Reaction of <i>tert</i>-Alkoxyl and Alkyl Radicals with Styrene Studied by the Nitroxide Radical-Trapping Technique

Abstract

The reactions of tert -alkyl peroxypivalates 1 (R = methyl, ethyl, and n -propyl) with styrene in the presence of the free-radical scavenger (1,1,3,3-tetramethyl-2,3-dihydro-1 H -isoindol-2-yl)oxyl ( 2 ) have been studied at 60 °C. tert -Butyl and tert -alkoxyl radicals ( tert -butoxyl, tert -pentyloxyl, and tert -hexyloxyl radicals) were generated from the thermolysis of 1, and the derivative alkyl radicals (methyl, ethyl, n -propyl, and 4-hydroxy-4-methylpentyl radicals) were formed by subsequent unimolecular reactions (β-scission and 1,5-H shift) of the corresponding tert -alkoxyl radicals. The extent of the unimolecular reactions of the tert -alkoxyl radicals (versus addition to styrene) and the relative reactivity of alkyl radicals toward addition to styrene were obtained from the competitive addition/trapping reactions. The absolute rate constants for the addition of tert -butyl, ethyl, methyl, and n -propyl radicals to styrene at 60 °C were estimated to be (7.4, 4.7, 5, and 5.4) × 10 5 M -1 s -1, respectively.