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  Mar. 1, 2001  Vol.3 No.3 P.13 Copyright cij17logo.gif (917 bytes)

The synthesis and crystal structure of 5,5'-bis(azidomethyl)-3,3' -bis(1,2,4-oxadiazole)

Li Zhanxiong, Ou,Yuxiang, Chen Boren
(School of Chemical Engineering and Material Sciences, Beijing Institute of Technology, Beijing, 100081,China）

Received Sep. 20, 2000

Abstract 5,5'-bis(azidomethyl)-3,3' -bis(1,2,4-oxadiazole) was synthesized and characterized by elemental analysis, IR, 1H NMR and MS as an energetic compound. The mechanism of the rearrangement of 1,2,5-oxadiazole to form a 1,2,4-oxadiazole system was studied. The crystal structure of the title compound was determined by X-ray diffraction.
Keywords synthesize, crystal structure, furazan, isofurazan

N. D. Zelinsky Institute of Organic Chemistry have been studying 1,2,5-oxadiazole(furazan) for about two decades[1,2]. They found that aromaticity of the furazan ring usually increased the thermal stability of its derivatives, and the planarity of the ring provided them with high density. In 1965, R. A. Olofson and J. S. Michelman pointed out that the furazan ring system was an aromatic heterocycle[3]. The weakness of the N-O bond in furazan was suggested by an analysis of its mass spectrums. It agrees with the results of the resonance forms of furazan , which is calculated by E. Saegebrath [4].
    In 1977, N. Vivona found that when N-C=S sequences were present in the side-chain of the phenylthioureido derivatives, the systems may rearrange and new five-member heterocycles may be obtained with 1,2.4-oxadiazole(isofurazan) system.[5] this must be ascribed to the superior nucleophilic properties of the sulphur atom in attacking the nitrogen atom of furazan ring.
    In this work, the N-C=O sequence was introduced into the 3-position of furazan and an isofurazan system was obtained.

1 SYNTHESIS
General information. Virtually compound II is potentially dangerous high energetic explosives and should be handled carefully. Melting points (uncorrected) were measured on a XT4A micro-meldometer and elemental analysis on a heraeus CHN-RAPID instrument.IR spectra were recorded on a MAGANT-560, MS on a KYKY-5#, and 1H NMR on a ARX400MHz NMR spectrometers (TMS as internal standard) respectively.
    Treatment of 3,4-diaminofurazan(DAF) with chloroacetyl chloride (CAC) can give 5,5'-bis(chloromethyl)-3,3' -bis(1,2,4-oxadiazole) (compound I) which is deemed to rearrange from 1,2,5-oxadiazole (scheme 1). Then compound I was treated with sodium azide to give 5,5'-bis(azidomethyl)-3,3' -bis(1,2,4-oxadiazole) (compound II).
    The structure of compound I and II were identified by elemental analysis, IR, 1H NMR, MS(FAB), and the crystallography shows that compound II is a bis(isofurazan) derivatives ulteriorly.
   Compound I. (procedure a) from DAF. Chloroacetic chloride 5.4g (48mmol) was added slowly to a solution of 1.2g(12mmol) DAF in DMF (10mL) at 0°C. This mixture was stirred for 1h at 0°C and for 2h at room temperature. Pouring the reaction mixture onto 60g of crushed ice /water, the white solid was collected and recrystallized from 15mL of acetone/water(1:1) giving 1.99g (67.7%) of the products. M.p.= 100~101°C.IR(KBr): 2987(m), 1574(s), 1210(s), 1178, 906(s), 782 cm-1. C6H4N4O2Cl2 : cal.C30.64，H1.70，N23.83. Found:C30.66，H2.49，N23.80. 1H NMR(acetone-d6):δ5.06 (4H,-CH2-).
    (procedure b) from diaminoglyoxime(DAG). The procedure of this way is same to (a) basically. Treatment DAG with CAC at 40°C give 1.60g (54.4%) of the product. IR(KBr): 2989,1569(s),1214(s),1175,904(s),780cm-1. C6H4N4O2Cl2: cal. C30.64，H1.70， N23.83. Found: C30.68，H2.45，N23.62. 1H NMR(acetone-d6):δ5.06 (4H,-CH2-).
       Scheme 1

