Confined rapid thermolysis/FTIR/ToF studies of methyl-amino-triazolium- based energetic ionic liquids

Article abstract of DOI:10.1016/j.tca.2010.03.022

Thermal decomposition of the energetic ionic liquids 1-methyl-4-amino-1,2, 4-triazolium iodide (Me4ATI), 1-methyl-4-amino-1,2,4-triazolium nitrate (Me4ATN), 1-amino-3-methyl-1,2,3-triazolium iodide (Me1ATI), and 1-amino-3-methyl-1,2,3-triazolium nitrate (Me1ATN) was studied by confined rapid thermolysis. Sub-milligram quantities of the compounds were subjected to decomposition under isothermal conditions achieved by initially heating the sample at rates of approximately 2000 K/s. The products formed by decomposition under the afore-mentioned conditions were sampled by rapid scan FTIR spectroscopy and time-of-flight mass spectrometry. Decomposition studies involving the iodide salts were carried out around 270-290.C, whereas the nitrate salts were subjected to 320-340.C. The amino group was found to be involved in the initiation reaction, forming copious quantities of ammonia from the iodide compounds and, N₂^O and H₂ ^O from the nitrate compounds. The extent of decomposition of the triazole ring was minimal at the considered temperatures.

Full text of DOI:10.1016/j.tca.2010.03.022

Thermochimica Acta 505 (2010) 33–40
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Thermochimica Acta
journal homepage: www.elsevier.com/locate/tca
Confined rapid thermolysis/FTIR/ToF studies of methyl-amino-triazolium-based
energetic ionic liquids
∗
Arindrajit Chowdhury, Stefan T. Thynell
Department of Mechanical and Nuclear Engineering, The Pennsylvania State University, University Park, PA 16802, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
Thermal decomposition of the energetic ionic liquids 1-methyl-4-amino-1,2,4-triazolium iodide
Received 6 February 2010
Accepted 28 March 2010
Available online 24 April 2010
(Me4ATI), 1-methyl-4-amino-1,2,4-triazolium nitrate (Me4ATN), 1-amino-3-methyl-1,2,3-triazolium
iodide (Me1ATI), and 1-amino-3-methyl-1,2,3-triazolium nitrate (Me1ATN) was studied by confined
rapid thermolysis. Sub-milligram quantities of the compounds were subjected to decomposition under
isothermal conditions achieved by initially heating the sample at rates of approximately 2000 K/s. The
products formed by decomposition under the afore-mentioned conditions were sampled by rapid scan
FTIR spectroscopy and time-of-flight mass spectrometry. Decomposition studies involving the iodide
Keywords:
Ionic liquids
Thermal decomposition
FTIR spectroscopy
ToF mass spectrometry
◦
◦
salts were carried out around 270–290 C, whereas the nitrate salts were subjected to 320–340 C. The
amino group was found to be involved in the initiation reaction, forming copious quantities of ammonia
from the iodide compounds and, N2O and H2O from the nitrate compounds. The extent of decomposition
of the triazole ring was minimal at the considered temperatures.
©
2010 Elsevier B.V. All rights reserved.
1
. Introduction
tional groups, the family of the triazole salts has been expanded to
include azido, amino, nitro, and nitramino azolium salts. However,
most of the thermal decomposition studies have been carried out
using thermogravimetric analysis (TGA) and differential scanning
calorimetry (DSC) under slow heating rates without any particular
emphasis on the chemical kinetics of these decomposition reac-
tions. Though these studies were carried out under low heating
rates, the underlying trends provide valuable insights into the ther-
mal stability of these compounds, the effects of various groups
substituting the protons on the triazole ring, and their decomposi-
tion behavior under elevated heating rates.
Nitrate, perchlorate and dinitramide salts of 3,4,5-triamino-
1,2,4-triazole were synthesized and characterized by Drake
et al. [21]. The dinitramide salt of the cation was found to be
the least stable, followed by the nitrate and the perchlorate.
