Hebei University of Science and Technology, Shijiazhuang, China.
J Chromatogr A. 2010 Sep 3;1217(36):5718-23. doi: 10.1016/j.chroma.2010.07.016. Epub 2010 Jul 16.
Eight chiral pesticides, which were selected to cover different pesticide species and origins of chirality, were investigated to explore their chiral stability in organic solvents and water. Profenophos, fenamiphos, quizalofop-ethyl, dichlorprop-methyl (DCPP-methyl) and acetochlor were showed stable under all test conditions. However, significant racemization was observed for malathion, phenthoate and fenpropathrin in methanol, ethanol and water, but not in n-hexane, isopropanol, acetone or methylene chloride. The kinetic parameters (rate constant k and half-life T(1/2)) of the abiotic racemization were calculated through a mathematical model of the first-order reaction. Furthermore, the extent of racemization varied among the solvents and was also affected by temperature dependence. The racemization of malathion, phenthoate and fenpropathrin in water was documented to be pH-dependent and took place more rapidly at pH 7.0 than at pH 5.8. The observed racemization was deduced to occur via a proton exchange process at the chiral center, and the relationship between the abiotic racemization and pesticide structure was further explored. Findings from this study are useful for better understanding enantioselectivity of chiral pesticides in environment and also for proper analysis, formulating or handling of enantiopure products.
八种手性农药被选择以覆盖不同的农药种类和手性来源，以研究它们在有机溶剂和水中的手性稳定性。在所有测试条件下，丙溴磷、苯硫磷、精噁唑禾草灵、二甲四氯甲酯（DCPP-甲酯）和乙草胺都表现出稳定。然而，马拉硫磷、苯醚菊酯和溴氰菊酯在甲醇、乙醇和水中发生明显的外消旋化，但在正己烷、异丙醇、丙酮或二氯甲烷中则没有。通过一级反应的数学模型计算了非生物外消旋化的动力学参数（速率常数 k 和半衰期 T(1/2)）。此外，外消旋化的程度在溶剂之间有所不同，并且还受到温度依赖性的影响。马拉硫磷、苯醚菊酯和溴氰菊酯在水中的外消旋化被证明是 pH 依赖性的，在 pH 7.0 时比在 pH 5.8 时发生得更快。观察到的外消旋化是通过手性中心的质子交换过程发生的，进一步探讨了非生物外消旋化与农药结构之间的关系。本研究的结果有助于更好地理解手性农药在环境中的对映选择性，也有助于对手性纯产品的正确分析、配制或处理。
