Enzymes Catalyzed Reactions And Area Selectivity Of Nitration Of Phenol In Microemulsion

It is well known that direct esterification of carboxylic acid/alcohol and transesterification of ester/alcohol play important roles in the production of organic esters, especially for some important products and intermediates in the organic, bioorganic, pharmaceutical industries and related fine-chemical synthesis. To acquire higher transformation rate and reaction rate, lots of works have been performed, in which enzymes, a kind of biocatalyst, catalyzed reactions are being attracted more and more attention because of their much milder reaction conditions and environmental benign property.Enzymes catalyzed medium project experienced a process of water-organic solvent-microemulsion. Many enzymes exhibit different catalytic activity in two-phase-system or organic mediums. Whereas, most of enzymes can hold their fine catalytic activity and stability even put up super-activity in reverse microemulsion system for the nature circumstance is simulated successfully. As a result, enzymes catalyzed reactions in reverse microemulsion have become a hot focus recently.A microemulsion is a thermodynamically stable, isotropic, optically transparent and low viscidity solution consisting of water, oil and a surfactant. Often, the formation of microemulsion requires the presence of a co-surfactant. The formed microemulsion affects, modulates and controls many chemical reactions by its local concentration effect, static effect, polarity effect, orientation effect and low viscidity effect, and the effects of surfactant and microemulsion on chemical reactions is always one of the research fields attracting much interest. Besides catalytic characteristic, another merit of microemulsion is that it can act as a kind of modulating template for one or more reagents by taking advantage of the interface of oil/water, which leads to the achievement of area selectivity of organic reactions.In this paper, lipase-catalyzed synthesis of isoamyl isobutyrate in AOT/hexane, CTAB/hexane, CTAB/isooctane, DBSA/isooctane reverse microemulsions are discussed, respectively, and the effects of water content (W0), pH value of buffer solution and reaction temperature on the transformation rate of esterification are investigated, and optimal condition is put forward. The research results indicate that the activity of enzymes in CTAB/hexane reverse microemulsions is higher as six times as that in organic phase and the effect of lipase (CCL) in DBSA/isooctane reverse microemulsions is better than that in CTAB/hexane reverse microemulsions. Moreover, a ternary mechanism of microemulsion catalyzation, enzyme catalyzation and proton acid catalyzation in microemulsion system is proposed.On the other hand, the nitration products of phenol in AOT/isooctane/water, CTAB/n-Decyl alcohol/isooctane/water and DBSA/ isooctane/water reverse microemulsion systems were investigated by gaschromography inner mark method; The results indicate that it has obviously ortho-selectivity of the nitration reation of phenol in reverse microemulsion system, and the selectivity is the highest in the anionic surfactant DBSA system. It should be related to the double effect of microemulsion catalyzed and acid catalyzed.