Chemistry of urea nitro derivatives: II. Synthesis of nitramide from N,N′-dinitrourea. New reactions of nitramide

Article abstract of DOI:10.1023/A:1015334703526

Study of the hydrolysis of N,N′-dinitrourea resulted in the development of convenient procedures for synthesizing nitramide on the basis of urea. New reactions of nitramide were examined.

Full text of DOI:10.1023/A:1015334703526

Russian Journal of Organic Chemistry, Vol. 38, No. 1, 2002, pp. 1 6. Translated from Zhurnal Organicheskoi Khimii, Vol. 38, No. 1, 2002,
pp. 11 16.
Original Russian Text Copyright
2002 by Lobanova, Il’yasov, Popov, Sataev.
Chemistry of Urea Nitro Derivatives:
II.* Synthesis of Nitramide from N,N -Dinitrourea.
New Reactions of Nitramide
A. A. Lobanova, S. G. Il’yasov, N. I. Popov, and R. R. Sataev
Altai Federal Research and Production Center, ul. Sotsialisticheskaya 1, Biisk, 659322 Russia
fax: (3854)226620
Received June 29, 2000
Abstract Study of the hydrolysis of N,N -dinitrourea resulted in the development of convenient procedures
for synthesizing nitramide on the basis of urea. New reactions of nitramide were examined.
Nitramide NH2NO2, which was synthesized more
sulfuric acid. The kap values no longer changed in
than 100 years ago [2], still attracts researchers’ atten- sulfuric acid solutions with a concentration greater
tion as a simplest reactive starting compound for
preparation of new structures, as the first member
of the nitramine homologous series, as starting com-
pound for synthesis of dinitramide, etc. Unfortunately,
all known procedures for synthesis of nitramide are
fairly complex, and they cannot ensure large-scale
preparation of this product.
than 0.05 N. Raising the medium acidity in the range
of H0 from 0.8 to 0.3kap resulted in increase of
kap, and further increase in H0 led to reduction of kap
(see figure). At a sulfuric acid concentration of more
than 60%, the contribution of the denitration process
becomes appreciable, and nitrourea can be isolated
from the reaction mixture:
Our previous study [1] on the synthesis of N,N -di-
nitrourea (I) and its properties showed that it readily
undergoes hydrolysis with formation of nitramide (II):
Nitramide is formed almost quantitatively in the
reaction of dinitrourea I with an equimolar amount of
water. However, pure dinitrourea I is a highly reactive
compound, which is extremely sensitive to mechanical
disturbance, so that work with this substance is dif-
ficult and hazardous. Therefore, it was necessary to
develop a convenient preparative procedure for syn-
thesis of nitramide. Study of the kinetics of hydrolysis
of dinitrourea I in water (c0 = 0.1 M) showed that the
apparent rate constant kap calculated on the assump-
tion of first order of the reaction depends on the
current dinitrourea concentration. A possible reason
may be considerable change of the acidity of the
medium in the course of hydrolysis since dinitrourea
is a strong acid. This was confirmed by the results of
Comparison of our results with the pKa value of
dinitrourea I in water (0.13 0.05; determined by
a series of experiments on hydrolysis of I in aqueous
____________
Plot of the apparent rate constants for hydrolysis of N,N -di-
nitrourea (I) versus acidity of the medium; 30 C.
*
For communication I, see [1].
1070-4280/02/3801-0001$27.00 2002 MAIK Nauka/Interperiodica

