Acetone-Sensitized Photolysis of the Herbicide 3-(5-tert-Butyl-3-isoxazolyl)-1, 1-dimethylurea (Isouron)

Abstract

An aqueous solution of 3-(5-tert-butyl-3-isoxazolyl)-1, 1-dimethylurea at 100μg/ml remained unchanged even when exposed to sunlight or a combination of black light and fluorescent light. However, in the presence of acetone as a sensitizer, more than 60% and 80% of isouron was lost on exposure to sunlight and artificial light for 32hr, respectively. Two products, 3-(5-tert-butylisoxazolyl)-1-methyl-1-formylurea and 3-(5-tert-butylisoxazolyl)-1-methylurea, were isolated and identified by comparison of their nmr and mass spectra with those of synthetic standards. Also, formaldehyde was identified in the photolysis solution by preparing methylenebisdimedone. The formation of formaldehyde suggests that unstable 3-(5-tert-butylisoxazolyl)-1-hydroxymethyl-1-methylurea is an intermediate in the formation of 3-(5-tert-butylisoxazolyl)-1-methylurea. The photolysis of 3-(5-tert-butylisoxazolyl)-1-formyl-1-methylurea also yielded 3-(5-tert-butylisoxazolyl)-1-methylurea.