Heat Capacity of Room-Temperature Ionic Liquids: A Critical Review Yauheni U. Paulechkaa… Chemistry Faculty, Belarusian State University, Leningradskaya 14, 220030 Minsk, Belarus 共Received 11 May 2010; accepted 21 June 2010; published online 27 September 2010兲
Experimental data on heat capacity of room-temperature ionic liquids in the liquid state were compiled and critically evaluated. The compilation contains data for 102 aprotic ionic liquids from 63 literature references and covers the period of time from 1998 through the end of February 2010. Parameters of correlating equations for temperature dependence of the heat capacities were developed. © 2010 American Institute of Physics. 关doi:10.1063/1.3463478兴 Key words: critically evaluated data; correlating equations; heat capacity; ionic liquids.
CONTENTS 1. 2. 3. 4. 5. 6.
1. 2. 3. 4.
5. 6. 7. 8. 9. 10. 11.
12.
13.
Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Experimental Techniques for Determination of Heat Capacity of Ionic Liquids. . . . . . . . . . . . . . Criteria for Estimation of Uncertainties in Experimental Data. . . . . . . . . . . . . . . . . . . . . . . . . Trends in Heat Capacity of Ionic Liquids. . . . . . Establishment of Recommended Values. . . . . . . . References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2 2 8 12 18 22
14. 15. 16. 17. 18.
List of Tables
19.
Calorimeters used for determination of heat capacity of ILs. . . . . . . . . . . . . . . . . . . . . . . . . . . Abbreviations of IL cations. . . . . . . . . . . . . . . . . Abbreviations of IL anions. . . . . . . . . . . . . . . . . . Summary of data on heat capacity of 1-alkyl-3-methylimidazolium ILs 关Cnmim兴An 共n = 1 – 3兲. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Summary of data on heat capacity of 1-butyl-3-methylimidazolium halides. . . . . . . . . . Summary of data on heat capacity of 关C4mim兴BF4 共174501-65-6兲. . . . . . . . . . . . . . . . . Summary of data on heat capacity of 关C4mim兴PF6 共174501-64-5兲. . . . . . . . . . . . . . . . . Summary of data on heat capacity of 关C4mim兴CF3CO2 共174899-94-6兲. . . . . . . . . . . . . Summary of data on heat capacity of 关C4mim兴OTf 共174899-66-2兲. . . . . . . . . . . . . . . . . Summary of data on heat capacity of 关C4mim兴NTf2 共174899-83-3兲. . . . . . . . . . . . . . . . Summary of data on heat capacity of 1-butyl-3-methylimidazolium ILs with various anions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Summary of data on heat capacity of 1-hexyl-3-methylimidazolium ILs. . . . . . . . . . . .
20. 2 3 5
21.
14 15 15 16 17 17 18 19
List of Figures
10
1. 2.
10
3.
10
4.
11
5.
11
6.
11
7. 8.
12 9. 13
a兲
0047-2689/2010/39„3…/033108/23/$47.00
14
8
10. Electronic mail:
[email protected] © 2010 American Institute of Physics.
Summary of data on heat capacity of 1-octyl-3-methylimidazolium ILs. . . . . . . . . . . . . Summary of data on heat capacity of disubstituted imidazolium ILs. . . . . . . . . . . . . . . Summary of data on heat capacity of trisubstituted imidazolium ILs. . . . . . . . . . . . . . . Summary of data on heat capacity of monosubstituted pyridinium ILs. . . . . . . . . . . . . . Summary of data on heat capacity of polysubstituted pyridinium ILs. . . . . . . . . . . . . . . Summary of data on heat capacity of ammonium ILs. . . . . . . . . . . . . . . . . . . . . . . . . . . Summary of data on heat capacity of phosphonium ILs. . . . . . . . . . . . . . . . . . . . . . . . . . Summary of data on heat capacity of pyrrolidinium and piperidinium ILs. . . . . . . . . . . Coefficients of recommended polynomials for heat capacity of ILs. . . . . . . . . . . . . . . . . . . . . . .
