新农药O,O-二甲基-1-(2,4-二氯苯氧基乙酰氧基)乙基膦酸酯的水解

研究了新型除草剂O,O-二甲基-1-(2,4-二氯苯氧基乙酰氧基)乙基膦酸酯(HW-02)在不同pH及温度下的水解动态,并初步探讨了其水解机理。结果表明:25℃时,HW-02在pH 5、7和9的缓冲液中的水解半衰期分别为191.3、6.2和0.2 h,即其在碱性环境中的水解速率较在中性和酸性中的快;在pH 7的缓冲液中,25、35、45和55℃下的水解半衰期分别为6.1、4.2、1.8和0.7 h,温 度效应系数(Q)为1.46～2.64,即其水解速率随温度的升高而加快;HW-02水解反应的活化能与温度之间无明显相关性,且其平均活化能和活化焓均较小,分别为60.51 kJ/mol和57.70 kJ/mol,而其活化熵的绝对值却随温度的升高而增加,表现出显著的相关性,其平均活化熵为-81.00 kJ/(mol·K),表明其水解主要由反应的活化熵驱动。采用气相色谱-质谱联用(GC-MS)技术对HW-02的水解产物进行了分离和鉴定,初步确定其水解产物主要为2,4-二氯苯氧基乙酸,推测其主要水解途径为酯键断裂。

Study on hydrolysis of novel herbicide O,O-dimethyl-1-(2,4-dichlorophenoxy-acetoxy) ethyl phosphonate in buffered solutions

HW-02,O,O dimethyl-1-(2,4-dichlorophenoxy-acetoxy) ethyl phosphonate,is a novel herbicide discovered and developed by Huazhong Normal University,China.The hydrolysis kinetics and mechanisms of HW-02 were studied in buffered aqueous solutions under pH 5-9 at ambient temperature and under pH 7 with the stored temperature of 25℃-55℃.The results showed that HW-02 hydrolyzed very rapidly in the buffered solutions.Its hydrolysis rate was characterized by the first-order kinetics and accelerated with the increasing of pH and temperature.The calculated half lives of HW-02 hydrolysis in the solutions of pH 5,7 and 9 were 191.3 h,6.2 h and 0.2 h at 25℃,respectively.It is indicated that HW-02 was not stable in the aqueous environments.HW-02 hydrolyzed much faster in the basic solution than in acidic and neural solution at the same temperature.The hydrolysis rate of HW-02 increased as the temperature increases and its half lives in the buffered solution of pH 7 were 6.1 h,4.2 h,1.8 h and 0.7 h at 25℃,35℃,45℃ and 55℃,respectively.The temperature coefficient of hydrolysis for HW-02 was 1.46-2.64.There were no obvious correlation between the activation enthalpy of HW-02 hydrolysis and temperatures.Its average activation energy and activation enthalpy were 60.51 kJ/mol and 57.70 kJ/mol,respectively.The activation entropy absolute values of HW-02 hydrolysis increased with the increasing temperatures in the environment.The average value of-81.00 kJ/(mol·K) suggested that hydrolysis of HW-02 in the aqueous solutions was driven by the activation entropy.Through isolation and identification of HW-02 hydrolytic products using GC-MS detection,it was found that HW-02 was hydrolyzed through ester cleavage.The main degradation product was 2,4-dicholorphenoxyaceate.