Replacement of two ring H atoms with amino groups had no
effect on the decomposition temperature of the dinitramide
salt, but the perchlorate and the nitrate salts demonstrated an
increased thermal stability. 1-amino-3-alkyl-1,2,3-triazolium
nitrates (alkyl = methyl, ethyl, n-propyl, 2-propenyl, and n-butyl)
were also synthesized and characterized by vibrational spec-
tra, multinuclear NMR analyses, and DSC studies [22]. The DSC
studies on these compounds showed that the thermal stabil-
ity was decreased as the alkyl chain length increased. Salts
formed by pairing the 1-methyl-3,4,5-triamino-1,2,4-triazolium
cation with azide, nitrate, perchlorate, dinitramide, nitrotetra-
zolate, and azotetrazolate were characterized by Darwich et
al. [23]. The order of thermal stability was found to be perchlo-
A wide range of attractive properties [1–8] have drawn the
interest of the scientific community to ionic liquids, a unique class
of compounds with melting points below 100 C. The exceptional
◦
chemical and thermal stability of these compounds, coupled with
their low vapor pressures and low melting points have put them
forth as potential replacements of many noxious organic solvents
used in the chemical industry [9,10]. Also their easy recoverability
after usage has made them popular as ‘green solvents’. However,
attention has recently been drawn to energetic heterocyclic ionic
liquids with nitrogen-rich cations, such as imidazoles, triazoles
and, tetrazoles, coupled with oxygen-rich anions such as nitrates,
nitramides, and perchlorates, because of their thermal stability and
high energy density. These compounds are easy to synthesize, and
their properties can be tailored to suit specific requirements by
minor alterations in their molecular structure.
A
comprehensive overview of recent studies regarding
triazolium-based salts has been presented in our previous work
11]. Significant effort in developing salts based on various deriva-
[
tives of 1,2,4-triazole or 1,2,3-triazole as cations and nitrates,
perchlorates, and dinitramides as anions have been exerted by
Shreeve et al. [12–19] and Drake et al. [20–22]. Since the hydrogen
atoms on these azoles can be substituted easily by various func-
∗ Corresponding author. Tel.: +1 814 863 0977; fax: +1 814 863 4848.
E-mail address: Thynell@psu.edu (S.T. Thynell).
0
040-6031/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.tca.2010.03.022

3
4
A. Chowdhury, S.T. Thynell / Thermochimica Acta 505 (2010) 33–40
Table 1
Vibrational frequencies of experimentally observed gaseous products.
Description
Wavenumber (cm−1)
Reference
H2O
HCN
NH3
CH3I
HNO3
MeONO2
CO2
N2O
NO
NO2
HNCO
3657, 1595
[31]
[31]
[31]
[31]
[32]
[33]
[31]
[31]
[27]
[32]
[34]
3311, 712
3337, 1627, 950
2974, 1435, 1252, 882
3551, 1710, 1326, 879
2962, 1667, 1291, 1019, 855
2349, 667
Fig. 1. Structure of 1-methyl-4-amino-1,2,4-triazolium X (X = iodide and nitrate)
and 1-amino-3-methyl-1,2,3-triazolium X (X = iodide and nitrate).
2224, 1285
1875
1617, 1320
3530, 2269
rate > nitrate > azide > azotetrazolate > nitrotetrazolate > dinitramide.
The introduction of the methyl group increased the decomposition
◦
temperature from 245 to 261 C for the nitrate salt.
The aim of the current work is to identify the mechanism
determining the initiation of decomposition of energetic amino-
methyl-triazolium salts under high temperatures and heating rates.
The synergistic diagnostic tools, Fourier transform infrared (FTIR)
spectroscopy and time-of-flight (ToF) mass spectrometry (MS),
were utilized to afford better probabilities of identifying the decom-
position productsand thus, determiningthe reactionpathways. The
energetic salts of primary interest are Me4ATN and Me1ATN. Since
the complexity of the secondary reactions is considerably higher
for the oxygen-rich anions, the relatively simple iodides Me4ATI
and Me1ATI were studied initially. The molecular structures of the
molecules are shown in Fig. 1. Studies were also conducted on the
building blocks for these rather complex molecules, including 4-
amino-1,2,4-triazole (4AT), 1-methyl-1,2,4-triazole (1MeTA), and
roughly 300 ␮m in height, enables heating rates in the range of
2000 K/s.
The gaseous products evolving from the condensed phase are
sampled by a modulated FTIR beam passing through two ZnSe
windows. Thus the spectra are obtained in near real-time with a
−
1
spectral resolution of 2 cm and a temporal resolution of 50 ms.
