...
JWBK121-09 October 11, 2006 21:24 Char Count= 0356 Dinitrogen Pentoxide – An Eco-Friendly Nitrating Agentthe form of zinc chloride or the hydrochloride salt of the amine does allow theN-nitration
of more basic amines under acid conditions.^46 Such a route has been used to synthesize
many energetic polynitramine explosives. The powerful nitrating agent composed of 20–30%
dinitrogen pentoxide in nitric acid has found extensive use in this respect.N
HH
NN
HH
NNON N
O
N NNNNNON N
O
N
NO 2 NO 2NO 2 NO 212
13N 2 O 5 , 100 % HNO 3Figure 9.9The furazan-based heterocycle (12) isN-nitrated to the corresponding nitramine (13) with
nitrogen pentoxide in nitric acid without chloride catalyst because of the inherent low basicity
of the methylenediamine functionality.^47N
HH
NN
HH
N
O
NNNN
ONO 2
16NO (^2) NO
2
NO 2
(K-56)
14
. 2HCl N
H
H
NH
NN
HO. 2HCl N
NNNOO 2 NO 2 NNO 2NO 2
17
(K-55)15Figure 9.10TheN-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 energeticN,N′-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)^48 and K-55 (17)^49 have been prepared from the dihydrochloride
salts (14) and (15) respectively.NNNNONO 2
19
(DINGU)O
N
HH
NH
NN
HOO18or
HNO 3 , H 2 SO 4HHO 2 NNNNNONO 2NO 220
(TNGU)OO 2 NO 2 N100 % HNO 3 HNO 3 , P 2 O 5Figure 9.11The synthesis of 1,3,4,6-tetranitroglycouril (20) (TNGU or Sorguyl) uses a mixture of
phosphorous pentoxide in absolute nitric acid to effect the nitration of 1,4-dinitroglycouril
(DINGU) (19).^50 This reagent is a convenient but crude source of dinitrogen pentoxide in
nitric acid when the pure reagent is not readily available.