Direct nitration of amines 205R 3 N+N 2 O 5CH 2 Cl 2
R 3 NNO 2 NO 3 (Eq. 5.10)
-20 °C to -30 °CFigure 5.24Tertiary alkylamines react with dinitrogen pentoxide in carbon tetrachloride at subambient
temperature to give tertiary alkylnitramine nitrate salts (Equation 5.10).^40
5.3.2.5 Dinitrogen tetroxide
Dinitrogen tetroxide can react as a nitrating or nitrosating agent depending on the conditions of
the reaction.^42 ,^43 Solutions of dinitrogen tetroxide in methylene chloride react with secondary
aliphatic amines at− 80 ◦C to give the nitramine and the nitrite salt of the amine without
appreciable nitrosamine formation.^42 At higher temperatures nitrosamine formation becomes
increasingly competitive and dominates at room temperature. The solvent appears to be impor-
tant; the reaction of diethylamine with dinitrogen tetroxide in diethyl ether at− 80 ◦C results in
a 1:1 mixture of nitramine and nitrosamine, whereas the same reaction in methylene chloride
exclusively yields the nitramine. The reaction of dinitrogen tetroxide with primary amines is
not a feasible route to primary nitramines due to competing deamination of both the starting
material and primary nitramine product, leading to alcohol and nitrate ester products.^42 ,^44
Solutions of dinitrogen tetroxide in carbon tetrachloride react with aliphatic cyclic and
acyclic tertiary amines between 0◦C and 45◦C to give nitrosamines via nitrosolysis.^45
5.3.2.6 Nitronium tetrafluoroborate
CH 2 Cl 2 , 20 °C
2 R^1 R^2 NH+NO 2 BF 4 R^1 R^2 NNO 2 +R^1 R^2 NH. HBF 4 (Eq. 5.11)Figure 5.25While nitramines are formed from the reaction of secondary amines with nitronium salts
the success of the reaction depends on the basicity of the amine (Equation 5.11).46–49Thus,
amines of low to moderate basicity areN-nitrated in good yields. The nitration of more
basic amines is slow and the nitrosamine is often observed as a significant by-product, a
consequence of the partial reduction of the nitronium salt to the nitrosonium salt during the
reaction.^48 Increased reaction temperature is also found to increase the amount of nitrosamine
formed.^48 The amine substrate is usually used in excess to compensate for the release of
the strong mineral acid formed during the reactions. Both nitronium tetrafluoroborate and
the more soluble hexafluorophosphate are commonly used forN-nitrations. Solvents like
acetonitrile, methylene chloride, nitromethane, dioxane, sulfolane, ethyl acetate and esters of
phosphoric acid are commonly used.
The reaction of nitronium salts with primary amines is not usually a feasible route to
primary nitramines, except in the case of some electron-deficient arylamines^50 ,^51. Picramide