V-Nitrosamides

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. 

Fig. 2 Representative chemical formulas of various types of /V-nitrosamides (a) /V-nitroso-/V-methyl-acetamide, (b) N-nitrosobenzthiazuron, (c) iV-methyl-lV-iiitroso-lV -nitroguanidme (MNNG), (d) /V-nitroso-carbaryl, (e) iV-methyl-iV-nitrosocyanamide, (f) /V-nitroso-/V-mcthyl-p-tolucnesulfonamide.

Saturated /V-haloamides and /V-nitrosamides, upon UV photolysis, undergo remote functionalizations 8 to nitrogen on the alkyl or, less effec-... 

From bioassay results of more than 330 NNAs plus knowledge of fewer than sixty specific NNAs in MSS, it is obvious that the MSS NNAs cannot meet criterion (3). Over 330 /V-nitroso compounds variously administered to forty different species have been reported as tumorigenic. No laboratory species is resistant to NNAs. In their summary of the results from 323 V-nitroso compounds bioassayed from 1956 to 1984, Preussmann and Stewart (2991) reported that 87% of the /V-nitroso compounds are tumorigenic. Over 70% of the /V-nitroso compounds studied were NNAs the remainder were /V-nitrosamides. 

V-Methyl- V-nitrosamides are converted into diazomethane, CH2N2, upon treatment with aqueous base. 

Inhibition of Nitrosamine Formation. Nitrites can react with secondary amines and A/-substituted amides under the acidic conditions of the stomach to form /V-nitrosamines and A/-nitrosamides. These compounds are collectively called N-nitroso compounds. There is strong circumstantial evidence that in vivo A/-nitroso compounds production contributes to the etiology of cancer of the stomach (135,136), esophagus (136,137), and nasopharynx (136,138). Ascorbic acid consumption is negatively correlated with the incidence of these cancers, due to ascorbic acid inhibition of in vivo A/-nitroso compound formation (139). The concentration of A/-nitroso compounds formed in the stomach depends on the nitrate and nitrite intake. 

Decomposition studies confirmed that N-nitrosamides are much less stable than volatile N-nitrosamines such as NPYR and NDMA (79). Thermal studies utilizing heating conditions commonly encountered in the cooking of bacon and pork roasts indicated that N nitrosomethylpropionamide (NOMP) was degraded to the extent of 74-97% compared to 3-14% for NPYR and NDMA (Table V). It was tentatively concluded that the major... 

Nitrosamines, which are the amides of nitrous acid, are more stable and are derived from secondary amines with nitrous acid. iV-nitrosamides are substances which have a carbonyl group attached to a nitrogen-bearing NO group, e.g. iV-nitrosamides, iV-nitrosocarbamates and /V-nitrosoLireas see Figure 10. 

The study of the mechanism of the fast SCR over V-W-Ti-0 catalysts was addressed first by Koebel and co-workers [65-68]. They suggested that (i) the reoxidation ofthe catalyst is rate determining at low temperature in the redox cycle of standard SCR catalyst, (ii) NO2 reoxidizes the catalyst faster than O2 the NO2-enhanced reoxidation of the catalyst was demonstrated by in situ Raman experiments, (hi) the reaction occurs via the nitrosamide intermediate in both standard and fast SCR and (iv) ammonium nitrate is considered an undesired side-product. 

Whereas base-induced decomposition of N-nitrosourethanes has been utilized (9) as a popular method of generating diazoalkanes, only limited investigations on base treatments of nitrosamides have been reported (10). The primary product in the base treatment is assumed, in analogy to better investigate nitrosourethane cases, to be diazo hydroxides V via attack of a base on the carbonyl group as in IV. A diazo hydroxide V has been related to the diazo ester III by a reaction with benzoyl chloride. 

Broadly, NOC are divided into two groups (a) /V-nitrosamines and (b) N-nitrosamides. In jV-nitrosamines, the two remaining substituent groups on the >N—N=0 atom can be either alkyl or aryl, or they can form the part of a heterocyclic ring (as in N-nitrosopyrrolidine). On the other hand, in N-nitrosamides, more correctly called N-acyl-N-nitroso compounds, one of these... 

Recent advances in chromatography have made it possible to employ microbore HPLC for the determination of NOC. Its main advantage is that it uses a very low mobile-phase flow (20-100 /rl/min). This might make the TEA compatible with a reversed-phase system. Massey et al. (73), in fact, have successfully used reversed-phase chromatography for the HPLC-TEA determination of V-nitroso-V, 7V -di methylpiperazinium iodide. A 500-mm X 1-mm microbore ODS column and a mobile phase consisting of 0.1 M ammonium heptane-sulfonate in methanol water (70 30) (flow rate 20 /zl/min) was used for the HPLC separation. In another study, Riihl and Reusch (74) used a microbore Spherisorb 3 SW column for HPLC-TEA determination of volatile V-nitrosamines. The mobile phase was a mixture of 2-propanol and n-hexane (2.5 97.5). Further application of such techniques for the determination of various polar NOC, especially A-nitrosamides, in foods is desirable. 

Darbeau, R. W., Pease, R. S., Perez, E. V., Gibble, R. E., Ayo, E. A., Sweeney, A. W. N-Nitrosamide-mediated Ritter-type reactions.Part II. The operation of "persistent steric" and "rc -acceptor agostic-type" effects. J. Chem. Soc., Perkin Trans. 2 2002, 2146-2153. 

Diazomethane reacts rapidly with unesterified fatty acids in the presence of a little methanol, which catalyses the reaction, to form methyl esters. The reagent is generally prepared as a solution in diethyl ether by the action of alkali on a nitrosamide, e.g. N-methyl-/V-nitroso-p-toluene-sulfonamide (Diazald, Aldrich Chemical Co., Milwaukee, U.S.A.). Solutions of diazomethane are stable for short periods If stored refrigerated in the dark over potassium hydroxide pellets. If they are kept too long, polymeric byproducts form which may interfere with the subsequent GC analysis. 

The chemical and mechanistic aspects of the SCR-NH3 process over metal oxide catalysts have been discussed in details by Busca et al. [38]. Their conclusions are that the mechanism on V(W, Mo)-Ti02 catalysts is based on the dissociative chemisorption of ammonia on Lewis (vanadium) acid sites and that NO reacts with the amide chemisorbed species to form a nitrosamide key intermediate which then decomposes to N2 and H2O. The catalytic cycle is closed by reoxidation of the reduced catalyst by gas-phase oxygen. 

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