The inhibited autoxidation of styrene. Part VI. The relative efficiencies and the kinetics for inhibition by N-aryl anilines and N-alkyl anilines

Abstract

The kinetics and deuterium isotope effects for the N-aryl aniline and N-alkyl aniline inhibited autoxidation of styrene indicate that the rate-controlling step for inhibition involves abstraction of the amino hydrogen by a peroxy radical. The rate constants for this reaction have been correlated by means of the Hammett equation with the σ⁺ constants of the substituents for diphenylamines (ρ = −0.89) and N-methylanilines (ρ = −1.6). A numerical difference involving a factor of two between the simple kinetic expression applicable to most aromatic amine inhibitors and the expression applicable to most phenols and p-phenylenediamines is suggested. The important role played by the substrate in studies of inhibitor action is emphasized.