The gaseous species are also sampled by a ToFMS system, equipped
with a 1 m flight tube and a 44 mm microchannel plate detector, via
a 100 ␮m orifice plate. The molecular beam entering the third stage,
−
7
maintained at 10 Torr, is ionized by electron impact ionization set
at 70 eV. Individual mass spectra are acquired at 1000 Hz, and time-
2
to-mass scaling is performed using the expressions m = a(t − t0) ,
where the two constants for each mass spectrum are obtained from
known positions of helium and argon. The species concentrations
of various species, such as H2O, N2O, NO2, NO, NH3, CO2, CO, MeOH,
1
-amino-1,2,3-triazole.
HCN, and HNO are extracted by a non-linear, least-squares method
3
by comparison with theoretical transmittance. The radiative prop-
erties, such as partition function, halfwidth of spectral lines, and its
temperature exponent, are determined from the HITRAN database
2
. Experimental approach
The experimental setup as well as the data-reduction tech-
[
27].
niques utilized to extract mole fractions of individual species from
the FTIR spectra were discussed is earlier works [24–26]. The
technique utilized to study the rapid thermal decomposition of
energetic materials, termed confined rapid thermolysis (CRT), is
used in conjunction with two synergistic diagnostic tools, a Fourier
transform infrared spectrometer and a time-of-flight mass spec-
trometer. The method is very sensitive to decomposition processes
occurring in the condensed phase, compared to the gas phase, as
the molecules are quenched by the relatively cooler atmosphere
into which they evolve. Typically, a small quantity, 0.5 mg of a
solid or 0.5 ␮L of a liquid, of the sample is rapidly heated in
between two heated surfaces maintained under isothermal con-
ditions in a constant pressure chamber purged by an inert gas.
The use of a small sample volume enclosed in a confined space,
3. Results and discussion
3.1. Thermal decomposition pathways of Me4ATI
Me4ATI is a light orange crystalline solid under standard condi-
tions, with a melting point of 101 C [17]. Approximately 0.5 mg of
◦
the sample was rapidly thermolyzed in the temperature range of
◦
230–300 C. Fig. 2a shows the products evolving from the decom-
◦
position of Me4ATI at a representative temperature of 270 C and
1 atm. The vibrational frequencies of the experimentally observed
species evolving from the compounds studied are listed in Table 1.
As seen from Fig. 2a and Table 1, the major decomposition prod-
◦
◦
Fig. 2. FTIR spectrum of species from rapid thermolysis of (a) Me4ATI at 270 C and 1 atm N2, and (b) MeTA at 250 C and 1 atm N2.

A. Chowdhury, S.T. Thynell / Thermochimica Acta 505 (2010) 33–40
35
◦
◦
Fig. 3. Mass spectrum from rapid thermolysis of Me4ATI at 270 C and 1 atm Ar, He
Fig. 4. Mass spectrum from rapid thermolysis of MeTA at 250 C and 1 atm Ar, He
and residual air (average of 10 spectra).
and residual air (average of 10 spectra).
uct is ammonia, with its rotational doublet near 900 cm−1, as well
as peaks at 1626 and 3336 cm . The rotational lines due to the
be explained by the formation of methyl-iodo-triazole, produced
as a by-product during the formation of ammonia from the amino
group. The lack of a peak at m/z = 142 proves the absence of CH3I.
The peak at m/z = 28 has contributions from molecular N2 as well
as fragmentation of 1MeTA.
The availability of the ToFMS data facilitates the determination
of the decomposition pathways of Me4ATI. As postulated earlier,
the presence of large quantities of ammonia and 1MeTA indi-
cates the involvement of the amino group in the initiation stage
of decomposition. The most probable initiation pathway, as shown
in Scheme 1, is the deamination of the Me4AT cation to form
1MeTA and NH2I. Similar decomposition pathways were observed
during the decomposition of 1-amino-4,5-dimethyl-tetrazolium
−
1
protonated anion HI or the vibrational bands from CH I were not
3
detected.
