Rresearch On Photoloysis Of Typical Chiral Pesticides And The Chiral Stability Of Degradation In Soil

Chiral pesticides account for more than 25% of currently used pesticides. The biological acitivity of a chiral pesticide usually exists at only one or several enanitomers. The enantiomer-specific profiles of chiral pesticides have become important topics at eh forefront of chemistry and toxicology research. The study of chiral pesticides on enantiomeric level has great importance on proper evaluation of their environmental behavior as well as ecological risk in the environment. The present thesis consists of three parts: (1) Chiral separation of chiral pesticides on HPLC; (2) Rresearch on photolysis of typical chiral pesticides; 3) Enantioselective degradation and chiral stability of quizalofop in soils.Chiral separation of eight chiral pesticides. The pesticides studied mainly included profenophos,malathion,phenthoate,triadimefon,fenpropathrin,β-Cypermethrin,quizalofop and quizalofop acid. The separation conditions were optimized and the eight pesticides were successfully enantioseparated on a Chiralcel OD-H column and a Chiralcel OJ-H column.Photolysis of typical chiral pesticides. Six chiral pesticides were investigated in this study related to their photolysis characteristics by using mercury lamp as light source. Profenophos, malathion, phenthoate, triadimefon and fenpropathrin each has one chiral center and thus exists as two enantiomers. The photolysis of individual enantiomers from one chiral pesticide showed similar dissipation rates of the two enantiomers. No enantiomerization was observed for the five chiral pesticides. The three organophosphorus insecticides were photolyzed very rapidly, whereas fenpropathrin had the slowest photolysis rate with a half-life time of 280 h. Cypermethrin has three chiral centers and consists of eight enantiomers. The eight enantiomers constitute four diastereoisomers (Ⅰ,Ⅱ,ⅢandⅣ) which could be separated on achiral silica-gel column. Further photolysis was performed for a single enantiomer from diastereoisomerⅣ?-trans-2. The results documented that certain amounts of diastereoisomersⅠ,ⅡandⅢwere produced, suggesting isomerization took place along with photolysis process. By summing the concentrations of the four diastereoisomers the total half-life was calculated to be 66.7 h. Enantioselective degradation and chiral stability of quizalofop in soils. Quizalofop has one chiral center and exists as tow enantiomers. The herbicidal activity of quizalofop was mainly originated from the R-enantiomer, which has been produced and applied as quizalofop-P in the agriculture.(a) The degradation of quizalofop in a Baoding alkaline soil and a Wuhan acidic soil showed certain enantioselectivity. The S-enantiomer was degraded faster than R-enantiomer in the first part of the degradation. However, in the later part of the degradation, the two enantiomers showed similar degradation rates. In the two soils, quizalofop was hydrolyzed to quizalofop-acid rapidly. It was found that the S- quizalofop acid was dissipated faster than and the R-quizalofop acid in the two soils. (b) The degradation of R-quizalofop in the two soils showed the the R-enantiomer was chirally stable in the two soils. Moreover, no conversion of R-quizalofop acid to S- quizalofop acid was observed. (c) The degradation of S-quizalofop showed certain convertion of S-quizalofop to R-quizalofop took place in the soils. It was interesting that the converstion of S-quizalofop acid to R-quizalofop acid was very rapid and the amount R-quizalofop acid was higher than S-quizalofop acid in the latr part of the degradation. The obversions demonstrated the enantiomerization of quizalofop as well as quizalofop acid was single directional.