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Improved preparation of 3,7-dinitro-1,3,5,7-tetraazabicyclo[3,3,1] nonane
(DPT) from urea
Xiaobing Liu, Ming Lu *, Xiaoyu Yu
Chemical Engineering College, Nanjing University of Science and Technology, Nanjing 210094, China
Received 20 March 2010; received in revid form 27 May 2010; accepted 30 May 2010
Abstract
An improved and facile preparation of 3,7-dinitro-1,3,5,7-tetraazabicyclo [3,3,1] nonane (DPT) has bee
n developed starting from urea. In the procedure DPT was synthesized via N,N’-dinitrourea (DNU) as intermediate and various operating parameters such as temperature, pH and molar ratio of reagents have been optimized to give maximum yield of the desired product. The low cost method is conci, operationally simple and offers high purity and satisfactory yield of DPT.
Keywords: 3,7-dinitro-1,3,5,7-tetraazabicyclo[3,3,1]nonane (DPT); Urea; Nitration; N,N’-dinitrourea (DNU).
1. Introduction
3,7-dinitro-1,3,5,7-tetraazabicyclo[3,3,1]nonane (DPT) is a key precursor to octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) [1,2], the most powerful explosive manufactured in bulk at prent. Reported ma工程管理专业排名
nufacturing process for HMX involved the modified Bachmann process [3-5], in which the nitrolysis of hexamine with ammonium nitrate-nitric acid solution and acetic anhydride occurred and DPT was identified as a key intermediate. The modified Bachmann process has been brought about industrialization but it costs lot and involves complex ries and parallel reactions. In view of the vital importance of DPT in the synthesis of HMX, a low cost method for producing this intermediate would provide a significant contributio经济类书籍
n toward reducing cost of manufacturing HMX.
G.F. Wright and coworkers [6] found that DPT could be prepared by admixture of a solution of nitramide (NH 2NO 2) in aqueous formaldehyde with a solution of formaldehyde and ammonia, but nitramide cannot be ud as a large-scale starting material for its hydrolytic instability. R. A. Strecker et al. [7] invented a process for producing DPT by utilizing nitrourea as starting material in place of nitramide. The nitrourea can be obtained from urea nitrate [8], which in turn can be produced from low cost urea [9], but this process was loaded down with trivial details and the yield of DPT was low.
Recently much attention has been paid to N,N’-dinitrourea (DNU) and its derivatives due to their relatively high densities [10-14]. DNU was also found to be a good precursor to nitramide. Journal of the Iranian Chemical Rearch
IAU-ARAK J. Iran. Chem. Res. 3 (2010) 133-139
X. Liu & et al. / J. Iran. Chem. Res. 3 (2010) 133-139
S.G. Il’yasov et al. [15] disclod the application of DNU as intermediate for synthesis of DPT, but no systematic synthetic or mechanistic studies were reported.
Herein we report an improved and facile preparation of DPT, starting from low cost urea. In the procedure DNU (1) was prepared in situ without isolation of the compound, and the hydrolysis of DNU to give nitramide (2) in the prence of formaldehyde occurred through formation of N-dimethylol nitramide (3) since the subquent neutralization with ammonia obtained DPT (4) (Scheme 1). We prepared the three intermediates to confirm the procedure and investigated various reaction conditions to get optimal conditions.
Scheme 1 Synthesis of DPT from urea.
2. Experimental
2.1. Materials and Methods
Melting points were determined on a Thomas Hoover capillary apparatus and were uncorrected. The IR spectra were recorded with a Bomem Michelson model 102 FTIR. 1H NMR spectra were recorded on a Bruker DRX (500 MHz) spectrometer. Elemental analys were performed on a Yanagimoto MT3CHN recorder. Mass spectra were recorded on a VG ZAB-HS mass spectrometer using fast atom bombardment (FAB) ionization mode. All starting chemicals (AR grade) were purchad from commercial suppliers and ud without further purification.
2.2. Experimental procedures
To handle the energetic materials, best safety pra创意营销案例
ctices (leather gloves, face shield) are strongly encouraged.