In order to identify the source of the rovibrational bands from
−1
1
500 to 1000 cm , 1MeTA was acquired from Sigma-Aldrich and
used without further purification, and the resulting FTIR spectrum
◦
of vaporized 1MeTA attained at 250 C and 1 atm is displayed in
Fig. 2b. 1MeTA was found to be stable under comparable condi-
tions, as evident from the lack of detection of any smaller products,
such as HCN or CH CN. Although the presence of the NH rotational
3
3
−1
lines from 1200 to 750 cm proved to be a hindrance in clearly
identifying the vibrational bands from 1MeTA in that region, the
presence of 1MeTA among the decomposition products of Me4ATI
iodide [29]. NH I being a reactive species, promptly reacts with the
2
−
1
neutral 1MeTA to abstract an H-atom to form NH3 and methyl-iodo-
triazole. The exact location of abstraction is difficult to ascertain due
to the existence of two similar locations on the ring carbon atoms
is recognized by the ring torsion frequency around 680 cm and
−
1
the strong band around 1500 cm . The lack of HCN among the
products shows that the ring structure is intact at the applied tem-
peratures. N2 could not be detected due to its IR-inactivity. Based
on the prodigious quantities of ammonia liberated and the forma-
tion of 1MeTA, the initiation of decomposition occurs most likely
through the amino group. Proton transfer does not occur directly
to form HI.
(
position C and C5), as well as the methyl group. NH I subsequently
3
2
decomposes to form NH , N2 and molecular iodine. The lack of HI
3
among the FTIR spectra or the mass spectra precludes the possibil-
ity of a proton transfer from the methyl group or the amino group
as an initiation reaction. Also, due to almost undetectable levels
of CH I among the decomposition spectra, a nucleophilic transfer
3
To assist in the identification of species evolved during the
decomposition of Me4ATI, Fig. 3a and b shows the results from
the thermolysis of Me4ATI under an inert atmosphere of Ar and
involving the methyl group to form CH I is neglected as a significant
3
decomposition pathway.
◦
He, acquired at 270 C and 1 atm Ar, He and residual air, under an
ionization potential of 70 eV at 1000 Hz. In order to provide better
signal-to-noise ratios in the mass spectra, 10 consecutive spectra
were averaged, providing a temporal resolution of 0.01 s. Although
the mass spectrum in Fig. 3a and b, split in order to provide clarity,
appears at a first glance as quite complicated due to the fact that
a high ionization potential is used, it facilitates comparison with
available mass spectral data bases for a wide range of chemical
compounds [28].
The prominent peaks at m/z = 17 and m/z = 83 attests to the for-
mation of ammonia and 1MeTA, respectively. The signal at m/z = 84
was formed by the excess protonation of 1MeTA, due to the pres-
ence of H+ ions in the flight tube of the ToFMS. The fragmentation
of the ring of 1MeTA is seen in Fig. 4a, with the most prominent one
seen at m/z = 56, due to the loss of an HCN fragment. Similar frag-
ments found in Fig. 3a substantiate the formation of 1MeTA during
the decomposition of Me4ATI. 1MeTA also dimerizes to a limited
extent, as seen by the peak at m/z = 166. The peak at m/z = 209 can
3.2. Thermal decomposition pathways of Me4ATN
Unlike its iodide salt, the nitrate salt of the methyl-amino-
triazolium cation is a clear viscous liquid with a melting point of
◦
◦
−60 C. Thermal decomposition measured by DSC was initiated at
221 C [17]. Confined rapid thermolysis of approximately 0.5 ␮L of
◦
the sample was carried out at temperatures around 320 C. The
hygroscopic nature of the salt made it difficult to clearly study the
decompositionbehavior ofthe compound. Thesamplewasdried for
24 h under vacuum (40 mTorr) and then stored in a sealed container
to avoid contamination by moisture. Fig. 5a depicts an FTIR spec-
◦
trum of species from rapid thermolysis of Me4ATN at 320 C and
1 atm. Nitric acid (HNO ), with several rovibrational bands from
3
−
1
−1
1700 to 800 cm and an overtone above 3500 cm , was imme-
diately discernable as a major species. The other major species
detected were H O, N O, and CO . Also identified were small quan-
2
2
2
tities of HNCO and HCN. Fig. 5b shows the spectrum obtained by

3
6
A. Chowdhury, S.T. Thynell / Thermochimica Acta 505 (2010) 33–40
Scheme 1. Proposed reaction pathway for Me4ATI.
