Bio-Synthesis Of (S)-α-Cyano-3-phenoxybenzyl Acetate And Its Kinetics Study

The importance of chiral technology and the progress on the preparation of optical active cyanohvdrin by lipases were reviewed. The advantages and disadvantages of enzyme catalysis in organic media were concluded. Factors which affect the efficiency of enzyme catalysis in organic media were discussed. In all of the factors. water activity and solvent are the two important factors. The characteristics of the reaction kinetics of enzyme catalysis in organic solvents were outlined.Optical (S )-ct-cvano-3 -phenoxybenzyl alcohol (CPBA) is an important intermediate of pyrethroids. This alcohol is very active and unstable even at room temperature. Therefore, it is a reasonable choice to make it into its ester. Taking use of the compatibility of chemical catalysts and biological catalysts to prepare CPB acetate in one reactor is the basic idea of this paper.It is necessary to choose an appropriate chemical catalyst for this reaction system. Weakly basic ion-exchange resin named D301 was chosen because it can tolerate organic media. does not break in organic media, possesses good catalytic ability and get along with the enzyme quite well. The catalytic nature of D301 in different solvents and at different temperatures was studied. Diisopropyl ether was found to be an appropriate solvent, and 55 C was found to be an optimum temperature. The internal and external diffusional limitation could be excluded. The reaction was found to be a reversible one. The intrinsic kinetics of the reaction system was studied and the model equation was deduced to be the following formula.k1k,R0S0 -R0(k1k. +k1k,)PdP!dt=v=-k ±k, +k1S0 +(k2 -k1)PLipase is a widely-used enzyme in organic solvents. The catalytic ability of lipases from different sources differs greatly. 15 kinds of lipases from different sources were screened and l#iipas~ was found to be a best one to catalyze the transesterification ofiiid~i~Eh~tt!i t~htL~AbstractCPBA in organic media. The conversion of the substrate CPBA reached 51 .06% at only 550mm while some other lipases can not catalyze this reaction at all! This not only has important realistic sense but also provides great convenience for the kinetic study. Immobilization of lipases was primarily studied and several carriers were used to compare which was the best. Medicinal stone ( "maifanshi" ) was found to be a considerable choice.The concentrations of CPB acetate were measured using capillary gas chromatograph. The best chromatographic conditions were found finally after a series of experimental tests. The method of measuring ee values by NMR and optical rotation method was founded, thus the problem due to lack of appropriate chiral column was solved.CPB acetate was synthesized and purified successfully by ourselves. Because commercial CPB acetate could not be purchased, this work was proved to be very important for this paper.The transesterification of CPBA and vinyl acetate were systematically studied Solvent test revealed that diisopropyl ether is the ideal solvent for this reaction system, and vinyl acetate is the second one to the best. The reaction rate and conversion get the highest point at 50 C. The lower the reaction temperature is, the higher the stereoselectivitv of the enzyme will be. The value of Ea of the reaction was calculated to be 26.029kJ.mo] ~. The external diffusional limitation could be excluded when rotational speed reached 220r.min'. Enzyme concentration test and radius test verified that the internal diffusional limitation could not be excluded. The effective diiThsion coefficient was measured and calculated to be 3.1 OSx 1 p10 m2.sec'. The effective factor ri was calculated to be 0.406. Substrate inhibition was not found through the CPBA concentration test (from 104 to 31 3mmol.L'). The reaction mechanism was hypothesized to he ping-pong bi-bi reaction. The initial rate equation is:KA[A]±KE[BI±KA~[A3[B] K ±KBtB]+K[B] K,4The rate equation is expressed as the following formula:'VII..4...