The Reaction Mechanism and Kinetics for the Reaction of OH Radicals with Atmospheric Metolachlor

Abstract

Metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide], has been used as a chloroacetanilide herbicide to control annual grass weeds and broadleaf weeds in corn, cotton, peanuts, soybeans and beans. In this paper, aRS-metolachlor has been used as a model to investigate the reaction of OH radicals with atmospheric metolachlor. The reaction mechanism was obtained at the MPWB1K/6-311 + g(3df,2p)//MPWB1K/6-31 + g(d,p) level of theory and the rate constants were deduced over the temperature range of 180–370 K using canonical variational transition state (CVT) theory with the small curvature tunneling (SCT) method. The atmospheric lifetime of aRS-metolachlor determined by OH radicals is about 3.97 h, which indicates that it can be degradaded in the gas phase easily and doesn’t have the potential for long-range transport.