Application of Laser to Selective Partial Oxidation of Hydrocarbons by Dioxygen

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Study of partial oxidation of hydrocarbons, such as ethane, propane, cyclohexane and benzene, initiated by irradiation of ArF or KrF excimer laser on various initiators, has led to the conclusions as follows ;(1) Partial oxidation of paraffins initiated by N_2O or O_3 photolysisReaction is initiated by photochemical decomposition of either N_2O or O_3 by excimer laser light. The singlet oxygen produced by the photolysis of N_2O reacted with hydrocarbons by insertion into C-H bond to produce "hot" alcohols. The product distribution of the reaction in which O_3 is introduced as an initiator shows that use of KrF laser light to generate O(^1D) from ozone was found to have the advantage, over ArF laser and N_2O, of better selectivity for cyclohexanol and cyclohexanone. The advantage essentially results from the fact that KrF laser light does not promote the decarbonylation of cyclohexanone to cyclopentane and carbon monoxide, while ArF laser light does.(2) Partial oxidation of cyclohexane in liquid phaseIn the liquid phase oxidation, selectivity for oxygen-containing compounds is over 85%, and quantum yield is more than 10^3 times larger than that in gas phase reaction, which may be due to higher concentration of cyclohexane. The formation of compounds formed by radical recombination, which was not observed in gas phase reaction at all, can be explained by the cage effect in the liquid phase oxidation.(3) Reactions of aromatics by irradiation of excimer laserIn the photoreactions of aromatics (benzene and toluene), decomposition into C_2 - C_4 olefins occurs and no oxygen-containing compounds are observed, due to the photolysis of the reactant itself by absorbing of either ArF or KrF excimer laser light.