Correlating structure with thermal properties for a series of 1-alkyl-4-methyl-1,2,4-triazolium ionic liquids

Article abstract of DOI:10.1021/jo4003932

Thermal properties (T_m and T_d) are reported for a series of 1-alkyl-4-methyl-1,2,4-triazolium ionic liquids where the alkyl chain length R and anion [X^-] were varied. The highest melting transitions were observed when a lo

Full text of DOI:10.1021/jo4003932

Note
pubs.acs.org/joc
Correlating Structure with Thermal Properties for a Series of 1‑Alkyl-
4-methyl-1,2,4-triazolium Ionic Liquids
Lucas A. Daily and Kevin M. Miller*
Department of Chemistry, Murray State University, 1201 Jesse D. Jones Hall, Murray, Kentucky 42071, United States
S
* Supporting Information
ABSTRACT: Thermal properties (Tm and Td) are reported for a series of
1-alkyl-4-methyl-1,2,4-triazolium ionic liquids where the alkyl chain length
R and anion [X−] were varied. The highest melting transitions were
observed when a longer alkyl chain or smaller anion was employed.
Thermal stability was the greatest when anions with weak hydrogen
1
bonding capability were used. Correlations were also made between H
NMR chemical shift values in acetone-d6 and the hydrogen bonding capability of the anion.
hile the ionic liquid field has been dominated by the 1,3-
dialkylimidazolium cation, there remains a strong desire
structure. The two parameters of interest include (1) the length
of the N-1 alkyl chain R and (2) the anion [X−]. While both of
these structural features have a profound influence on the
thermal properties of 1,3-dialkylimidazolium ionic liquids, a
similar study has yet to be reported for the 1,4-dialkyl-1,2,4-
triazolium system.12−14
A number of methods have been reported for the
regioselective N-1 alkylation of 1,2,4-triazole, the majority of
which employ basic conditions such as sodium alkoxide,
sodium hydroxide, or 1,8-diazabicyclo[5.4.0]undec-7-ene
(DBU).15−17 We found that Shreeve’s procedure (Scheme 1)
W
to explore other classes of ionic liquids in order to tailor
physical properties for specific applications.1,2 Nitrogen-rich
ionic liquids in particular have gained interest due to their
potential advantages over conventional energy-rich materials,
the properties of which include higher densities and heats of
formations, improved thermal stabilities and lower vapor
pressures and flammabilities.3 Within this group, 1,2,4-
triazolium-based ionic liquids are of interest since the
nitrogen-rich heterocycle possesses a large, positive heat of
formation (ΔHf° (1,2,4-triazole) = 109 kJ/mol compared to
ΔHf°(imidazole) = 58.5 kJ/mol).4 Additionally, since molecular
nitrogen is a primary product of decomposition for the 1,2,4-
triazole ring, the corresponding 1,2,4-triazolium ionic liquids
have been envisioned as a more environmentally acceptable
alternative to many materials currently used in the propellant
and explosives industries.3
Scheme 1. Synthesis of 1-Alkyl-4-methyl-1,2,4-triazolium
Ionic Liquids 2
While the interest in 1,2,4-triazolium-containing ionic liquids
has increased over the past decade, the majority of research has
focused on materials specifically designed for energetic and
electrochemical applications.3,5,6 Shreeve and co-workers
recently reviewed their work on “energy-rich” triazolium ionic
liquids in which a number of amino-, nitro-, or azido-
substituted 1,2,4-triazolium cations were combined with
energy-rich anions such as perchlorate or nitrate.7 Shreeve
has also explored the properties of several fluoroalkylated 1,2,4-
triazolium salts as well as the free-radical polymerization of 1-
vinyl-1,2,4-triazolium monomers in an attempt to make energy-
rich polymeric materials.8−10 The utility of the 1,2,4-triazolium
ring in “tunable” aryl/alkyl ionic liquids has also recently been
explored by Strassner.11
Despite these advances in the chemistry and applications of
1,2,4-triazolium ionic liquids, we are interested in exploring a
more fundamental structure−activity study. In this paper, the
preparation of a series of 1-alkyl-4-methyl-1,2,4-triazolium ionic
liquids is reported where we attempt to correlate thermal
properties such as melting point (Tm) (or glass transition Tg)
and thermal stability (Td) with variations in ionic liquid
provided the highest yields of 1-alkyl-1,2,4-triazoles 1a−h after
high vacuum distillation.8 For each synthetic experiment, 1,2,4-
triazole was alkylated at the N-1 position with the appropriate
1-bromoalkane in the presence of sodium methoxide. The
resulting 1-alkyl-1,2,4-triazoles 1a−h were then quaternized at
the N-4 position with methyl iodide to provide the desired 1-
alkyl-4-methyl-1,2,4-triazolium iodides 2a−h. All of the ionic
liquids were solids at room temperature with the exception of
Received: February 22, 2013
Published: March 26, 2013
© 2013 American Chemical Society
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The Journal of Organic Chemistry
Note
2b (R = propyl), which was a viscous, yellow oil. Compound
identification and purity were determined by 1H and 13C NMR
spectroscopy and elemental analysis.
