Absolute rate constants for the reactions of primary alkyl radicals with aromatic amines

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 (k^373K = 3.5 × 10³ M^-1 s^-1), diphenylamine (k^373K = 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 AT-deuteriodiphenylamine the deuterium kinetic isotope effect, k_NH/k_ND, was found to be 2.3 at 373 K.