Nitrosamines photolysis

The effects of uv radiation on V/-nitroso compounds depend on the pH and the medium. Under neutral conditions and ia the absence of radical scavengers, these compounds often appear chemically stable, although the E—Z equiUbrium, with respect to rotation around the N—N bond, can be affected (70). This apparent stabiUty is due to rapid recombination of aminyl radicals and nitric oxide [10102-43-9] formed duting photolysis. In the presence of radical scavengers nitrosamines decay rapidly (71). At lower pH, a variety of photoproducts are formed, including compounds attributed to photoelimination, photoreduction, and photo-oxidation (69). Low concentrations of most nitrosamines, even at neutral pH, can be eliminated by prolonged kradiation at 366 nm. This technique is used ki the identification of /V-nitrosamines that are present ki low concentrations ki complex mixtures (72). 

Like nitrosamines, nitrosohydrazines probably undergo rapid photolysis in sunlight. 

The sudden consumption of the remaining UDMH, and the increased relative importance of N-nitrosamine formation at -30 minutes into the photolysis can be rationalized by assuming that at that time the [NO I/ENO] ratio, and thus the photostationary state [O3], has become sufficiently high that O3 may be reacting with the hydrazine directly, and that reaction (3) begins to dominate over reaction (10). This results in higher rates of UDMH consumption by the OH radicals formed in the UDMH + O3 reaction (1), and by the OH radicals generated by the reaction of NO... 

Under these conditions, although nitrosamine formation appears to occur to some extent, formation of an unknown product (or set of products) is also observed. On the basis of mechanistic considerations we believe this product to be primarily a nitroso-hydrazine. Upon photolysis, this compound may give rise to an N-nitrohydrazine, or, when O3 is present, to the nitrosamine. 

The effort required to establish identity of a nitrosamine in an environmental sample depends on the nature of the problem and the specificity of the primary detection system. TEA response is much stronger evidence of identity than response from a flame ionization or nitrogen-specific detector. If TEA response is supported by chemical (9) or ultraviolet photolysis (8) supporting data, identification is adequate for many... 

Possible exposure to pesticide-derived N,-nitroso compounds depends on environmental processes that influence formation, movement, and degradation of the compounds. Although laboratory studies have shown the feasibility of environmental nitrosamine formation, there has been little evidence that it is an important process. Nitrosamines vary greatly in their environmental stabilities, but all seem to be susceptible to one or more modes of decomposition including photolysis, microbiological degradation, and plant metabolism. 

The low-temperature photolysis at —150 °C in an ethanol-methanol mixture containing trifluoroacetic acid (0.01 M) adds another dimension to nitrosamine chemistry163 irradiation at 313 nm under these conditions gives a new species showing absorption at 391,... 

The crucial requirement of excited-state proton transfer (ESPT) is suggested by the failure of 1-naphthyl methyl ether to undergo self-nitrosation under similar photolysis conditions. The ESPT is further established by quenching of the photonitrosation as well as 1-naphthol fluorescence by general bases, such as water and triethylamine, with comparable quenching rate constants and quantum yield. ESPT shows the significance in relation to the requirement of acid in photolysis of nitrosamines and acid association is a photolabile species. 

Nitramines are known to photodissociate from their jt,jt state to give aminyl and nitric oxide radicals in the presence of an acid the aminyl radicals are protonated to give aminium radicals, which can initiate addition to olefins. As a synthetic reaction, photolysis of nitramines in the presence of acids can be conveniently run under oxygen to give oxidative addition similar to those shown in equation 145 indeed TV-nitrodimethylamine is photolysed with triene 299 under such conditions to give a mixture of 301 and 302, similar to results observed in the oxidative nitrosamine photoaddition169. To simplify the isolation, the crude products are reduced with LAH to form the open-chain amino alcohol 303. Some other oxidative photoadditions of N-nitro dimethylamine to other olefins are reported. As the photoreaction has to use a Corex filter and product yields are no better than those shown by nitrosamines, further investigations were scarcely carried out. 

Various nonvolatile nitrosamines were analyzed using HPLC-UV photolysis-CLD. This was applied for determination of V-nitrosamides in dried squid589 and N-nitrosodiphenylamine (278c) in treated apples590. 

At temperatures low enough to suppress thermal decomposition, a nltrosamlde XIV In polar or non-polar solvents Is photolytlcally decomposed to amldyl and nitric oxide radicals 4,16,17,18), This Is In sharp contrast to the photostahility of nitrosamines in neutral solvents (Including acetic acid) (ii), although the pattern of photodecomposition Is similar to that of nitrosamines In dilute acidic conditions. However, the overall photolysis pattern of nltrosamldes Is complicated by disproportionation of nitric oxide and existence of a radical pair XV (20,21,22). ... 

