Study On Enantioselective Separation Of Chrysanthemum Acid Enantiomers And Its Mechanism

Single optical isomers of chiral pesticides have become an important field of research and development because of its high efficiency, high selectivity and high security. Pyrethroid is an important chiral pesticide, and the key to synthesize these pyrethroids is to obtain single optical isomers chrysanthemic acid from the itermediates of pyrethroid. A series of tartrates have been synthesized in this dissertation, and used as chiral extractants for separation of five racemic chrysanthemic acid enantiomers. Based on these, a new method, biphasic recognition chiral extraction, has been presented to separate two kinds of chrysanthemic acid enantiomers and the separation ability was improved significantly. The dissertation has provided new theory and technical basis for preparation of high-efficient but low toxicity pesticides.By using CHIRALPAK QN-AX, HPLC was established to analyze trans-chrysanthemic acid, cis-and trans-permethrinic acid, lambda-cyhalothric acid and fenvaleric acid, and the baseline separations of five enantiomers were achieved.A series of tartrates have been synthesized in this dissertation, and the factors affecting the yield of synthesis has been investigated. The best experimental conditions have been gained. Taking the synthesis of L-tartaric acid iso-butyl as an example, the best experimental conditions are that the molar rate of alcohol (22.24 g) and L-tartaric acid (15 g) is 3:1, with catalyst tosylate of 1.0 g and toluene of 60 ml.The dissertation has studied the distribution behavior of five chrysanthemic acid enantiomers with tartrate esters as chiral extractants and investigated the factors affecting the extraction performance.1) Both D-and L-tartaric acid ester can be used as chiral extractants to separate the five kinds of chrysanthemum acid enantiomers, and the seperation factor can reach at 1.25-1.5.2) Tartaric acid ester alkyl length and its steric have a certain impact on the separation factors. The larger alkyl length and alkyl steric (with branched-chain or ring structure) are, the larger separation factors are; 3) Extractant concentrations also has a greater impact on extraction performance. With the increase of extracant concentrations, the partition coefficients increase, but the separation factors first increase then decrease after up to the peak. The appropriate extractant concentrations are between 0.20-0.30 mol·L-1; 4) The partition coefficientsand the separation factors decrease with the increase of pH value. The best value of pH is between 2.50-5.50; 5) 1, 2-dichloroethane solution and chloroform will be the proper solvents.Biphasic recognition chiral extraction system has been constructed, in which two kinds of extractant with opposite recognition direction (hydrophobic D-/L-tartaric acid esters and water-soluble cyclodextrin derivatives) are added in the organic phase and water phase, respectively. This system is used to separate of two kinds of chrysanthemic acid enantiomers.β-CD derivatives have stronger recognition abilities for S-chrysanthemic acid than those for R-chrysanthemic acid, while L-tartrate derivatives have reversed recognition abilities. Thus the use of appropriate two-phase chiral extractant greatly enhances separation ability. Adding HP-β-CD, the separation factor value can be enhanced from 1.30 and 1.20 for the single-phase to 1.70 of 1.80 for two-phase extraction. Extraction conditions also have an impact on k and a. Take the separation of cyanide-chrysanthemic-acid as an example, the best separation factor is 1.80 under conditions that the concentrations of L-iso-butyl tartrate and HP-β-CD are 0.30 mol·L-1 and 4.0 mmol·L-1, respectively, with 1,2-dichloroethane as solvent containing 20% methanol solution at pH 4.0.Tartaric acid ester molecule has two chiral carbon atoms, special three-dimensional structure and multiple action spots which have different intermolecular forces with chrysanthemum acid enantiomers, thus it has the function of chiral recognition. The special three-dimensional ring structure-"hydrophilic outside, hydrophobic inside" ofβ-cyclodextrin (β-CD) can form inclusion complex with chrysanthemic acid, and the inclusion complex stability of the two enantiomers is different and thus it has the ability of chiral recognition.