C-H Activation by Ozone in Liquid CO2 Using Cyclohexane and Iso-octane as Substrates

Abstract

The study of cyclohexane and isooctane activation by ozone with liquid CO2 as reaction medium in a Parr reactor equipped with in situ infrared detector demonstrated a facile and efficient method for alkane activation. The dominant presence of CO2 in vapor phase imparts safety to system by maintaining vapor concentration of reactants below the lower flammability limit. At 280 K, 6.9 MPa, with a molar feed ozone: cyclohexane ratio of approximately 50%, the cyclohexane conversion was approximately ~12% with KA oil (a mixture of cyclohexanone and cyclohexanol) yield around 11%. Small but measurable amount of hydrogen peroxide was formed during the reaction. The observed products are consistent with predicted reaction pathways via the hydrotrioxide route. The absence of any detectable water in the product and the close match of cyclohexane conversion and product yield rule out significant combustion of cyclohexane. The various oxygenated products detected from the ozonolysis of isooctane in liquid CO2 medium suggest that ozone has the ability in activating all types of C-H bonds within isooctane. These results pave the way for systematic investigations of C-H bond activation in lighter alkanes such as methane and those present in natural gas liquids.