◦
Fig. 5. FTIR spectrum of species from rapid thermolysis of (a) Me4ATN at 320 C and
◦
◦
Fig. 7. Species evolution from rapid thermolysis of Me4ATN at 320 C and 1 atm N2.
1
atm N2, and (b) MeTA at 250 C and 1 atm N2.
were present in the mass spectra acquired during the event. Similar
to the decomposition of Me4ATI, the signal at m/z = 84 was formed
+
by the excess protonation of 1MeTA, due to the presence of H ions
in the flight tube of the ToFMS. The peak at m/z = 44 is attributed
to N O and CO , also present in the FTIR spectra. Additionally, the
2
2
lack of a peak at m/z = 69 proves the absence of 1-H-triazole, a by-
product of the decomposition of 4-amino-triazole under similar
conditions [11], hence negating the possibility of involvement of
the methyl group during the initiation reaction.
As shown in Fig. 7, the species evolution profiles, extracted from
the FTIR spectra acquired at 320 C, reveals further information
◦
◦
Fig. 6. Mass spectrum from rapid thermolysis of Me4ATN at 320 C and 1 atm Ar,
He and residual air (average of 10 spectra).
on the decomposition pathways of Me4ATN. Although HNO3 was
found to be a major product during the decomposition of Me4ATN,
its rate of evolution was significantly delayed compared to the
faster rates of H O and N O. CO and HCN were found to evolve
vaporizing 1MeTA for identification of the bands in the ‘fingerprint
region’. It was clear that the decomposition products of Me4ATN
contained the stable compound 1MeTA, as evident from the pres-
ence of the C–H wags near 850 cm , and the ring torsion near
80 cm . As expected, methyl nitrate (CH ONO ) was not detected
2
2
2
at smaller quantities. The right vertical axis shows the absorbance
−
1
−1
of the band from 1100 to 1175 cm arising from 1MeTA. As seen
−
1
6
from this plot, 1MeTA desorbs at a rate comparable to H O and N O
3
2
2 2
among the products.
from the condensed phase.
The findings obtained from FTIR analysis were confirmed by ToF
mass spectra. Fig. 6 showsaspectrum fromthe ToFMS acquireddur-
ing the pyrolysis of Me4ATN at 320 C and 1 atm Ar, He and residual
The nitrate anion and the complex structure of the amino-
methyl-triazole results in a wide variety of reactions leading to
◦
the decomposition of Me4ATN. However, the formation of H O
2
air. At a first glance, the HNO detected from the FTIR spectra seem
and N O early in the event, and the lack of methyl nitrate suggest
3
2
to be absent due to the lack of a strong peak at m/z = 63. However,
that the initiation reaction involves the amino group. As shown in
previous studies [30] showed that HNO readily decomposes under
Scheme 2, the initiation reaction is through an N –N bond scission
3
4
the high ionization potential used to form NO (m/z = 46), NO+
+
to form 1MeTA and the reactive species, NH ONO . NH ONO sub-
2
2
2
2
2
(
m/z = 30), H+ (m/z = 1) and a number of other smaller ions, which
sequentlyforms N O, H O andN throughsecondaryreactionswith
2 2 2

A. Chowdhury, S.T. Thynell / Thermochimica Acta 505 (2010) 33–40
37
◦
Fig. 8. FTIR spectrum of species from rapid thermolysis of Me1ATI at 290 C and 1 atm N2.
Scheme 2. Proposed reaction pathway for Me4ATN.
the parent molecule Me4ATN. Methyl-triazolium nitrate, formed as
a by-product during these reactions, decomposes to form the HNO3
detected at a later stage, and additional 1MeTA. 1MeTA produced
during the initiation and secondary steps is further reduced to a lim-
ited extent to CO , HCN, HNCO, H O and N by the strong oxidizer,
2
2
2
HNO3.
