Thermal behavior of copper(II) 4-nitroimidazolate

Article abstract of DOI:10.1007/s10973-007-8708-1

The thermal behavior of copper(II) 4-nitroimidazolate (CuNI) under static and dynamic states are studied by means of high-pressure DSC (PDSC) and TG with the different heating rates and the combination technique of in situ thermolysis cell with rapid-scan

Full text of DOI:10.1007/s10973-007-8708-1

Journal of Thermal Analysis and Calorimetry, Vol. 96 (2009) 1, 195–201
THERMAL BEHAVIOR OF COPPER(II) 4-NITROIMIDAZOLATE
L. Ji-zhen*, F. Xue-zhong, H. Rong-zu, Z. Xiao-dong, Z. Feng-qi and G. Hong-Xu
Xi’an Modern Chemistry Research Institute, Xi’an, Shaanxi 710065, China
The thermal behavior of copper(II) 4-nitroimidazolate (CuNI) under static and dynamic states are studied by means of high-pressure
DSC (PDSC) and TG with the different heating rates and the combination technique of in situ thermolysis cell with rapid-scan Fou-
rier transform infrared spectroscopy (thermolysis/RSFTIR).
The results show that the apparent activation energy and pre-exponential factor of the major exothermic decomposition reac-
tion of CuNI obtained by Kissinger’s method are 233.2 kJ mol–1 and 1017.95 s–1, respectively. The critical temperature of the thermal
explosion and the adiabatic time-to-explosion of CuNI are 601.97 K and 4.4~4.6 s, respectively. The decomposition of CuNI begins
with the split of the C–NO2 and C–H bonds, and the decomposition process of CuNI under dynamic states occurs less readily than
those under static states because the dynamic nitrogen removes the strong oxidative decomposition product (NO2). The above-men-
tioned information on thermal behavior is quite useful for analyzing and evaluating the stability and thermal charge rule of CuNI.
Keywords: copper(II) 4-nitroimidazolate, DSC, IR, kinetics, TG, thermolysis
Introduction
4-Nitroimidazole, an energetic material, which was
studied as the intermediate of medicines [1–3], is
Scheme 1 Structure of CuNI
found to be used as a main intermediate of dinitro-
imidazoles, trinitroimidazoles and metal 4-nitroimid-
azolates which can be used to improve the character-
Experimental instruments and conditions
istics of cast explosives and solid propellants [4–8].
Copper(II) 4-nitroimidazolate (CuNI), a kind of new
PDSC measurements were carried out on
a
metal 4-nitroimidazolate, can be used as a main com-
ponent, combustion catalyzer, of solid propellants.
The study of thermal behavior is a very important
starting point for the selection and exploitation of
CuNI in applications, but there is no report on it until
today.
Model DSC204 Netzsch instruments. The operation
conditions were as follows: heating rates, 5, 10, 15, 20
and 40°C min–1; sample mass, 0.5 to 1.0 mg; aluminium
sample cell; atmosphere, static nitrogen with 1.0 MPa.
TG/DTG measurements were performed on a
Model TA2950 TGA instruments. The conditions of
TG/DTG were as follows: sample mass, 1.0 to
2.0 mg; heating rates, 5, 10, 15 and 20°C min–1; atmo-
sphere, flowing rate of N2 gas, 60 mL min–1.
The aim of this work is to study the thermolysis
kinetics of CuNI under static and dynamic state and
the real-time thermal decomposition [9] of CuNI by
means of PDSC, TG [10–12] and the combination
technique of in situ thermolysis cell with rapid-scan
Fourier transform infrared spectroscopy (thermolysis/
RSFTIR).
Thermolysis/RSFTIR measurements were con-
ducted using a Nicolet Model NEXUS 870 FT-IR In-
strument and in situ thermolysis cell (Xiamen Univer-
sity, China) in the temperature range of 20~455°C and
heating rate of 10°C min–1. KBr pellet samples, well
mixed by about 0.7 mg CuNI and 150 mg KBr, were
used. Infrared spectra in the range of 4000~400 cm–1
were obtained by a model DTGS detector at a rate of
11 files min–1 and 8 scans file–1 with 4 cm–1 resolution.
