Study On Photoloysis Of Photics Pesticide And The Chiral Conversion Of Degradation In Soil

Synthetic pyrethroids are insecticides widely used in veterinary medicines, agriculture and households. Pyrethroid insecticides generally contain one to three asymmetric carbons and therefore have two to eight enantiomers, making them a pesticide family with one of the highest chirality. Different enantiomers from one pyrethroid generally exhibit different biological activity and toxicity as well as biodegradation behavior in the environment. It is obvious the application of racemic pesticides would not only affect the efficacy of the pesticides, but bring about serious environmental pollution because of the influence of invalid ingredients. Photolysis and soil microbial degradation are two important pesticide dissipation processes, therefore it is important to investigate the photolysis and microbial degradation of chiral pesticides on the ennatiomeric level. The enantiaomer-specific study of chiral pesticides has become important topics at the forefront of chemistry and toxicology research, and also provides data support for the development of new types of high efficient pesticides.In this thesis, three important cyclopropanecarboxylic acid pyrethroids, i.e., permethrin. cypermethrin and cyflurthrin, were selected to investigate their chiral separation by high-performance liquid chromatography. On this basis, the enantioselective and stereoselective photolysis and chiral stability for the three pyrethroids were studied in details. In addition, the stereoseiective degradation in soil of another important triazole fungicide, i.e., triadimenol, was also studied in details. Results from this thesis are useful for better understanding the chiral profiles as well as risk assessment of relevant chiral pesticides in the environment. The main contents of the thesis are:1) Chial separation and determination of absolute configurations of pyrethroid enantiomers by HPLCPermethrin contains 2 chiral carbons (1-C and 3-C) and thus possesses four enantiomers. and cypermethrin and cyfluthrin each has 3 chiral carbons (1-C,3-C and α-C) and thus contains eight enantiomers. In this thesis, a novel two-step separation method was used to resolve the enantiomers of the three pyrethroids. An achiral system was used to resolve the enantiomer pairs, or diastereomers, on a common silica-gel column, then a chiral separation was carried out to resolve each couple of enantiomers under study. Moreover, the enantiomer absolute configurations or elution orders of permethrin. zypermethrin and cyfluthrin were determined by an indirect permethrinic acid enantiomer separation-identification method.The identification method was also confirmed to be reliable by comparison the chromatograms of zeta-cypermethrin standard,which only consists of four aS-enantiomers of eyoermethrin.2) Photolysis and chiral stability of permethrin enantiomers Enantiopure enantiomers of permethrin were isolated by chiral HPLC.Further photolysis of the enantiomers showed significant isomerization occurred along with the dissipation process,leading to the formation of the other three stereoisomers.The photolysis was documented to be faster with mercury lamp irradiation than outdoor sunlight irradiation and with the trans- isomers than with the cis-iscmers.3) Photolysis and chiral stability ofcyfiuthrin enantiomersFour enantiopure enantiomers of cyfluthrin were isolated by chiral HPLC,and then irradiated with mercury lamp or outdoor sunlight to characterize their photolysis process. The results showed isomerization occurred along with the photolysis process for the four C-2 positions.Moreoyer, the isomerization was docunmented to occur at chiral C-1 and/or C-2 positions,whereas α-C kept stable during the photolysis period.As a result the somerization led to the formation of the other thee C-1 and/or C-2 inversed nereoisomers.In addition,similar to permethrin,The photolysis of cyfluthrin was documented to be faster wih mercury lamp iIrradiation tha outdoor sunlight irradiation, and with the trans-isomers than with the cis-isomers.4) Degradation and chiral stability of triadimenol in soilEnantiopure 1R-trans-triadimenol was incubated in two soils under laboratory condition. The results showed significant isomerization occurred along with the degeradationp rocess,and degradation was faster Hubei acid soil with a half-life of 33 days than in Baoding allcaline soil with a half-life of 50 days.