Thermochemistry of Alkyl Pyridinium Bromide Ionic Liquids
J. Phys. Chem. A, Vol. 114, No. 11, 2010 3787
Ti
0
T
0
0
p,m
0
m
bromide ionic liquids. Results indicate that EPBr has higher
melting and thermal decomposition temperature and phase
transition enthalpy and entropy but lower heat capacity than
PPBr due to the different molecular structures.
H - H
)
∫
C
(s)dT + ∆ H +
298.15
fus
298.15
T
0
∫
C
p,m(l)dT (10)
Tf
Acknowledgment. This work was financially supported by
the National Nature Science Foundation of China under Grant
NSFC 20373072, 20753002, and the Talented Personnel Funds
for Scientific Research of Dalian University of Technology,
China under Grant 893110.
0
p,m
0
C
(s)
∆ H
m
Ti
fus
0
0
S - S
)
∫
dT +
+
T
298.15
[
]
2
98.15
T
Tm
0
p,m
C
(l)
T
∫
[
]
dT (11)
Tf
T
Supporting Information Available: This material is avail-
able free of charge via the Internet at http://pubs.acs.org.
where T
i
is the temperature at which the solid-liquid phase
transition started; T
phase transition ended; ∆fus
of fusion; T is the temperature of solid-liquid phase transition.
f
is the temperature at which the solid-liquid
References and Notes
0
m
H is the standard molar enthalpy
(
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7
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0
0
0
The standard thermodynamic functions, H
298.15 of the two ILs, are listed in Table 2.
T
- H298.15, S
T
-
0
S
7
84.
(
3
.4. The Thermostability Tested by TG-DTG. The TG-
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4
80 K, reaches the maximum rate of weight loss at 541.229 K
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75 K. Similar one-step decomposition process occurs for PPBr
(
5
(
beginning at about 460 K and finishing at about 570 K while
the peak temperature of decomposition is 536.021K.
(
3
.5. Comparison and Estimation of Thermodynamic
(
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Properties for Alkyl Pridinium Bromide Ionic Liquids.
According to experimental data in Sections 3.3-3.4, the
thermodynamic properties as well as the structure of EPBr and
PPBr were compared and estimated as follows:
(
(
(
4
(
a) Molar heat capacity Cp,m(EPBr) < Cp,m(PPBr) reveals that
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ature due to shorter carbon chain in pyridinium cation of
EPBr.
(
(
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(
b) Melting temperature T
transition enthalpy ∆H
m
(EPBr) > T
m
(PPBr) and phase
(PPBr) are pos-
1
m
(EPBr) > ∆H
m
Yun, Y. S. EnViron. Sci. Technol., 2009, 43, 516–521.
sibly because of the fact that the H-π bond effects of
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the more the steric hindrance strengthened, which results
in a decrease of the melting temperature and enthalpy.
c) Thermal decomposition temperature Tdecomp(EPBr) >
(
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(
5
(
(
T
decomp(PPBr) indicates that EPBr is more thermostable
(
than PPBr which is favorable in practical applications
for EPBr.
(
Calorim. 2009, 95, 469–475, 2009.
Conclusions
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Two ionic liquids 1-ethylpyridinium bromide (EPBr) and
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(
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1
-propylpyridinium bromide (PPBr) were prepared and char-
1
090–1093.
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, 371–375.
1
acterized. The structure and purity were verified by H NMR.
The thermodynamic properties of EPBr and PPBr were studied
with adiabatic calorimetry and thermogravimatric analysis. The
phase change behavior and thermodynamic properties were
compared and estimated in the series of alkyl pyridinium
(
(
5
JP9047538