CHLORONICOTINYL INSECTICIDES .6. STABILITY COMPARISON OF IMIDACLOPRID AND RELATED-COMPOUNDS UNDER SIMULATED SUNLIGHT, HYDROLYSIS CONDITIONS, AND TO OXYGEN

Lipophilicity and the tendency for decomposition of imidacloprid and related compounds by oxygen, hydrolytic mediums, and simulated sunlight were studied to see whether these physicochemical factors have any relation to the biological activity of the compounds in vitro, in a greenhouse, or under field conditions. Lipophilicity indices based on HPLC bore no definite relationship with the binding affinity to the acetylcholine receptor. However, the compounds having high insecticidal potential in greenhouse tests were generally less hydrophilic. In neutral water or in an oxygen-saturated solution, the compounds tested were completely stable. An evident difference was observed in their behavior toward the sunlight wavelength, the nitromethylene compounds decomposing far more rapidly than nitroimines like imidacloprid. The photolability of the nitromethylenes is ascribed to their longer maximum absorption wavelength of over 320 nm.