A KINETIC SCALE FOR DIALKYLAMINYL RADICAL REACTIONS

A kinetic scale for dialkylaminyl radicals was established by measurin g unimolecular rate constants for a series of dialkylaminyl radical cl ocks that spans eight orders of magnitude and using clock reactions to measure the second order rate constants for reactions of several hydr ogen atom donors. N-Hydroxypyridine-2-thione derivatives of carbamic a cids (so-called PTOC carbamates) were used as radical precursors in di rect, laser-flash kinetic measurements and in indirect, radical chain kinetic studies. The calibrated radical clocks are N-methyl-6,6-diphen yl-5-hexenaminyl, N-methyl-trans-5-phenyl-4-pentenaminyl, N-methyl-5,5 -diphenyl-4-pentenaminyl, N-methyl-trans-2-phenylcyclobutanaminyl, and N-methyl-trans-2-phenylcyclopropanaminyl. Calibrated hydrogen atom do nors are Bu(3)SnH, t-BuSH, PhSH, and PhSeH. Whereas the tin hydride re actions with dialkylaminyl radicals are slower than reactions with alk yl radicals, the polarity-matched reactions of the electron-rich dialk ylaminyl radicals with the electron-poor hydrogen donors t-BuSH, PhSH, and PhSeH have rate constants nearly equal to those for reactions of alkyl radicals with the same donor.