Theoretical and experimental evidence of the photonitration pathway of phenol and 4-chlorophenol: A mechanistic study of environmental significance

Abstract

Light-induced nitration pathways of phenols are important processes for the transformation of pesticide-derived secondary pollutants into toxic derivatives in surface waters, and for the formation of phytotoxic compounds in the atmosphere. Moreover, phenols can be used as

Secondary Formation of Aromatic Nitroderivatives of Environmental Concern: Photonitration Processes Triggered by the Photolysis of Nitrate and Nitrite Ions in Aqueous Solution

“…In neutral solution, in both cases, the photonitration process has been shown to involve a reaction between phenol and • NO2, with the likely involvement of the phenoxyl radical as a reaction intermediate (Scheme 3). This most likely reaction pathway has been suggested by quantum chemistry calculations as well [27]. The following sections provide a number of case studies concerning the photonitration of several aromatic compounds, highlighting the main nitrating agents that are involved in the process and, when available, describing the underlying nitration mechanism(s).…”

“…The above reaction accounts for most of the formation of the nitrating agent • NO2 in the presence of irradiated nitrite [27,37]. Interestingly, the occurrence of • NO and • NO2 in the same system triggers an efficient process of nitrite regeneration:…”

Indirect Photochemistry in Sunlit Surface Waters: Photoinduced Production of Reactive Transient Species

“…With Equations (43) and (44) as sinks and the sources considered above, the steady-state [CNO 2 ] in environmental waters could be in the range of 10 À11 -10 À9 m. [221] Nitrogen dioxide is a nitrating agent, which is particularly effective in the case of electron-rich aromatic compounds, such as phenols (HPhOH). In this case, nitration takes place by the intermediate formation of a phenoxy radical (HPhOC) and it involves two CNO 2 radicals: [223] HPhOH þ CNO 2 ! HPhOC þ HNO 2 ð45Þ…”

Phototransformation of the sunlight filter benzophenone-3 (2-hydroxy-4-methoxybenzophenone) under conditions relevant to surface waters

“…As far as • NO 2 is concerned, phenolic compounds such as BP3 produce nitrophenols upon reaction with nitrogen dioxide. The upper theoretical limit of nitrophenol yield with respect to reacted nitrogen dioxide is 50%, because the nitration process involves two • NO 2 (Bedini et al, 2012b). Moreover, there is evidence that the actual yield is not far from the upper limit (Vione et al, 2001).…”