Nitrosamides reactions

N-nitrosamide and the solvent acidity, but generally denitrosation is more strongly acid-catalysed hence, it is a minor reaction ( <109 ) above pH 2 and the major pathway in concentrated acid ... 

The N-nitrosation of these amides was subsequently studied as a function of pH and temperature (78). There was no apparent pH maximum for the reaction, N-nitrosamide formation increasing with increasing hydrogen ion concentration. The rates of N-nitrosation decreased rapidly as the pH increased and little reaction occurred above pH 3. A unit drop in pH from 2 to I increased the rate of N-nitrosation by a factor of 5-8 times. 

Under appropriate condition, the peptide bond may react with aqueous nitrous acid to form a nitrosamide (32). It has been shown (33, 34, 35) in model systems that N-substituted amines can be formed by reaction between free amines and triglycerides. 

Mirvish (53,54) discovered that vitamin C could inhibit ni-trosation reactions. The purely chemical interaction of ascorbic acid with nitrite has been studied for theoretical reasons and because of its importance in the preservation of foods. This interaction has received increased attention for minimizing the presence of nitrosamines and nitrosamides in the environment, and especially in foods. We have studied the relationship in gastric carcinogenesis between high levels of nitrite, including pickling, and of vitamin C as a protective and inhibiting element. 

Nitrosation of primary amides results in deamination to produce carboxylic acid and nitrogen as products. Secondary amides, when nitrosated, give the corresponding nitrosamides in a reversible process [51]. In order to obtain good yields of the nitrosamides, it is best to add a base to remove the acid formed (Scheme 3.2). This reaction also occurs with ureas and carbamates. 

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. 

The mechanism of fast SCR over a zeolite-based catalyst has also been addressed by Sachtler and co-workers using an IR technique [69, 70]. They concluded that nitrogen is produced through fast decomposition of ammonium nitrite (the hydrated form of nitrosamide), vhich is formed from equimolar NO/NO2 feeds via N2O3 and its reaction vith water and ammonia ... 

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. 

In contrast to a straightforward and predictable decomposition pattern of photolysis with >400 nm light, irradiation of nitrosamides under nitrogen or helium with a Pyrex filter (>280 nm) is complicated by the formation of oxidized products derived from substrate and solvent, as shown in Table I, such as nitrates XXXIII-XXXV and nitro compound XXXVI, at the expense of the yields of C-nitroso compounds (19,20). Subsequently, it is established that secondary photoreactions occur in which the C-nitroso dimer XIX ( max 280-300 nm) is photolysed to give nitrate XXXIII and N-hexylacetamide in a 1 3 ratio (21). The stoichiometry indicates the disproportionation of C-nitroso monomer XVIII to the redox products. The reaction is believed to occur by a primary photodissociation of XVIII to the C-radical and nitric oxide followed by addition of two nitric oxides on XVIII and rearrangement-decomposition as shown below in analogy... 

Nitrosamides and nitrosamines exhibit considerably different reaction patterns when thermolysed or photolysed. The differences are discussed in relation to the ground state electronic configurations of these two classes of nitroso compounds. At -150 ,... 

Many N-unsubstituted pyrazoles can be obtained from A-allyl-TV-nitrosamides (90H(30)789), e.g. (56) — (57). Reactions of l-azido-3-chloropropane with Grignard reagents afford intermediates (58) that cyclize into azimines of A -pyrazolines (59) (92TL4683). 

PREPARATION OF THE METHYL ESTER—TRIMETHYLSILYL ETHER. The standard acid (0.5 mg) or the residue obtained from the urine extraction was dissolved in 0.5 cm3 of methanol. Ethereal diazomethane (1 cm3) was then added and allowed to stand for 1 min. Ethereal diazomethane was prepared by the reaction of p-tolylsulphonyl-methyl nitrosamide with an alcoholic solution of KOH. 

The next pesticide analyzer is described by Singer, et al (6) and used post-column derivatization for a nitrosamide-specific reaction. Following chromatographic separation and UV detection, the stream was air-segmented and treated with the Griess Reagent (Figure 11). The... 

A-nitrosamides behave in acid solution like A-nitrosamines they are reduced to acylated hydrazines. In this way alkylhydrazines may be prepared from primary amines by the following reactions [216]. 

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. 

In this section, all the reactions have in common the formation of an N—C bond as the last step in the synthesis of pyrazoles and indazoles. First, pyrazoles and then indazoles are discussed. Pyrazole itself and many other N f-pyrazoles have been obtained from A-allyl-A-nitrosamides <90H(30)789> to illustrate the reaction. Scheme 6 represents the case of pyrazole (7). The reaction of... 

When mixed with the equimolar solution of amides R C(0)NHR (41) in CHCI3, complex 38 reacted quickly at room temperature, yielding up to 95% of A-nitrosamides (42, Fig. 17) (76). Dark-blue solutions of 38 lost their color upon addition of the substrates, which is a reasonable visual test for the reaction. Among the variety of amides (41), only those possessing A-Me substituents were transformed to the corresponding A-nitrosamides (42). No reaction occurred for substrates with bulkier groups. Consequently, no color discharge... 

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