2
LOBANOVA et al.
Scheme 1.
the procedure described in [3]) suggests that the reac-
tive species in the hydrolysis is neutral molecule I
(Scheme 1). Water is not the only nucleophile in this
reaction. The formation of nitramide was also ob-
served in anhydrous solvents, which may be explained
by solvolysis.
Our results allowed us to develop several proce-
dures for preparation of nitramide on the basis of
extraction of compound I from aqueous solutions
by water-immiscible solvents, followed by hydrolysis.
As initial compounds we used urea, N,N -dinitrourea
(I), and salt Ia formed by urea and dinitrourea.
No systematic studies of the salt effect were carried
out. It was found that the rate of hydrolysis of dinitro-
urea in a 22% solution of ammonium nitrate is lower
by a factor of 2.1 2.2 than in pure water. In going
to a 40% solution of ammonium sulfate the rate of
hydrolysis decreases 15-fold. Here, the main factor is
likely to be ion exchange.
Salt Ia is stable, weakly sensitive to shock, and
poorly soluble in water; it is easy to store. In order
to obtain nitramide from compound Ia it is sufficient
to dissolve the latter in aqueous sulfuric acid, extract
dinitrourea into ether, and subject it to hydrolysis. In
any case the yield of nitramide is no less than 75%.
The procedure for preparation of nitramide from urea
without isolating intermediate products is the safest,
but the product always contains small amounts of
nitrourea and ethyl nitrocarbamate (which are formed
from dinitrourea); these impurities can be removed
only by reprecipitation and recrystallization.
This reaction can be regarded as a convenient route
to dinitrourea salts, which are poorly soluble in water
and hence can readily be isolated.
Water-saturated solvents with small dielectric con-
stants turned out to be attractive for carrying out
the hydrolysis of dinitrourea due to the possibility
for reducing its degree of dissociation and sufficient
stability of nitramide in these media (see table).
Apparent rate constants of the hydrolysis of N,N -dinitro-
urea (I) at 30 C
1
Solvent
[4]
[H2O], % kap 105, s
Using salt Ia as starting compound, highly pure
nitramide is obtained, which does not require addi-
tional purification. The product was identified by
the IR spectra and chemical transformations, such as
quantitative conversion into dinitramide by known
procedure [5] and condensation with formaldehyde
and ammonia to give dinitropentamethylenetetraamine
whose yield exceeds that reported in [6].
1,4-Dioxane
Ethyl acetate
Ethyl acetate
Acetone
Methyl isobutyl
ketone
2.2
6.0
6.0
4.9
1.7
3.3
4.9
34
55
62
51
20.7
13.7
36.2
1.9
4.9
39
50
Acetonitrile
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 38 No. 1 2002

CHEMISTRY OF UREA NITRO DERIVATIVES: II.
3
Scheme 2.
Having developed convenient methods for prepara-
tion of nitramide, we were able to focuse on some its
reactions, primarily on decomposition in acid medium.
The only identified products of nitramide decomposi-
tion in solutions of strong acids are nitrogen(I) oxide
and water [2, 7], although denitration of nitramide in
acid media was the subject of numerous studies.
In the course of decomposition of nitramide in
concentrated sulfuric acid at 0 5 C we succeeded in
detecting formation of up to 2.5% of nitric acid by
spectrophotometry. Above 20 C, no nitric acid could
be detected. We also failed to observe formation of
nitric acid when the decomposition was performed in
sulfuric acid with a concentration smaller that 90%.
Taking into account the composition of the products,
decomposition of nitramide in concentrated sulfuric
acid can be illustrated by the following scheme:
As early as 1895, Thiele and Lachman [2] reported
on the possibility for formation of nitric acid in the
course of decomposition of nitramide in acid medium.
Hopkinson and Csizmadia [8] performed a theoretical
analysis of the state of nitramide molecule protonated
We also found that nitramide is quite stable in con-
centrated acids at low temperature. When nitramide
was added to 94% sulfuric acid at 25 to 30 C,
20 min later the mixture contained up to 50% of the
initial compound which is capable of being involved
in various reactions. Nitramide readily reacts with
formaldehyde in 90% sulfuric acid to give a mixture
of products:
at the amino nitrogen atom; the authors revealed
+
lengthening of the N N bond, which suggests its
possible dissociation [8]. Nevertheless, even traces
of nitric acid were not detected. We have considered
possible ways of nitramide decomposition in acid
medium (Scheme 2) and presumed that the reaction
path leading to formation of nitric acid should be
favored by addition of a substrate capable of reacting
with nitric acid at a high rate. Such substrate may
be toluene, ethyl carbamate, and nitramide itself.
The reactions were carried out in concentrated sulfuric
acid or in its mixture with sulfur(VI) oxide. We found
that nitramide acts as nitrating agent.
Treatment of the resulting nitramine mixture with
potassium hydroxide in water leads to formation of
65% of methylenedinitramine dipotassium salt:
In the presence of ethyl acetate at 5 to 8 C the
yield of methylenedinitramine increases to 90%.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 38 No. 1 2002

