Nitration of glycoluril derivatives in liquid carbon dioxide

Article abstract of DOI:10.1016/j.mencom.2015.01.004

Dinitroglycolurils and 1,4,6-trinitrohexahydroimidazo[4,5-d]imidazol-2(1H)-one were prepared in 56-89% yield by N-nitration of the corresponding glycoluril precursors with dinitrogen pentoxide in liquid carbon dioxide.

Full text of DOI:10.1016/j.mencom.2015.01.004

Mendeleev
Communications
Mendeleev Commun., 2015, 25, 15–16
Nitration of glycoluril derivatives in liquid carbon dioxide
Mikhail N. Zharkov, Ilya V. Kuchurov, Igor V. Fomenkov, Sergei G. Zlotin* and Vladimir A. Tartakovsky
N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, 119991 Moscow, Russian Federation.
Fax: +7 499 135 5328; e-mail: zlotin@ioc.ac.ru
DOI: 10.1016/j.mencom.2015.01.004
Dinitroglycolurils and 1,4,6-trinitrohexahydroimidazo[4,5-d]imidazol-2(1H)-one were prepared in 56–89% yield by N-nitration of
the corresponding glycoluril precursors with dinitrogen pentoxide in liquid carbon dioxide.
NO2
Dinitroglycoluril 1a is a high-energy (velocity of detonation,
R
R
H
N
H
N
H
N
~7580 m s–1, d = 1.99 g cm–3), termally (deflagration temperature,
225–250°C) and hydrolytically stable explosive that is used
in a low-sensitive molding compositions with trinitrotoluene,
as a substitute for the Research Department explosive (RDX,
1,3,5-trinitro-1,3,5-triazacyclohexane).1 Commonly, it is prepared
by N-nitration of glycoluril 2a with nitric acid, acetyl nitrate or
mixed acids at 20–65°C under neat conditions.2 This procedure
requires the use of a significant concentration of the reactants,
which complicates efficient temperature control and enhances
the fire and explosion risks.
N
O
O
O
O
O
O
O
O
N
H
N
H
N
N
H
R
R
O2N
2a–c
1a–c
N2O5
liq-CO2, 80 bar,
5–20 °C
Me
Me
NO2
H
N
N
N
N
N
N
H
N
N
a R = H
b R = Me
c R + R = (CH2)4
Me
Me
NO2
Recently, we have developed an alternative procedure for the
synthesis of N-nitroamides and N-nitroureas by nitration of the
corresponding N-alkylamides or N-alkylureas with dinitrogen
pentoxide in liquid carbon dioxide (liq-CO2) medium.3 Due to
a considerably higher heat capacity of liq-CO2 as compared to
conventional solvents (Cp 6.35 J g–1 K–1 at 25°C and a pressure
of 64 bar,4 cf. for dichloromethane Cp 1.70 J g–1 K–1 at 20°C5),
this neoteric solvent efficiently consumes exothermic reaction heat
and suppresses undesirable side reactions and makes a work-up
operation significantly simpler (decompression of CO2).
Herein, we report the use of liq-CO2 as reaction medium for
nitration of glycoluril derivatives. First, to find optimal condi-
tions, we studied the nitration of 2a as a model. Treatment of
suspended in liq-CO2 2a with a solution of N2O5 (2.2–4.0 equiv.)
in the same solvent at 5–20°C and 80 bar afforded desirable
1,4-dinitroglycoluril 1a (Scheme 1, Table 1, entries 1–5). The
3
4
Scheme 1
best yield of 1a (82%) was attained on using 4.0 equiv. of N2O5
within 2 h (entry 5). Nitric acid additive (N2O5/100% HNO3,
1:1) did not affect the reaction (entry 6 vs. entry 3). Mixtures of
N2O5 (or 100% HNO3) with acetic anhydride when acetyl nitrate
is generated6 appeared inactive under these or even more rigorous
conditions corresponding to a supercritical CO2 state (entries 7
and 8). However, under the action of 100% HNO3–TFAA or
NH4NO3–TFAA mixtures (TFAA is trifluoroacetic anhydride)
when nitronium trifluoroacetate would likely form as the nitrating
agent7 2a was converted to 1a in up to 89% yield (entries 9 and 10).
Based on these results, we chose less environmentally harmful
(producing just recoverable nitric acid as acidic by-product)
nitrogen(v) oxide as nitrating agent in further experiments.
The C- or N-alkylglycolurils 2b,c and 3 gave the corresponding
dinitro compounds 1b,c and 4 in 73–83% yield under proposed
conditions (4.0 equiv. of N2O5, liq-CO2, 2 h) (Scheme 1, Table 1,
entries 11–13).† Notably, compound 4 contained both nitro groups
at the same urea fragment.
Table 1 Synthesis of dinitroglycolurils in liquid CO2.a