2.3. Synthesis of DPT (4)
Urea, 6 g (0.1 mol), was added in portions to a mixture of 22.5 g of 98% nitric acid and 22.5g of oleum (20 % SO3) at -5 to 0 C under continuous stirring. After the addition the mixture was stirred for 1h at 0 to 5 C and poured into 30 g of an ice-water mixture, and 50 mL of a 37 % ormaldehyde solution was added at a temperature not exceeding 20 C. The mixture was heated to 35 C, stirred for 30 min, cooled, and neutralized to pH 6 with 25 % aqueous ammonia at 20-25 C. It was then stir
red for 45 min at 20 C, and the precipitate was filtered off, washed with water, and dried at room temperature until constant weight. Yield 14.7 g (67.4 %, calculated on urea), m.p. 209-210 C; published data: 205-206 C [16]. IR (cm-1): 3032, 2937 (CH2); 1529, 1288 (NNO2). 1H NMR (DMSO-d6): 5.49 (d, 4H), 4.93 (d, 4H), 4.11 (s, 2H). MS (FAB): 219 ([M+1]+). Anal. Calcd. for C5H10N6O4: C, 27.53; H, 4.62; N, 38.52; Found: C, 27.51; H, 4.59; N, 38.40 %.
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2.4. Preparation of DNU(1)
Urea, 6 g (0.1 mol), was added in portions to a mixture of 21 g of 98 % nitric acid and 21 g of oleum (20 % SO3) at -5 to 0 C under continuous stirring. After the addition the mixture was stirred for 1h at 0 to 5 C, during this time a white precipitate formed. The precipitate was quickly filtered off through a glass funnel, washed with trifluoroacetic acid (310 mL), and squeezed. The product was dried over vacuum at room temperature. Yield 10.34g (68.9%, calculated on urea). IR (cm-1): 3217, 3194 (NH); 1744 (C=O); 1605, 1454, 1319 (NNO2). 1H NMR (DMSO-d6): 13.71 (s, 2H). Anal. Calcd. for CH2N4O5: C, 8.00; H, 1.34; N, 37.34; Found: C, 7.96; H, 1.39; N, 37.65 %.
2.5. Preparation of nitramide (2)
The nitration of urea was carried out as described above. After keeping stirring for 1h at 0 to 5 C, the mixture was poured into 30g of an ice-water mixture, maintaining the temperature below 10 C. The mixture was extracted with ethyl acetate (430 mL), and the extract was washed with water (320 mL), kept for 2h at 20 C, and evaporated to dryness under reduced pressure. The product was dissolved in 20 mL of ether, and the solution was poured into 250 mL of hexane, and the precipitate was filtered off. Additional recrystallization from dichloroethane and 2-propanol (9:1) gave nitramide. Yield 7.56 g (61.0 %, calculated on urea), m.p. 80-81 C. IR (cm-1): 3366, 3259 (NH); 1535, 1402, 1321 (NO2). 1H NMR (DMSO-d6): 11.18 (s, 2H). Anal. Calcd. for H2N2O2: H, 3.25; N, 45.16; Found: H, 3.17; N, 45.12 %.
2.6. Preparation of N-dimethylol nitramide (3)
The nitration of urea was carried out as described above. After keeping stirring for 1h at 0 to 5 C, the mixture was poured into 30 g of an ice-water mixture, and 50ml of a 37% formaldehyde solution was added at a temperature not exceeding 20C. The mixture was heated to 35 C, stirred for 30min, cooled, and extracted with ether (550ml). The extract was dried over MgSO4, and the solve
nt was distilled off under reduced pressure to obtain a yellowish oily substance. Yield 11.3g (46.3%, calculated on urea). IR (cm-1): 3500~3300 br (OH); 2974, 2918 (CH2); 1541, 1296 (NNO2). Anal. Calcd. for C2H6N2O4: C, 19.68; H, 4.95; N, 22.95; Found: C, 19.75; H, 4.97; N, 22.86 %.
3. Results and discussion
In the procedure of DPT synthesis, DNU was an important intermediate. DNU was obtained via a direct nitration of urea with a mixture of equal parts of 98% HNO3 and 20 % oleum at low temperature. DNU was initially reported to undergo decomposition at room temperature which could lead to spontaneous ignition [11]. This behavior was due to trace amounts of acids in crude DNU product. The drawback was overcome by washing with trifluoroacetic acid to remove all acidic impurities and the pure DNU was stable for veral weeks in a desiccator over silica gel at room temperature [10, 13].
