Inhibition of the thin-film oxidation of n-dodecane by p-methoxyphenol

Abstract

The inhibition by p-methoxyphenol (PMP) of the oxidation of a thin film of n-dodecane has been studied over the temperature range 180–230 °C by following the consumption of gaseous oxygen, the disappearance of the inhibitor and the formation of peroxides. At the start of the reaction there is an induction period which increases linearly with the initial concentration of inhibitor. During the induction period [PMP] falls to zero and the removal of PMP follows a zero-order rate law. Thus PMP must react preferentially with the chain centres as they are formed in the initiation reaction. Once reaction starts, however, the consumption of oxygen is effectively independent of the initial concentration of PMP. It is shown that PMP must react with alkyl radicals and not alkylperoxy radicals in the primary inhibition reaction. This reaction involves the abstraction of the phenolic hydrogen to form phenoxy radicals, and these are sufficiently stable to either dimerse or react with alkyl or hydroperoxy radicals to give chain termination.