4
LOBANOVA et al.
The apparent first-order rate constants were calcu-
lated using standard equation. Doubly distilled water,
purified and freshly distilled organic solvents, and
sulfuric acid of chemically pure grade were used in
experiments; N,N -dinitrourea was synthesized by the
procedure described in [1].
Alternatively, a solution of nitramide in ethyl
acetate can be used. The other solvents are ineffective.
The most important factor in the above reaction is
the nitramide formaldehyde ratio which should be
(2.8 3.0):1. Raising the amount of formaldehyde
leads to formation of 3,7-dinitro-1,5-dioxa-3,7-diaza-
cyclooctane (dioxaoctogen):
Preparation of nitramide from urea. Oleum
(20% of SO3), 35 g, was added to 35 g of nitric acid
(d = 1.5 g/cm3), and 10 g (0.1667 mol) of urea was
added in portions at 5 to 0 C under continuous stir-
ring. The mixture was stirred for 40 min at 0 to 5 C
and poured while stirring into 300 g of an ice water
mixture, maintaining the temperature below 10 C. The
mixture was extracted with ethyl acetate (2 100 ml
and 4 50 ml), and the extract was washed with water
(3 40 ml), kept for 2 h at 20 C, and evaporated to
dryness under reduced pressure. Yield 15.5 g (75%).
The product was dissolved in 30 ml of ether, the
solution was poured into 400 ml of hexane, and the
precipitate was filtered off. Additional recrystalliza-
tion from dichloroethane 2-propanol (9:1) gave 13 g
(63%) of nitramide with mp 78 C. UV spectrum
At a nitramide formaldehyde ratio of 1:2, dioxa-
octogen is formed in more than 80% yield.
An interesting reaction was that between nitramide
and acetic anhydride. Apart from decomposition,
the formation of N-nitroacetamide was observed
(yield 40%). Treatment of N-nitroacetamide with
an alcoholic solution of potassium hydroxide gives
a fairly stable salt:
1
(H2O): max = 206 nm, = 7600 l mol 1 cm .
Preparation of nitramide from dinitrourea. The
nitration of urea was carried out as described above.
After keeping for 40 min at 0 5 C, the mixture was
cooled to 12 C, and the precipitate of dinitrourea
was filtered off through a glass filter, washed with
cold methylene chloride (3 10 ml), and squeezed.
The product was dissolved in 300 ml of ether at 0 C
under continuous stirring, and the solution was
washed with water (2 20 ml), kept for 4.5 h at 20 C,
and evaporated to dryness under reduced pressure.
Yield 15 g (73%).
Acylation of nitramide with carboxylic acid an-
hydrides was not reported previously. This reaction
opens one more way of utilizing nitramide in the
synthesis of organic compounds.
Preparation of nitramide from the urea salt of
dinitrourea. Dinitrourea was synthesized following
the above procedure. A 13.6-g (0.09-mol) portion
of dinitrourea was added to a solution of 6.6 g
(0.11 mol) of urea in 12 ml of water at a temperature
not exceeding 20 C. The mixture was kept for 15 min
and cooled to 5 C, and the precipitate was filtered
off, washed with a small amount of ice water, and
dried in air. Yield of salt Ia 15.45 g (90%), mp 91
95 C (decomp.). The resulting salt was added in
small portions to a solution of 15 g of sulfuric acid
in 35 ml of water, stirred at 20 C. When the mixture
became homogeneous, it was extracted with ether
(3 60 ml), and the extract was left to stand for
4 h at room temperature and was then evaporated to
dryness under reduced pressure. Yield 8.24 g (90%),
mp 83 84 C (Boetius device), 81 82 C (in a capil-
EXPERIMENTAL
The IR spectra were recorded on a Specord M-80
instrument in KBr. The UV spectra were measured
on Specord UV-Vis and Specord M-40 spectrometers
in water.
Kinetic measurements. A sample of N,N -dinitro-
urea was dissolved in appropriate medium to attain
an initial concentration of 10 g/l. The solution was
stirred using a magnetic stirrer, maintaining the tem-
perature with an accuracy of 0.1 C. When necessary,
samples were withdrawn from the reaction mixture.
They were diluted with water, and the concentration
of dinitrourea was determined by spectrophotometry.
The concentration of dinitrourea (c) in the reaction
mixture was calculated by the equation c = M D n/ ,
where M is the molecular weight of dinitrourea, D
is the optical density, n is the dilution factor, and
lary), 79.7 C (DSC). UV spectrum (H2O):
=
max
1
1
= 13000 l mol 1 cm .
206 nm,
= 7680 l mol 1 cm .
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 38 No. 1 2002