Entry Product Nitrating agent (equiv.)
t/h
Yield (%)
1
2
1a
1a
1a
1a
1a
1a
1a
1a
1a
1a
1b
1c
4
N2O5 (2.2)
0.5
1.0
2.0
1.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
46
49
52
64
82
50
–
N2O5 (2.2)
3
N2O5 (2.2)
The H, 13C and 14N NMR spectra were recorded in DMSO-d6 with
BrukerAM 300 at 300, 75 and 22 MHz, respectively. Starting compounds
2a,8 2b,9 2c,10 3,11 512 and N2O5 were prepared by reported methods.
†
1
4
N2O5 (4.0)
5
N2O5 (4.0)
13
6b
7c
8d
9e
10f
11
12
13
N2O5 (2.2) + 100% HNO3 (2.2)
N2O5 (2.2) + Ac2O (2.2)
HNO3 (4.4) + Ac2O (4.4)
HNO3 (4.4) + TFAA (2.2)
NH4NO3 (4.4) + TFAA (4.4)
N2O5 (4.0)
Carbon dioxide (99.995%) was supplied by Linde Gas (Russia).
General nitration procedure. A steel autoclave (25 cm3) was charged
with 2, 3 or 5 (2.5 mmol), filled with liquid CO2 to a pressure of 60 bar
and cooled to 5°C. Then nitrating agent (5.5–10.0 mmol, see Table 1)
dissolved in liquid CO2 (~3.5 g) was added in ten steps for 15 min. The
reaction mixture was gradually warmed to room temperature and stirred
for 2 h at 80 bar [for supercritical conditions (Table 1, entry 8), the tem-
perature and the pressure were raised to 45°C and 100 bar, respectively,
after the addition of the nitrating agent]. After 2 h stirring, the ice water
(2 ml) was pressurized into the autoclave to destroy the access of nitrating
agent. The CO2 was removed and additional amount of ice water (20 ml)
was added to the residue at atmospheric pressure. The precipitate was
filtered and dried at 40°C for 2 h to afford nitration product 1, 4 or 6,
–
89
70
76
83
73
N2O5 (4.0)
N2O5 (4.0)
a Unless otherwise specified, the reactions were carried out with 2 or 3
(2.5 mmol), N2O5 (5.5–10.0 mmol) at 80 bar and 5–20°C. b N2O5 and
100% HNO3 (5.5 mmol each). c N2O5 and Ac2O (5.5 mmol each), 100 bar,
45°C. d HNO3 (11.0 mmol), Ac2O (5.5 mmol), 100 bar, 45°C. e HNO3
(11.0 mmol), TFAA (5.5 mmol). f NH4NO3 and TFAA (11.0 mmol each).
© 2015 Mendeleev Communications. Published by ELSEVIER B.V.
on behalf of the N. D. Zelinsky Institute of Organic Chemistry of the
Russian Academy of Sciences.
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Mendeleev Commun., 2015, 25, 15–16
The method is applicable to the nitration of hexahydro-
economically beneficial: the nitration agent N2O5 can be generated
from available N2O4,16 and the CO2 solvent is easily separable
from the products and can be reused.
In summary, we have developed a new environment-friendly
and explosion-safe synthesis of dinitroglycoluril and its analogues
by N-nitration of corresponding glycoluril derivatives with N2O5
in liquid carbon dioxide medium.
imidazo[4,5-d]imidazol-2(1H)-one dihydrochloride 5 in which
cyclic urea fragment is fused with the imidazolidine unit. In this
case, trinitro derivative 6 formed in 56% yield under the action
of N2O5 (4 equiv.) in liq-CO2 medium (Scheme 2).
O2N
NO2
H
N
H
N
N
N
N2O5 (4.0 equiv.)
O
This work was supported by the Russian Foundation for Basic
Research (grant no. 13-03-12223-ofi_m).
O
liq-CO2, 80 bar,
5–20 °C, 2 h
N
H
N
H
N
N
2 HCl
H
O2N
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5
6 (56%)
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Scheme 2
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1
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3
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1
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1c: TID 199°C. 1H NMR, d: 1.29 (m, 2H, CH2), 1.63 (m, 2H, CH2), 2.08
(m, 2H, CH2), 2.59 (d, 2H, CH2, J 14.0 Hz), 9.97 (s, 2H, NH). 13C NMR,
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1
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1,4,6-Trinitrohexahydroimidazo[4,5-d]imidazol-2(1H)-one 6: mp 196°C
1
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J 10.8 Hz, J 185.7 Hz), 6.09, 7.37 (AB quartet, 2H, CH2, J 7.1 Hz,
J 374.7 Hz), 9.89 (s, 1H, NH). 13C NMR, d: 205.3, 75.2, 67.3, 64.6.
14N NMR, d: –48.3, –36.5, –34.5.
Received: 22nd July 2014; Com. 14/4430
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