Pirimiphos-methyl (CAS 29232-93-7)

Pirimiphos-methyl (PMM) is an organophosphorous pesticide that belongs to the class of organic thiophosphates. It is characterized by the substitution of a methyl group at position 6 and a diethylamino group at position 2 of O,O-dimethyl O-pyrimidin-4-yl phosphorothioate. With its role as an inhibitor of acetylcholinesterase (EC 3.1.1.7), it serves as an acaricide, agrochemical, insecticide, and environmental contaminant. Derived from a 2-diethylamino-6-methylpyrimidin-4(1H)-one, pirimiphos-methyl exhibits properties of an organic thiophosphate and an aminopyrimidine. Pirimiphos-methyl is a yellow liquid that possesses corrosive properties towards tin and mild steel. Primarily used as an insecticide, it acts systemically by inhibiting cholinesterase, which serves as the sole known mechanism of its toxic action. Interestingly, even though rats rapidly absorb the pesticide, clear signs of poisoning were not observed until 24 hours later, when brain cholinesterase inhibition reached 46%. Recovery of cholinesterase activity commenced within 72 hours, with complete restoration in plasma enzyme observed by 96 hours, while the red cell enzyme exhibited a slower recovery rate.