Reasearch On Esterification Reaction By DBSA And Microemulsions Catalytic

A microemulsion is defined as a thermodynamically stable,isotropic dispersion of two relatively immiscible liquide,consisting of microdomains of one or both liquids stabilized by an interfacial film or surface-active molecules. Due to the unique ability of solubilizing the polar and nonpolar substance, it is expressing the character of condensing and separating the different polar reactants which is remarkable increase local concentration, improve the rate of reaction and catalyze the reaction directly.The large oil-water interface of microemulsions can be used as templates for organic reactions.Organic molecules with one more polar and one less polar end will accumulate at the oil-water interface of microemulsions. They will orient at the interface so that the polar part of the molecule extends into the water domain and the nonpolar part extends into the hydrocarbon domain. This tendency for orientation at the interface can be taken advantage of to induce regiospecificity of an organic reaction. Therefore ,in recent years ,as a reaction medium for chemical preparation and organic reactions microemulsion has become one of colloid and interface research focuses currently.Surfactant is a very important factor in formation of microemulsion system, most of the catalytic reactions were performed in microemulsion or reverse micelles stabilized by AOT and CTAB surfactant, few attention has been paid to the other surfactants. So we initiated our experiment to use DBSA, a relatively cheap and widely used commercial surfactant to form reverse microemulsion.Organic carboxylic ester is an important product and intermedia in the chemical industry and harmaceutical industry. Shortchain ester is frequently used in foods and cosmetics, pharmaceutical industry due to its unique fragrance. Market analysts say, isoamyl acetate and isoamyl butyrate in the future market will maintain a good momentum of growth.Gemerally,direct esterification is carried out in organic solvents and needs either of two methods to shift the equilibrium between reactants and products.One is removal of water generated as the reactant proceed and the other is use of large excess amounts of one of the reactants.Now ,we usually use concentrated sulfuric acid as catalyst .As catalyst,it is inexpensive and active,but it induses series of by products,because of its oxidative and dehydative.And concentrated sulfuric acid is corrosive ,making lot of waste acid as well as the reaction of sulfur dioxide emissions will cause serious environmental pollution.So replacing the catalyst has received considerable attention in esterification.We have investigated a esterfication reaction of hexanol and hexanoic acid inDBSA/cyclohexane/water microemulsion system. The esterfication reaction in this system can perform rather rapidly and obtain relatively considerable conversion. The mechanism of reaction was also explored. On this basis,we carried out the esterfication of substrates with verious carbon chain length of the straight-chain, branched chain, and unsaturation aromatic compounds etc in DBSA/cyclohexane microemulsion system.According to our investigation,we concluded that it is suitable for the esterification of medium chain length carbon in DBSA/cyclohexane microemulsion system. And the shorter of the carbon chain, the faster the rate of esterification , the higher the conversion . This proved that relatively high conversion in DBSA system is ascribed to the two-fiod functions of DBSA, which are surfactant as well as acid catalyst. We research the feasibility of synthesis of isoamyl acetate and tetrahydrofurfuryl acetate,by DBSA as catalyst directly.without use cychohexane.we obtained better results in synthesis of isoamyl acetate,but the conversion rate of tetrahydrofurfuryl acetate is very low.we consisder that it is caused by electric exclusion and steric hindrance.