3.3. Thermal decomposition pathways of Me1ATI
Me1ATI, an isomer of Me4ATI, is a light yellow crystalline solid
under standard conditions. The decomposition temperatures for
Me1ATI were found to be relatively similar to those of Me4ATI.
◦
Thermolysis tests were typically conducted at 290 C. Fig. 8 shows
◦
the species evolving from rapid thermolysis at 290 C and 1 atm.
As listed in Table 1, the principal product is ammonia, with
its prominent rotational doublet and numerous rotational lines
−1
near 900 cm , similar to the decomposition products of Me4ATI.
Unlike Me4ATI, the lack of the reference compound 3-methyl-1,2,3-
triazole (3MeTA) rendered accurately determining the peaks in
the ‘fingerprint region’ difficult. However, the presence of a sharp
◦
Fig. 9. Mass spectrum from rapid thermolysis of Me1ATI at 290 C and 1 atm Ar, He
and residual air (average of 10 spectra).
−1
peak at 760 cm , typically attributed to ring torsion, confirms the

3
8
A. Chowdhury, S.T. Thynell / Thermochimica Acta 505 (2010) 33–40
◦
Fig. 10. FTIR spectrum of species from rapid thermolysis of 1ATA at 350 C and 1 atm N2.
◦
◦
Fig. 13. Mass spectrum from rapid thermolysis of Me1ATN at 340 C and 1 atm Ar,
He and residual air (average of 10 spectra).
Fig. 11. Mass spectrum from rapid thermolysis of 1ATA at 350 C and 1 atm Ar, He
and residual air (average of 10 spectra).
presence of a cyclic triazole. The presence of a –CH stretch near
3
−
1
3
000 cm indicates the possibility of the formation of 3MeTA. HCN
and HI were not detected among the products. Due to overlap-
ping of bands, it was not possible to accurately identify CH I in the
3
spectra. As in the case of Me4ATI, the copious amount of ammonia
leads to the possibility of the involvement of the involvement of
the amino group in the initiation reaction.
Results from the use of the ToFMS provide additional details on
the rapid thermolysis behavior of Me1ATI. Fig. 9a and b shows a
spectrum from the ToFMS acquired during the pyrolysis of Me1ATI
◦
at 290 C and 1 atm Ar, He and residual air. Careful observation of
the spectrum reveals that m/z = 17 (NH ) and m/z = 83 (3MeTA) are
3
the major species. The peaks at m/z = 55, 54, 52, 42, and 27 were
suspected to be formed due to fragmentation of 3MeTA. Similar
to the fragmentation of 1MeTA, the large peak at m/z = 28 is par-
tially formed by the fragmentation of 3MeTA. The major deviation
from the mass spectra obtained from Me4ATI was the formation
◦
Fig. 14. Species evolution from rapid thermolysis of Me1ATN at 340 C and 1 atm
N2.
tively. However, proton transfer to form HI is not a possibility.
The NH I formed in the initiation step reacts with 3MeTA at posi-
tion C4 or C5, or the methyl group to form methyl-iodo-triazole
or iodo-methyl-triazole. The initiation reaction pathways and the
subsequent secondary steps are shown in Scheme 3. Decomposi-
of the methyl iodide (CH I), evident from the peak at m/z = 142.
3
This shows the presence of a secondary reaction pathway through a
nucleophilic methyl group transfer to the iodide anion. The smaller
peaks at m/z = 209 and m/z = 166 account for methyl-iodo-triazole
and the 3MeTA dimer, respectively.
2
tion of NH I also takes place in a manner similar to those observed
From the information revealed by the ToFMS and FTIR spectra,
it is clear that the decomposition of Me1ATI proceeds primarily
through a ring N –N bond scission to form NH I and 3MeTA. How-
2
in Scheme 1, forming NH , N , and I .
3
2
2
1
2
ever, there exists a secondary reaction pathway, leading to the
3.4. Thermal decomposition pathways of Me1ATN
formation of CH I and 1-amino-1,2,3-triazole (1ATA). 1ATA was
3
◦
found to be stable when subjected to thermolysis at 350 C. The
Me1ATN is a colorless crystalline solid with a high degree of
hygroscopicity. Hence, this salt was also dried under vacuum for
FTIR and mass spectra of 1ATA are shown in Figs. 10 and 11, respec-
◦
Fig. 12. FTIR spectrum of species from rapid thermolysis of Me1ATN at 340 C and 1 atm N2.

