Sol-gel Encapsulated Metal Complex Catalysts For Air Oxidation Of Organic Sulfides

Sol-gel science is a new cross-linked subject that was developed in early 1980s and since mid 1990s, it has been used to immobilize homogeneous catalysts by which tremendous success has been achieved. We can say that manufacturing catalysts with high activity and selectivity by sol-gel technique is the latest development and breakthrough in the method of preparing catalysts, is the most active sphere in chemistry research nowadays.Recently, aerobic oxidation has been arousing chemists' increasing interest because oxygen is cheap and has high selectivity, and more important, it's friendly environmental. In this research, we mainly studied the preparation and activity and selectivity of sol-gel physically encapsulated metal complex catalysts. The reactions involved are air oxidation of penicillin G derivatives to corresponding sulfoxides and mercaptan to disulfide, so that essential ground can be supplied on the aspect of pharmaceutical development and environment protection.In sol-gel process using tetraethoxysilane (TEOS) as matrix to encapsulate Co(acac)3, orthogonal test was employed to study the effect of many factors on gelation time and further on catalytic activity and selectivity to air oxidation of penicillin G/7-methoxybenzyl ester (PGPMB) to sulfoxide. The factors involve pH, the molar ratio of water to precursor and cosolvent to precursor, temperature of encapsulating and drying, and so on. Furthermore we optimized the conditions of sol-gel process and air oxidation, so that Co(acac)3 catalyst encapsulated in SiO: was prepared, which has high activity, high selectivity and is leach proof. For the air oxidation of PGPMB, the conversion is 98.8%, the selectivity of PGPMB to PGPMBO is 100%, and the sol-gel catalyst can recycle more than 15 runs without loss of activity. The reason for the reduction of the encapsulated catalyst's activity is that the pore of the matrix was badly blocked. But the catalyst can recover its activity if sonicated. FTIR shows that Co(acac)3 was physically encapsulated in SiC^ without any chemical action, N2 adsorption indicates that there is corresponding relation between different pore structure and preparation conditions, so thatcatalyst with required pore structure can be manufactured.Co(acac)3 was also encapsulated firmly in Al2O3 and TiO2 by sol-gel technique, which is leach proof and has very high activity to air oxidation of penicillin G p-methoxybenzyl ester. But the catalysts have such little rigidity that it's difficult to adapt to factory manufacture.We found that sol-gel encapsulated Co(acac)3, ether in SiO2 or in Al2O3, in TiO2, is leach proof and has very high activity to air oxidation of penicillin G diphenylmethyl ester too. Moreover, controlling the reaction time can control the selectivity of the reaction.Finally, sol-gel encapsulated Cobalt phthalocyanine in SiO2 was prepared, which was applied primarily to air oxidation of butyl mercaptan to butyl disulfide with leach proof and certain activity. But the conversion was only 61.65%, for which the reason may be that Cobalt phthalocyanine in same pore has been aggregated or that the pores of the matrix have been badly blocked which need further study.