temperature and pressure dependence of k 1 , there are several published measurements with which our results can be compared. In addition to the two "direct" studies discussed above, there have been a number of competitive kinetics studies of reaction 1, [9][10][11][12][13]16 two of which 13,16 report results where meaningful comparisons can be made with our results. The magnitude of Davis et al's rate coefficients seems a little low compared to values one might expect based on our measurements in N 2 buffer gas, and the ratio k 1 (100 Torr of He)/k 1 (15 Torr of He) ) 1.25 obtained from Davis et al's results is smaller than one would predict based on the 297 K falloff curve we have obtained using N 2 as the buffer gas ( Figure 4).…”

Addition of chlorine atom on vinyl chloride

“…As it is very close to the number of collisions, reaction ( 2 ) must have very little or no activation energy. This value of k2 compared to those obtained for the other ethylenes (see table 1) indicates that the addition of a chlorine atom is the m s t rapid on vinyl chloride and cis-l,Z-dichloroethylene. and Rabinovitch (4) for whom they are a h s t the slowest processes.…”

Kinetics and mechanism of the pyrolysis of pentachloroethane

“…The rate constants at 710°K were calculated to be kxa = 4 X lo8 (sec-l) and k-3* = 1.3 X 1O' O (l./ mole-sec) [12]. Thus since (Cl) << (C2C15) [13] and the TCE concentration is about mole/l., the reversibility of this reaction appears to be negligible.…”

“…This conclusion is only partially consistent with the predictions made using the elementary rate constants reported in the literature. The rate constants at 710°K were calculated to be kxa = 4 X lo8 (sec-l) and k-3* = 1.3 X 1O' O (l./ mole-sec) [12]. Thus since (Cl) << (C2C15) [13] and the TCE concentration is about mole/l., the reversibility of this reaction appears to be negligible.…”