The oxidation of decane in the liquid and gaseous phases

Studies have been made of the uncatalysed oxidation of decane in both the liquid and gaseous phases in the same temperature region; this hydrocarbon is probably the lowest molecular mass alkane for which such a direct comparison can be made. Although the mechanisms of oxidation in both phases are in many ways similar, some notable differences exist. The absence of C 10 O-heterocycles and the relatively high selectivity of initial attack of decane in the liquid phase can be ascribed to a ‘cage effect’, so that abstractive reactions are predominantly intermolecular. Rather unexpectedly, in the gas phase, the initial attacking radical, even at the low temperatures used, is almost exclusively the hydroxyl radical. In the gas phase there is a marked dependence on oxygen concentration of the rates of formation of the various classes of products, particularly decane dihydroperoxides. The low solubility of oxygen in liquid decane and hence its small concentration may thus also be partly responsible for the absence of dihydroperoxides among the liquid-phase oxidation products. Lower molecular mass oxygenated compounds, which are the most abundant products of the gaseous oxidation of decane, appear to be derived mainly from further reactions of decane dihydroperoxides; and the small amounts of such products found in the liquid phase are con­sistent with the virtual absence of their normal precursors under these conditions. The analytical technique used has permitted the first unambi­guous quantitative determination of very small amounts of hydroper­oxides produced during the gaseous oxidation of hydrocarbons.