11. 033108-1
Heat capacity of ILs at T = 298.15 K. . . . . . . . . . Deviation of experimental heat capacities from Eq. 共2兲 for 关C2mim兴BF4. . . . . . . . . . . . . . . . . . . . Deviation of experimental heat capacities from Eq. 共2兲 for 关C2mim兴NTf2. . . . . . . . . . . . . . . . . . . Deviation of experimental heat capacities from Eq. 共2兲 for 关C2mim兴EtSO4. . . . . . . . . . . . . . . . . . Deviation of experimental heat capacities from Eq. 共2兲 for 关C4mim兴Br. . . . . . . . . . . . . . . . . . . . . Deviation of experimental heat capacities from Eq. 共2兲 for 关C4mim兴BF4. . . . . . . . . . . . . . . . . . . . Deviation of experimental heat capacities from Eq. 共2兲 for 关C4mim兴PF6. . . . . . . . . . . . . . . . . . . . Deviation of experimental heat capacities from Eq. 共2兲 for 关C4mim兴OTf. . . . . . . . . . . . . . . . . . . . Deviation of experimental heat capacities from Eq. 共2兲 for 关C4mim兴NTf2. . . . . . . . . . . . . . . . . . . Deviation of experimental heat capacities from Eq. 共2兲 for 关C4mim兴N共CN兲2. . . . . . . . . . . . . . . . . Deviation of experimental heat capacities from
18 19 19 20 20 20 20 20 20 21
J. Phys. Chem. Ref. Data, Vol. 39, No. 3, 2010
033108-2
12. 13. 14. 15.
YAUHENI U. PAULECHKA
Eq. 共2兲 for 关C6mim兴BF4. . . . . . . . . . . . . . . . . . . . Deviation of experimental heat capacities from Eq. 共2兲 for 关C6mim兴NTf2. . . . . . . . . . . . . . . . . . . Deviation of experimental heat capacities from Eq. 共2兲 for 关C8mim兴BF4. . . . . . . . . . . . . . . . . . . . Deviation of experimental heat capacities from Eq. 共2兲 for 关C8mim兴NTf2. . . . . . . . . . . . . . . . . . . Deviation of experimental heat capacities from Eq. 共2兲 for 关C4mprl兴NTf2. . . . . . . . . . . . . . . . . . .
21
Reference
21 21 21
1. Introduction Heat capacity is one of the basic thermodynamic properties of liquids. The temperature dependence of thermodynamic properties of a compound such as entropy, enthalpy, and Gibbs energy is calculated from its heat capacity. The effect of temperature on reaction enthalpies and equilibrium constants is also evaluated using heat capacities of the participants. Room-temperature ionic liquids 共ILs兲 are a group of liquids which attract interest due to their possible use in various fields of science and technology. The potential of ILs as heat transfer fluids for heat exchange in chemical plants and solar thermal power generation was considered in Refs. 1 and 2, and heat capacity was noted to be an important criterion determining the applicability of these liquids. At present, the most exhaustive compilation of IL heat capacities is the IL Thermo database,3 which contains raw heat capacity data with assigned uncertainties from major thermodynamic and thermophysical journals. The uncertainties in that database are based mainly on the typical uncertainty of the method used. In the latest supplement of a wellknown review on heat capacity of liquids by Zábranský et al.,4 experimental data on heat capacity of 50 ILs from nine literature sources were evaluated and the recommended values were presented. The IUPAC round-robin project 2002005-1-100 “Thermodynamics of ionic liquids, ionic liquid mixtures, and the development of standardized systems” was recently completed.5,6 In the course of the project, thermophysical properties including heat capacity as well as phase equilibrium properties for the reference sample of 1-hexyl-3methylimidazolium bis共trifluoromethanesulfonyl兲imide and its mixtures were measured in various laboratories, and the recommended values were developed. In this compilation, experimental data on heat capacity of ILs in the liquid state were compiled and critically evaluated using various criteria. The compilation contains data for 102 aprotic ionic liquids from 63 literature sources and covers the period of time from 1998 through the end of February 2010. Based on the evaluated dataset, parameters of correlating equations for the temperature dependence of the heat capacities were developed.
