Photolysis of Diuron

Abstract

:The major photoproducts observed in the photolysis of diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] (2) in aqueous solution resulted from a heterolytic substitution of chlorine by OH (photohydrolysis). A wavelength e †ect was observed : at 254 nm the formation of 3-(4-chloro-3-hydroxyphenyl)-1,1-dimethylurea (3) accounted for more than 90% of the conversion, whereas when the solution was irradiated in "black lightÏ (85% of photons emitted at 365 nm, about 7% at 334 nm), the major photoproduct was 3-(3-chloro-4-hydroxyphenyl) -1,1-dimethylurea (4). The presence of methanol favoured the photoreduction into 3-(3-chlorophenyl)-1,1-dimethylurea (5).Completely di †erent reactions were observed when 2 was irradiated in dry aerobic conditions on silica. They resulted from elimination or oxidation of methyl groups. The main photoproducts initially formed were 3-(3,4-dichlorophenyl)-1-methyl urea (6) and 3-(3,4-dichlorophenyl)-1-formyl-1-methylurea (7). In the second stage (6) was transformed into (3,4-dichlorophenyl)-urea (8) and 3-(3,4-dichlorophenyl)-1-formylurea (9) ; some other minor products such as monuron (1) were also identiÐed. The formation rate of 6 and 7 was much slower on clay (montmorillonite or kaolin) than on silica.In contrast with products 6 and 8, the formation of 7 and 9 needed the presence of oxygen : they did not appear when diuron was irradiated in deoxygenated It can be concluded that the photolysis of diuron is highly dependent C 2 Cl 3 F 3 . on the conditions of irradiation.

FI-photoinduced Chemiluminescence Method for Diuron Determination in Water Samples

“…In both cases, the main products identified were hydroxylated compounds in the ring, as a result of a chlorine atom being replaced by -OH at the meta or para position, giving 3-(4-chloro-3-hydroxyphenyl)-1,1-dimethylurea and 3-(3-chloro-4-hydroxyphenyl)-1,1-dimethylurea, respectively. These same compounds were mentioned as the main photoproducts by Jirkovský et al 8 when an aqueous solution of diuron was irradiated with 254 nm light. According to the latter authors, at 254 nm the hydroxylated product abounds more in the para position (90% of the conversion) whereas the meta position is more abundant at longer wavelengths (365 and 334 nm).…”

“…For instance, it has been found that the presence of small percentages of methanol gave rise to photoreduction to monuron 41 or to 3-(3-chlorophenyl)-1,1-dimethylurea. 8 However, it is very unlikely that this is the phototransformation mechanism in the proposed system, since the highest percentage of ethanol used was only 0.1%, whereas the methanol concentrations employed in the studies above cited were around 3 -4%; moreover, additional assays showed that in the presented system the monuron signal was very small.…”

“…The absorption spectrum of diuron 8 in an aqueous solution presents two main peaks, at around 247 and 284 nm. Following irradiation with 254 nm UV light, the absorption increases between 270 and 310 nm and decreases between 240 and 260 nm, but no new absorption bands are observed.…”

“…Diuron is stable against hydrolysis (at neutral pH and room temperature) and sunlight, 5 although it hydrolyzes at acid or alkaline pH; 3,4-dichloroaniline is the main product, 6 which is highly toxic. 7 It is also degraded photochemically 8,9 and by ozonation. 10 Diuron is persistently adsorbed to the colloids (half-life up to eleven months); hence it can be used in deep-rooted crops.…”

Evaluation of Fish Models of Soluble Epoxide Hydrolase Inhibition

“…With the fathead minnow sEH, compound III was a 14-fold more potent inhibitor than compound II, while the other tested orthologs showed only a 2.2 ± 0.9-fold enhancement. Because N-dealkylation is a dominant metabolic transformation and degradation route of many alkylureas (28)(29)(30), this finding suggests that medaka may provide a better model for mouse and human sEH inhibition than fathead minnow.…”