Hydroxyl reaction with nitrite

The kinetics of the various reactions have been explored in detail using large-volume chambers that can be used to simulate reactions in the troposphere. They have frequently used hydroxyl radicals formed by photolysis of methyl (or ethyl) nitrite, with the addition of NO to inhibit photolysis of NO2. This would result in the formation of 0( P) atoms, and subsequent reaction with Oj would produce ozone, and hence NO3 radicals from NOj. Nitrate radicals are produced by the thermal decomposition of NjOj, and in experiments with O3, a scavenger for hydroxyl radicals is added. Details of the different experimental procedures for the measurement of absolute and relative rates have been summarized, and attention drawn to the often considerable spread of values for experiments carried out at room temperature (-298 K) (Atkinson 1986). It should be emphasized that in the real troposphere, both the rates—and possibly the products—of transformation will be determined by seasonal differences both in temperature and the intensity of solar radiation. These are determined both by latitude and altitude. 

Lomustine Lomustine, l-(2-chloroethyl)-3-cyclohexyl-l-nitrosourea (30.2.4.3), is made by reacting ethanolamine with cyclohexylisocyanate, which forms l-(2-hydroxyethyl)-3-cyclohexylurea (30.2.4.1). Upon reaction with thionyl chloride, the hydroxyl gronp in it is replaced with a chlorine atom, giving l-(2-chloroethyl)-3-cyclohexylurea (30.2.4.2). This is nitrated in non-aqueons conditions with formic acid and sodinm nitrite to give lomustine (30.2.4.3) [67,68]. 

However, these reactions can actually be considered as electron transfer or oxygen atom transfer reactions, as in the case of the ozone reactions with the hydroxyl and hydroperoxide ions or with the nitrite ion, respectively ... 

Phenol transforms in the presence of nitrate and nitrite under UV irradiation. In all cases of oxidation/hydroxylation, nitrosation and nitration products have been detected. The oxidation and hydroxylation of phenol is initiated by reaction with hydroxyl, while nitrosation is probably due to reaction with N2O3. The formation of 2- and 4-nitrophenol from phenol is a consequence of the reaction of the substrate with nitrogen dioxide ( NO2/N2O4), although the details of the mechanism are still uncertain. It is, however, very doubtful that phenol photonitration involves phenoxyl as an intermediate, since nitra-... 

The irradiation of nitrophenols in the presence of nitrite and nitrous acid mainly results in hydroxylation processes upon reaction with OH, leading to the corresponding dihydroxynitrobenzenes [109]. The absorption spectra of nitrophenols, nitrite and nitrous acid overlap, thus irradiation also results in the direct excitation of nitrophenols, with possible photolysis. Accordingly, it is very likely that many of the minor intermediates detected in the cited sys-... 

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]. 

The formation of nitrosamines in the reaction of amines with nitrites under acidic conditions in the stomach can be considered as nonenzymatic activation of amines present in food. Nitrosamines undergo further metabolism, catalyzed enzymatically by cytochrome P450, involving hydroxylation (Anon., 1993). 

Nitryl chloride, formed from peroxynitrite and HOCl is also capable of nitrating, chlorinating and hydroxylating tyrosine [ 116]. However, the reduction of nitrotyrosine by hypohalous acid has also been demonstrated. Several recent studies indicate that peroxynitrite can lead to generation of both nitrated and hydroxylated phenylalanine residues. The formation of 3-nitrotyrosine and 4-nitrophenylalanine was favoured over the hydroxylation reaction when phenylalanine was treated with peroxy nitrite in vitro [117]. 

Audley, G.J., D.L. Baulch, I.M. Campbell, D.J. Waters, and G Watling (1982), Gas-phase reactions of hydroxyl radicals with alkyl nitrite vapours in H2O2 + NO 4- CO mixtures, J. Chem. Soc., Faraday Trans. 1, 78, 611-617. 

Baulch, D.L., I.M. Campbell, and S.M. Saunders (1985), The rate constants for the reaction of the hydroxyl radical with methyl, n-propyl, and n-butyl nitrites, Int. J. Chem. Kinet. 17, 355-366. 

Campbell, I.M., and K. Goodman (1975), Rate constants for reactions of hydroxyl radicals with nitromethane and methyl nitrite vapours at 292 K, Chem. Phys. Lett., 36, 382-384. 

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