Ab initio molecular orbital study of the C2H4+Cl2 → C2H4Cl2 reaction

A new mechanism of the C2H4 + Cl-2 --> C2H4Cl2 reaction in gas phase has been theoretically proposed using ab initio molecular orbital methods; Cl is abstracted from Cl-2 by C2H4, which leads first to the production of C2H4Cl + Cl radicals and then to immediate recombination to form C2H4Cl2. It was predicted that this abstraction reaction, C2H4 + Cl-2 --> C2H4Cl + Cl, is 25.1 kcal mol(-1) endothermic with no transition state at the PMP4(SDTQ,full)/6-311 + + G(d,p)//MP2(fc)/6-31 + G(d,p) level of theory. The previously proposed mechanism, direct Cl-2 addition to C2H4 to produce C2H4Cl2, has also been examined and an energy barrier of 36.3 kcal mol(-1) was obtained at the same level of theory. Therefore one concludes that the new mechanism is energetically more feasible than the direct Cl-2 addition to C2H4 for the C2H4 + Cl-2 --> C2H4Cl2 reaction in the gas phase. (C) 2000 Elsevier Science B.V. All rights reserved.