%0 Journal Article
%T Photochemical Behaviour of Carbamates Structurally Related to Herbicides in Aqueous Media: Nucleophilic Solvent Trapping versus Radical Reactions
%A Monica Passananti
%A Flavio Cermola
%A Marina DellaGreca
%A Maria Rosaria Iesce
%A Lucio Previtera
%A Rosalia Sferruzza
%A Fabio Temussi
%J International Journal of Photoenergy
%D 2014
%I Hindawi Publishing Corporation
%R 10.1155/2014/864361
%X Irradiation of N-aryl O-aryl carbamates has been carried out in H2O/CH3CN (1£¿:£¿1£¿v/v) solutions at £¿nm. When chlorine is on the N-aryl ring, halogen-substituted products are found. These photoproducts derive from the trapping of the intermediate radical cation by water and, even, by acetonitrile leading to phenols and N-arylacetamides (photo-Ritter products), respectively. Unsubstituted N-aryl carbamates slowly undergo photo-Fries reaction. 1. Introduction Interaction of light with matter is one of the most important processes responsible for abiotic transformations of a xenobiotic in the environment, mainly in surface water [1¨C3]. Often the transformation process forms products that are more toxic than the parent compound [4¨C7]; hence, there is a need to consider transformation products during the environmental risk assessment process [8]. Although the photochemical behaviour of a molecule depends on the presence of peculiar functional groups, given the heterogeneity and, often, the structural complexity of these pollutants, it is frequently difficult to predict or rationalize their photochemical behavior. Carbamate function is present in a wide number of biologically active compounds. In particular, carbamate pesticides are an important group which are widely used through the world [9]. Although weak, carbamates exhibit absorption of radiation present in sunlight (>290£¿nm), and this requires the understanding of their photochemical behaviour [10]. The most general photochemical event, mainly observed in O-aryl derivatives, leads to rearranged products, via photo-Fries reaction and/or fragmentation [10, 11]. Less frequent is this type of photorearrangement in N-aryl carbamates [12, 13]. Recently, we studied the photochemical reactivity of two carbamate herbicides, chlorpropham, and phenisopham (Scheme 1) [14]. Scheme 1 Irradiation of phenisopham in aqueous solution at 310£¿nm led to photo-Fries rearranged products involving the cleavage of O-aryl N-aryl carbamate function. As observed in other cases [12], the O-alkyl N-aryl carbamate was unreactive, and this result was also found in the irradiation of chlorpropham. In the latter case the N-aryl moiety reacted and gave isopropyl 3-hydroxycarbanilate by photosubstitution of aryl chlorine with a hydroxyl group [12, 14]. For the two pesticides different phototransformations were observed [14]. These results induced us to gain more information about the photochemical reactivity of N-aryl O-aryl carbamates that combine functions present in the pesticides examined. In particular, we prepared six model
%U http://www.hindawi.com/journals/ijp/2014/864361/