Scheme 2. Synthesis of 1-Butyl-4-methyl-1,2,4-triazolium
Ionic Liquids 3
Thermal transitions (Tm or Tg) of the 1-alkyl-4-methyl-1,2,4-
triazolium liquids 2a−h were determined by differential
scanning calorimetry (DSC), the results of which are
summarized in Table 1. The ability to correlate melting point
Table 1. Thermal Properties of 1-Alkyl-4-methyl-1,2,4-
triazolium Ionic Liquids 2
−
−
[NTf2 ], and tetrafluoroborate [BF4 ]. Compound identifica-
tion and purity were determined by 1H and 13C NMR
spectroscopy and high-resolution mass spectrometry (HRMS).
The amount of residual iodide in each ionic liquid was
determined to be less than 0.01% w/w by ion chromatog-
raphy.21
compd
R
Tm (°C)
Td (°C)
a
methyl
ethyl
122
2a
2b
2c
2d
2e
2f
33.9
194
194
194
188
184
181
180
177
propyl
butyl
−53.2 (Tg)
54.7
pentyl
hexyl
70.3
1-Butyl-4-methyl-1,2,4-triazolium ionic liquids 2c and 3a−g
were analyzed by 1H NMR spectroscopy, and a summary of the
chemical shift values for triazolium ring protons H3 and H5 in
acetone-d6 and DMSO-d6 (0.05 M of ionic liquid) is provided
in Table 2. In general, the 1,2,4-triazolium ring protons
96.3
heptyl
octyl
108.4
113.2
126.7
2g
2h
dodecyl
a
Reference 10.
1
Table 2. Triazolium Ring H NMR Chemical Shift Data for
1-Butyl-4-methyl-1,2,4-triazolium Ionic Liquids 3
and structure for ionic liquids is critical since many of the
prospective applications rely heavily on the depressed melting
points (Tm) and viscosities that result from decreased
symmetry and weak intermolecular interactions between the
cation and anion. An initial decrease in melting point (Tm)
value was observed when the alkyl chain R was increased from
R = methyl (literature Tm = 122 °C), ultimately resulting in a
glass transition (Tg) value of −53.2 °C for 1-propyl-4-methyl-
1,2,4-triazolium iodide 2b (lit.10 Tg −52 °C).This initial
decrease in thermal transition is attributed to a disruption of
symmetry properties, resulting in poorer crystal packing and a
decrease in ionic interactions. Upon further increasing the alkyl
chain from 2b (R = propyl) to 2h (R = dodecyl), a steady rise
in Tm value was observed. As the chain length and mass of the
compound increases, a greater amount of energy is needed to
overcome the growing number of van der Waals interactions.
Thermal decomposition (Td) values for the 1,2,4-triazolium
iodides 2 were determined by thermogravimetric analysis
(TGA) and are also summarized in Table 1. Although there is
not a large variation, a small but consistent decrease in Td value
was observed as the chain length was increased from 2c (R =
butyl) to 2h (R = dodecyl). We speculate that this trend may
be due to an increase in the stability of the degradation
product(s), however a comprehensive decomposition study was
beyond the scope of this work. Both of the observed trends in
Tm and Td values are comparable to compiled data for a
number of analogous 1,3-dialkylimidazolium ionic liquids.12 All
thermal measurements (DSC and TGA) were completed in
duplicate with an error of 2 °C on samples that had been
stored in a vacuum oven at 60 °C for 48 h.