The specific heat capacity (Cp, J mol–1 K–1) of
CuNI was determined with continuous Cp mode on a
Micro-DSC III mircocalorimeter (Setaram Co., France).
Experimental
Material
CuNI used in this work was prepared by Xi’an Mod-
ern Chemistry Research Institute, whose purity was
more than 99.0%. Its structure is shown in Scheme 1.
*
Author for correspondence: jizhenli@126.com
1388–6150/$20.00
Akadémiai Kiadó, Budapest, Hungary
Springer, Dordrecht, The Netherlands
© 2009 Akadémiai Kiadó, Budapest

JI-ZHEN et al.
Results and discussion
From the original data in Tables 2 and 3, the value
of Ea corresponding to the values of a for the thermal
decomposition reaction under static and flowing N2 gas
conditions obtained by integral isoconversional non-lin-
ear (NL-INT) equation (3) [17]
The thermal decomposition behavior of CuNI under
static N2 gas conditions and flowing N2 gas
The PDSC and TG curves for CuNI at different heat-
ing rates are shown in Figs 1 and 2. PDSC curves
show that there are two exothermic peaks before
430°C. A major exothermic peak before 360°C is
caused by the decomposition of CuNI. An exothermic
process at the temperature of higher than 370°C is due
to further decomposition of the decomposition prod-
ucts in coacervate phase. The TG curves also show
two-stage mass loss processes.
n
n
b I (Ea ,Ta,i )
j
min =
-n(n-1)
(3)
åå
j¹i b I (Ea ,Ta,j )
i
i
are shown in Figs 3–4 and Tables 2–3. It is clear that
the values of Ea do not seem to remain constant in the
Analysis of kinetic data
In order to obtain the kinetic parameters (the apparent
activation energy Ea and pre-exponential constant A) of
the major exothermic decomposition reaction of CuNI, a
multiple heating method [13] (Kissinger’s method) is
employed. From the original data in Table 1, Ea is deter-
mined to be 233.21 kJ mol–1 and A as 1017.95 s–1. The lin-
ear correlation coefficient (rk) is 0.9868. The values of
Ea and r0 obtained by Ozawa’s method [14] are
231.52 kJ mol–1 and 0.9879, respectively.
Under the condition of static N2 gas, the value
(Te0) of the onset temperature (Te) corresponding to
b®0 by Eq. (1) taken from [15] using the data of Te
and b in Table 1 are 589.85 K,
Fig. 1 PDSC curves of CuNI at different heating rates
Tei =Te0 +bb +cb2 +db3, i=1, 2, …, 5
(1)
i
i
i
where, b, c and d are the coefficients.
The value of the critical temperature of thermal
decomposition (Tb) obtained from Eq. (2) taken from
[16] using the value of Te0 and Eo in Table 1 is
601.97 K,
Eo - Eo2 -4EoRTe0
Tb =
(2)
2R
where R is the gas constant (8.314 J mol–1 K–1) and Eo
the value of E obtained by Ozawa’s method
(231.5 kJ mol–1).
Fig. 2 TG curves of CuNI at different heating rates
Table 1 Kinetic parameters of thermal decomposition of CuNI under static atmosphere calculated by Kissinger’s method and
Ozawa’s method*
b/K min–1
a
Ek /
kJ mol–1
a
Ak /
s–1
b
E0 /
kJ mol–1
c
Tb /K
rk
r0
Te0/K
5
10
15
20
40
Te/K 603.16 610.13 619.29 620.22 629.03
Tp/K 604.54 612.75 621.56 622.33 630.56
230.60
231.52
0.9891 589.85 601.97
0.9879
233.21
1017.95 0.9868
*Te – onset temperature in the DSC curve; Tp – maximum peak temperature; b – heating rate; Teo – the value (Teo) of the onset
temperature (Te) corresponding to b®0 by Eq. (1); Tb – critical temperature of thermal explosion; Ea – apparent activation energy;
A – pre-exponential constant; r – linear correlation coefficient; subscript k – data obtained by Kissinger’s method; subscript
o – data obtained by Ozawa’s method. aValues of Ek and Ak calculated from the relationship of ln(bi/Tp2i ) vs. 1/Tpi; bValues of Eo
calculated from the relationship of lgbi vs. 1/Tei or Tpi; cThe value of Tb obtained from Eq. (2) using the data of Eo and Te0.