In our preliminary study, DNU was parated and added under stirring to a 37 % formaldehyde solution, and with subquent addition of ammonia after hydrolysis of DNU the yield of DPT did not exceed 40 %. We optimized reaction conditions and developed a facile sy思乡之情的诗
nthesis of DPT. In the modif粮食安全的重要性
ied process, DNU underwent hydrolysis to give nitramide without isolation of pure DNU. Due to
instability of nitramide in acid medium (Scheme 2) [17], the prence of formaldehyde was requisite for the hydrolysis of DNU to form relatively stable N-dimethylol nitramide (Scheme 3).
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Scheme 2 The hydrolysis of DNU and the decomposition of nitramide in acid medium.
Scheme 3 The relatively stable N-dimethylol nitramide formed in the prence of formaldehyde.
The subquent addition of ammonia in the prence of formaldehyde formed methylenediamine, which reacted with N-dimethylol nitramide to give the precipitation of DPT (Scheme 4) [6]. The precipitation of DPT was filtered off, water-washed and dried at room temperature. The yield of DPT was up to 67.4% (urea basis) with m.p. 209-210 C (published data: 205-206 C) [16].
Scheme 4 DPT formed with the addition of ammonia in the prence of formaldehyde.
3.1. Optimization of reaction conditions
To get a good yield of DPT, we investigated various reaction conditions and get optimal conditions as described in experimental ction. Using the optimal conditions thus established, we altered some conditions to discuss their effect. The nitrolysis of urea was carried out with a mixture of 98 % HNO3 and 20 % oleum at 0 to 5C for DNU may undergo decomposition at higher nitration temperature. Ol
eum was requisite for the procedure and the usage of 98 % H2SO4 would obtain neither DNU nor DPT in the process. Our efforts here were directed toward the reduction of HNO3 and oleum consumed. The results were summarized in Table 1.
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Table 1
Nitrolysis of urea with a mixture of 98% HNO 3 and 20 % oleum a .
entry HNO 3 (mol) 98 % HNO 3 (g) 20 % Oleum (g) Yield of DPT (%) 1 0.20 12.8 22.5 42.2 2 0.25 16.0 22.5 52.5 3 0.30 19.2 22.5 53.2 4 0.35 22.5 11.2 41.1 5 0.35 22.5 16.8 53.3 6 0.35 22.5 22.5 67.4 7 0.35 22.5 28.0 63.6 8 0.35 22.5 34.0 58.7 9 0.40 26.0 22.5 55.7 a urea, 0.1mol; 37% formaldehyde solution, 50 mL.
We noted that a molar ratio of HNO 3/urea 3.5:1 (mol:mol) led to a higher yield of DPT. We fixed the
molar number of urea and HNO 3, and changed the amount of oleum to find the relationship among them. As the results shown in entries 4-8, there was建议书范文
a significant effect on the yield when changing the amount of oleum. The optimal amount of oleum was equal to 98% HNO 3, and the higher amount of oleum did not improve the result to a greater extent.
When the reaction was finished, DNU was prepared in situ without isolation of the compound. The hydrolysis of DNU in the prence of formaldehyde occurred under the optimized reaction conditions as described in experiment ction. The yield of DPT altered with the amount of formaldehyde and the results were prented in Fig. 1. It can easily be en that a molar ratio of formaldehyde/urea 5:1 (mol: mol) led to a higher yield of DPT. 1 mol of formaldehyde corresponds to 100 mL of a 37 % formaldehyde solution. In the prence of excess formaldehyde, the yield of DPT was decread. The reason may be that nitramide reacts with excess formaldehyde to give a little polycondensate or cyclic product [17, 18].
Y i e l d (%)n(formaldehyde):n(urea)
Fig. 1. Effect of n(formaldehyde) : n(urea) on the reaction.
In the procedure of the hydrolysis of DNU, the effect of temperature on the yield of DPT was studied. Experiments were carried out as shown in Fig. 2. Here one can obrve that the appropriate temperature of the hydrolysis reaction was 30-40 C.