    Compound II. 0.65g (10mmol) of sodium azide in 4mL of water was added drop wise with stirring to a solution of 1.25g (5mmol) of compound I in 30mL of acetone. The mixture was refluxed for 4h and then poured into ice/water (150mL). The precipitate was collected and recrystallized from 12mL of acetone/water(1:1) to yield 0.71g (56.3%) of the product. M.p.= 67°C. IR(KBr): 2998,2160(s),2125(s),1565(s)1207(s),964,906,772 cm-1.C6H4N10O2: cal.C29.03 H1.61， N56.45. found: C29.75，H1.37, N57.24. 1H NMR(acetone-d6):δ4.97(4H,-CH2-). MS(FAB) (M+1)+=249（28%).
    Treatment of DAF with CAC could introduce N-C=O sequence into the 3-position of furazan and the rearrangement took place. This gave an isofurazan ring and an oximido group. Then the oximido acted on CAC to give a chloroacetoxy group. As the result of dehydrating of chloroacetoxy and the adjacent amino group, another isofurazan ring formed. In this way we obtained compound I.
    To confirm the cyclizing mechanism of chloroacetoxy and the adjacent amino group of procedure (a), we selected diaminoglyoxime(DAG) to react with CAC . The oximido group of DAG could react with CAC to give a chloroacetoxy sequence with an adjacent amino group. In this way, we got the same compound I followed by treatment with sodium azide to give compound II.
    Compound II was identified as a bis(isofurazan) derivatives with low hydrogen content and low melting point. It may be used as energetic additives.

2 STRUCTURE OF COMPOND II
2.1 Diffraction data collection of compound II
The product was dissolved in a acetone water mixture (1:1) and the solvents were evaporated slowly to obtain a colorless single crystal with size of 0.60×0.20×0.08mm. It was used for X-ray diffraction analysis.
    The diffraction analysis was carried out on Siemens P4 diffractometer and the graphite monochromator with radiation MoK\α( l=0.071 073 nm) was used. The scan type 2q-w, q range for data collection was 2.09 to 24.99 degree All 1007 reflections were collected, 869 Independent reflections [I>2s(I)] were used for structure refinement.
    The crystal structure was solved by direct method. All atomic coordinates and equivalent isotropic thermal parameters of non-hydrogen atoms were refined by full-matrix least-squares method with R indices (all data) R1 = 0.0395, wR2 = 0.0766, Final R indices [I>2s(I)] R1 = 0.0286, wR2 = 0.0703.
2.2 Structure refinement
The empirical formula of compound II is C6H4N10O2 , formula weight 248.19. Crystal system belongs to Triclinic，Space group P 1. a=0.858 18(2)nm, b=1.143 36(4)nm, c=1.432 75(5) nm. Z=4, Volume 2.4953(9) nm3, dc=1.652 kg/m3.
    Figure 1 and figure 2 show the molecular configuration and cell packing respectively. Atomic coordinates and equivalent isotropic thermal parameters of non-hydrogen atoms are listed in table1 and table2 and the Anisotropic displacement parameters in table 3.

Fig 1 Molecular configuration of compound II

Fig 2 Cell packing of compound II

Table 1. Atomic coordinates and equivalent isotropic thermal parameters of non-hydrogen atoms

atoms

 X×104

Y×104

Z×104

Ueq×105/ nm2

O(1)
N(1)
N(2)
N(3)
N(4)
N(5)
C(1)
C(2)
C(3)

2799(3)
6708(3)
2379(3)
8144(3)
6007(4)
4354(5)
5413(3)
4746(3)
6524(4)

6111(2)
7527(2)
4587(2)
8948(2)
7988(2)
7111(3)
7780(2)
5523(2)
9596(2)

7688(1)
9471(1)
8447(1)
6441(1)
5439(1)
4444(2)
8363(1)
9468(1)
7738(1)

47(1)
40(1)
47(1)
51(1)
53(1)
83(1)
36(1)
35(1)
42(1)

Table 2. Bond lengths [nm] and angles [deg]

bond

bond length

bond

bond angle

O(1)-C(1)
O(1)-N(2)
N(1)-C(1)
N(1)-C(2)
N(2)-C(2)
N(3)-N(4)
N(3)-C(3)
N(4)-N(5)
C(1)-C(3)
C(2)-C(2A)

