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 gro ups from chalcogen-substituted acetate, acetonitrile, malonate, and ma lononitrile compounds, from N-(phenylthio) phthalimide and from Me2S2 and Ph2S2 to primary alkyl radicals, have been determined by competiti on kinetics using PTOC esters as the radical precursors and competing trapping agents. Thio group transfers from malononitrile derivatives a re marginally faster than the corresponding group transfer from the sy mmetrical disulfide, and the rate constant for PhSe group transfer fro m PhSeSePh is greater than those from the derivatives studied here. Su bstituent effects suggest that the chalcogen transfer reactions may be concerted. For three cases in which direct comparisons can be made, t he rate constants for reactions of phenylchalcogenides are approximate ly equal to those for halogen atom transfer when the chalcogen and hal ide are in the same row of the periodic table and the radical resultin g from displacement is the same. The rate constants reported in this w ork will be useful for the rational design of synthetic schemes based on homolytic group transfer chemistry.