Determination of rate constants for trifluoromethyl radical addition to various alkenes via a practical method

Abstract

A simple and practical method for the determination of rate constants for trifluoromethyl radical addition to various alkenes by applying competition kinetics is introduced. In the kinetic experiments the trifluoromethyl radicals are generated in situ from a commercially available hypervalent-iodine-CF₃ reagent (Togni-reagent) by SET-reduction with TEMPONa in the presence of TEMPO and a π-acceptor. From the relative ratio of TEMPOCF₃ and CF₃-addition product formed, which is readily determined by ¹⁹F-NMR spectroscopy, rate constants for trifluoromethyl radical addition to the π-acceptor can be calculated. The practical method is also applicable to measure rate constants for the addition of other perfluoroalkyl radicals to alkenes as documented for CF₃CF₂-radical addition reactions.