Oxidation of Dibenzothiophene with Molecular Oxygen in the Presence of Aldehydes and Transition Metal Salts

An oxidation system for dibenzothiophene consisting of molecular oxygen, aldehyde, and transition metal catalysts in hydrocarbon solvents was evaluated using both batch and flow reactors. The effects of solvents and the presence of nitrogen-containing compounds were examined in the reaction using the batch reactor. The properties of the hydrocarbon solvents significantly affected the reaction rates; hydrogen donor solvents such as tetralin disturbed the reaction, whereas oxidation proceeded rapidly in solvents with no donatable hydrogens such as benzene. The presence of pyrrolic compounds disturbed the reaction, whereas pyridinic compounds had rather small effects. Using a continuous flow type reactor, the oxidation of dibenzothiophene could be carried out and the combination of MnCl2 or CoCl2 and HY-zeolite showed the optimum catalytic performance. The types of solvents and presence of nitrogen-containing compounds also affected the reaction rate drastically, as both hydrogen donor solvents and nitrogen-containing compounds such as quinoline disturbed the reaction. Likely mechanisms are discussed based on the effects of the solvents and nitrogen-containing compounds.