Photodegradation of the Herbicide Bromobutide in Water

TAKAHASHI Naohiro, MIKAMI Nobuyoshi, YAMADA Hirohiko, MIYAMOTO Junshi

doi:10.1584/jpestics.10.247

Photodegradation of bromobutide [N-(1-methyl-1-phenylethyl)-2-bromo-3, 3-dimethyl-butanamide], (P1), in water was studied using ¹⁴C preparations labeled separately at the phenyl ring or carbonyl group. Upon exposure to sunlight, P1 was photodecomposed with half-lives of ca. 13 weeks in distilled water, 12 weeks in sea water, 11 weeks in paddy field water and 1.3 weeks in 2% aqueous acetone. The photoreactions involved were oxidation at one of the gem-dimethyl or tert-butyl methyl group, hydroxylation at the phenyl ring, substitution of bromine by hydroxyl group, cleavage of the amide, carbon-bromine or benzylic carbon-nitrogen bond, and photomineralization of the phenyl and carbonyl carbon to ¹⁴CO₂. Most of the photochemical reactions can be rationalized by a mechanism involving free radical intermediates. The carbon-bromine bond cleavage and photomineralization to ¹⁴CO₂ were predominant in any water tested. The hydroxylation at the phenyl ring was much enhanced by UV irradiation of P1 in distilled water containing hydrogen peroxide or by treatment with Fenton's reagent, and consequently involvement of hydroxyl radical in the reaction was suggested. However, singlet molecular oxygen was unreactive to P1.

Photodegradation of the Herbicide Bromobutide in Water

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