Effect of crown ethers and polyglycols on the catalytic oxidation of cyclohexane and alkylarenes

The effect of crown ethers and polyglycols on the liquid-phase oxidation of cyclohexane and alkylaromatic hydrocarbons (toluene and p-xylene) with molecular oxygen catalyzed by transition metal salts has been investigated. It has been determined that crown ethers increase the reaction rate at both low and high conversion levels of cyclohexane and alkylaromatic hydrocarbons. The additives under study primarily affect the selectivity of the oxidation products. Crown ether and polyglycol additives to cobalt naphthenate increase the cyclohexanone to cyclohexanol molar ratio in cyclohexane oxidation. The crown ether additives to cobalt acetate increase the selectivity for alcohol in the initial stage of toluene and p-xylene oxidation. At higher alkylarene conversion, the additives enhance the selectivity for carboxylic acids. We assume that crown ethers and polyglycols form complexes with transition metal ions, changing the redox potential of the ions. This change in redox potential affects both the reaction rate and the selectivity of the oxidation products. The study concludes that crown ether and polyglycol additives influence the stages of the catalytic liquid-phase oxidation of hydrocarbons.