2. Experimental Techniques for Determination of Heat Capacity of Ionic Liquids In most works, heat capacity of ILs is determined by calorimetric methods. Types of calorimeters used for the meaJ. Phys. Chem. Ref. Data, Vol. 39, No. 3, 2010
TABLE 1. Calorimeters used for determination of heat capacity of ILs
21
7 and 8 9 10–13 14–16 17 18–25
26 17 21 27 28 29 and 30 31–33 34 35 36 37 38–41 42 43 and 44 45 46 and 47
48
49 and 50 51 42 52
42 53 54–56 57–59 60–63 64 and 65 66 67
Calorimeter
Typical uncertainty 共%兲
Adiabatic calorimeters 共AC兲 Homemade Homemadea Homemade Jecc Torisha JTA-2000C TAU-1 TAU-10
1.5 4 7 0.1–0.2 0.4 0.4
Differential scanning calorimeters 共DSC兲 Commercial DSC Homemade Homemadeb Mettler Toledo DSC821e Mettler Toledo DSC821e/700 Mettler Toledo DSC822e Mettler Toledo DSC822e PerkinElmer Diamond DSC PerkinElmer Pyris 1 DSC PerkinElmer Pyris Diamond TG/DTA TA Instruments TA Instruments DSC 2010 TA Instruments Q100 DSC TA Instruments Q100 DSC TA Instruments Q100 DSC TA Instruments Q1000 DSC
6 5 10 40 5c 20 11 20 20 12 60 13 5 12 12 11
Isoperibol calorimeters 共IC兲 Homemade
2
Modulated DSC 共MDSC兲 TA Instruments DSC 2910 TA Instruments DSC 2920 TA Instruments Q100 DSC TA Instruments Q2000 DSC Tian-Calvet DSC 共TC兲 Setaram BT2.15 Setaram C-80 Setaram MicroDSCII Setaram MicroDSCIII Setaram MicroDSCIII Setaram MicroDSCIII Setaram DSC 111 Setaram TG-DSC 111
25 25 5 15
5 0.7c 0.6 0.6 3 20 3c 13
a
Adiabatic scanning calorimeter. One-cup scanning calorimeter. c Below 370 K. b
surements and their typical uncertainties evaluated as described in Sec. 3 are presented in Table 1. Differential scanning calorimeters 共DSCs兲 and modulated DSC 共MDSC兲 are the most popular instruments, but their uncertainty is at least 5%. The unexpectedly high uncertainty of the DSC measurements for ILs was also noted in Ref. 5. More accurate data were obtained with adiabatic and Tian–Calvet DSC calorimeters; the uncertainty in the best works was less than 1%. As follows from Table 1, the calorimeter itself is not a guarantee of high quality of the results. Uncertainties of the data obtained with calorimeters of the same model in different laboratories may vary considerably.