acetone-d6 (ppm)
DMSO-d6 (ppm)
compd
anion
H3
H5
H3
H5
−
3a
3b
2c
3c
3d
3e
3f
[CF3CO2
]
9.19
9.20
9.21
9.23
9.18
9.06
9.06
9.03
11.02
10.80
10.73
10.68
10.54
10.01
9.99
9.17
9.14
9.14
9.14
9.13
9.12
9.12
9.11
10.18
10.06
10.05
10.06
10.05
10.02
10.02
10.01
−
[NO3
[I−]
]
[OMs−]
[OTs−]
[OTf−]
−
[NTf2
]
−
3g
[BF4
]
9.87
appeared further downfield in acetone-d6. The effect of solvent
on the chemical shift values of imidazolium ring protons has
been reported by Lue and Gibson, and their results are
consistent with the findings reported here.18,22 Ions are better
solvated in DMSO-d6 and thus cause a decrease in hydrogen
bonding interaction between the anion and the cation. This
results in chemical shift values that appear further upfield with
little change being observed when the anion is varied. Use of
acetone-d6 resulted in tighter ion pairs and downfield chemical
shift values that are more dependent upon the choice of anion
due to poorer solvation.
The chemical shift values are strongly dependent upon the
hydrogen-bonding capability of the anion, with the largest
separation in values and greatest downfield shifts observed for
the more acidic H5 proton in the weakly solvating acetone-
d6.17,23 In this series, the largest chemical shift value was
observed at 11.02 ppm when the strongly coordinating
To probe the effects of anion selection, a series of 1-butyl-4-
methyl-1,2,4-triazolium ionic liquids 3 was prepared (Scheme
2). From the previously prepared 1-butyl-4-methyl-1,2,4-
triazolium iodide 2c, anion-exchange reactions using the
appropriate silver or lithium salt were performed to achieve
the desired triazolium-based ionic liquids 3a−g.18−20 The
anions were chosen to encompass a wide variety of sizes and
hydrogen bond capabilities and included trifluoroacetate
−
trifluoroacetate [CF3CO2 ] was employed. Conversely, ionic
liquids which employed anions with the weakest hydrogen
bonding capability, namely triflate [OTf−], bis-
−
(trifluoromethylsulfonyl)imide [NTf2 ], and tetrafluoroborate
−
[BF4 ], provided the furthest upfield shifts at 10.01 ppm, 9.99
ppm and 9.87 ppm, respectively. Overall, the chemical shift of
the H5 proton generally increased in acetone-d6 with increasing
−
−
−
[CF3CO2 ], nitrate [NO3 ], mesylate [OMs−], tosylate
anion basicity and ability to hydrogen bond: [CF3CO2 −] >
−
[OTs−], triflate [OTf−], bis(trifluoromethylsulfonyl)imide
[NO3 ] > [I−] > [OMs−] > [OTs−] > [OTf−] > [NTf2 ] >
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Note
20
[BF4 ]. The separation of chemical shift values between H3
and H5 was observed to decrease with decreasing hydrogen
bonding ability, presumably due to increased delocalization of
the cation in the ring, resulting in a greater similarity in
chemical environment for the two protons. In comparison to
values reported for analogous 1-butyl-3-methylimidazolium
ionic liquids, hydrogen bonding capability had a greater effect
on the magnitude of the chemical shift values of the 1,2,4-
triazolium ionic liquids. We speculate that this finding is due to
the increased acidity of the triazolium ring.23,24
−
Table 3. Thermal Properties of 1-Butyl-4-methyl-1,2,4-
triazolium Ionic Liquids 3
compd
anion
Tm (°C)
Td (°C)
−
3a
3b
2c
3c
3d
3e
3f
[CF3CO2
]
−74.0
9.2
167
190
194
254
264
310
316
272
−
[NO3
[I−]
]
54.7
[OMs−]
[OTs−]
−58.0
−40.6
−68.1
−70.2
−16.1
[OTf−]
−
Correlation between anion hydrogen bond ability and the 1H
NMR chemical shift values of the H2 proton for a series of 1-
butyl-4-methylimidiazolium ionic liquids was reported by
Spange.25,26 In their study, they determined a hydrogen bond
accepting capability parameter βN, which was based upon UV/
vis absorption data of a solvochromatic dye, normalized with
1H NMR data. The chemical shift values for the H5 proton of
our 1,2,4-triazolium ionic liquids 2c and 3a−g in acetone-d6
were plotted against Spange’s βN values (Figure 1), and a
[NTf2
]
−
3g
[BF4
]
rings of the tosylate group to participate in π-stacking
interactions.
