Direct nitration of amines 197The directN-nitration of the amino groups of the hexahydrotriazine (23) is only possible due
to the inherent low basicity of the methylenediamine functionality.^19 The methylenediamine
unit is present in many cyclic and bicyclic polyamines and these are potential precursors to
energetic polynitramines. Unfortunately, this route to polynitramines is rarely possible because
such polyamines are usually intrinsically unstable and will readily equilibrate to a lower en-
ergy, less strained system. For the same reason, polyamines containing the methylenediamine
functionality are difficult to prepare and isolate, often rapidly decomposing in both aqueous and
acidic solution. A far more common route involves the preparation ofN-protected versions
of the polyamine followed by ‘nitrolysis’ (Section 5.6). Even so, examples of heterocyclic
methylenediamineN-nitration exist.
N
HH
NH
NN
HF 3 CF 3 CF 3 CF 3 CF 3 CF 3 CCF 3CF 3CF 3CF 3NH
N NN
HCF 3CF 3NO 2NO 2NN NNF 3 CF 3 CCF 3CF 3
NO 2NO 2 NO 2HNN NNNO 2 NO 2NO 2 NO 2100 % HNO 325 262728HNO 3 , Ac 2 O
88 %HNO 3 , P 2 O 542 %67 %Figure 5.103,3,7,7-Tetrakis(trifluoromethyl)-2,4,6,8-tetraazabicyclo[3.3.0]octane (25) is an interesting
example.^20 This polyamine can be isolated as the free base and is fairly stable because of the
‘gem-dimethyl effect’. Stability is further enhanced by the replacement of the methyl protons
with fluorine atoms. The introduction of the first nitro groups into (25) requires particular
care and a low nitration temperature, and even then, the yield is low (42 %) because of acid-
catalyzed ring-opening. These nitro groups protect (26) from further ring-opening and so more
vigorous nitrating conditions are employed for the synthesis of the tetranitramine (28).
N
HH
NN
HH
NNON N
O
N N NON N
O
NNO 2N
NO 2NNO 2
NNO 2TFAA, HNO 329
30or
N 2 O 5 in 100 % HNO 3Figure 5.11TheN-nitration of the furazan-based heterocycle (29) has been reported.^21 The corre-
sponding tetranitramine (30) is an unstable substance, but obtained on treating (29) with either
trifluoroacetic anhydride (TFAA) in nitric acid or dinitrogen pentoxide in nitric acid. In this
case the furazan rings stabilize the 1,4,5,8-tetraazadecalin structure and further reduce the
basicity of the amidine amino groups. A number of other furazan and nitrogen-rich nitramines