CHEMISTRY OF UREA NITRO DERIVATIVES: II.
5
Hydrolysis of dinitrourea. Distilled water, 0.18 g
(0.01 mol), was added to 1.5 g (0.01 mol) of dinitro-
urea prepared by the procedure desribed in [1]. The
mixture was carefully stirred and was left to stand
for 8 h at room temperature. Initially, a moderate gas
evolution was observed. When the reaction was
complete, we isolated 1.21 g (98%) of nitramide,
mp 73 C. The product contained 99% of the main
substance (no dinitrourea impurity was detected by
spectrophotometry).
Decomposition of nitramide. Nitramide, 6.2 g
(0.1 mol), was carefully added over a period of 30 min
to 37 g of 94% sulfuric acid maintained at 5 C. The
mixture was kept for 3 h at that temperature and
poured into 100 ml of water. Spectrophotometric
94% sulfuric acid, and the mixture was kept for
45 min at 5 to 2 C. It was then poured onto ice,
and the oily substance was separated, washed with
water, and kept under reduced pressure until constant
refractive index. Yield of o-nitrotoluene 2.5 g (18%),
nD = 1.5448 [9].
Preparation of methylenedinitramine. A solution
of 1.5 g (0.05 mol) of paraformaldehyde in 30 ml of
90% sulfuric acid was added at 10 to 8 C to a solu-
tion of 9.3 g (0.15 mol) of nitramide (98.8% purity)
in 30 ml of ethyl acetate. The mixture was kept for
20 min at 8 to 5 C and poured into 100 ml of
water. The organic layer was separated, and the
aqueous layer was extracted with ethyl acetate
(3 50 ml). The combined extracts were washed with
water (2 40 ml), dried over magnesium sulfate, and
evaporated to dryness under reduced pressure. The
crystalline residue was evacuated for an additional
20 min. Yield 6.25 g (92%, calculated on the form-
aldehyde taken), mp 94 98 C. After recrystallization
from dichloroethane, mp 102 104 C (published data
[10]: mp 101 C).
analysis revealed the presence of nitric acid,
=
max
1
203 nm, = 9000 l mol 1 cm , 0.16 g (2.5%). For
comparison, we also analyzed by spectrophotometry
a solution of 94% sulfuric acid and a solution of
nitramide decomposition products in 80% H2SO4.
No absorption was observed in the range 200 210 nm.
Preparation of dinitramide. Nitramide, 6.2 g
(0.1 mol), was added in small portions to 33 g of
oleum (20% of SO3) at 30 C. After 10 min, a 1-ml
portion of the mixture was withdrawn and poured into
25 ml of water; dinitramide was detected by spectro-
Preparation of a mixture of methylenedinitr-
amine and 1,3,5-trinitro-1,3,5-triazapentane. Nitr-
amide, 3.31 g, was added in portions at 5 C to
a solution of 0.6 g of paraformaldehyde in 20 ml of
90% sulfuric acid. The mixture was kept for 10 min at
5 to 0 C and poured into 50 ml of water containing
ice. The precipitate was filtered off, washed with
a small amount of cold methanol and with ether, and
dried. Yield of 1,3,5-trinitro-1,3,5-triazapentane 0.5 g,
mp 130 133 C (decomp.). After repeated treatment
with ice-cold ether, the melting point rose to 153
1
photometry, max = 285 nm, = 5670 l mol 1 cm .
Nitration of urea. Nitramide, 18.6 g (0.3 mol),
was added in portions over a period of 1 h to a solu-
tion of 6 g (0.1 mol) of urea in a mixture of 40 ml of
94% sulfuric acid and 10 ml of 30% oleum, main-
tained at 5 C. After 10 min (from the reaction start),
1
nitrourea was detected by spectrophotometry,
=
154 C. IR spectrum, , cm : 3360 (N H); 3040,
max
260 nm (pH 8). After 45 min, the mixture was poured
into ice water, and the precipitate was filtered off. The
filtrate was extracted with ethyl acetate (5 50 ml),
and the precipitate was dissolved in the extract. The
extract was washed with water, dried over MgSO4,
and evaporated to dryness. Yield of nitrourea 1.3 g
(12%), mp 154 159 C (with decomposition).
Nitration of ethyl carbamate. Nitramide, 12.4 g
(0.2 mol), was added in small portions at 0 5 C to
a solution of 8.9 g (0.1 mol) of ethyl carbamate in
30 ml of 94% sulfuric acid. The mixture was kept for
30 min, poured into an ice water mixture, and ex-
tracted with ether (5 50 ml). The extract was washed
with water, dried over MgSO4, and evaporated. Yield
of ethyl N-nitrocarbamate 2 g, mp 61 62 C (pub-
lished data [2]: mp 64 C).
2920 (CH2); 1600, 1550 (NO2). Found, %: C 10.8;
H 3.0; N 39.8. C2H6N6O6. Calculated, %: C 11.42;
H 2.85; N 40.0.
The filtrate was extracted with ethyl acetate
(3 50 ml). The extract was washed with water, dried
over magnesium sulfate, and evaporated under
reduced pressure to obtain 1 g of methylenedinitra-
mine with an impurity of 1,3,5-trinitro-1,3,5-triaza-
1
pentane (a characteristic sharp peak at 3360 cm in
the IR spectrum), mp 104 109 C. By fractional crys-
tallization from acetone ether we isolated 0.3 g of
1,3,5-trinitro-1,3,5-triazapentane with mp 130 135 C.
Evaporation of the organic phase under reduced pres-
sure gave 0.6 g of methylenedinitramine, mp 102
104 C. The overall yield of the condensation products
was 65%. The yield of purified 1,3,5-trinitro-1,3,5-tri-
azapentane was 35%.
Nitration of toluene. Nitramide, 18.6 g (0.3 mol),
was added over a period of 1.5 h at 15 to 10 C to
a solution of 9.2 g (0.1 mol) of toluene in 40 ml of
Preparation of 3,7-dinitro-1,5-dioxa-1,7-diaza-
cyclooctane. To a solution of 3 g (0.1 mol) of para-
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 38 No. 1 2002