A. Chowdhury, S.T. Thynell / Thermochimica Acta 505 (2010) 33–40
39
Scheme 3. Proposed reaction pathway for Me1ATI.
and the –CH3 stretch near 3000 cm 1 indicate its formation. Due
to overlapping of bands, it was not possible to exactly identify
CH ONO , if present, among the products.
−
2
8
4 h and stored in a desiccator. Me1ATN has a melting point of
6–88 C, and decomposition is initiated at 185 C, as measured
◦
◦
by DSC [22]. Small quantities of the sample were thermolyzed
at temperatures near 340 C. Fig. 12 shows an FTIR spectrum of
the gaseous products generated during thermolysis of Me1ATN at
3
2
◦
Fig. 13 shows a ToFMS spectrum from the thermolysis of
Me1ATN taken at 340 C and 1 atm Ar, He and residual air. Simi-
lar to Me4ATN, the decomposition products include HNO , as seen
◦
◦
3
40 C and 1 atm. According to Table 1, the major species present
3
among the decomposition products were HNO , H O and N O,
from the peaks at m/z = 46 and m/z = 30. Although these peaks are
3
2
2
similar to the FTIR spectra obtained from Me4ATN. Besides these
principal species, smaller quantities of CO , NO , and HNCO were
also indicative of CH ONO , formation of this species is most likely
limited due to lack of conclusive evidence. The peaks at m/z = 83 and
m/z = 84 shows the presence of 3MeTA and its protonated form. The
3
2
2
2
also detected. Though it was difficult to exactly ascertain the pres-
−
1
ence of 3MeTA, the band due to ring torsion around 760 cm
smaller species found in the FTIR spectra, such as H O at m/z = 18,
2
Scheme 4. Proposed reaction pathway for Me1ATN.

4
0
A. Chowdhury, S.T. Thynell / Thermochimica Acta 505 (2010) 33–40
N O and CO at m/z = 44 are also present. The fragmentation of
1-0432, with Dr Michael Berman serving as the program manager.
The authors are grateful to Dr J.M. Shreeve of the University of
Idaho for the preparation and shipment of the materials used in this
study.
2
2
3
MeTA leads to the smaller peaks at m/z = 55, 54, 52, 42, and 27.
In order to further elucidate the decomposition pathways of
Me1ATN, the species evolution profiles were extracted from the
◦
FTIR spectra at 340 C and displayed in Fig. 14. The pattern of evo-
lution of various species was found to be remarkable similar to
References
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2
2
[
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2] J.S. Wilkes, M.J. Zaworotko, J. Chem. Soc., Chem. Commun. (1992) 965–967.
at a fast rate, followed by HNO . As observed in case of Me4ATN,
3
the evolution of HNO3 is considerably delayed. Based on the FTIR
and ToFMS spectra, and the knowledge gained from studying the
decomposition of Me1ATI and Me4ATN, the decomposition path-
ways of Me1ATN are shown in Scheme 4. The decomposition of
Me1ATN was mostly similar to that of Me4ATN, barring the ambigu-
ity regarding the involvement of the methyl group in the initiation
reaction, as seen in Me1ATI. The primary reaction pathway involves
[3] J.D. Holbrey, K.R. Seddon, Clean Prod. Process. 1 (4) (1999) 223–236.
[
[
4] A.S. Larsen, J.D. Holbrey, F.S. Tham, C.A. Reed, J. Am. Chem. Soc. 122 (2000)
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7
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[
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the formation of NH ONO2 and 3MeTA. The smaller species N O
2
2
[8] J. Shah, J. Brennecke, E. Maginn, Green Chem. 4 (2002) 112–118.
[9] M.J. Earle, K.R. Seddon, Pure Appl. Chem. 72 (7) (2000) 1391–1398.