HEAT CAPACITY OF IONIC LIQUIDS
033108-3
TABLE 2. Abbreviations of IL cations Abbreviation
Structure
Chemical Name Imidazolium cations
关Cnmim兴+
1-Alkyl-3-methyl-1H-imidazolium
H
N n
+
关C3CNmim兴+
N
N 关C6Fmim兴+
F
F F
N
F F
F
1-Methyl-3-共3,3,4,4,5,5,6,6,6-nonafluorohexyl兲-1H-imidazolium
N
F F
1-共3-Cyanopropyl兲-3-methyl-1H-imidazolium
N
+
+
F
N
关Cnmmim兴+
1-Alkyl-2,3-dimethyl-1H-imidazolium
H
N n
N
+
关C3CNmmim兴
3-共3-Cyanopropyl兲-1,2-dimethyl-1H-imidazolium
N
N
N
+
Pyridinium 关Cnpy兴
H
+
+
1-Alkylpyridinium
N
n 关C3CNpy兴+
1-共3-Cyanopropyl兲pyridinium
N
+
N 关Cn3mpy兴+
H
+
1-Alkyl-3-methylpyridinium
N
n 关C44mpy兴+
1-Butyl-4-methylpyridinium +
N 关Cnapy兴+
N
+
H
1-Alkyl-4-共dimethylamino兲pyridinium
N
n
J. Phys. Chem. Ref. Data, Vol. 39, No. 3, 2010
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YAUHENI U. PAULECHKA TABLE 2. Abbreviations of IL cations—Continued
Abbreviation
Structure
Chemical Name
关共Cn兲2nic兴+
3-共Alkoxycarbonyl兲-1-alkylpyridinium
H
+
O
N
n
H n
O
关C6mmpy兴+
1-Hexyl-3,5-dimethylpyridinium
+
N 关C6mapy兴+
4-共Dimethylamino兲-1-hexyl-3-methylpyridinium
N +
N 关C6C3共C2兲2py兴+
3,5-Diethyl-1-hexyl-2-propylpyridinium
+
N
Ammonium 关C4mmmN兴+
N , N , N-Trimethyl-1-butanaminium
+
N 关共C4兲3mN兴+
N , N-dibutyl-N-methyl-1-butanaminium +
N 关共C4兲4N兴+
N , N , N-Tributyl-1-butanaminium +
N 关C2OHCnmmN兴+
H
+
N-共2-Hydroxyethyl兲-N , N-dimethyl-1-alkanaminium
N
n
HO 关cpma兴+
H
+
O
N x
n
Cocosalkyl pentaethoxy methylammoniuma
H O
H y
n ~ 13, = 5 Phosphonium 关共C4兲4P兴+
Tetrabutylphosphonium +
P
J. Phys. Chem. Ref. Data, Vol. 39, No. 3, 2010
HEAT CAPACITY OF IONIC LIQUIDS
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TABLE 2. Abbreviations of IL cations—Continued Abbreviation
Structure
Chemical Name
关共C6兲3C14P兴+
Trihexyl共tetradecyl兲phosphonium +
P
H 14
Pyrrolydinium and piperidinium 关Cnmprl兴
+
1-Alkyl-1-methylpyrrolidinium
+
N
H n
关C3mpip兴+
1-Methyl-1-propylpiperidinium
+
N
a
Referred to in Chemical Abstracts as N-关2-关2-共2-Hydroxyethoxy兲ethoxy兴ethyl兴-N-关共2-hydroxyethoxy兲ethyl兴-N-methyl-1-tridecanaminium. TABLE 3. Abbreviations of IL anions
Abbreviation
Structure
Name Halides
Cl
−
Br I
Cl
−
−
Chloride
−
Bromide
Br
−
I
−
Iodide Fluorine-containing anions
F
BF−4
Tetrafluoroborate -
F
B
F
F PF−6
F
F
-
P
F CF3CO−2
Hexafluorophosphate
F F
F F
O
F
O
F
F
OTf−
F
Trifluoromethanesulfonate
S F
F
O
F
O
-
O O
-
S
-
O
F
NTf−2
Trifluoroacetate
N
O O
S F
1,1,1-trifluoro-N-关共trifluoromethyl兲sulfonyl兴methanesulfonamide
F F
J. Phys. Chem. Ref. Data, Vol. 39, No. 3, 2010
033108-6
YAUHENI U. PAULECHKA TABLE 3. Abbreviations of IL anions—Continued
Abbreviation
Structure
Name
F
CTf−3
Tris关共trifluoromethyl兲sulfonyl兴methide
F O O
F
S
O O
-
S
F FAP
F
O O
F
−
S
F
Tris共pentafluoroethyl兲trifluorophosphate
F
F FF
F
F
F
F
F
F
F FF
-
P
F F F
F
F
F F Sulfates and sulfonates
MeSO−4
O
O
-
Methylsulfate
S O
O EtSO−4
O
O
-
Ethylsulfate
S O
O OctSO−4
O
O
-
Octylsulfate
H
S O
O
8 CH3共OC2H4兲2SO−4
O
O
-
2-共2-Methoxyethoxy兲ethylsulfate
O
S Tos−
O
O
O S O
Doc−
O O O
-
O
S O
O
O O
J. Phys. Chem. Ref. Data, Vol. 39, No. 3, 2010
4-Methylbenzenesulfonate
O
-
1,4-bis共2-ethylhexyl兲sulfobutanedioate
HEAT CAPACITY OF IONIC LIQUIDS
033108-7
TABLE 3. Abbreviations of IL anions—Continued Abbreviation
Structure
Name Amino-acid anions
O
Ser−
L-Serinate
H2N
O
-
OH Cys
O
−
L-Cysteinate
H2N
O
-
SH H N
Pro−
L-Prolinate
O O
-
O
Val−
H2N
L-Valinate
O
-
O
