Oxidation of cyclohexene. The hydroperoxide chain

Early investigators found that cyclohexene oxidized readily at 30— 40° C if exposed to daylight or UV and used this method to prepare the 

Bolland and Gee [16] reported the first detailed kinetic investigation of the oxidation of cyclohexene in 1946 using photoinitiation with the hydroperoxide at several concentrations of oxygen and cyclohexene, mostly at 10°C. They showed that the rate of oxygen consumption corresponded very closely to the rate of formation of hydroperoxide with a rate law 

The form of this expression is identical to that developed by Bolland [17] in his classic study of the thermal initiated oxidation of ethyl lineolate where the detailed mechanism proposed was 

In eqn. (5), /a is the absorbed light leading to dissociation of ROOH and is equivalent to the rate of initiation, Ru k is a composite rate coefficient, k = kpl(2kt)1/2, and f[02] = fe3[02]/(l + fe3[02]). Experimentally, at p02 50 torr, the latter term reduces to unity and eqn. (5) reduces to the general form of the rate law for autoxidation of a great variety of organic compounds 

Two characteristic features of the kinetics are significant in establishing the foregoing mechanism. These are quantum yields much greater than unity and half power dependence on Rt (or /a), which demonstrate that oxidation proceeds by way of a chain reaction terminated by interaction of two chain carriers. Moreover, since the principal product in the oxidation of cyclohexene is cyclohexenyl hydroperoxide, the principal chain carrier must be the cyclohexenylperoxy radical. 

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