Inhibition kinetics of initiated autoxidations

Abstract

In the kinetic analysis of the inhibition of initiated autoxidations, it has to be taken into account that peroxyl radicals derived from the initiator (R′O₂˙), as well as those generated from the substrate (RO₂˙), may participate in the reaction. They become increasingly important the shorter the kinetic chain. This manifests itself in deviations of the rate constants calculated by usual analyses. If R′O₂˙ is more reactive towards the substrate RH than RO₂˙, the calculated rate constants for the reaction of RO₂˙ with the inhibitor AH are too small, and decrease with increasing antioxidant concentration.

Kinetic equations are derived which take into account the participation of peroxyl radicals derived from the initiator and which allow the estimation of consistent rate constants from the rates of inhibited oxidations. The application of these equations to the oxidation of tetralin and cumene inhibited by t-butylphenols is demonstrated.