Radical addition of iodine monochloride to vinylidene fluoride

The radical addition of iodine monochloride to 1,1-difluoroethylene or vinylidene fluoride (VDF) leading to a ClCF2CH2I (I)/ClCH2CF2I (II) mixture is described. Four different ways of initiation (thermal, photochemical, presence of radical initiators or redox catalysts) were used and all of them led to a high amount (≥98%) of isomer (I). The percentages of (I) and (II) isomers were determined by 19F NMR and they were also deduced from those of ClCF2CH3 and ClCH2CF2H obtained by selective reduction of the iodine atom of the product mixture, by tributylstannane. The reactivity of ICl to VDF 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 the SOMO of radicals and the HOMO of the fluoroolefin show that the mechanism of such a reaction occurs via the addition of I to the less fluorinated side of VDF.