Nitrophenols atmospheric formation

Environmental aspects, as well as the requirement of efficient mixing in the mixed acid process, have led to the development of single-phase nitrations. These can be divided into Hquid- and vapor-phase nitrations. One Hquid-phase technique involves the use of > 98% by weight nitric acid, with temperatures of 20—60°C and atmospheric pressure (21). The molar ratios of nitric acid benzene are 2 1 to 4 1. After the reaction is complete, excess nitric acid is vacuum distilled and recycled. An analogous process is used to simultaneously produce a nitrobenzene and dinitrotoluene mixture (22). A conversion of 100% is obtained without the formation of nitrophenols or nitrocresols. The nitrobenzene and dinitrotoluene are separated by distillation. 

Vione D, V Maurino, C Minero, E Pelizzetti (2005) Aqueous atmospheric chemistry formation of 2,4-nitrophenol upon nitration of 2-nitrophenol and 4-nitroophenol in solution. Environ Sci Technol 39 7921-7931. 

Titanium dioxide suspended in an aqueous solution and irradiated with UV light X = 365 nm) converted benzene to carbon dioxide at a significant rate (Matthews, 1986). Irradiation of benzene in an aqueous solution yields mucondialdehyde. Photolysis of benzene vapor at 1849-2000 A yields ethylene, hydrogen, methane, ethane, toluene, and a polymer resembling cuprene. Other photolysis products reported under different conditions include fulvene, acetylene, substituted trienes (Howard, 1990), phenol, 2-nitrophenol, 4-nitrophenol, 2,4-dinitrophenol, 2,6-dinitro-phenol, nitrobenzene, formic acid, and peroxyacetyl nitrate (Calvert and Pitts, 1966). Under atmospheric conditions, the gas-phase reaction with OH radicals and nitrogen oxides resulted in the formation of phenol and nitrobenzene (Atkinson, 1990). Schwarz and Wasik (1976) reported a fluorescence quantum yield of 5.3 x 10" for benzene in water. 

In model (laboratory) experiments, the half-life of MCPA was about 3 days, suggesting that particles might have to be airborne for appreciable time periods in order for breakdown to occur. However, atmospheric drift of emulsified parathion (0 0-diethyl G-p-nitrophenyl phosphorothionate) underwent substantial photooxidation, isomerization, and p-nitrophenol formation within a few minutes (Figure 4) (14). 

Nitrate and nitrite photochemistry might also play a role in atmospheric hydrometeors. Nitrite photolysis has been shown to account for the majority of hydroxyl photoformation in irradiated fog water from a polluted site [ 14]. In addition, the generation of mutagenic and carcinogenic compounds from amino acids and amines dissolved in fog water [147] is a process that can be linked with nitrite photochemistry [20,141]. Furthermore, the formation of atmospheric nitrophenols partially takes place in aqueous solution. Reactions in the aqueous phase can account for about 30% of the atmospheric sources of mononitrophenols and for the vast majority of the dinitrophenol ones [ 148], and irradiation of nitrate and nitrite can possibly play a role in the process (see Sect. 3.2). Mono- and dinitrophenols are toxic compounds, and their occurrence in rainwater is thought to be a contributory factor in forest decline [149-151]. 

Another common similarity between the CdS-(GSH) and ZnS-(GSH) nanoparticles was the ability to photoreduce methylviologen and /j-nitrophenol (PNP) in solution. Under an inert atmosphere, reduction was evident from the clear formation of the characteristic spectrum of reduced methylviologen. P-nitrophenol was similar in that an optimal reduction occurred when the ratio of PNP to nanocrystal was approximately five to ten. In fact, when the ratio was higher, a decreased reduction rate was evident. Over time, complete reduction of the PNP occurred. ... 

Nitrated hydroxyaromatics may enter into the atmosphere from both primary and secondary sources. The formation of nitrophenols and nitrocresols in die combustion processes of motor vehicles has been reported by Tremp et al. (1993). Others primary sources may be combustion of coal, wood, manufacture of phenol-formaldehyde resins, pharmaceuticals disinfectants, dyes and explosives (Harrison et al., 2005). Studies in our and other laboratories have shown that an additional important source of diese compounds in the atmosphere could be the gas-phase OH-radical initiated photooxidation of aromatic hydrocarbons such as benzene, toluene, phenol, cresols and dihydroxybenzenes in the presence of NOx during the daytime as well as the reaction of NO3 radicals widi these aromatics during the night time (Atkinson et al., 1992 Olariu et al., 2002). Once released or... 

Presently very little is known about the atmospherie behaviour of nitrophenols and nitrocresols. The aim of the present study is to increase our knowledge with respeet to the fate of this compound class under simulated tropospheric conditions in the laboratory. Reeent smdies in our laboratory on the photolysis of nitrophenol and nitroeresols with aetinie lamps (Philips TL 05/40 W 320 < k< 480, Xmax = 360 nm) have indieated that these eompounds could be important secondary organic aerosol sources (Bejan et al., 2003). In order to assess the importance of this aerosol formation pathway for the atmosphere, kinetie information concerning other atmospherie loss processes, e.g. reactions with OH and NO3 radicals, is required. 

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