Absolute Rate Constants for the Reactions of Primary Alkyl Radicals with Aromatic Amines1

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Abstract
Hydrogen abstraction from diarylamines (4-X-C6H4)2NH [X = H, CH3, C8H17, CH3O, and Br] by the 2-methyl-2-phenylpropyl radical in n-dodecane solution was investigated by thermolysis of 3-methyl-3-phenylbutanoyl peroxide in the presence of various concentrations of the amines. The reaction is a non-chain process in which the 2-methyl-2-phenylpropyl radical and its rearrangement product, the 2-benzylpropan-2-yl radical, abstract hydrogen from both the solvent and the amine. Cross-disproportionation reactions of the rearranged radical led to the formation of significant amounts of β,β-dimethylstyrene. Rate constants for hydrogen abstraction by the unrearranged, primary alkyl radical from n-dodecane (k373K = 3.5 × 103 M-1 s-1), diphenylamine (k373K = 1.3 × 106 M-1 s-1), and the substituted diarylamines were determined from the product yields and the known rate constant for the radical rearrangement. From kinetic experiments with N-deuteriodiphenylamine the deuterium kinetic isotope effect, kNH/kND, was found to be 2.3 at 373 K.