Fungicides

The photodegradation of benzimidazole-based fungicides: benomyl ({1- [(butylamino) carbonyl)-1H-benzimidazol-2-yl} carbamic acid methyl ester), thiabendazole (2-(4-thiazolyl)-1H-benzimidazole) and fuberidazole (2-(2-furyl)-1H-benzimidazole) by ultraviolet radiation has been studied. Benomyl in an organic solvent (chloroform) undergoes a rapid degradation even without any UV radiation; UV radiation and air agitation will increase the rate of the reaction. The degradation product was found to be methyl 2-benzimidazolecarbamate (MBC) in all cases. The degradation of thiabendazole and fuberidazole in methanol was also studied under different conditions but degradation was observed only under UV radiation and in the presence of oxygen, 7-8 Photodegradation products were found in the mixture after irradiation of thiabendazole but only 2 of them were separated from the mixture and identified. Benzimidazole-2-carboxamide and dimethyl oxalate were two of the final photodegradation products of thiabendazole in methanol. It is clear that the thiazole ring is the most vulnerable part of the molecule and suffers ring cleavage. No photodegradation products of fuberidazole were identified so far.

The photodegradation of propiconazole (1-{[2-(2,4-dichlorophenyl)-4-propyl-1,3-dioxolan-2-yl]methyl}-1 H-1,2,4-triazole), a systemic fungicide, by ultraviolet radiation has been studied. After 12 hours of continuous irradiation, propiconazole undergoes degradation in aqueous solution. The process requires the presence of oxygen and continuous agitation. Similarly, propiconazole undergoes degradation in organic solvents as well (methanol, hexane).