RATE CONSTANTS FOR CHALCOGEN GROUP TRANSFERS IN BIMOLECULAR SUBSTITUTION-REACTIONS WITH PRIMARY ALKYL RADICALS

Rate constants for group transfers of the MeS, PhS, PhSe, and PhTe groups from chalcogen-substituted acetate, acetonitrile, malonate, and malononitrile compounds, from N-(phenylthio) phthalimide and from Me2S2 and Ph2S2 to primary alkyl radicals, have been determined by competition kinetics using PTOC esters as the radical precursors and competing trapping agents. Thio group transfers from malononitrile derivatives are marginally faster than the corresponding group transfer from the symmetrical disulfide, and the rate constant for PhSe group transfer from PhSeSePh is greater than those from the derivatives studied here. Substituent effects suggest that the chalcogen transfer reactions may be concerted. For three cases in which direct comparisons can be made, the rate constants for reactions of phenylchalcogenides are approximately equal to those for halogen atom transfer when the chalcogen and halide are in the same row of the periodic table and the radical resulting from displacement is the same. The rate constants reported in this work will be useful for the rational design of synthetic schemes based on homolytic group transfer chemistry.