Dinitrogen tetroxide in nitrosation

The nitrosations are usually carried out with conventional reagents. The most common procedures involve (a) sodium nitrite with acids in an aqueous system, (b) sodium nitrite in acetic anhydride, (c) nitrogen trioxide, (d) nitrosyl chloride in the presence of a base, and (e) dinitrogen tetroxide in the presence of a base. 

Five methods for the nitrosation of amides will be mentioned here. Of these, the methods using dinitrogen tetroxide appears to have the widest applicability in terms of the classes of amides which can be nitrosated and the purity of the products obtained. However, the other methods also have special utility. 

In view of the general applicability of dinitrogen tetroxide as a nitrosating agent for amides, the application of this reagent for reaction with other nitrogen compounds is strongly indicated. 

When the higher A,A -dialkyloxalamides were nitrosated with dinitrogen tetroxide, the resultant nitroso compounds were found to be red oils which tended to decompose when attempts were made to distill them. These compounds were, apparently, reasonably stable when stored in the cold in dark bottles. 

Dinitrogen tetroxide is the most versatile of the nitrosating reagents and, in addition, it is readily available. The nitro-soamide method of deamination gives far superior yields and much less skeletal isomerization than the nitrous acid method (which is essentially limited to aqueous media), and it leads to a greater retention of optical activity than the triazene method.8... 

Nitrolic acids, which can be isolated from sources such as nitroalkanes and aldoximes, are also probable intermediates in a wide variety of furoxan preparations involving nitric and nitrous acid, and nitrogen oxides. Diacylfuroxans have been synthesized via nitrosation of methyl ketones for example acetone reacts with anhydrous dinitrogen tetroxide or nitric acid/sodium nitrite to give diacetylfuroxan. 

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). 

Reagents for amination, nitrosation and nitration of tertiary alkylamines are discussed in the appropriate reviews listed in Sections 6.1.3.1.4 and 6.I.3.I.5. Tertiary amines can be nitrosated with dealkylation by dinitrogen tetroxide for example, 1-methylpiperidine gave 1-nitrosopiperidine (80%). lliis reaction probably starts by one-electron oxidation of the amine, the aminium ion then undergoing dealkylation. Other oxidative d ylations and dealkylations include the formation of iV-nitrosodibenzylamine in high yield from the acid chloride (PhCH2)2NCOCl and sodium nitrite and the conversion of the amine (43) into the nitramine (44) with nitric acid. ... 

Nitrosation in aprotic solvents is possible, either with an alkyl nitrite in the presence of an equivalent of acid, or with nitrosyl chloride (Bakke, 1967), or with dinitrogen tetroxide (Wudl and Lee, 1971 Barton and Narang, 1977). Doyle et al. (1978) generated nitrosyl chloride in situ by the reaction of titanium tetrachloride... 

The diazotisation of aniline in aqueous nitric acid has also been studied. At low acidities (below 0-2 m), nitrous anhydride is the most important reagent . At higher acidities the kinetics of the reaction are similar to those for equivalent concentrations of perchloric acid and the rate increases rapidly with acidity . This catalysis has been attributed to nitrosation by dinitrogen tetroxide (nitrosyl nitrate) , but other studies of catalysis by neutral nitrate salts indicate the contribution to the overall rate of nitrosation by dinitrogen tetroxide is slight It seems, therefore, that the reagents at high acidity are the nitrous acidium and nitrosonium ions, as for perchloric acid. 

Aryl azides can be obtained from A-nitrosation reaction of aromatic hydrazines, using nitrosation reagents such as nitrous acid, dinitrogen tetroxide, nitrosonium tetrafluorobo-rate and nitric oxide in the presence of oxygen (Scheme 3.40). The use of hydrazones is also possible. ... 

---