Thr−
H2N
L-Threonate
O
-
OH Lys
−
O
O
Tau−
-
L-Lysinate
H2N H2N
NH2
O S
Taurinate
O
-
O Other NO−3
O O
-
Nitrate
N
O -
N共CN兲−2
N-cyanocyanamide
N
N
N Cl
FeCl−4
Cl
Tetrachloroferrate -
Fe Cl Cl
AcO
−
O O
Acetate -
J. Phys. Chem. Ref. Data, Vol. 39, No. 3, 2010
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YAUHENI U. PAULECHKA
3. Criteria for Estimation of Uncertainties in Experimental Data All available data were critically evaluated. The following criteria were used in this evaluation: 共1兲 共2兲 共3兲 共4兲 共5兲 共6兲
uncertainty reported by the authors; typical uncertainty of the used technique; consistency of the data from different sources for one IL; consistency of the data for one series of ILs; uncertainty of the data for different ILs measured in one laboratory; purity of the samples.
The evaluation procedure involved a step-by-step application of these criteria to all ILs until a consistent set of uncertainties was obtained. Temperature dependence of the uncertainties was not considered. Criterion 共3兲 allowed one to reveal uncertainty of the heat capacities for the compounds studied in a number of works. Criterion 共4兲 made it possible to extend the evaluation procedure to series of ILs differing by anion 共for example, 1-butyl-3-methylimidazolium ILs兲, cation 共for example, tetrafluoroborate ILs兲, or length of the alkyl chain 共for example, 1-alkyl-3-methylimidazolium bromides兲. This was realized by applying the methods described in Sec. 4. Criterion 共4兲 was especially useful for the data with uncertainties exceeding ⫾1%. Generally, uncertainty of all data obtained in a laboratory using the same technique and
instrument and evaluated with criteria 共1兲–共5兲 was assumed to be equal to their maximum uncertainty. Purity of the samples was also considered in the analysis of the heat capacity data. Normally, either the minimum content of a title compound in the sample or the amount of some impurities such as halides, water, metal, or ammonium ions are reported. In adiabatic calorimetry, the total amount of impurities is often determined by the fractional melting technique as well. The influence of impurities on heat capacity of ILs was analyzed in Ref. 25. At the reported impurity level, only water may have a significant effect on heat capacity of ILs. If the mass fraction of water was determined in the original paper either as a definite value or an upper limit, it was taken into account in the evaluation of the uncertainty. It was assumed that water had an additive contribution to the specific heat capacity of a sample. The effect of other impurities was not considered. All uncertainties given in this article are the combined expanded uncertainties corresponding to the 95% confidence interval for the normal distribution 共coverage factor k = 2兲. Abbreviations of IL ions mentioned in this paper are shown in Table 2 and Table 3. The ions are split into groups according to their chemical nature. Within one group, the ions are ordered subject to the number of substituents and the amount of nonhydrogen atoms in them. The available data on heat capacity of ILs are presented in Tables 4–20. The compounds in the latter tables are arranged according to the order of cations in Table 2. The arrangement of compounds with the same cation corresponds to the order of anions in Table 3.