196
J. Therm. Anal. Cal., 96, 2009

COPPER(II) 4-NITROIMIDAZOLATE
decomposition process, but varied with the extent of
Adiabatic time-to-explosion
conversion. This fact indicates that the thermal de-
composition process of CuNI is a multiple reaction.
Therefore, it is difficult to properly interpret the Ea
dependence on a by means of kinetic mechanism.
The adiabatic time-to-explosion (t) of CuNI obtained
from Eq. (4) taken from [18] is 4.6 s for n=2, 4.5 s for
n=1 and 4.4 s for n=0.
Table 2 Apparent activation energies of thermal decomposition of CuNI under static N2 gas condition obtained using integral
isoconversional method
Ti/K (i=1, 2, …, n)
Eq. (3)
ai
No.
b/K min–1
5
10
15
20
40
Ea/kJ mol–1
min
1
2
0.125
0.150
0.175
0.200
0.225
0.250
0.275
0.300
0.325
0.350
0.375
0.400
0.425
0.450
0.475
0.500
0.525
0.550
0.575
0.600
0.625
0.650
0.675
0.700
0.725
0.750
0.775
0.800
0.825
0.850
0.875
0.900
0.925
0.950
0.975
1.000
602.13
602.84
603.16
603.61
603.86
604.02
604.18
604.31
604.43
604.55
604.66
604.77
604.89
605.01
605.22
605.38
605.58
605.81
606.08
606.45
606.88
607.48
608.27
609.31
650.60
612.12
613.89
616.00
618.61
622.00
626.57
632.55
639.47
647.41
657.19
668.00
609.11
610.06
610.74
611.22
611.60
611.90
612.14
612.38
612.60
612.83
613.06
613.31
613.55
613.84
614.22
614.67
615.33
616.14
617.19
618.45
619.90
621.49
623.26
625.17
627.33
629.82
632.76
636.40
640.83
645.79
650.90
655.95
660.90
666.14
672.64
680.59
617.75
618.83
619.57
620.09
620.47
620.77
621.01
621.22
621.45
621.65
621.84
622.09
622.33
622.59
622.92
623.30
623.78
624.42
625.25
626.30
627.56
629.00
630.60
632.34
634.28
636.51
639.13
642.39
646.55
651.57
657.01
662.55
668.02
673.69
680.63
688.76
619.51
620.42
620.96
621.36
621.63
621.87
622.04
622.26
622.45
622.66
622.84
623.05
623.27
623.52
623.79
624.08
624.43
624.84
625.34
625.97
626.80
627.90
629.24
630.87
632.77
634.91
637.35
640.25
643.86
648.63
654.65
661.36
668.21
675.35
683.92
694.11
629.12
629.63
629.86
630.06
630.24
630.42
630.57
630.75
630.92
631.06
631.27
631.47
631.70
631.87
632.09
632.33
632.60
632.88
633.20
633.55
633.97
634.44
635.00
635.70
636.59
637.85
639.57
641.84
644.63
648.01
652.21
658.08
667.65
680.52
693.99
710.91
224.76
226.41
227.19
229.19
229.94
229.89
230.12
229.89
229.53
229.45
228.95
228.32
227.56
227.20
227.53
226.89
226.71
226.27
225.29
223.79
220.78
217.24
213.28
209.38
205.04
199.44
192.16
182.23
169.40
156.82
150.51
156.75
178.73
195.09
199.72
211.11
0.1647
0.1835
0.2165
0.2243
0.2363
0.2443
0.2512
0.2517
0.2578
0.2610
0.2590
0.2694
0.2688
0.2777
0.2887
0.3068
0.3366
0.3984
0.5066
0.6787
0.9225
1.2270
1.5894
1.9804
2.4209
2.8883
3.3837
3.9698
4.7110
5.4525
5.9119
5.6401
3.7473
1.3009
0.2688
4.7121
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
*ai – the degree of CuNI decomposition; min, the minimum on the right side of Eq. (3)
J. Therm. Anal. Cal., 96, 2009
197

JI-ZHEN et al.
apparent activation energy, Ea=233210 J mol–1; A,
T Cp exp(E/RT )
dT
(4)
t=ò
pre-exponential constant, A=1017.95 s–1; Q, heat of de-
composition, Q=1644 J g–1; R, the gas constant,
QAf (a )
T
0
R=8.314 J mol–1 K–1; a, the conversion degree,
where
Cp,
specific
heat
capacity,
T
(Cp /Q)dT; T, the integral upper limit,
a =ò
Cp=–0.02176296+0.003168681T, K; f(a), differential
mechanism function f(a)=(1–a)n; n, the rate order; E,
T
0
T=Tb=601.92
K;
T0,
the
lower
limit,
T0=Te0=289.85 K.
