Secondary amines reactions with nitrous acid

Secondary Amines, Nitroso Amines.—When a secondary amine reacts with nitrous acid the reaction is entirely different. A compound containing the group (—NO), in place of the one hydrogen of the amine and known as a nitroso amine is formed. 

The test makes use of one of the classic procedures for the distinction between primary, secondary, tertiary, and quaternary amines, reaction with nitrous acid and coupling with P-napthol. 

Cycloaliphatic amines are strong bases with chemistry similar to that of simpler primary, secondary, or tertiary amines. Upon reaction with nitrous acid,... 

Reaction with Nitrous Acid. Primary, secondary, and tertiary aromatic amines react with nitrous acid to form a variety of products. Primary aromatic amines form diazonium salts. ... 

In Table 1 is a list of the environmental secondary and tertiary amines which have been tested by feeding to rats together with nitrite. Of these, several react very readily with nitrite in acid solution, but some, for example phenmetrazine (2 , 27), give rise to a noncarcinogenic N-nitroso derivative. On the other hand, aminopyrine reacts extremely readily with nitrous acid, although it is a tertiary amine, and forms the potent carcinogen nitrosodimethylamine in high yield (28, ). The other amines vary considerably in the extent to which they form N-nitroso derivatives by reaction with nitrous acid, especially at the relatively low concentrations which model human exposure more closely... 

Chemical classification of the amine function. The classification of primary, secondary or tertiary amines should be carried out by means of the reaction with nitrous acid. 

Nitrosamine and para Nitroso Methyl Aniline.—The reaction with nitrous acid is characteristic of secondary amines and yields phenyl methyl nitrosamine, the nitroso group entering the amino radical. This, however, undergoes rearrangement with the transference of the nitroso group to the ring yielding a nitroso benzene compound. 

In water, tertiary amines form quaternary ammonium compounds, e. g. with methyl halogenides. In aqueous solution, secondary (aliphatic and aromatic) amines react with nitrous acid HONO (namely the nitrosonium ion NO ) as already mentioned (reaction 5.217) to generate nitrosamines ... 

Secondary amines, whether aliphahc or aromahc, undergo reaction with nitrous acid to give N-nitrosamines, as illustrated by the reachon of piperidine with nitrous acid. 

Nitrosation (Section 22 15) The reaction of a substance usu ally an amine with nitrous acid Pnmary amines yield dia zonium 10ns secondary amines yield N nitroso amines Tertiary aromatic amines undergo nitrosation of their aro matic ring... 

If primary or secondary amines are used, A/-substituted amides are formed. This reaction is called aminolysis. Hydra2ines yield the corresponding hydra2ides, which can then be treated with nitrous acid to form the a2ides used in the Curtius rearrangement. Hydroxylamines give hydroxamic acids. 

Ring nitrosation with nitrous acid is normally carried out only with active substrates such as amines and phenols. However, primary aromatic amines give diazonium ions (12-47) when treated with nitrous acid, " and secondary amines tend to give N-nitroso rather than C-nitroso compounds (12-49) hence this reaction is normally limited to phenols and tertiary aromatic amines. Nevertheless secondary aromatic amines can be C-nitrosated in two ways. The N-nitroso compound first obtained can be isomerized to a C-nitroso compound (11-32), or it can be treated with another mole of nitrous acid to give an N,C-dinitroso compound. Also, a successful nitrosation of anisole has been reported, where the solvent was CF3COOH—CH2CI2. " ... 

When secondary amines are treated with nitrous acid, N-nitroso compounds (also called nitrosamines) are formed. The reaction can be accomplished with dialkyl-, diaryl-, or alkylarylamines, and even with mono-N-substituted amides RCONHR -I-HONO RCON(NO)R. Tertiary amines have also been N-nitrosated, but in these cases one group cleaves, so that the product is the nitroso derivative of a secondary amine.The group that cleaves appears as an aldehyde or... 

Reaction of amines with nitrous acids Primary Secondary Primary RNH2 + HONCM>N2 + other products Secondary R2NH + HONO—>R2N—NO... 