0.133 9(2)
0.140 8(2)0.129 1(2)0.137 3(2)0.129 5(2)0.123 3(2)0.147 8(2)0.112 5(2)0.148 7(2)0.145 2(3)

C(1)-O(1)-N(2)
C(1)-N(1)-C(2)
C(2)-N(2)-O(1)
N(4)-N(3)-C(3)
N(5)-N(4)-N(3)
N(1)-C(1)-O(1)
N(1)-C(1)-C(3)
O(1)-C(1)-C(3)
N(2)-C(2)-N(1)
  N(2)-C(2)-C(2A)
   N(1)-C(2)- C(2A)
N(3)-C(3)-C(1)

106.41(10)
101.96(11)
102.65(10)
114.04(12)
172.70(2)
113.45(12)
128.94(12)
117.56(12)
115.53(12)
121.30(2)
123.19(14)
110.74(11)

Table 3. Anisotropic displacement parameters(×105/ nm2)

U11

U22

U33

U23

U13

U12

O(1)
N(1)
N(2)
N(3)
N(4)
N(5)
C(1)
C(2)
C(3)

51(1)
44(1)
52(1)
49(1)
69(1)
109(1)
36(1)
36(1)
44(1)

42(1)
34(1)
39(1)
58(1)
52(1)
88(1)
33(1)
32(1)
39(1)

42(1)
38(1)
44(1)
48(1)
45(1)
48(1)
35(1)
34(1)
41(1)

16(1)
11(1)
18(1)
21(1)
20(1)
4(1)
6(1)
8(1)
14(1)

-8(1)
-2(1)
-5(1)
8(1)
11(1)
-6(1)
3(1)
4(1)
1(1)

-3(1)
2(1)
-3(1)
10(1)
24(1)
36(1)
6(1)
5(1)
7(1)

   The planar equations of C3N3N4N5 and N1N2O1C1C2C3are:
                  -0.877(0.007)X+6.593(0.003)Y-4.402(0.007)Z=2.349(0.005)
                  -3.176(0.002)X-3.230(0.003)Y-4.384(0.006)Z=4.440(0.005)
    The dihedral angel of two planes is 69.21(10) degree. Two azido groups are not in the plane of the bis(isofurazan).

2.3 Results and discussions    
The molecules of compound I and compound II are centrosymmetric. In compound II, the bis(isofurazan) system is in a plane and the five-member heterocycle is a conjuge structure as the furazan system. The distance of two bis(isofurazan) planes is 0.3177(2) nm. Because two azido groups are not in the plane of bis(isofurazan) system, the density of this energetic compound is not very high(dc=1.652 kg/m3).
    The C=N bond length in bis(isofurazan) system (0.1291nm and 0.1295nm) is between the carbon-nitrogen distances in formaldoxine (0.1276nm) and in pyridine (0.1340nm), and it is shorter than the C=N distance in furazan (0.1300nm). The difference suggests that there is more electron delocalization in iso-furazan than in furazan, and there is less aromaticity in the former than in the latter.
    There is no special reciprocity between two adjacent bis(isofurazn) molecules besides the tail end nitrogen atom in the azido group and the oxygen atom of the adjacent isofurazan ring system. The distance between these two atoms is 0.3080nm. It is shorter than the averaging distance of two bis(isofurazan) molecule in the plane of ring system(0.330nm).
    The applications study of this azide as energetic additives are under progress being carried out.

REFERENCES
[1] Sheremetev A B, Valentina O K, Lyndmina V B et al. Proc. Twenty-second International Pyrotechnics Seminar, USA, July 15-19, 1996, 377.
[2] Pivina T S, Sukhachev D V, Evtushenko A V et al. Propellants, Explosives, pyrotechnics. 1995, 20: 5.
[3] Olofson R A, Michelman J S. J. Org. Chem., 1965, 30: 1854.
[4] Saegebarth E, Cox A P. Journal of Chemical Physics, 1965, 43: 166.
[5] Vivona N, Cusmuno G, Macaiuso G. J. Chem. Soc. (Perkin I), 1977, 1616.

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