Unlike melting point values, thermal stability can be directly
correlated to the ability of an anion to hydrogen bond.12,18,20 In
the 1-butyl-4-methyl-1,2,4-triazolium ionic liquid series 3, use
of a strongly coordinating anion such as trifluoroacetate
−
[CF3CO2 ] led to the poorest thermal stability (Td = 167
°C) whereas use of weaker anions such as triflate [OTf−] or
−
bis(trifluoromethylsulfonyl)imide [NTf2 ] lead to Td values in
excess of 300 °C. Overall, the Td values observed for ionic
liquids 3 are comparable with the reported values for other
1,2,4-triazolium-containing ionic liquids,8,10 but they are
generally less stable than the analogous 1-butyl-3-methylimida-
zolium ionic liquids, many of which are stable in excess of 400
°C.12,20
In summary, a series of 1-alkyl-4-methyl-1,2,4-triazolium
ionic liquids was prepared and analyzed by 1H NMR
spectroscopy, DSC and TGA. Two parameters were targeted
as part of this structure−activity study: the length of the alkyl
chain R at position N-1 and the anion [X−]. The highest
melting transitions (Tm or Tg) were observed when ionic
liquids with long alkyl chains or large anions were tested.
Comparison of the 1H NMR chemical shift values of the acidic
H5 proton for 1-butyl-4-methyl-1,2,4-triazolium ionic liquids 2c
and 3a−g indicated a correlation with the hydrogen bonding
ability of the anion. The highest thermal stability (Td) was
observed when weakly coordinating anions (such as bis-
1
Figure 1. Correlation of the H NMR chemical shift values of the H5
proton with the hydrogen-bond accepting parameter βN.
reasonable correlation (r2 = 0.93) was found. Thus, it appears
that the relationship between H NMR chemical shift values
and anion hydrogen bonding ability reported for imidazolium
ionic iquids is translatable to the 1,2,4-triazolium system
reported here.
1
−
(trifluoromethylsulfonyl)imide [NTf2 ] or triflate [OTf−])
were employed.
As before, all samples were stored in a vacuum oven at 60 °C
for 48 h prior to thermal analysis. All thermal measurements
(DSC and TGA) were completed in duplicate with an error of
2 °C. When comparing the thermal transitions of the 1-butyl-
4-methyl-1,2,4-triazolium ionic liquids 3, as determind by DSC,
all compounds exhibited an endothermic transition which
corresponded to a melting point (Tm). Melting point
correlations in imidazolium-containing ionic liquids have been
difficult to establish, but the size of the anion appears to be of
greater importance than hydrogen bonding ability.18,20,27 This
general trend was also observed for 1-butyl-4-methyl-1,2,4-
triazolium ionic liquids 3 (Table 3). Implementation of larger
EXPERIMENTAL SECTION
■
General Experimental Methods. All commercial reagents were
used without further purification. All solvents were reagent or HPLC
grade. Anhydrous acetone and acetonitrile (CH3CN) were used
1
without further purification. H and 13C NMR spectra were obtained
on a 400 MHz spectrometer at ambient temperature. Chemical shift
values are reported in parts per million relative to using residual
solvent signals as internal standards (acetone-d6: H, 2.05 ppm; 13C,
1
1
1
29.84 ppm, DMSO-d6: H, 2.50 ppm; 13C, 39.52 ppm, or CDCl3: H,
7.27 ppm; 13C, 77.00 ppm). Ionic liquids 2 and 3 were stored in a
vacuum oven at 60 °C for 48 h prior to spectroscopic and thermal
analyses. Differential scanning calorimetry (DSC), at a heating rate of
10 °C/min on 5−10 mg samples, was performed to determine thermal
transitions (Tm and Tg). Reported values were determined from the
second heating cycle. Thermal stabilities were studied under a constant
nitrogen flow (50 mL/min) using a thermogravimetric analyzer
(TGA) at a heating rate of 10 °C/min. All thermal experiments were
completed in duplicate and values are reported with an error of 2 °C.
High resolution mass spectrometry (HRMS) was conducted on a
MALDI-TOFMS in the positive or negative ion mode.