Table 3 Apparent activation energies of thermal decomposition of CuNI under flowing N2 gas conditions obtained using inte-
gral isoconversional method
Ti/K (i=1, 2, …, n)
Eq. (3)
ai
No.
b/K min–1
5
10
15
20
Ea/kJ mol–1
min
1
2
0.125
0.150
0.175
0.200
0.225
0.250
0.275
0.300
0.325
0.350
0.375
0.400
0.425
0.450
0.475
0.500
0.525
0.550
0.575
0.600
0.625
0.650
0.675
0.700
0.725
0.750
0.775
0.800
0.825
0.850
0.875
0.900
0.925
0.950
0.975
1.000
573.31
580.42
585.18
589.15
592.37
594.17
596.51
598.99
600.99
602.66
604.10
605.32
606.42
607.37
608.26
609.07
609.81
610.54
611.18
611.79
612.39
612.94
613.50
613.99
614.49
614.97
615.44
615.90
616.35
616.81
617.23
617.68
618.12
618.61
619.13
619.70
599.55
602.94
605.56
607.74
609.56
611.05
612.43
613.59
614.68
615.62
616.49
617.28
618.05
618.74
619.38
620.00
620.57
621.14
621.66
622.16
622.65
623.13
623.58
624.02
624.47
624.88
625.29
625.70
626.10
626.49
626.87
627.28
627.67
628.08
628.58
629.20
602.52
606.01
608.78
610.97
612.87
614.46
615.83
617.03
618.09
619.06
619.94
620.75
621.42
622.11
622.77
623.40
624.01
624.56
625.08
625.59
626.06
626.53
626.98
627.40
627.82
628.22
628.61
629.02
629.40
629.77
630.15
630.53
630.92
631.33
631.82
632.37
603.65
607.49
610.58
613.04
615.06
616.65
618.09
619.38
620.48
621.50
622.44
623.28
624.09
625.00
625.51
626.14
626.75
627.31
627.86
628.38
628.87
629.35
629.80
630.26
630.69
631.12
631.52
631.93
632.34
632.74
633.14
633.54
633.97
634.43
634.94
635.53
101.94
120.86
134.27
147.71
159.63
162.70
172.48
186.68
198.35
208.05
216.24
222.80
228.73
231.86
237.31
240.89
243.74
247.21
249.53
251.71
254.26
256.02
258.48
259.73
261.45
263.02
264.77
266.12
267.48
269.24
270.17
271.63
272.56
274.01
274.81
275.09
0.6042
0.5148
0.4385
0.3787
0.3302
0.3149
0.2855
0.2398
0.2125
0.1851
0.1631
0.1468
0.1344
0.1149
0.1138
0.1075
0.1002
0.0959
0.0909
0.0867
0.0836
0.0816
0.0784
0.0762
0.0758
0.0731
0.0719
0.0705
0.0689
0.0668
0.0650
0.0646
0.0618
0.0581
0.0575
0.0608
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
198
J. Therm. Anal. Cal., 96, 2009

COPPER(II) 4-NITROIMIDAZOLATE
Thermolysis in the slowly heated IR cell
(u
u
and u
) ) at 1525 and 1382 cm–1, the
s(C– NO 2
as(C–H) and us(C–H) peaks at 3169 and 3111 cm–1 for the
as(C–NO 2
)
Thermolysis/RSFTIR was used to analyze the con-
densed phase products of the thermal decomposition
of CuNI under the linear temperature rise condition in
real time.
C–H bonds, the uC=C and uC=N peaks at 1495 and
1458 cm–1 for the C=C and C=N bonds, the dC–H in the
plane at 1275–975 cm–1 for the C–H bonds, and the dC–H
perpendicular to the plane at lower than 900 cm–1 for the
C–H bonds can be observed from Fig. 5.
