Cu2+对新农药噻虫嗪水解的影响

通过模拟试验研究了Cu2 对噻虫嗪水解的影响。结果表明,噻虫嗪的水解符合一级动力学方程,Cu2 (包括Cu(OH) 、Cu(OH)-3等)对噻虫嗪的水解具有明显的催化作用,且其催化作用基本不受温度和pH的影响,Cu(OH)2对噻虫嗪的水解无催化作用。根据GC-MS对水解产物的鉴定,发现噻虫嗪的主要水解产物为3-(2-氯-噻唑-5-亚甲基)-5-甲基-4-氧代-(1,3,5)恶二嗪,从而推测了Cu2 对其水解的催化机理,这对于了解噻虫嗪在环境中的迁移、转化具有重要意义。

The Effect of Cu2+ on the Hydrolysis of Thiamethoxam

Thiamethoxam belongs to a new class of insecticides known as neonictinoids,and will be degraded when it enters the environment by all ways.In this paper,a series of experiments were designed to investigate the effects of Cu2 on the hydrolysis of thiamethoxam in water systems.The results showed that the hydrolysis of thiamethoxam was fit with the first-order kinetics.Cu2 ,Cu(OH) and Cu(OH)etc could promote the hydrolysis of thiamethoxam obviously.Cu(OH)2 had almost no effect on the hydrolysis of thiamethoxam.Temperature and pH value had little effect on the catalysis of Cu2 .Identification and analysis of the hydrolytic products with GC-MS demonstrated that 3-(2-chloro-thiazolyl-5-methylene)-5-methyl-4-oxo-oxadiazine was the primary hydrolytic product.Based on these results and degradation products of thiamethoxam,the hydrolytic mechanism and the catalytic mechanism of Cu2 were suggested as followed:(1)Cu2 is coordinated with the atom of N of the group of C=N,and leads to withdrawing electron density away from the carbon atom and generating a more reactive electrophile.So the bond of C-N is more easily broken when it was attacked by OH-.(1)Cu2 can induce the deprotonation of coordinated water molecules,thereby generating metal hydroxo species,e.g.,CuOH ,which is the stronger nucleophile than OH-.