−
anions such as bis(trifluoromethylsulfonyl)imide [NTf2 ] and
−
trifluoroacetate [CF3CO2 ] resulted in ionic liquids that
exhibited reduced Tm values, presumably due to the disruption
of crystal lattice packing. Ionic liquids containing smaller anions
such as iodide [I−], nitrate [NO3 ] and tetrafluoroborate
−
−
[BF4 ] displayed the highest melting transitions. Within the
sulfonate anion series, use of the tosylate [OTs−] anion
provided a Tm value that was higher than expected, an
observation that we postulate is due to the ability of the phenyl
Preparation 1-Alkyl-1,2,4-triazoles 1a−h. Triazoles 1a,16 1b,10
1c,8 1d,15 1e,28 1f,8 and 1g29 have been previously reported. The
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The Journal of Organic Chemistry
Note
synthesis of 1-docedyl-1,2,4-triazole 1h has not been previously
reported. 1-Dodecyl-1,2,4-triazole 1h was prepared by following
Shreeve’s method as described below.8
method described above: 1H NMR (400 MHz, acetone-d6) δ 10.72 (s,
1 H), 9.28 (s, 1 H), 4.56 (t, J = 7.4 Hz, 3 H), 4.19 (s, 3 H), 1.95−2.03
(m, 2 H), 1.21−1.45 (m, 8 H), 0.85 (t, J = 7.3 Hz, 3 H); 13C NMR
(100 MHz, acetone-d6) δ 146.1, 143.9, 53.1, 35.2, 32.2, 29.4, 29.3,
26.6, 23.1, 14.2. Anal. Calcd for C10H20IN3: C, 38.85; H, 6.52; N,
13.59. Found: C, 38.85; H, 6.53; N, 13.48.
1-Dodecyl-1,2,4-triazole (1h). To a solution of 1,2,4-triazole (1.00
g, 14.4 mmol) in methanol (15 mL) was added sodium methoxide
solution (2.7 mL of 5.4 M solution in methanol, 14.3 mmol). 1-
Bromododecane (3.46 g, 14.6 mmol) was then added dropwise using
an addition funnel. The resulting solution was allowed to stir at room
temperature for 2 h followed by warming to 60 °C, where the stirred
solution was held for 24 h. The methanol was then removed under
reduced pressure, and the resulting oily solid was purified by high
vacuum distillation (105−108 °C, 0.1 mmHg) to afford a colorless oil,
which solidified upon cooling to give a white solid (2.91 g, 85% yield):
1H NMR (400 MHz, CDCl3) δ 8.03 (s, 1 H), 7.91 (s, 1 H), 4.12 (t, J =
7.3 Hz, 2 H), 1.80−1.91 (m, 2 H), 1.17−1.32 (m, 18 H), 0.80−0.89
(m, 3 H); 13C NMR (100 MHz, CDCl3) δ 144.3, 143.1, 53.3, 35.8,
32.0, 29.7, 29.7, 29.6, 29.48, 29.46, 29.1, 28.9, 26.4, 22.8, 14.3. Anal.
Calcd for C14H27N3: C, 70.83; H, 11.46; N, 17.70. Found: C, 70.59; H,
11.37; N, 17.88.
1-Octyl-4-methyl-1,2,4-triazolium Iodide 2g. 1-Octyl-4-methyl-
1,2,4-triazolium iodide (2g) was obtained as an off-white solid after
recrystallization from hot acetonitrile (87% yield) following the
1
general method described above: H NMR (400 MHz, acetone-d6) δ
10.71 (s, 1 H), 9.26 (s, 1 H), 4.58 (t, J = 7.2 Hz, 2 H), 4.20 (s, 3 H),
1.99−2.07 (m, 2 H), 1.21−1.46 (m, 10 H), 0.85 (t, J = 7.2 Hz, 3 H);
13C NMR (100 MHz, acetone-d6) δ 146.2, 144.0, 53.1, 35.3, 32.4, 29.7,
29.6, 29.4, 26.7, 23.2, 14.3. Anal. Calcd for C11H22IN3: C, 40.88; H,
6.86; N, 13.00. Found: C, 40.67; H, 6.99; N, 12.93.
1-Dodecyl-4-methyl-1,2,4-triazolium Iodide (2h). 1-Dodecyl-4-
methyl-1,2,4-triazolium iodide (2h) was obtained as a white solid
after recrystallization from hot acetonitrile (84% yield) following the
1
general method described above: H NMR (400 MHz, acetone-d6) δ
Preparation of Ionic Liquids 2a−h. 1-Alkyl-4-methyl-1,2,4-
triazolium iodides 2 were prepared by following a modification of
Shreeve’s procedure.10 1-Propyl-4-methyl-1,2,4-triazolium iodide 2b
has been previously reported.10 The remaining ionic liquids 2a and
2c−h have not been reported. Representative procedures for ionic
liquids 2a and 2c are provided below along with reaction yields and
characterization data for the remaining ionic liquids 2d−h.
