Schippers Nicole, Schwack Wolfgang
Institute of Food Chemistry, University of Hohenheim, Garbenstrasse 28, 70593 Stuttgart, Germany.
J Agric Food Chem. 2008 Sep 10;56(17):8023-9. doi: 10.1021/jf801251u. Epub 2008 Aug 9.
The photochemical behavior of the neonicotinoid insecticide imidacloprid was studied with regard to different chemical environments. Different model solvents simulated the structure moieties mainly occurring in waxes and cutin of the plant cuticle. Cyclohexane and cyclohexene substituted saturated and unsaturated hydrocarbon chains, whereas ethanol and 2-propanol were models for primary and secondary alcohol groups of cuticular components. After 5 h of irradiation, imidacloprid was completely degraded in all solvents. With 88-96 mol% 1-[(6-chloropyridin-3-yl)methyl]imidazolidin-2-imine was formed as the main product, whereas 1-[(6-chloropyridin-3-yl)methyl]imidazolidin-2-one was identified as minor product in the range 4-6 mol%. By contrast, besides the photoproducts formed in organic solvents, irradiation of the solid imidacloprid on a glass surface delivered a complex variety of unidentified photoproducts. The nucleophilic addition reaction of the main photoproduct, 1-[(6-chloropyridin-3-yl)methyl]imidazolidin-2-imine, with both cyclohexene oxide and methyl 9,10-epoxystearate as model compounds indicates that epoxidized cutin acids are possible reaction partners for the formation of plant cuticle bound residues of imidacloprid, which could explain the reported findings of nonextractable residues of imidacloprid in plants.
针对不同化学环境，研究了新烟碱类杀虫剂吡虫啉的光化学行为。不同的模型溶剂模拟了植物角质层蜡质和角质中主要存在的结构部分。环己烷和环己烯分别模拟饱和和不饱和烃链，而乙醇和2-丙醇则是角质层成分中伯醇和仲醇基团的模型。照射5小时后，吡虫啉在所有溶剂中完全降解。主要产物为1-[(6-氯吡啶-3-基)甲基]咪唑烷-2-亚胺，产率为88 - 96 mol%，而1-[(6-氯吡啶-3-基)甲基]咪唑烷-2-酮为次要产物，产率在4 - 6 mol%范围内。相比之下，除了在有机溶剂中形成的光产物外，玻璃表面固态吡虫啉的照射产生了多种无法鉴定的光产物。主要光产物1-[(6-氯吡啶-3-基)甲基]咪唑烷-2-亚胺与环氧环己烷和9,10-环氧硬脂酸甲酯这两种模型化合物的亲核加成反应表明，环氧化角质酸可能是吡虫啉在植物角质层中形成结合残留的反应伙伴，这可以解释报道中植物中存在不可提取的吡虫啉残留的现象。
