Dinitrogen nitrating agent

Solutions of dinitrogen tetroxide (the mixed anhydride of nitric and nitrous acids) in sulphuric acid are nitrating agents ( 4.3.2), and there is no doubt that the effective reagent is the nitronium ion. Its formation has been demonstrated by Raman spectroscopy and by cryoscopy ... 

Dinitrogen tetroxide is an effective Eriedel-Crafts nitrating agent (152) for aromatics in the presence of aluminum chloride, ferric chloride, or sulfuric acid (153). Dinitrogen pentoxide is a powerhil nitrating agent, even in the absence of catalysts, preferably in sulfuric acid solution (154). SoHd dinitrogen pentoxide is known to be the nitronium nitrate, (N02) (N02). The use of BE as catalyst has been reported (155). 

More obscure reagents used for 0-nitration include mixtures of phosphoric and nitric acids, and anhydrous nitric acid in which phosphorous pentoxide has been dissolved. The latter mixture contains dissolved dinitrogen pentoxide and is a powerful nitrating agent. A mixture of anhydrous nitric acid containing catalytic amounts of boron trifluoride has been reported to lead to the rapid 0-nitration of alcohols. "... 

A solution of dinitrogen tetroxide in sulfuric acid is also a powerful nitrating agent. In this medium dinitrogen tetroxide is ionized to nitronium and nitrosonium ions. Titov reported using a solution of dinitrogen tetroxide in oleum for the nitration of nitrotoluene to dinitrotoluene and then to trinitrotoluene, the two separate steps proceeding in 98 % and 85 % yields respectively. 

Dinitrogen tetroxide forms a stable complex with boron trifluoride but this is a weak nitrating agent. Aromatic nitrations with other Lewis acids have been reported, including AICI3, FeCls, TiCU, BCI3, PF3, BF3, AsFs and SbFs. i " ... 

The first use of dinitrogen pentoxide as an A-nitrating agent appears to have been for the conversion of aromatic amines to arylnitramines. Difficulties in preparing pure dinitrogen pentoxide meant that reactions with aliphatic amines were not properly examined for another 60 years. 

Von Runge and Triebs used a solution of dinitrogen pentoxide in chloroform for the N-nitration of both amides and imides. Solutions of dinitrogen pentoxide in chlorinated solvents are not neutral nitrating agents when amides and imides are nitrated - the presence of acidic N-H protons in these substrates leads to the formation of nitric acid. Sodium fluoride acts like a base towards nitric acid and so its addition to these reactions can increase product yield. Sodium acetate has been used for the same purpose during the nitration of n-butyl-V, V -dimethylurea. The effectiveness of dinitrogen pentoxide for the V-nitration of ureas is further illustrated by its use in the conversion of 2-imidazolidinone to N, V -dinitro-2-imidazolidinone in 90 % yield. In the presence of sodium fluoride the yield for this reaction exceeds 90 %. 

Solutions of dinitrogen pentoxide in chlorinated solvents. These are less active nitrating agents but much milder and more selective in their nitrations. These reactions are more controlled and usually very clean, nonoxidizing and, consequently, high yielding. With... 

In the solid state, dinitrogen pentoxide is ionic, existing as N02+N03 and sometimes called nitronium nitrate. The same is true of dinitrogen pentoxide in polar solvents like nitric acid where complete ionization to nitronium and nitrate ions is observed. In the vapour phase, and in nonpolar solvents, a covalent structure is observed. This dichotomy of behavior in both physical state and in solution means that no single nitrating agent is as diverse and versatile as nitrogen pentoxide. 

The complex formed between dinitrogen pentoxide and boron Uifluoride is a powerful nitrating agent and has been used in organic solvents like carbon tetrachloride, nitromethane and sulfolane for the nitration of deactivated aromatic substrates, including the conversion of benzoic acid to 1,3-dinitrobenzoic acid in 70% yield. Olah and co-workers" studied aromatic nitrations with dinitrogen pentoxide in the presence of other Lewis acids. 

The Af-nitration of urea and imide functionality is usually quite difficult compared to the analogous amides. Solutions of dinitrogen pentoxide in nitric acid are frequently employed to synthesize energetic Af, Af -dinitroureas. Yields are often very high and go to completion unlike with many conventional nitrating agents which frequently yield partially nitrated products. Energetic bicycles K-56 (16)" and K-55 (17)" have been prepared from the dihydrochloride salts (14) and (15) respectively. 

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