Kinetics and mechanism of the hydrolysis of thiamethoxam

Abstract

The degradation of thiamethoxam [(EZ)-3-(2-chloro-1,3-thiazol-5-yl-methyl)-5-methyl-1,3,5-oxadiazinan-4-ylidene (nitro) amine] insecticide in buffers at different pH and temperature levels was investigated in laboratory studies. Acidic hydrolysis under conventional heating conditions and alkaline hydrolysis under both conventional heating and microwave conditions were carried out. Different hydrolysis products were found to form under alkaline and acidic conditions. Hydrolysis of thiamethoxam in acidic, neutral and alkaline buffers followed first-order reaction rate kinetics at pH 4, 7 and 9.2, respectively. Thiamethoxam readily hydrolyzed in alkaline buffer but was comparatively stable in neutral buffer solution. The main products formed under different conditions were characterized on the basis of infrared (IR), ¹H-NMR and Mass spectroscopy. The possible mechanisms for the formation of these hydrolysis products have also been proposed.

Keywords:

• Thiamethoxam
• hydrolysis
• microwave
• kinetics
• pH
• degradation products
• mechanism

Acknowledgments

Financial assistance provided by Indian Council of Agricultural Research (ICAR) is gratefully acknowledged by the first author. Publication contribution No. 961. Division of Agricultural Chemicals, Indian Agricultural Research Institute, New Delhi.

This paper was presented at the IUPAC sponsored International Conference on Agrochemicals Protecting Crop, Health and Natural Environment held in New Delhi, India, January 8-11, 2008.

Notes

*Values in parenthesis denote percent dissipation of thiamethoxam.

^#B:A – benzene:acetone; C:M – chloroform:methanol

*Spectroscopic details (IR, NMR, MS, LC/MS) for compounds 2-8 are presented in the sub-section “Identification of hydrolysis” products under “Results and discussion.”

*Taken as the maximum amount formed during the experiment.