Addition of cyclohexane to slowly reacting H2–O2 mixtures at 480 °C

Abstract

Elementary reactions involved in the oxidation of cyclohexane have been studied by adding the compound to slowly reacting H₂–O₂ mixtures at 480 °C. Kinetic studies of the relative rates of consumption of cyclohexane and H₂ have given values of k₂₁=(1.41 ± 0.20)× 10¹⁰ and k₂₂=(2.8 ± 0.4)× 10⁹ dm³ mol^–1 s^–1. These values show that the rates of H and OH attack on an individual CH₂ group in cyclohexane and in linear alkanes are effectively indistinguishable, particularly when allowance is made for near-neighbour groups.

OH+c-C₆H₁₂[graphic omitted]c-C₆H₁₁+H₂O (21), H+c-C₆H₁₂[graphic omitted]c-C₆H₁₁+H₂(22), Analytical studies over a range of mixture composition show that the major initial products are cyclohexene, 1,2-epoxycyclohexane, 1,4-cyclohexane oxide and hex-5-en-1-al. Benzene and cyclohexa-1,3-diene are formed as major secondary products. The mechanism of oxidation is similar to that observed for alkanes. Generally, no ring rupture occurs in the formation of the initial products, although 1,3-cyclohexane oxide is unstable and forms hex-5-en-1-al. The impact of chair and boat forms of cyclohexane and its derivatives on the product distribution is discussed, and rate constants are obtained for a number of the elementary reactions.