Rate Constants and Arrhenius Functions for Hydrogen Atom Transfer from tert-Butyl Thiol to Primary Alkyl Radicals

Article abstract of DOI:10.1021/jo00280a028

The radical clock method was used to determine rate constants for hydrogen atom transfer from t-BuSH to primary alkyl radicals over the temperature range -45 to 50 deg C.Three clocks, cyclization of the 5-hexenyl radical (3a), ring opening of the cyclopropylcarbinyl radical (3b), and rearrangement of the 2,2-dimethyl-3-butenyl radical (3c), were used in THF, and 3a was used in toluene.Arrhenius functions for the two studies with 3a and the one with 3b were quite similar, and the Arrhenius function for 3c, when adjusted for direct comparison to reactions with simple primary radicals, was also similar.Combining the results from 3a and 3b in THF gave an Arrhenius function for hydrogen atom transfer from t-BuSH to primary radicals of log(k/M^-1 s^-1) = (8.37 +/- 0.08) - (2.00 +/- 0.09)/2.3RT; the calculated rate constant at 25 deg C is 8.0 * 10⁶ M^-1 s^-1.This study ultimately relates the t-BuSH rate constants to those for hydrogen atom transfer to primary radicals from both Bu3SnH and PhSH and serves to compare the latter two sets of kinetic data; it also demonstrates that the fast radical clock reactions of 3a and 3b are calibrated against equivalent standards.