Radical addition of iodine monochloride to trifluoroethylene

The addition of iodine monochloride to trifluoroethylene (TrFE) leading to a ClCF2CFHI (I)/ClCFHCF2I (II) mixture is described. Four different ways of initiation (thermal, photochemical, presence of radical initiator, or redox catalyst) were used and all of them led to a high amount (> 89%) of isomer (I). The amounts of (I) and (II) isomers were determined by H-1 and F-19 NMR and also they were deduced from those of ClCF2CFH2 and ClCFHCF2H obtained by selective reduction of the iodine atom of the former mixture, in the presence of tributylstannane. The reactivity of ICl to TrFE and the high proportion of isomer (I) were interpreted by means of a thermodynamical approach from the enthalpy of formation of (I) and (II), respectively, determined by semi-empirical computations. In addition, heats of formation of both isomers and interactions between SOMO of radicals and HOMO of fluoro-olefin enable to show that the mechanism of such a reaction occurs via the addition of I-. to the less fluorinated side of TrFE. (C) 1998 Elsevier Science S.A. All rights reserved.