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[13] H. Xue, J.M. Shreeve, Adv. Mater. 17 (2005) 2142–2146.
and H O are formed via fast secondary reactions. Methyl-triazolium
2
[
[
nitrate, formed as a by-product during these reactions, decomposes
to form the HNO3 detected at a later stage, and more 3MeTA. Addi-
tionally, 3MeTA was oxidized by nitric acid to form the smaller
molecular weight species.
[
[
14] Y.R. Mirzaei, H. Xue, J.M. Shreeve, Inorg. Chem. 43 (2004) 361–367.
15] H. Xue, S.W. Arritt, B. Twamley, J.M. Shreeve, Inorg. Chem. 43 (2004)
7
972–7977.
4
. Conclusions
[
[
[
[
[
16] H. Xue, Y. Gao, B. Twamley, J.M. Shreeve, Inorg. Chem. 44 (2005) 5068–5072.
17] H. Xue, Y. Gao, B. Twamley, J.M. Shreeve, Chem. Mater. 17 (2005) 191–198.
18] H. Xue, B. Twamley, J.M. Shreeve, J. Org. Chem. 69 (2004) 1397–1400.
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Pyrot. 28 (2003) 174–180.
Confined rapid thermolysis studies with FTIR spectroscopy and
ToF mass spectrometry as the diagnostic tools were conducted
on four methyl-amino-triazolium-based compounds, Me4ATI,
Me4ATN, Me1ATI, and Me1ATN. The change in the ring structure
from a 1,2,4-triazole to a 1,2,3-triazole did not have a significant
effect on the thermal stability and the major decomposition path-
ways for the compounds. For both the iodide compounds Me4ATI
and Me1ATI, the amino group was involved in the initiation reac-
tion, leading to the formation of NH3 and methyl-iodo-triazoles.
However, unlike Me4ATI, in case of Me1ATI, the secondary initia-
[
[
21] G.W. Drake, T.W. Hawkins, J. Boatz, L. Hall, A. Vij, Propel. Explos. Pyrot. 30 (2005)
156–163.
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(2007) 15–23.
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24] E.S. Kim, H.S. Lee, C.F. Mallery, S.T. Thynell, Combust. Flame 110 (1997)
[
[
2
39–255.
[25] A. Chowdhury, S.T. Thynell, Thermochim. Acta 443 (2006) 164–177.
[
[
26] C.F. Mallery, S.T. Thynell, Combust. Sci. Technol. 122 (1997) 113–129.
27] L.S. Rothman, D. Jacquemart, A. Barbe, D. Chris Benner, M. Birk, L.R. Brown,
M.R. Carleer, J.C. Chackerian, K. Chance, L.H. Coudert, V. Dana, V.M. Devi, J.M.
Flaud, R.R. Gamache, A. Goldman, J.M. Hartmann, K.W. Jucks, A.G. Maki, J.Y.
Mandin, S.T. Massie, J. Orphal, A. Perrin, C.P. Rinsland, M.A.H. Smith, J. Tennyson,
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Spectrosc. Radiat. Transfer 96 (2) (2005) 139–204.
[28] W.G. Linstrom, Mallard (Eds.), NIST Chemistry WebBook, NIST Standard Refer-
ence Database Number, vol. 69, National Institute of Standards and Technology,
Gaithersburg, MD, 2005.
tion pathway involving a methyl group transfer to form CH I was
3
found to be active. In case of the nitrate compounds, decomposition
was initiated by the nitrate ion scavenging the amino group to form
NH ONO and the corresponding methylated triazole. NH ONO
2
2
2
2
reacted vigorously with the parent nitrates to form H O, N O and
2
2
N2 through secondary reactions. The methylated triazoles were
subsequently oxidized by HNO3 to form smaller molecular weight
species.
[
[
29] A. Chowdhury, S.T. Thynell, P. Lin, Thermochim. Acta 485 (2009) 1–13.
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131–139.
Acknowledgment
[31] T. Shimanouchi, Natl. Bur. Stand. (1972) 1–160.
[
[
32] T. Shimanouchi, J. Phys. Chem. Ref. Data 6 (1977) 993–1102.
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This material is based upon work supported by the U.S. Air
Force Office of Scientific Research under Contract No. FA9550-07-
[34] G. Herzberg, C. Reid, Discuss. Faraday Soc. 9 (1950) 92.