6
LOBANOVA et al.
formaldehyde in 18 ml of 90% sulfuric acid we added
15 ml of ethyl acetate and, at 12 to 10 C, 3.1 g
(0.05 mol) of nitramide. The mixture was kept for
30 min at 10 to 5 C and poured into 60 ml of water
containing ice. The solvent was evaporated under
reduced pressure, and the precipitate was filtered off,
washed with water, and dried. Yield 4.3 g (80%),
mp 264 266 C (decomp., from acetone); published
data [11]: mp 263 264 C.
under the title Konstanty ionizatsii kislot i osnovanii,
Moscow: Khimiya, 1964, p. 64.
4. Gordon, A.J. and Ford, R.A., The Chemist’s Compa-
nion, New York: Wiley, 1972. Translated under the
title Sputnik khimika, Moscow: Mir, 1976, pp. 12 21.
5. Luk’yanov, O.A., Shvedova, S.N., Shepelev, E.V.,
Varfolomeeva, O.N., Milkina, N.N., and Tartakov-
skii, V.A., Izv. Akad. Nauk SSSR, Ser. Khim., 1996,
no. 6, pp. 1569 1570.
6. Richmond, H.H., Myers, G.S., and Wright, G.F.,
J. Am. Chem. Soc., 1948, vol. 70, no. 11, pp. 3659
3665.
Preparation of N-nitroacetamide. Nitramide,
1.86 g (0.03 mol), was dissolved at 18 20 C in 40 ml
of acetic anhydride, and the solution was kept for
2 days. The solution was evaporated to dryness under
reduced pressure at a temperature not exceeding 40 C.
Yield 1.12 g (36%), mp 81 82.5 C; published data
[12]: mp 79 C. Found, %: C 23.2; H 4.0; N 28.4.
C2H4N2O3. Calculated, %: C 23.08; H 3.87; N 26.92.
7. Hughes, M.N. and Wimbldon, P.E., Inorg. Chim.
Acta, 1982, vol. 65, no. 4, pp. 129 130.
8. Hopkinson, A.C. and Csizmadia, J.L., Theor. Chim.
Acta, 1974, vol. 34, pp. 93 103.
9. Khimicheskaya entsiklopediya (Chemical Encyclo-
paedia), Moscow: Bol’shaya Rossiiskaya Entsiklo-
pediya, 1992, p. 559.
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