Nitric acid nitrosation

The theory that the catalysed nitration proceeds through nitrosation was supported by the isolation of some />-nitrosophenol from the interrupted nitration of phenol, and from the observation that the ortho.-para ratio (9 91) of strongly catalysed nitration under aqueous conditions was very similar to the corresponding ratio of formation of nitrosophenols in the absence of nitric acid. ... 

Nitration at the encounter rate and nitrosation As has been seen ( 3.3), the rate of nitration by solutions of nitric acid in nitromethane or sulpholan reaches a limit for activated compounds which is about 300 times the rate for benzene imder the same conditions. Under the conditions of first-order nitration (7-5 % aqueous sulpholan) mesitylene reacts at this limiting rate, and its nitration is not subject to catalysis by nitrous acid thus, mesitylene is nitrated by nitronium ions at the encounter rate, and under these conditions is not subject to nitration via nitrosation. The significance of nitration at the encounter rate for mechanistic studies has been discussed ( 2.5). 

The evidence outlined strongly suggests that nitration via nitrosation accompanies the general mechanism of nitration in these media in the reactions of very reactive compounds.i Proof that phenol, even in solutions prepared from pure nitric acid, underwent nitration by a special mechanism came from examining rates of reaction of phenol and mesi-tylene under zeroth-order conditions. The variation in the initial rates with the concentration of aromatic (fig. 5.2) shows that mesitylene (o-2-0 4 mol 1 ) reacts at the zeroth-order rate, whereas phenol is nitrated considerably faster by a process which is first order in the concentration of aromatic. It is noteworthy that in these solutions the concentration of nitrous acid was below the level of detection (< c. 5 X mol... 

Thus, strong arguments against all of the obvious nitrating species acting alone can be found. However, as has been pointed out, the extent to which ions require solvation by nitric acid molecules in this medium is unknown, and such solvation would influence the apparent order with respect to the stoichiometric nitric acid. The possibility also exists that more than one mechanism of nitration, excluding nitrosation, is operative. 

Alloxan forms an oxime (1007) which is the same compound, violuric acid, as that formed by nitrosation of barbituric acid likewise, a hydrazone and semicarbazone. Reduction of alloxan gives first alloxantin, usually formulated as (1008), and then dialuric acid (1004 R = OH) the steps are reversible on oxidation. Vigorous oxidation with nitric acid and alkaline hydrolysis both give imidazole derivatives (parabanic acid and alloxanic acid, respectively) and thence aliphatic products. Alloxan and o-phenylenediamine give the benzopteridine, alloxazine (1009) (61MI21300). 

Nilrosated fluoro compounds are frequently prepared by electrophilic nitrosation on an electron-nch center of oxygen, nitrogen, or carbon The preparation of fluorochloronitronitrosomethane from the decarboxylation of fluorochloronitro-acetic acid in nitric acid is unique [f ] (equation 1)... 

Zingiberene also forms a nitrosate, C,5H24. N2O4, when the sesquiterpene dissolved in an equal volume of glacial acetic acid, is cooled to 0°, and ethyl nitrite, and then nitric acid added. The nitrosate is dissolved in acetic ether and precipitated with alcohol. It forms a yellow powder, melting with decomposition at 86°. 

As already mentioned, Bunton and Halevi (Ref 38) found that ca 60% nitric acid requires the presence of nitrous acid for it to be a nitrating agent. Ingold et al (Ref 36c) postulated the action of nitrous acid to proceed via reactions 9, 10 11. Now in competition with reaction 11, there may be a nitrosation reaction ... 

Recently it has been claimed (Ref 42) that PA may be prepd by nitrosating phenol with Na nitrate and Oxidizing the resulting nitrosophenols with nitric acid,... 

A kinetic study of nitration by nitric acid in carbon tetrachloride has been briefly reported and is of interest because of the third-order dependence of rate upon nitric acid concentration, for nitration of N-methyl-N-nitrosoaniline. This is believed to arise from equilibria (28) and (29) below, which give rise to a nitrosating species and nitration is achieved through subsequent oxidation of the nitrosated aromatic69. 

