Rate Constants for Reduction of substituted Methylperoxyl Radicals by Ascorbate Ions and N,N,N',N'-tetramethyl-p-phenylenediamine

Article abstract of DOI:10.1021/j100347a045

Absolute rate constants (k) for reduction of substituted methylperoxyl radicals by ascorbate ions and by TMPD (N,N,N',N'-tetramethyl-p-phenylenediamine) in aqueous solutions have been determined by pulse radiolysis.The rate constants vary from 1E6 to 1E9 M^-1 s^-1, increasing as the electron-withdraving capacity of the substituent on the peroxyl group increases.Linear correlations are observed between log k and the Taft substituents ?^* for a wide variety of substituents, but not all substituents fit the same line.In the case of ascorbate as reductant, the points for peroxyl radicals that contain halogens on the α-carbon lie on a different line (ρ^*=0.41) than that for the other substituents (ρ^*=1.25).In the case of TMPD there are alsotwo families of peroxyl radicals: Those comprimising the electron-donating groups Me through t-Bu (ρ=5.6) and those containing electron-withdrawing substituents (ρ^*=0.64).