The Studies On Selective Aerobic Sulfides Oxidation With Molecular Oxygen

The transformation from sulfides to the corresponding sulfoxides is one of the most important topics in organic chemistry. It is of great importance to develop high-efficiency catalytic system. In the past decades, many research efforts have been directed at using molecular oxygen as the terminal oxidant. In this dissertation, a catalytic aerobic oxidation system has been successfully established in the selective oxidation of sulfides to sulfoxides using use tert-butyl nitrite (TBN) as the NO equivalents for the activation of molecular oxygen.In this study, the catalytic aerobic selective oxidations of sulfides were carried out with methyl phenyl sulfide as the typical substrate, TBN as catalyst and para-toluene sulfonic acid (TsOH) as co-catalyst. On the basis of establishment of a quantitative analysis method, the reaction conditions, including solvents, catalyst loading, temperature, and reaction time, were optimized via the help of in-process analysis. An optimal condition for the selective oxidation of methyl phenyl sulfide to methyl phenyl sulfoxide in high conversion and selectivity was achieved using 5mol% of TBN and 1mol% of TsOH in acetic acid under room temperature.Under the above optimal condition, various sulfide substrates could be smoothly converted into their corresponding sulfoxides by slightly adjusting the catalyst amount and reaction time. A simple workup can provide pure products in a yield from 88 to 97%. Carefully studies showed that the oxidation activities were significantly affected by the electronic and steric properties. Electron-riched sulfide substrates were more active than those electron-deficient substrate during the oxidation. For example, methyl 4-nitrophenyl sulfide almost showed no activity under room temperature because of the strons electron with drawing group. Even the reaction was carried out under 120℃overnight, only 23% of conversion was obtained. Comparing to effect of electronic property on the reactivity, the steric effect was also observed on the reaction rates. For examples, the oxidation of methyl 4-methylphenyl sulfide can be completed in 2h, while its 2-substituted analog needs 24h to complete.Considering the potential of inconveniente for the synthesis in autoclave, the reactions under atmospheric oxygen (balloon) were also tried. The results showed the oxidation reaction under atmospheric pressure could be completed by slightly extending the reaction time.