For a given concentration of nitrous acid, the first-order rate coefficients increase as the sixth to seventh power of the nitric acid concentration and this catalysed nitration is presumed to be nitrosation followed by oxidation, reactions (41) and (42), viz. 

The kinetics of aromatic nitrosation at ring carbon have received little attention. The first attempt to determine the nature of the electrophile was made by Ingold et a/.117, who measured the rates of the nitrous acid-catalysed nitration of 4-chloroanisole by nitric acid in acetic acid which proceeds via initial nitrosation of the aromatic ring. Assuming that the electrophiles are the nitrosonium ion and... 

A further point of preparative significance still requires explanation, however. Highly reactive aromatic compounds, such as phenol, are found to undergo ready nitration even in dilute nitric acid, and at a far more rapid rate than can be explained on the basis of the concentration of N02 that is present in the mixture. This has been shown to be due to the presence of nitrous acid in the system which nitrosates the reactive nucleus via the nitrosonium ion, NO (or other species capable of effecting nitrosation, cf. p. 120) ... 

The sulfonation-nitration strategy also provides a route to styphnic acid (5) (2,4,6-trinitroresorcinol) from resorcinol (22) but the control of temperature in this reaction is very important. The synthesis of styphnic acid (5) from the nitration of 2,4-dinitroresorcinol (24) with mixed acid or concentrated nitric acid is a higher yielding route. 2,4-Dinitroresorcinol (24) is conveniently prepared from the nitrosation of resorcinol (22) followed by oxidation of the resulting 2,4-dinitrosoresorcinol (23) with dilute nitric acid. 2,4-Dinitrosoresorcinol (23) also generates styphnic acid (5) on treatment with concentrated nitric acid. ... 

Trinitrophloroglucinol has been synthesized via the nitrosation of phloroglucinol followed by nitric acid oxidation. The direct nitration of phloroglucinol must be conducted at subambient temperature to avoid excessive oxidation, and even then, the yield rarely exceeds 70... 

Wilier and Atkins used solutions of 30 % nitrogen pentoxide in nihic acid for the nitrolysis of 1,3-dinitrosoamines (28) the latter synthesized from the reaction of 1,3-diamines with formaldehyde followed by in situ nitrosation of the resulting 1,3-diazacycles. Cychc, bicychc and spirocyclic polynitramines like (30), (31) and (32) have been synthesized via this method. Incomplete niholysis is observed when absolnte nitric acid alone is used in these reactions. 

Triamterene Triamterene, 2,4,7-triamino-6-phenylpteridine (21.5.13), is synthesized in by the following scheme. Reacting guanidine with malonodinitrile gives 2,4,6-triaminopyrimi-dine (21.5.11). This undergoes nitrosation by reacting it with nitric acid, which results in the... 

Nitrosation of glycoluril derivatives has also been reported by simple exposure to nitric acid and sodium nitrite (Equation 11) <1998RJOC34>. 

According to White [38a], nitrosation involving the use of dinitrogen tetroxide ( nitrogen tetroxide ) represents the most general method of nitrosating amides. The method is quite rapid, yields are high, and purity of products is excellent. Since nitric acid is a coproduct of the reaction, the normal procedure involves the use of an excess of anhydrous sodium acetate as a base. If the base is not added, dinitrosation takes place. 

The method of preparation given by Hartman and Phillips [51] involves nitrosation with sodium nitrite and ice-cooled nitric acid as the acid. The method has been adopted by other workers for related derivatives [52, 53]. 

It has been established that cyclotrimethylenetrinitrosoamine (II), a product of the nitrosation of hexamethylenetetramine, is oxidized with nitric acid (about 40%) to cyclonite (I). This confirms the structure of cyclonite. 

Amines and amides can be N-nirra/erf549 with nitric acid,55" N205,551 or N02, 552 and aromatic amines can be converted to triazenes with diazonium salts. Aliphatic primary amines can also be converted to triazenes if the diazonium salts contain electron-withdrawing groups.555 C-Nitrosation is discussed at 1-3 and 2-8. 

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