10.57 (s, 1 H), 9.15 (s, 1 H), 4.57 (t, J = 7.08 Hz, 2 H), 4.19 (s, 3 H),
1.97−2.07 (m, 2 H), 1.21−1.45 (m, 18 H), 0.86 (t, J = 6.3 Hz, 3 H);
13C NMR (100 MHz, CDCl3) δ 152.0, 142.8, 49.9, 32.0, 29.8, 29.6,
29.5, 29.4, 29.1, 19.7, 14.2. Anal. Calcd for C15H30IN3: C, 47.50; H,
7.97; N, 11.08. Found: C, 47.51; H, 8.01; N, 11.14.
Preparation of Ionic Liquids 3a−h. Anion-exchange reactions
followed the general guidelines of previously published proce-
dures.18−20,27 The quantity of residual iodide was determined by ion
chromatography under the following conditions: 4.5 mM CO32−/1.4
1-Ethyl-4-methyl-1,2,4-triazolium Iodide (2a). In a 50-mL round-
bottomed flask equipped with a magnetic stir bar was dissolved 1-
ethyl-1,2,4-triazole (1a) (1.40 g, 14.0 mmol) in anhydrous acetonitrile
(20 mL) under nitrogen. Methyl iodide (3.07 g, 22.0 mmol) was then
added, and the resulting stirred solution was warmed to 60 °C and
held for 24 h. The solvents and excess methyl iodide were removed
under reduced pressure to afford 2a as a light yellow solid (3.29 g, 95%
−
mM HCO3 eluent concentration, 1.2 mL/min flow rate, 31 mA
suppressor current. After chromatographic calibration via aqueous
standards prepared by serial dilution of 1000 ppm [I−] stock (from
sodium iodide), 10−15 mg of each ionic liquid 3a−h was dissolved in
1 mL of DI water and injected.21 The amounts of residual iodide in
each ionic liquid were determined to be less than the method
detection limit, which was 0.01% w/w.
1
yield): H NMR (400 MHz, acetone-d6) δ 10.67 (s, 1 H), 9.27 (s, 1
H), 4.59 (q, J = 7.2 Hz, 2 H), 4.19 (s, 3 H), 1.60 (t, J = 7.2 Hz, 3 H);
13C NMR (100 MHz, acetone-d6) δ 146.1, 143.8, 48.5, 35.3, 14.1.
Anal. Calcd for C5H10IN3: C, 25.12; H, 4.22; N, 17.58. Found: C,
24.95; H, 4.38; N, 17.31.
1-Butyl-4-methyl-1,2,4-triazolium Trifluoroacetate (3a). In a 25
mL round-bottomed flask was dissolved 1-butyl-4-methyl-1,2,4-triazole
iodide (2c) (1.00 g, 3.74 mmol) in anhydrous acetone (10 mL). Silver
trifluoroacetate (0.84 g, 3.87 mmol) was then added, and the resulting
mixture was allowed to stir overnight at room temperature in the dark.
The solids were then filtered, and the solvent was removed under
1-Butyl-4-methyl-1,2,4-triazolium Iodide (2c). In a 25 mL round-
bottomed flask was dissolved 1-butyl-1,2,4-triazole (1c) (1.00 g, 7.99
mmol) in anhydrous acetonitrile (10 mL). Iodomethane (2.27 g, 15.0
mmol) was then added, and the resulting stirred solution was warmed
to 60 °C and held for 24 h. The solvent and excess iodomethane was
then removed under reduced pressure to afford a light orange solid
(1.96 g, 92% yield): 1H NMR (400 MHz, acetone-d6) δ 10.73 (s, 1 H),
9.31 (s, 1 H), 4.58 (t, J = 7.2 Hz, 2 H), 4.21 (s, 3 H), 1.99 (m, 2 H),
1.43 (m, 2 H), 0.95 (t, J = 7.2 Hz, 3 H); 13C NMR (100 MHz,
acetone-d6) δ 146.2, 144.1, 52.8, 35.2, 31.3, 19.9, 13.6. Anal. Calcd for
C7H14IN3: C, 31.48; H, 5.28; N, 15.73. Found: C, 31.78; H, 5.27; N,
15.41.
