Photolysis of Diuron

Abstract

The major photoproducts observed in the photolysis of diuron [3-(3,4dichlorophenyl)-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)-1,1dimethylurea (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.

Phototransformation of metoxuron [3‐(3‐chloro‐4‐methoxyphenyl)‐1,1‐dimethylurea] in aqueous solution

“…A similar reaction has previously been observed with several halogenophenylureas 1. 2 This was tentatively explained in the case of diuron by the intermediate formation of a methyl enolate 10. A similar mechanism might therefore be proposed for metoxuron, as shown in Fig 6(d).…”

Sources and pathways of biocides and their transformation products in urban storm water infrastructure of a 2 ha urban district

“…It is slowly degraded by hydrolysis and biodegradation with a half-life of a month up to a year (Giacomazzi and Cochet, 2004). Johann et al (2018) showed an increase in sorption of diuron in the soil passage with an increase in organic matter. Bollmann et al (2017a) estimated a half-life of diuron of more than 2500 d in soil.…”

“…Diuron, terbutryn, and OIT used in facade coatings degrade to various transformation products (TPs; Hensen et al, 2020). Jirkovský et al (1997) describe TPs of diuron formed by photolysis, and Giacomazzi and Cochet (2004) give an overview of all degradation pathways of diuron. Bollmann et al (2016) investigate photodegradation products formed at facades of terbutryn and Bollmann et al (2017b) of OIT.…”

Reviews of Environmental Contamination and Toxicology

“…A volatilization chamber elaborately designed to simulate well real environmental conditions was developed to evaluate the dissipation profiles of methyl parathion (136) applied to French beans (MUller et al 1995). The former system was introduced to examine the mineralization of pesticides on a silica gel surface (Parlar 1990), and its concept has been used to examine photolysis of diuron (53) adsorbed on sand, clays, and iron oxide (Jirkovsky et al 1997). A similar wind tunnel apparatus was successfully introduced to estimate volatilization and degradation profiles of fenpropimorph (227) on dwarf beans, sugar beet, and radish ).…”

“…Katagi Ureas Jirkovsky et al (1997) reported that diuron (53) was photodegraded on sand via N-demethylation and oxidation to the N-formyl-N-methyl derivative with a trace formation of monuron (52). Katagi Ureas Jirkovsky et al (1997) reported that diuron (53) was photodegraded on sand via N-demethylation and oxidation to the N-formyl-N-methyl derivative with a trace formation of monuron (52).…”