Secondary amines. The reaction of secondary amine type compounds with nitrous acid (HO NO) has been reviewed extensively by Turney and Wright (17), Ridd (18), Scanlan (19) and Mirvish (20). In a system containing (HO NO) as the nitrosating agent, the possible nitrosyl carriers are (H2O NO), (NO2 NO) and (NO+). The reactivity of (NO+) is very low and it is not considered an effective nitrosating form. Nitrous acidium ion (H2O NO+) plays a significant role only at concentrated acidic condi tions. Therefore, it seems likely that at the dilute acidic conditions that are encountered in the environment, it is nitrous anhydride (N2O3 = NO2 NO) which nitrosates secondary amines. 

Chemists have long been aware that amines can react with various nitrosating agents, under a variety of conditions, to form a wide array of N-nitroso derivatives (1 ). It was generally assumed that only secondary amines can effectively form stable N-nitrosamines. However, it has now become apparent that primary and tertiary amines, as well as tetraalkylammonium salts, can all form N-nitroso derivatives under the appropriate reaction conditions (2-10). It has also become apparent that there are several mechanisms possible for the formation of the most common N-nitroso derivatives. Thus, in addition to the more customary reaction of an amine with nitrous acid, N-nitroso derivatives can also form via the reaction of an amine with NO (NO2, N2O3, N2O4) ( ). Amines can also be transnitrosated with already formed N-N-nitroso or C-nitro compounds via a transnitrosation reaction, they can be converted into their N-nitroso derivatives ). 

On treatment of certain other tertiary aromatic amines with nitrous acid, it has been found that either C-nitroso compounds, nuclear nitro compounds, or jV-nitrosoamines are formed with loss of an alkyl group. In the case of the nitrodimethylanilines, the latter two types of reaction may occur. The formation of nitro-jV-nitrosomethylanilines predominate at room temperature, whereas the formation of polynitro compounds predominates at more elevated temperatures. The formation of nitrosoamines from iVW-dimethylanilines appears to be particularly favored when both ortho positions are occupied by nitro groups, although /V-nitroso compounds were also obtainable from other nitrodimethylanilines. The product of the reaction, of course, is an /V-nitroso secondary amine. 

Some of the most important reactions of amines are brought about by nitrous acid (HONO). The character of the products depends very much on whether the amine is primary, secondary, or tertiary. In fact, nitrous acid is a useful reagent to determine whether a particular amine is primary, secondary, or tertiary. With primary amines nitrous acid results in evolution of nitrogen gas with secondary amines insoluble yellow liquids or solid 7V-nitroso compounds, R2N—N=0, separate tertiary alkanamines dissolve in and react with nitrous acid solutions without evolution of nitrogen, usually to give complex products ... 

When oxides of nitrogen come in contact with water, both nitrous and nitric acids are formed (18) (Table IV). Toxic reactions may result from pH decrease. Other toxic reactions may be a consequence of deamination reactions with amino acids and nucleic acid bases. Another consideration is the reactions of oxides of nitrogen with double bonds (Table IV). The cis-trans isomerization of oleic acid exposed to nitrous acid has been reported (19). Furthermore, the reaction of nitrogen dioxide with unsaturated compounds has resulted in the formation of both transient and stable free radical products (20, 21) (Table V). A further possibility has been raised in that nitrite can react with secondary amines to form nitrosamines which have carcinogenic properties (22). Thus, the possible modes of toxicity for oxides of nitrogen are numerous and are not exhausted by this short list. 

Nitroxyl forms nitrous oxide, and the secondary amine reacts with more nitrous acid giving the nitrosamine. Based on the observed isotope effect, the rate-determining step was thought to be the loss of HNO. Nitrous oxide is believed to arise from elimination of nitroxyl in many other reactions. 

The reaction of aromatic amines with nitrous acid is of considerable importance and the formation of diazonium salts from the primary amines is discussed in detail in Section 8.6. Reaction of nitrous acid with secondary amines does not give diazonium salts, but results instead in A -nitrosation. Tertiary amines such as A, A -dimethylaniline do not N-nitrosate, but undergo electrophilic substitution by the nitrosonium cation (NO ) to give A, A -dimethyl-4-nitrosoaniline (Scheme 8.8). 

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