220 Synthetic Routes toN-Nitro
5.6.2.3 Methylenediamines
Methylenediamines are readily synthesized from the reaction of secondary amines with
formaldehyde. Many aliphatic amines are too basic for direct nitration without a chloride cata-
lyst, and even then, nitrosamine formation can be a problem. Their conversion into intermediate
methylenediamines before nitration is therefore a useful route to secondary nitramines. The
success of these nitrolysis reactions is attributed to the inherent low basicity of the methylene-
diamine nitrogens.
NNO 2O 2 N NO 2NNNNNO 2NO 2O 2 NO 2 NN
NNN3
(RDX)NN4
(HMX)104+NH 4 NO 3 ,
Ac 2 O, HNO 3Figure 5.51The most important nitrolysis reaction to date is the formation of RDX (3) and HMX (4) from
the caged methylenediamine known as hexamine (104). These important military explosives
were first mass manufactured by this route towards the end of the Second World War and they
are still prepared by this route today. The process uses a mixture of acetic anhydride, ammonium
nitrate and nitric acid. The nitrolysis of hexamine is one of the most widely studied reactions
in the history of explosives. Many other cyclic and linear polynitramines have been isolated
from these reactions and this rich chemistry is discussed in more detail in Section 5.15.
N
C
H 2NNNO 2O 2 N NO 2(CH 2 )N
NNNO 2 N NO 2O NO
ONNO 2
NH 4 NO 3 , Ac 2 O,
HNO 3 , 55 °Cnn
n = 2 or 3+
105106Figure 5.52Chapman^113 studied the nitrolysis of symmetrical methylenediamines. The nitrolysis of
N, N, N′,N′-tetramethylmethylenediamine with nitric acid–acetic anhydride–ammonium nitrate
mixtures gives both dimethylnitramine and RDX; the latter probably arises from the nitrol-
ysis of hexamine formed from the reaction of ammonium nitrate and formaldehyde released
from the hydrolysis of the methylenediamine. The same reaction with some morpholine-based
methylenediamines (105) allows the synthesis of 1,3,5-trinitro-1,3,5-triazacycloalkanes (106).
NNNNO 2 NO 2 NO 2
NNO 2NTFAA, HNO 321 %
107 1083Figure 5.53