1
reduced pressure to give a light yellow oil (0.88 g, 93% yield): H
NMR (400 MHz, DMSO-d6) δ 10.18 (s, 1 H), 9.17 (s, 1 H), 4.37 (t, J
= 7.2 Hz, 2 H), 3.90 (s, 3 H), 1.82 (m, 2 H), 1.28 (m, 2 H), 0.90 (t, J =
7.1 Hz, 3 H); 13C NMR (100 MHz, DMSO-d6) δ 157.9 (q, J = 31 Hz,
CO), 145.5, 143.1, 117.4 (q, J = 285 Hz, CF3), 51.2, 33.9, 30.2, 18.6,
13.2; HRMS (MALDI-TOF) m/z [M-CO2CF3]+ calcd for C7H14N3
140.1188, found 140.1191.
1-Butyl-4-methyl-1,2,4-triazolium Nitrate 3b. In a 25 mL round-
bottomed flask was dissolved 1-butyl-4-methyl-1,2,4-triazole iodide
(2c) (1.00 g, 3.74 mmol) in anhydrous acetone (10 mL). Silver nitrate
(0.65 g, 3.82 mmol) was then added, and the resulting mixture was
allowed to stir overnight at room temperature in the dark. The solids
were then filtered, and the solvent was removed under reduced
1-Pentyl-4-methyl-1,2,4-triazolium Iodide (2d). 1-Pentyl-4-meth-
yl-1,2,4-triazole (2d) was obtained as a light yellow solid (97% yield)
1
following the general method described above: H NMR (400 MHz,
acetone-d6) δ 10.74 (s, 1 H), 9.34 (s, 1 H), 4.56 (t, J = 7.2 Hz, 2 H),
4.22 (s, 3 H), 1.98−2.08 (m, 2 H), 1.32−1.42 (m, 4 H), 0.90 (t, J = 7.0
Hz, 3 H); 13C NMR (100 MHz, acetone-d6) δ 146.1, 143.9, 53.0, 35.3,
28.9, 28.6, 22.6, 14.0. Anal. Calcd for C8H16IN3: C, 34.18; H, 5.74; N,
14.95. Found: C, 33.95; H, 5.75; N, 14.90.
1-Hexyl-4-methyl-1,2,4-triazolium Iodide (2e). 1-Hexyl-4-methyl-
1,2,4-triazolium iodide (2e) was obtained as a white solid (93% yield)
after recrystallization from hot acetonitrile following the general
method described above: 1H NMR (400 MHz, acetone-d6) δ 10.70 (s,
1 H), 9.25 (s, 1 H), 4.58 (t, J = 7.2 Hz, 2 H), 4.20 (s, 3 H), 1.99−2.07
(m, 2 H), 1.28−1.46 (m, 6 H), 0.87 (t, J = 7.0 Hz, 3 H); 13C NMR
(100 MHz, CDCl3) δ 144.7, 142.6, 53.0, 35.7, 31.0, 28.7, 25.8, 22.3,
13.9. Anal. Calcd for C9H18IN3: C, 36.62; H, 6.15; N, 14.24. Found: C,
36.36; H, 6.26; N, 14.19.
1
pressure to give a clear, yellow oil (0.72 g, 95% yield): H NMR (400
MHz, acetone-d6) δ 10.80 (s, 1 H), 9.20 (s, 1 H), 4.52 (t, J = 7.2 Hz, 2
H), 4.13 (s, 3 H), 1.96 (m, 2 H), 1.38 (m, 2 H), 0.94 (t, J = 7.2 Hz, 3
H); 13C NMR (100 MHz, acetone-d6) δ 146.5, 145.1, 52.6, 34.7, 31.4,
19.9, 13.6; HRMS (MALDI-TOF) m/z [M − NO3]+ calcd for
C7H14N3 140.1188, found 140.1190.
1-Butyl-4-methyl-1,2,4-triazolium Mesylate (3c). In a 25 mL
round-bottomed flask was dissolved 1-butyl-4-methyl-1,2,4-triazole
iodide (2c) (1.00 g, 3.74 mmol) in anhydrous acetone (10 mL). Silver
mesylate (0.81 g, 3.97 mmol) was then added, and the resulting
mixture was allowed to stir for 48 h at room temperature in the dark.
