PHOTODEGRADATION OF THE CARBAMATE INSECTICIDE PIRIMICARB

In order to study the photoreactivity of pirimicarb )-5,6-dimethyl-pyr imidin-4-yl-N-dimethylcarbamate) on plant surfaces, model experiments with organic solvents were performed. Pirimicarb decomposed readily wh en irradiated (lambda > 280 nm) in the presence of the selected model solvents to form a number of products. Half-lives were in the order is opropanol < cyclohexane < cyclohexene (up to a maximum of 140 min). In the presence of all three solvents photooxidation predominated leadin g to N-formylpirimicarb and, in a second step, to N-desmethylpirimicar b as well as to further oxygenated products with the carbamate moiety intact. Photolysis in cyclohexene resulted in photomineralisation as t he main degradation pathway. Irradiation of pirimicarb in the presence of isopropanol also yielded an addition product of the parent compoun d with the secondary alcohol.