ABSOLUTE RATE CONSTANTS FOR HYDROCARBON AUTOXIDATION: III. α-METHYLSTYRENE, β-METHYLSTYRENE, AND INDENE

Abstract

Absolute rate constants for the copolymerization of α-methylstyrene and oxygen have been measured from 13 to 50 °C. The propagation and termination rate constants can be represented by[Formula: see text]Experiments with 2,6-di-t-butyl-4-methylphenol at 65 °C have shown that C 6 H 5 C(CH 3 ):CH 2 and C 6 H 5 C(CD 3 ):CD 2 have the same propagation rate constant but that chain termination involves a deuterium isotope effect (k t ) H /(k t ) D ≈ 1.5.Absolute rate constants for the copolymerization of oxygen with β-methylstyrene and with indene at 30 °C showed that a significant fraction of the oxidation chains were terminated by a kinetically first order process (rate constant k x ). The rate constants for β-methylstyrene and indene at 30 °C are k p = 51 and 142 l mole −1 s −1 , k t = 1.6 × 10 7 and 2.5 × 10 7 l mole −1 s −1 , and k x = 0.61 and 1.2 s −1 , respectively. The propagation rate constant for indene can be separated into a rate constant for the copolymerization with oxygen (k add = 128 l mole −1 s −1 ) and a rate constant for hydrogen atom abstraction (k abstr = 14 l mole −1 s −1 ). In the presence of heavy water the first order process for indene had a deuterium isotope effect (k x )/(k x ) D2O ≈ 3.