Effects of paddy water and some photosensitizers on the photolysis of the fungicide isoprothiolane

The fungicide isoprothiolane (diisopropyl 1,3-dithiolan-2-ylidenemalonate) decomposed slowly in deionized water under ultraviolet light or sunlight irradiation. Rice-paddy water greatly accelerated the photodegradation. This photosensitizing effect was comparable to that of 2% acetone. Soil extracts, rice-plant extracts, and chlorophylls showed little effect for the isoprothiolane photolysis. Tryptophan showed a relatively weak accelerating effect after a considerable lag time. Riboflavin exerted a remarkable acceleration of the photolysis. This effect was suppressed by a nitrogen gas stream.