The major atmospheric fate of the A-nitrosamines such as A-nitrosodimethylamine is photolysis (Tuazon et al., 1984) ... 

The mesoionic compounds known as sydnones serve as cyclic azomethine imines. Thus, sydnone (167), isolable after preparation from die corresponding nitrosamine, underwent cyclization as an azomethine imine at 20-35 C (Scheme 52).86 Photolysis of sydnones also results in cyclization but through nitrile imine intermediates vide infra). 

Nitrosamines, unlike nitrite esters, do not undergo cyclizations or other radical reactions upon photolysis in neutral conditions (73ACR354). Pre-... 

L 1 and 0.6 jag L, respectively. Due to photolysis, nitrate present in the water at a concentration of 55 mg L 1 was reduced to nitrite generating an additional problem (see section II.D.l). This is because nitrite is thought to be involved in the formation of nitrosamines. Experimental conditions in this plant have been investigated to provide the optimum operating conditions for the removal of herbicides and to minimize the impact of nitrate photolysis. The results obtained in this plant led to concentrations of atrazine and nitrite in the effluent lower than 0.1 and 100 pg L 1, respectively. It must be said, for safe operation of the plant, that an equivalent ozone dose higher than 3 kW energy and a radiant power for the UV lamp between 20 and 35 kW were needed. 

In their work on the explosive oxidation of ammonia, which has already been discussed earlier, Husain and Norrish also examined the hydrazine system. Their principal results, obtained by the method of flash photolysis and kinetic spectroscopy, were as follows (a) no induction period was observed (b) NH emission, observable in the photolysis of pure N2H4, was visible at the shortest delay times (c) NO and OH were produced as the NH was decaying d) NO added to the hydrazine-oxygen system did not disappear in the combustion ( ) NO represented only about 5 % of the final products. Since, unlike the oxidation of ammonia, the major nitrogenous product is N2 rather than NO, Husain and Norrish concluded that reaction (15 ) is not a part of the main reaction sequence. They felt that the N-N bond was not split in in the main chain propagation. They proposed a mechanism involving nitrosamine, NH2NO, as a chain carrier viz. 

RDX is a widely used military explosive. It is a synthetic compound and is not known to exist in nature. Effluents and emissions from Army ammunition plants are responsible for the release of RDX into the environment. When released to the atmosphere, RDX may be removed by reaction with photochemically generated hydroxyl radicals (half-life =1.5 hours). When released to water, RDX is subject to photolysis (half-life = 9-13 hours). Photoproducts include formaldehyde and nitrosamines. 

Some interesting classes of nitrosamines are decomposable by warm strong acids or by photolytic cleavage in alkaline media so that nitrite or nitrous acid is produced. They can be electrochemically detected as such or after further reaction. The availability of a voltametric detector for flowing solutions equipped with solid electrodes allows the direct anodic detection of the NO2 species produced by postcolumn photolysis. The Ce(IV) and iodide in acid medium have been investigated as postcolumn reagents for the oxidation and voltametric detection of the nitrite produced by the warm acid decomposition of nonvolatile nitrosamines. 

Nitrosamines derived from 5-amino-1,2,4-thiadiazoles are readily accessible stable compounds.3 Thermolysis of the substituted 5-nitrosoimino-1,2,4-thiadiazolines (48574 and 486383) produces the corresponding 5-ketones (487, 488) with evolution of nitrogen almost quantitatively. Their photolysis, involving n- n excitation, proceeds less uniformly. Irradiation of 486 in various solvents yields, as primary products, Hector s base (14b) and phenyl-cyanamide subsequent changes produce their 1 1-adduct, as well as 3,5-dianilino-l,2,4-thiadiazole, phenylurea, and other compounds, all in variable moderate yield. The photolytic fragmentation is more complex than that of comparable heterocyclic nitrosimines.384... 

The aqueous photochemistry of the sodium salt of l-(A, A -diethylamino)dia-zen-l-ium-l,2-diolate (70) (Scheme 12) has been examined experimentally and theoretically. Photolysis of (70) results in formation of the radical anion (71) and NO, via intersystem crossing and a triplet excited state. The product pair either undergoes electron transfer, before escape of NO from the cage, to form triplet NO and nitrosamine (minor pathway), or the radical anion (71) dissociates to give a second NO molecule and (ultimately) diethylamine (major pathway). 

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