Fungicides and photochemistry: Photodegradation of the dicarboximide fungicide vinclozolin

To examine the potential of the fungicide vinclozolin to undergo photochemical reactions on plant surfaces, model experiments (lambda > 280 nm) were performed in various organic solvents simulating the plant cuticle environment. On irradiation in 2-propanol and n-propanol vinclozolin was completely degraded within 1 h, but the degradation was substantially lower in benzene, cyclohexane, cyclohexene, ethanol, methanol, and tert-butyl methyl ether(TBME). In 2-propanol, n-propanol, and cyclohexane, the main reaction was photoaddition of the solvent molecules to the vinclozolin vinyl group; the photoproducts in further reactions were dechlorinated. In the presence of ethanol, photodehalogenation of the fungicide competed with photoaddition. On the other hand, in cyclohexene and benzene solutions, substitutions of the chlorines by solvent molecules were mainly observed. Photolysis in methanol or TBME yielded only dehalogenated photoproducts.