The solids were then filtered, and the solvent was removed under
1
reduced pressure to give a clear, colorless oil (0.83 g, 89% yield): H
1-Heptyl-4-methyl-1,2,4-triazolium Iodide (2f). 1-Heptyl-4-meth-
yl-1,2,4-triazolium iodide (2f) was obtained as a white solid (93%
yield) after recrystallization from hot acetonitrile following the general
NMR (400 MHz, acetone-d6) δ 10.65 (s, 1 H), 9.32 (s, 1 H), 4.51 (t, J
= 7.0 Hz, 2 H), 4.14 (s, 3 H), 1.95 (m, 2 H), 1.41 (m, 2 H), 0.94 (t, J =
7.0 Hz, 3 H); 13C NMR (100 MHz, acetone-d6) δ 146.6, 145.1, 52.5,
4199
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The Journal of Organic Chemistry
Note
40.1, 34.8, 31.4, 19.9, 13.6; HRMS (MALDI-TOF) m/z [M −
SO3CH3]+ calcd for C7H14N3 140.1188, found 140.1188.
AUTHOR INFORMATION
■
Corresponding Author
*Email address: kmiller38@murraystate.edu.
1-Butyl-4-methyl-1,2,4-triazolium Tosylate (2d). To a 25 mL
round-bottomed flask was dissolved 1-butyl-4-methyl-1,2,4-triazole
iodide (2c) (1.00 g, 3.74 mmol) in anhydrous acetone (10 mL). Silver
tosylate (0.41 g, 3.82 mmol) was then added, and the resulting mixture
was allowed to stir overnight at room temperature in the dark. The
solids were then filtered, and the solvent was removed under reduced
pressure to afford a light yellow oil (1.05 g, 89% yield): 1H NMR (400
MHz, acetone-d6) δ 10.54 (s, 1 H), 9.18 (s, 1 H), 7.65 (d, J = 7.8 Hz, 2
H), 7.12 (d, J = 7.8 Hz, 2 H), 4.42 (t, J = 7.3 Hz, 2 H), 4.09 (s, 3 H),
2.31 (s, 3 H), 1.87 (m, 2 H), 1.33 (m, 2 H), 0.86 (t, J = 7.3 Hz, 3 H);
13C NMR (100 MHz, acetone-d6) δ 146.7, 144.9, 139.2, 129.0, 126.7,
52.5, 34.8, 31.4, 21.2, 19.9, 13.7; HRMS (MALDI-TOF) m/z [M − p-
SO3PhCH3]+ calcd for C7H14N3 140.1188, found 140.1189; [M −
C7H14N3]− calcd for C7H7SO3 171.0116, found 171.0111.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We acknowledge financial support from the Research
Corporation for Science Advancement (Single-Investigator
Cottrell College Science Award) and the Department of
Chemistry at Murray State University. Thermal data were
acquired at the Jones/Ross Research Center at Murray State
University. NMR spectroscopy was provided as a result of
support from the National Science Foundation under CHE-
0922033 (awarded to MSU Chemistry Department). High-
resolution mass spectrometry was completed at the University
of Kentucky Mass Spectrometry Facility.
1-Butyl-4-methyl-1,2,4-triazolium Triflate (3e). To a 25 mL round-
bottomed flask was dissolved 1-butyl-4-methyl-1,2,4-triazole iodide
(2c) (0.50 g, 1.87 mmol) in DI water (5 mL). Silver triflate (0.50 g,
1.97 mmol) was then added, and the resulting mixture was allowed to
stir for 48 h at room temperature. The solids were then filtered, and
the solvent was removed under reduced pressure to afford a clear,
REFERENCES
■
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yellow oil (0.38 g, 93% yield): H NMR (400 MHz, acetone-d6) δ
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triazole iodide (2c) (1.00 g, 3.74 mmol) in anhydrous acetone (10
mL). Silver tetrafluoroborate (0.74 g, 3.82 mmol) was then added, and
the resulting mixture was allowed to stir overnight at room
temperature in the dark. The solids were then filtered and the solvent
was removed under reduced pressure to give a clear, yellow oil (0.78 g,
91% yield): 1H NMR (400 MHz, acetone-d6) δ 9.87 (s, 1 H), 9.03 (s,
1 H), 4.52 (t, J = 7.3 Hz, 2 H), 4.12 (s, 3 H), 1.93 (m, 2 H), 1.40 (m, 2
H), 0.94 (t, J = 7.3 Hz, 3 H); 13C NMR (100 MHz, acetone-d6) δ
146.2, 143.8, 52.8, 34.7, 31.4, 19.8, 13.7; HRMS (MALDI-TOF) m/z
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* Supporting Information
Spectroscopic data (1H and 13C NMR) for triazole 1h and
triazolium ionic liquids 2a,c−h and 3a−g. Representative DSC
thermograms for ionic liquids 2a,c−h and 3a−g. This material
is available free of charge via the Internet at http://pubs.acs.org.
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