The RSFTIR spectrum of CuNI at room tempera-
ture is shown in Fig. 5. The antisymmetric and symmet-
ric stretching vibration absorptions of C–NO2 bonds
The IR spectra of CuNI at different temperatures
are shown in Fig. 6. It can be clearly seen that the in-
tensity of the uas(C–H), us(C–H), u
and u
,
s(C– NO 2 )
as(C–NO 2
)
u
C=C and uC=N peaks at 3169, 3111, 1525, 1382, 1495
and 1458 cm–1 weaken rapidly at the temperature of
about 250°C, and the swift absorption peaks at 3169,
2361, 2336, 2165 and 1612 cm–1 emerge. The inten-
sity of all the other characteristic absorption peaks
weaken and disappear at 455.4°C, except for the char-
acteristic absorption peaks of CO2 at 2336, 2361 and
670 cm–1 and CO at 2165 cm–1.
The characteristic absorption peaks of CuNI and
its condensed phase products are chosen to make the
intensity vs. temperature curves. In Fig. 7, the disap-
pearance of the u
and u
peaks (1382
)
as(C–NO 2
)
s(C– NO 2
Fig. 3 The relation between Ea and a for the thermal decom-
position reaction of CuNI under static N2 gas condi-
tions at 1.0 MPa
and 1525 cm–1) and the emergence of u
peaks
NO2
(1612 cm–1) are easily recognized in the temperature
Fig. 6 The typical IR spectra of the condensed products at dif-
ferent temperatures during the thermal decomposition
process of CuNI
Fig. 4 The relation between Ea and a for the thermal decom-
position reaction of CuNI under flowing N2 gas condi-
tions at a flow rate of 60 mL min–1
Fig. 7 Intensity vs. temperature curves of the characteristic ab-
sorption peaks at 1382, 1525 and 1612 cm–1
Fig. 5 RSFTIR spectrum of CuNI at room temperature
J. Therm. Anal. Cal., 96, 2009
199

JI-ZHEN et al.
range of 220–260°C, and in Fig. 8, the disappearance
of the uC=C and uC=N peaks (1495 and 1458 cm–1) are
easily seen in the temperature range of 230–300°C.
Therefore, the C–NO2 bonds of CuNI are broken in
the temperature range of 220–260°C, whose strong
oxidative product NO2 destroy the unstable annulus
of CuNI (the C=C and C=N bonds are broken in the
temperature range of 230–300°C).
It can be seen from Fig. 9 that the intensity of the
uas(C–H), us(S–H) and dC–H peaks decrease rapidly in the
temperature range of 220–260°C, and in the tempera-
Fig. 10 Changes in the characteristic absorption peaks at
2165, 2336 and 2361 cm–1 during the thermal
decomposition process of CuNI
Fig. 8 Intensity vs. temperature curves of the characteristic ab-
sorption peaks at 1458 and 1495 cm–1
Fig. 11 Intensity vs. temperature curves of the characteristic
absorption peaks at 2336, 2361 and 2165 cm–1
ture range of 220–250°C, the us(C–H) peak at
3111 cm–1 combines with the uas(C–H) peak at
3169 cm–1 forming an absorption peak at 3136 cm–1.
In Figs 10 and 11, it is easily observed that the
oxides of carbon, gas products of CuNI decomposi-
tion, contain CO2 and CO, which characteristic ab-
sorption peaks (u
) , u
and uCO) at 2336, 2361
s(CO 2 )
as(CO 2
and 2165 cm–1 emerge from about 220 and 310°C, re-
spectively.
Thus, the C–NO2 and C–H bonds of CuNI are bro-
ken with the increase in temperature simultaneously,
whose strong oxidative product (NO2) destroy the unsta-
ble annulus of CuNI instantly, and finally, the conju-
gated C=C and C=N bonds of the five-membered ring
are broken. It confirmed the result of the two exothermic
peaks on PDSC and the two-stage mass loss processes
of TG curves of CuNI. The gas products of CuNI de-
composition consist of NO2, CO2 and CO.
