212 Synthetic Routes toN-Nitro
5.5.2.1 Dinitrogen pentoxide
Von Runge and Triebs^81 used a solution of dinitrogen pentoxide in chloroform for theN-
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.^82
Sodium acetate has been used for the same purpose during the nitration ofn-butyl-N, N′-
dimethylurea.^83 The effectiveness of dinitrogen pentoxide for theN-nitration of ureas is further
illustrated by its use in the conversion of 2-imidazolidinone toN, N′-dinitro-2-imidazolidinone
in 90 % yield.^82 In the presence of sodium fluoride the yield for this reaction exceeds 90 %.
Solutions of dinitrogen pentoxide in methylene chloride or chloroform have been used for
theN-nitration of the sodium salts of someN-alkylsulfamides.^84 Sulfonamide substrates with
both alkyl and aryl substituents areN-nitrated in excellent yields with this reagent. Aromatic
ring nitration occurs when aryl substituents are present.
A practical application of dinitrogen pentoxide in methylene chloride reagent involves the
nitration of either ammonium carbamate or nitrourethane, followed by ammonolysis to yield
ammonium dinitramide, an energetic oxidizer with enormous potential for use in future high
performance propellant compositions.^85 This important reaction is discussed in more detail in
Chapter 9.
5.5.2.2 Nitronium salts
Olsen and co-workers^46 used a solution of nitronium tetrafluoroborate in acetonitrile for
theN-nitration of acetamides and urethanes at− 30 ◦C. The following nitramides were ob-
tained by this method:N-nitroacetamide (13 %),N-nitro-2-chloroacetamide (55 %),N-nitro-
n-butylacetamide (40 %),N-nitrobenzamide (53 %), ethylN-nitro-n-butylcarbamate (91 %)
andN-nitrosuccinimide (43 %). The low yield ofN-nitroacetamide, a primary nitramide, is
attributed to competing hydrolysis due to the release of tetrafluoroboric acid as the reaction
progresses. The scope of the reaction is improved by moving to more basic solvents like ethyl
acetate, 1,4-dioxane and trimethyl phosphate.^86
NNNN NNO ONO 2NO 2NNNNNNO ONO 2NO 2
74 75NO 2NO 2O 2 NO 2 NNO 2O 2 N NO 2H
NO 2 BF 4 , CH 3 CN73 %Figure 5.39Boyer and co-workers^87 used a solution of nitronium tetrafluoroborate in acetonitrile for
the introduction of the final nitro group into the energetic dinitrourea (75).
5.5.2.3 Other nitrating agents
A number of reagents derived from nitrate salts and acid anhydrides have been reported for
theN-nitration of amides and related compounds. Crivello^88 first reported the use of metal
nitrates in trifluoroacetic anhydride (TFAA) for the nitration of aromatic systems. Chapman