Dimethoate
Dimethoate is a synthetic organothiophosphate compound (C5H12NO3PS2) classified as an organophosphate acetylcholinesterase inhibitor, employed as a contact and systemic insecticide to control a wide array of insect pests and mites on agricultural crops.[1][2] It targets species including aphids, leafhoppers, beetles, weevils, and mites through disruption of nerve impulse transmission via cholinesterase inhibition, enabling both foliar application and uptake by plant tissues for protection against sucking and chewing insects.[3][4] Commonly used on crops such as broccoli, corn, soybeans, alfalfa, and fruits, dimethoate supports resistance management in integrated pest control strategies, with annual U.S. application approximating 1.8 million pounds of active ingredient.[3][5] Despite its efficacy, dimethoate poses notable risks due to its toxicity profile, exhibiting acute and chronic effects in mammals through cholinesterase suppression, which can manifest as neurological symptoms, reproductive impairments, and developmental anomalies in exposed organisms.[6][7] In humans, occupational or environmental exposure has been linked to hematological alterations, immune disruption, and potential long-term neurobehavioral changes, prompting regulatory scrutiny and risk assessments by agencies like the EPA.[8][9] Ecologically, it demonstrates high hazard to aquatic species, causing teratogenesis, behavioral disruptions, and mortality via bioaccumulation and persistence in water bodies, which has led to restrictions in certain applications to mitigate off-target impacts.[10][7]Chemical Properties and Mechanism
Molecular Structure and Physical Properties
Dimethoate is an organophosphorus compound with the molecular formula C₅H₁₂NO₃PS₂ and a molar mass of 229.3 g/mol.[1] Its systematic name is O,O-dimethyl S-[2-(methylamino)-2-oxoethyl] phosphorodithioate, featuring a central phosphorus atom bonded to two methoxy groups, a sulfur atom linked to a methylcarbamoylmethyl chain, and another sulfur completing the dithioate structure.[11] This configuration distinguishes it from simpler organophosphates by incorporating both thioester and amide functionalities, contributing to its stability and reactivity as an insecticide prodrug.[12] The compound appears as a white to grey crystalline solid at room temperature.[13] Key physical properties include a melting point of 51–52 °C and a boiling point of 117 °C at 0.01 kPa.[14] Its density is 1.28–1.3 g/cm³, and it exhibits low volatility with a vapor pressure of 0.001 Pa at 25 °C.[14][15]| Property | Value |
|---|---|
| Solubility in water | 25 g/L at 21 °C |
| Partition coefficient (log Kow) | 0.78 at 20 °C |
| Flash point | 107 °C (closed cup) |