Nitrite, photochemical reactions with

Ghe, T. Mutagenicity of photochemical reaction products of polycyclic aromatic hydrocarbons with nitrite, Sci. Total Environ., 39(1/2) 161-175, 1984. 

Alkoxy radicals, 75 peroxyalkyl radicals reaction with, 101 photochemical preparation from alkyl nitrites... 

Elimination of NO and NO2 is observed in the photochemistry of a range of nitro and nitroso compounds, nitrites and nitrates. The photochemical reactions of aromatic compounds with tetranitromethane and other related reagents have been reviewed. These reactions proceed in the simplest cases by addition of the elements of tetranitromethane to the arene, e.g. to give nitro trinitromethyl adducts, but large numbers of other products can be formed by a diverse range of multistep sequences. 

Alkyl halides (RX X = Cl, I) are an important source of halogens in the atmosphere. The major tropospheric sinks of these compounds are photolysis (RBr, RI) and reaction with OH radicals. In the case of alkyl iodides (RI) relative kinetic studies of their OH reactions in photoreactors are complicated by fast reactions with the 0( P) atoms generated by the photochemical OH radical sources. Figure 1 below shows a In-ln plot of the kinetic data from an experiment performed in a large photoreactor to determine the OH rate coefficient for the reaction OH + CH3CH2CH2I relative to OH + ethene using the photolysis of methyl nitrite (CH3ONO) as the OH radical source. A recent example of the implementation of the relative kinetic technique for the determination of OH radical rate coefficients in a photoreactor can be found in Olariu et al. (2000). 

Subsequent work (84) confirmed these ideas. The addition of oxidized aquo salt to ferrocyanide-peroxide mixtures has the same effect as the same concentration of the reduced form, as it should. Further, addition of cyanide, nitrite, or nitrosobenzene to both illuminated ferrocyanide solutions and to ferrocyanide containing aquopentacyanoferrate, suppresses the catalytic decomposition. This effect is due to the reversal of the equilibrium (I) by a higher cyanide concentration, and to the removal of aquo salt by nitrite and nitrosobenzene to form the complex ions [Fe(CN)5N02]"" and [Fe(CN)6ONPh],/, respectively, reactions which are known to occur readily. It is also suggested (85) that even the catalytic decomposition by ferrocyanide in the dark is due to a small amount of aquopentacyanoferrite in purely thermal (as opposed to photochemical) equilibrium with ferrocyanide according to (I). 

Fluorenol (89) is reduced photochemically by triethylamine to give fluorene in high yield a small amount of 9-ethylidenefluorene is also formed. Other amines are effective, although the yields are generally lower, and 9-acetoxyfluorene also reacts to give fluorene in rather low yield. The photoreduction reaction is related formally to the photoreduction of dicyanopyrazine (84). An apparently straightforward replacement of hydrogen by nitro in the photolysis of butyl p-hydroxybenzoate (90) in aqueous sodium nitrite is shown to be more complex, and it seems possible that the initial attack is by HO radicals, followed by reaction with NO2. 

In order to produce oxime 199 in greater quantities, the authors subsequently evaluated the use of DMF as the reaction solvent due to the increased solubility of the nitrite precursor 277 (36 mM). In conjunction with two serially connected microreactors, each containing 16 microchannels [1,000 pm (wide) x 500 pm (deep) x 1.0 m (length)] and eight black lights, the photochemical synthesis was performed continuously for 20h at a flow rate of 250 pi min 1 (residence time = 32 min). After an off-line aqueous extraction and silica gel column, 3.1 g of the oxime 199 was obtained equating to an isolated yield of 60% and successfully demonstrating the ability to use photochemical synthesis for the scalable preparation of pharmaceutically relevant compounds. 

Peroxynitrous acid, ONOOH, forms in another photochemical channel at shorter wavelengths but is absent at k > 300 nm. The O-atoms generated in reaction 99 may react with 02([02 Water 0.3 mM) via reaction 100 or, preferably, with nitrate via reaction 101. Nitrite (smax = 22.5 M 1 cm1 at 360 nm) will undergo secondary photolysis, reaction 102, and oxidation by OH radicals, reaction 103 ... 

Among the manifold reactions in snow the photolysis of nitrate (NO3 ) is now the best characterized reaction due to a range of laboratory experiments. These studies have been used to extract information about the absorption coefficients and quantum yields of NO3 in ice as a function of wavelength, the formation of products like the hydroxyl radical (OH) and nitrite (N02), and the release of NOx to the gas phase. Limited information regarding the absorption coefficients and the formation of OH radicals can also be found for the photolysis of H202. " Investigations regarding the photolytic decomposition of further compounds with a potential relevance for photochemical processes in surface snow are limited to studies, in which reactions of HCHO and NO2 have been examined. 

Cyclizations of 5-alkyl-substituted 4-penten-l-oxyl radicals are faster and frequently more selective than those of terminal unsubstituted derivatives [48, 53]. This finding is in accord with the electrophilic nature of alkoxyl radicals in addition reaction to C-C double bonds. 5-Alkyl- or 5-phenyl-substituted 4-pentenoxyl radicals, such as intermediates 25 or 26, were generated from a number of different sources. For example, alkyl nitrites [39], A-alkoxypyridine-2(l//)-thiones [46], and A-alkoxy-(/ -chlorophenyl)thiazole-2(3/f)-thiones [54] in photochemically induced reactions, and A-alkoxyphthalimides [55] or type IV radical precursors [53] in thermally initiated reactions have been applied for this purpose (Scheme 6). 

Most of the inorganic anions of seawater are not subject to primary photochemical processes, because their electronic excitation energies lie well above the maximum photon energy available in sea surface sunlight. Nitrate and nitrite do, however, exhibit weak transitions with meixima at 303 nm (e ax 7 mole cm ) and 355 nm (e ax = 22.5 mole" cm" ), respectively. The primary photoreactions of both of these oxyanions produce free radical products in seawater (Zafiriou and True, 1979a, b). The overall reactions are ... 

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