Oxygen‐inhibited photochlorination of 1,2‐dichloroethane

Abstract

The oxygen-inhibited photochlorination of 1,2-dichloroethane has been studied in the gas-phase between 321 and 489,5"K. The following rate constants have been estimated log(kg, mole-' 1 sec-') = 7.8 and log(k-g, sec-') = -24,000/4.576 T+13 where k9 and k-9 refer to (9) ( -9 ) CH2ClCHCI. + 0 2 + CH2ClCHC103.These results are compared to those observed for the reactions of CzH6, CzHCI5, C2HC13 and C2C14. INTRODUCTIONThe rateequation for the oxygen-inhibited photochlorination of C2H6 [l] is very different from that observed for C,HC15 121, C2HC13 [3] and C,Cl, [2]. This can be explained by the fact that the removal of the alkyl chaincarriers Re by 0, is in equilibrium with the reverse reaction for highly chlorinated ethanes and ethylenes (R. = CHCl,CCI,-[4], CC13CC1,*) but not for ethane (R-= CH,CH2-). The cases p r e viously studied involve R* radicals where the C-atom with the free valency is either completely substituted by C1-atoms or not substituted at all. The study of a reaction where R-has an intermediate structure should lead to a better understanding of the inhibiting effect of oxygen on the photochlorinations of ethane and ethylene and their chlorinated derivatives. The present work deals with the reaction of 1,2-C2H,C1, which involves such a radical (R-= CH2ClCHC1-). EXPERIMENTALThe kinetic apparatus and the experimental technique have already been described [1,2]. The reactions were initiated by light at 436 nm and investigated by photometric measurement of the chlorine partial pressure and by gas chromatographic analysis. Commercial tank chlorine (Solvay) was purified as described earlier [I], 1,2-dichloroethane (*> contained less than 0.5% impurity as determined by gas (*) These unstabilized substances were kindly supplied by the Solvay Research Center, Brussels.14 L. Bertrand, J. Bizongwako, G. Huybrechts and J. Olbregts chromatography. Oxygen (Societe Belge de 1'Air Liquide, 99.95% pure) and nitrogen (I'Oxhydrique Internationale S.A.) containing < 30 ppm oxygen were used without further purification. The purities of the 1,1,2-C,H3C13*, 1,1,1,2-C2H2C14*, 1,1,2,2-C2H2Cl, (Schuchardt, reinst, distilled) and C2H3Cl* used in calibrating the gas chromatograph were all greater than 98%. RESULTSThe photochlorination of 1,2-dichloroethane has been studied in the presence of oxygen between 321 and 489.5"K. The pressure of 1,2-C2H4C1,, C1, and 0, and the absorbed light intensity I, were varied over the range given in table 1.