Trifluralin photodecomposition

Photolytic. Irradiation of trifluralin in hexane by laboratory light produced a,a,a-trifluoro-2,6-dinitro-A-propyl-jo-toluidine and a,a,a-trifluoro-2,6-dinitro-p-toluidine. The sunlight irradiation of trifluralin in water yielded a,a,a-trifluoro-A, 7 -dipropyl-5-nitrotoluene-3,4-diamine, a,a,a-trifluoro-A/ ,A/ -dipropyltoluene-3,4,5-triamine, 2-ethyl-7-nitro-5-(trifluoromethyl)benzimidazole, 2,3-dihydroxy-2-ethyl-7-nitro-l-propyl-5-(trifluoromethyl)benzimidazoline, and 2-ethyl-7-nitro-5-(trifluoromethyl)benzimidazole. 2-Amino-6-nitro-a,a,a-trifluoro-p-toluidine and 2-ethyl-5-nitro-7-(trifluoromethyl)benzimidazole also were reported as major products under acidic and basic conditions, respectively (Crosby and Leitis, 1973). In a later study, Leitis and Crosby (1974) reported that trifluralin in aqueous solutions was very unstable to sunlight, especially in the presence of methanol. The photodecomposition of trifluralin involved oxidative TV-dealkylation, nitro reduction, and reductive cyclization. The principal photodecomposition products of trifluralin were 2-amino-6-nitro-a,a,a-trifluoro-jo-toluidine, 2-ethyl-7-nitro-5-(trifluoromethyl)benzimida-zole 3-oxide, 2,3-dihydroxy-2-ethyl-7-nitro-l-propyl-5-(trifluoromethyl)benzimidazole, and two azoxybenzenes. Under alkaline conditions, the principal photodecomposition product was 2-ethyl-7-nitro-5-(trifluoromethyl)-benzimidazole (Leitis and Crosby, 1974). 

Crosby, D.G., Leitis, E. (1973) The photodecomposition of trifluralin in water. Bull. Environ. Contam. Toxicol. 10, 237. 

From these experiments it may be concluded that sunlight is indeed the predominate factor in the airborne conversions of both trifluralin and parathion, but that oxidant enhances the reaction rate in both cases. Vapor-nhase photodecomposition may be a primary dissipation process for the significant fractions of trifluralin (47, 79) and parathion (5) known or suspected to be volatilized following application. It may also explain why surprisingly small residues of potentially photo-reactive pesticides such as trifluralin, parathion, and related chemicals are found in surveys of atmospheric levels of pesticides near heavy use areas (9, 1(3, 1J, 413. 

Dinitro-r-anilines constitute a major group of pre-emergent herbicides. The photodecomposition of these herbicides has been simulated by studying the photolysis of one typical example, Trifluralin 47 (74MI1). The major product from the action of sunlight in aqueous alkaline media was the benzimidazole 48, and the by-products included the dihyroxybenzimidazo-line 49, the benzimidazole Y-oxide, and benzimidazoline derivatives of 48, all being derived by r-amino-effect chemistry (Scheme 17). 

Crosby and Leitis (1973) found similar photodecomposition products in the decomposition of trifluralin in water. 

Several investigations have dealt with the photodecomposition of trifluralin (Soderquist et ai, 1972 Leitis and Crosby, 1974) under laboratory and field conditions. 

The authors propose the following pathway for the photodecomposition of trifluralin ... 

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