Esterase-inhibiting photo-oxidation products from the organophosphorus insecticide pyrimithate

Pyrimithate (2‐dimethylamino‐6‐methylpyrimidin‐4‐yl diethyl phosphorothio‐nate) decomposes when exposed to u.v. light in the presence of air to a complex mixture of products, some of which inhibit esterases directly or indirectly. Separation of the mixture by thin‐layer and liquid chromatography gave five pure components in sufficient quantity for spectroscopic identification. A sixth was tentatively identified. The structures (II‐VII) show that oxidative attack occurs at the dimethylamino group and at the sulphur atom.