Because of the different test conditions, the tem-
perature data of thermolysis/RSTFIR are different
from those of DSC and TG-DTG. Thus,
thermolysis/RSTFIR measurement is used to make
qualitative analysis, while PDSC measurement is em-
ployed to make quantitative analysis.
Fig. 9 Intensity vs. temperature curves of the characteristic ab-
sorption peaks at 817, 1245, 1274, 3111, 3136 and
3169 cm–1
200
J. Therm. Anal. Cal., 96, 2009

COPPER(II) 4-NITROIMIDAZOLATE
2 S. R. Tannenbaum, Biochem., 41 (2002) 7508.
Conclusions
3 L. Jia, V. Shafirovich, R. Shapiro, N. E. Geacintov and
S. Broyde, Biochem., 45 (2006) 6644.
• The extrapolated onset temperature corresponding
to b®0 of the major exothermic process (Te0) is
589.85 K.
4 D. Reddy and J. Keerti, USP 5387297, 1993.
5 A. J. Bracuti, J. Chem. Cryst., 28 (1998) 367.
6 J. R. Cho, K. J. Kim, S. G. Cho and J. K. Kim, J. Hetero.
Chem., 39 (2002) 141.
• The critical temperature of thermal explosion of
CuNI (Tb) is 601.97 K.
7 J. R. Cho, S. G. Cho, K. J. Kim and J. K. Kim, Insensitive
Munitions & Energetic Materials Technology Symposium,
NDIA, San Diego 2000, p. 393.
• The adiabatic time-to-explosion from Te0 to Tb is
about 4.4–4.6 s.
8 S. Jerzy and S. Ewa, Pol. J. Chem., 61 (1987) 613.
9 J. Z. Li, G. F. Zhang, X. Z. Fan, R. Z. Hu and Q. Pan,
J. Anal. Appl. Pyrolysis, 76 (2006) 1.
• The apparent activation energy (Ea) and pre-expo-
nential constant (A) of the major exothermic de-
composition reaction of CuNI obtained by a multi-
ple heating method are 233.21 kJ mol–1 and
1017.95 s–1, respectively.
10 S. C. Mojumdar, G. Madgurambal and M. T. Saleh,
J. Therm. Anal. Cal., 81 (2005) 205.
11 G. Z. Papageorgiou, D. S. Achilias, D. N. Bikiaris and
G. P. Karayannidis, J. Therm. Anal. Cal., 84 (2006) 85.
12 Y. J. Wan, L. Q. Li and D. H. Chen, J. Therm. Anal. Cal.,
90 (2007) 415.
• The values of Ea in decomposition process variate
with the extent of conversion (a) indicating that it
is difficult to properly interpret the Ea dependence
on a by means of kinetic mechanism.
• The decomposition of CuNI, which contain two
steps with the temperature rise, begins with the
split of C–NO2 and C–H bonds. The gas products
detected of CuNI decomposition consist of NO2,
CO2 and CO.
13 H. E. Kissinger, Anal. Chem., 29 (1957) 1702.
14 T. Ozawa, Bull, Chem. Sec. Jpn., 38 (1965) 1881.
15 R. Z. Hu and Q. Z. Shi, Thermal Analysis Kinetics,
Science Press, Beijing 2001, p. 127.
16 T. L. Zhang, R. Z. Hu, Y. Xie and F. P. Li, Thermochim.
Acta, 244 (1994) 171.
17 R. Z. Hu, F. Q. Zhao, H. X. Gao, H. Zhang and
Q. C. Song, Chin. J. Energ. Mater., 19 (2007) 97.
18 R. Z. Hu, S. L. Gao, F. Q. Zhao, Q. Z. Shi, T. L. Zhang
and J. J. Zhang, Thermal Analysis Kinetics, Science Press,
Beijing 2007, p. 342.
• The decomposition process of CuNI under dy-
namic states occurs less readily than those under
static states because of the dynamic nitrogen taking
off the strong oxidative decomposition product
(NO2).
Received: September 17, 2007
Accepted: September 18, 2008
References
DOI: 10.1007/s10973-007-8708-1
1 T. Chu, S. Hu, B. Wei, Y. Wang, X. Liu and X. Wang,
Bioorg. Med. Chem. Lett., 14 (2004) 747.
J. Therm. Anal. Cal., 96, 2009
201