Esterification Of Carboxylic Acids, Transesterification, And Biodiesel Synthesis Using Zirconocene Bis(perfluorooctanesulfonate)s As A Catalyst

Presently, many documents have shown that the metallocene bis (triflate) s complexes of titanium and zirconium Cp₂M (OTf)₂ (Cp = C₅H₅; M = Ti, Zr, OTf= OSO₂CF₃) can efficiently accelerated various carbon–carbon bond forming reactions. But the complexes are air-sensitive. In 2009, our research group has synthetized air and water stable zirconocene bis(perfluorooctanesulfonate)s Cp₂Zr(OPf)₂(OPf=OSO₂C₈F₁₇), which has shown high Lewis acidity in glycation and acylation of carboxylic acids and alcohols.Direct esterification between carboxylic acids and alcohols and transesterification of carboxylic ether and alcohols are fundamental transformations in preparation of chemical and pharmaceutical important intermediates. However, these reactions are equilibria. We should excessively use one reactant or remove the product to bias the equilibrium to the benefit of the product side. There are some disadvantages such as toxicity, causticity, environmental unfriendly and low yield in traditional esterification catalyzed by sulfuric acid.So we studied the esterification between carboxylic acids and alcohols, transesterification between carboxylic ether and alcohols, and it's application in biodiesel synthesis, using zirconocene bis(perfluorooctanesulfonate)s Cp₂Zr(OPf)₂ as a catalyst under solvent-free condition.Catalytic amount of zirconocene bis(perfluorooctanesulfonate)s can efficiently promote esterification of carboxylic acids with equimolar amounts alcohols under solvent-free condition. The yield of the reaction of fatty acids with aromatic alcohols is more than 95%, compared to 90% of the reaction of aromatic acids with fatty alcohols. And the yield of long chain fatty acids esters is 85%. The catalyst can be reused 4 times with little loss of activity. What's more, our study shows that water (≤200 mol%) has no effect to the esterification. This reaction, under solvent-free, having no side reactions, being environment-friendly and reusable catalyst, agrees with demand of Green Chemistry.Catalytic amount of zirconocene bis(perfluorooctanesulfonate)s can efficiently promote transesterification of carboxylic ether with equimolar amounts alcohols under solvent-free condition. Generally, the yields of the reaction of carboxylic ether with alcohols are more than 90%. The reactive acidity of fatty alcohols is a little lower than aromatic alcohols. And the catalyst make no difference to the C-Br and C=C bond. This reaction has many advantages such as mild reaction condition, high yield, solvent-free, simplicity of operator and so on.The main synthetic approaches have been used for biodiesel production that is transesterfication of Vegetable oils or animal fats with a low molecular weight alcohol using a catalyst. In our study, we make biodiesel by transesterification of teaseed oil with methanol or ethanol using zirconocene bis(perfluorooctanesulfonate)s as a catalyst. The effect on reaction is the mole ratio of teaseed oil and alcohol, the amount of catalyst, and temperature. When the reaction temperature is the alcohol's boiling temperature, the pressure is atmospheric pressure, the amount of catalyst is 6 mol% (relative to vegetable oil), and methanol or ethanol is solvent, the yield is the highest (more than 90%). Significatively, the catalyst can be purified by precipitate and washed by petroleum ether, and can be reused more than 10 times with little loss of activity.