Nitration Nitrosating agent

Elimination or reduction of all potential nitrosating agents formed or added during the manufacturing process (e.g. nitrous acid resulting from nitration process during the process). 

They are more potent than nitrates and there is no development of tolerance [78]. Their drawbacks are that they are very volatile (and therefore difficult to deliver quantitatively) and photochemically and thermally unstable. Organic nitrites are excellent nitrosating agents, particularly for thiols (Eq. (17)). 

Owing to the susceptibility of indole, isoindole and pyrrole rings to oxidation (see Section 3.05.1.4) and acid-catalyzed dimerization and polymerization (see Section 3.05.1.2.2), the products of the reactions with nitrating and nitrosating agents are subject to the reaction conditions. 

In the past seven years N-nitrosamines have attracted wide attention due to their carcinogenic properties. In 1977, Ross et al. (67) reported the presence of N-nitrosodipropylamine in the formulation of dinitroaniline herbicide, trifluralin, at the 154 ppm level. Subsequent studies by other laboratories showed that nitrosamine impurities are common to all dinitroaniline-based herbicides. Nitrosamines contamination resulted from the nitration of dipropylamine by the excess nitrosating agent. 

The difference in the electron affinities, A E, approximately equal to k 5, necessary for the formation of the intermediate complex, depends to a great extent on the degree of steric accessibility and coordinative unsaturation of the nitrating and nitrosating agents. 

Monosubstituted hydrazines and hydrazides are converted into azides by a variety of nitrosating agents. The mildest reagent appears to be dinitrogen tetroxide, which can be used below 0 C in acetonitrile to convert benzoylhydrazine, p-toluenesulfonylhydrazine and 4-nitrobenzoylhydrazine, among others, into the corresponding azides in high yield. Another mild method involves the use of iron(lll) nitrate supported on clay. These reactions probably proceed by way of transient N-nitroso compounds (Scheme 19). 

Nitrosamines are formed whenever nitrosating agents come in contact with secondary amines. Indeed, more nitrosamines are probably synthesized within our body than enter it by environmental contamination. Enzyme-catalyzed reduction of nitrate (NOs ) produces nitrite (N02 ), which combines with amines present in the body to form A-nitroso amines. 

In biological systems, the presence of NO may affect proteins via nitration, nitrosation, or nitro-sylation. Nitration involves the addition of NOi. Although NO itself is not an effective nitrating agent, its metabolites like peroxynitrite or the NO2 radical may transform tyrosine residues into nitrotyrosine (Table 4). 

Electrochemically inactive organic compounds can be converted into an electrochemically active state by nitration, nitrosation, oxidation, hydrolysis, or some other preliminary chemical reaction, and can then be determined polarographically or voltammetrically. Examples of this are polarographic determinations of alkylbenzenesulfonates in natural water samples after extraction and nitration of the aromatic ring [77] and determinations of beta-receptor blocking agents in tablets after conversion to the corresponding V-nitroso derivatives [78]. 

---