Tk« hyûrogca abatraetion froa tha chlarinatad athaaaa hj ohloriaa ataaa hac baan iavaatigatad in tha gaa phaaa batvaaa 323 aad 423*X. Akaaluta Taluaa of tha rata eonatanta hara baan obtainad uaing a compatition nathod with ehlorefona ar aathjl ehlarida aa eospetltor. Tha aetiratian anargiaa aad tha pra->azponaatial faetora ara diaenaaad.
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.
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