Synthesis and reactions of 5,5-dinitrobarbituric acid

Article abstract of DOI:10.1016/S0040-4039(00)00086-1

Nitration of barbituric acid at 40°C gave the previously unknown 5,5- dinitrobarbituric acid (3), which readily underwent hydrolysis to dinitroacetylurea (5), which in turn could be hydrolysed in basic media to the potassium salt of dinitromethane. Alloxane was prepared in a one step procedure by thermal decomposition of 5,5-dinitrobarbituric acid in hot acetic acid. (C) 2000 Elsevier Science Ltd.

Full text of DOI:10.1016/S0040-4039(00)00086-1

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 41 (2000) 2011–2013
Synthesis and reactions of 5,5-dinitrobarbituric acid
Abraham Langlet,a Nikolaj V. Latypov,a,∗ Ulf Wellmar,a Patrick Goede a and Jan Bergman b,∗,†
aFOA, Defence Research Establishment, Department of Energetic Materials, S-147 25 Tumba, Sweden
bDepartment of Organic Chemistry, Royal Institute of Technology, S-100 44 Stockholm, Sweden
Received 25 November 1999; accepted 11 January 2000
Abstract
Nitration of barbituric acid at 40°C gave the previously unknown 5,5-dinitrobarbituric acid (3), which readily
underwent hydrolysis to dinitroacetylurea (5), which in turn could be hydrolysed in basic media to the potas-
sium salt of dinitromethane. Alloxane was prepared in a one step procedure by thermal decomposition of 5,5-
dinitrobarbituric acid in hot acetic acid. © 2000 Elsevier Science Ltd. All rights reserved.
Keywords: nitration; nitro compounds; nitrogen heterocycles.
Our interest in the formation of gem-dinitrocompounds prepared by nitration of various azolones1,4
lead us to investigate the nitration of barbituric acid (1), a typical example of such molecules. Mono-
nitration of barbituric acid (1) in concentrated nitric acid with the formation of 5-nitro barbituric acid has
long been known.2,3,5 We have studied the nitration of barbituric acid (1) with nitric acid in concentrated
sulfuric acid and under these conditions the formation of gem-dinitrated products was found to be
favourable. Thus the addition of 1 equivalent of nitric acid to a solution of barbituric acid (1) in sulfuric
acid at room temperature lead to quick formation of 5-nitrobarbituric acid in quantitative yield, which
was shown by comparing the UV spectrum of the quenched reaction solution with the corresponding
spectrum of an authentic sample (λmax=320 nm, ε=8600 l*mol−1). Addition of another equivalent of
nitric acid and increasing the temperature to 40°C lead to the appearance of a new maximum in the
UV spectrum (λmax=358 nm). This maximum slowly increased in intensity and was accompanied by
precipitation of a white solid from the reaction medium.
Analysis of the product showed it to be the previously unknown 5,5-dinitrobarbituric acid (3). 1,3-
Dimethylbarbituric acid (2) behaved in the same way, forming 1,3-dimethyl-5,5-dinitrobarbituric acid
(4) (Scheme 1).
The gem-dinitrated products were found to be extremely sensitive to several nucleophiles: e.g. reaction
with water at room temperature for both compounds lead to a quick hydrolysis with loss of carbon dioxide
and formation of the corresponding dinitroacetylureas (5 and 6). This behaviour is reminiscent to that
∗
†
Corresponding authors.
Also at the Department of Organic Chemistry, CNT, NOVUM Research Park, S-141 57 Huddinge, Sweden.
0040-4039/00/$ - see front matter © 2000 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(00)00086-1
tetl 16363

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Scheme 1.
of 5-chloro-5-nitrobarbituric acid as described by Ziegler and Kappe6. The dinitroacetylureas formed
in the hydrolysis are strong acids which are rather soluble in water. In contrast many of their metal
salts have a relatively low solubility. Potassium salts of both dinitroacetylurea (7) and 1,3-dimethyl-5,5-
dinitroacetylurea (8) were prepared and characterised. We also found that dinitroacetylurea (7 and 8) can
be further hydrolysed in basic media at elevated temperature (80–90°C) leading to the formation of salts
of dinitromethane (9), which provides a new efficient and safe method for making these compounds. The
overall yield of potassium dinitromethanide (9) obtained by this method is 80% from barbituric acid.
Unlike other gem-dinitroazolones1,4 5,5-dinitrobarbituric acid (3) is thermally relatively stable with
a decomposition temperature of around 150°C. Nonetheless, prolonged heating of (3) in boiling acetic
acid lead to the formation of alloxan (10) in 27% yield, in the presence of 5% acetic anhydride the yield
was increased to 38%. This thermal behaviour is analogous to that of 5-chloro-5-nitrobarbituric acid6
(Scheme 2).
Scheme 2.
All aspects of these reactions are under active investigation and will be published in due course.
Representative experimental procedure. Caution: All nitro compounds are explosives and should be
handled with appropriate precautions. Employ all standard energetic materials safety procedures in
experimental operations involving such substances.
Nitration of barbituric acid (1). To a mixture of barbituric acid (1) (12.8 g, 0.1 mol) dissolved in 95%
sulfuric acid (60 ml) was added fuming nitric acid (10 ml) while the temperature was kept below 25°C.
The reaction mixture was then heated to 45°C for 4 h. The resulting precipitate, was filtered, washed
with trifluoroacetic acid and dried, yielding 5,5-dinitrobarbituric acid (3) as a hemi hydrate (21.3 g,
0.094 mol, 94%), dec. temp. 150°C; IR (KBr): 3252 (NH), 1745 (C_O), 1611 (C_O), 1580 C(NO2)2,
1378 C(NO2)2; 1H NMR (DMSO-d6) δ 11.03 broad; 13C NMR (DMSO-d6) δ 113.5, 149.0, 155.1. Anal.
calcd for C4H2N4O7*1/2 H2O: C, 21.16; H, 1.33; N, 24.67. Found: C, 21.11; H, 1.23; N, 24.89.

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All compounds prepared had spectroscopic properties consistent with the proposed structures.
References
1. Bergman, J.; Bergman, S. Tetrahedron Lett. 1996, 37, 9263–9266.
2. Hartman, W. W.; Sheppard, O. E. Organic Synthesis 1932, 58–61 and references cited therein.
3. Kaupp, G.; Schmeyers, J. J. Org. Chem. 1995, 60, 5494–5503 and references cited therein.
4. Latypov, N. V.; Bergman, J.; Langlet, A.; Wellmar, U.; Bemm, U. Tetrahedron 1998, 54, 11525–11536.
5. Nutiu, R.; Sebe, I. Rev. Roum. Chim. 1971, 16, 919–923 and references cited therein.
6. Ziegler, E.; Kappe, T. Monatshefte 1964, 95, 1057–1060.