TABLE 4. Summary of data on heat capacity of 1-alkyl-3-methylimidazolium ILs 关Cnmim兴An 共n = 1 – 3兲
Reference
Temp. range 共K兲
Sample purity w 共impurity content兲a 共%兲
Method
Aparicio et al.65
318–368
关C1mim兴MeSO4 共97345-90-9兲 ⬎99.0 共0.020w兲
TC
Paulechka et al.19
350–370
关C2mim兴Br 共65039-08-9兲 99.79, 98.2 molb 共0.21w兲
AC
Yu et al.38 Van Valkenburg et al.49 Mutch and Wilkes50 Sanmamed et al.56 Waliszewski et al.57
303–358 273–403 283–403 283–323 283–358
关C2mim兴BF4 共143314-16-3兲 ⬎97.0 共0.065w, 0.113h, 1.59⫻ 10−4m兲 N/A ⬎98 共0.8w兲 共 ⬍ 0.4w兲
Holbrey et al.51
353–453
Ficke et al.33
Estimated uncertainty 共%兲
20
Reported C p共298.15 K兲 共J K−1 mol−1兲 341 共318.15 K兲
0.4
264.8 共350 K兲c
DSC MDSC MDSC TC TC
13 25 25 2.5 2
306 共303.2 K兲 251 253 305 308.1
共 ⬍ 0.2w兲
MDSC
25
289 共353.15 K兲
283–343
关C2mim兴CF3CO2 共174899-65-1兲 共0.0678w, 0.1h兲
DSC
11
316
283–343 303–358 315–425 328–413 313–423
共4.4⫻ 10 w兲 ⬎98.0 N/A N/A N/A
DSC DSC DSC MDSC TC
11 13 5 5 5
362 379 386 392 384
关C2mim兴PF6 共155371-19-0兲
关C2mim兴OTf 共145022-44-2兲 33
Ficke et al. Yu et al.38 Diedrichs and Gmehling42 Diedrichs and Gmehling42 Diedrichs and Gmehling42
J. Phys. Chem. Ref. Data, Vol. 39, No. 3, 2010
−3
共303.2 K兲 共315.15 K兲 共328.15 K兲 共313.13 K兲
HEAT CAPACITY OF IONIC LIQUIDS
033108-9
TABLE 4. Summary of data on heat capacity of 1-alkyl-3-methylimidazolium ILs 关Cnmim兴An 共n = 1 – 3兲—Continued Estimated uncertainty 共%兲
Reported C p共298.15 K兲 共J K−1 mol−1兲
Temp. range 共K兲
Sample purity w 共impurity content兲a 共%兲
Method
293–318
共⬍0.13w, ⬍0.055h兲
TC
Yamamuro et al.8 Shimizu et al.16 Paulechka et al.20 Fredlake et al.31 Ge et al.45 Waliszewski et al.57
180–300 271–300 260–370 298–327 293–358 283–358
关C2mim兴NTf2 共174899-82-2兲 N/A ⬎97e 98.4 molb ⬎99 共0.023w兲 共0.01w, ⬍5 ⫻ 10−4h, 2.35⫻ 10−4m兲 共 ⬍ 0.4w兲
AC AC AC DSC DSC TC
1.5 0.1 0.4 11 12 1.1
500d 506.5f 505.7 524 525 509.2
Zhang et al.10 Paulechka et al.25 Fernandez et al.27 Ficke et al.33 Yu et al.38 Ge et al.45 Zuo et al.48 García-Miaja et al.61–63 Tan et al.68
200–390 190–370 283–373 283–343 303–358 293–358 303–323 293–318 260–350
关C2mim兴EtSO4 共342573-75-5兲 N/A ⬎99 ⬎95 共0.2w, ⬍3 ⫻ 10−3h兲 共6.9⫻ 10−3w兲 ⬎99.2 共0.0279w兲 ⬎98.9g 共⬍0.13w, ⬍0.055h兲 N/A
AC AC DSC DSC DSC DSC IC TC N/Ah
7 0.4 40 11 13 12 2 3 6
378 382.8 421 376 430 共303.2 K兲 457 380 共303.15 K兲 394 403
Yu et al.38
303–358
关C2mim兴CH3共OC2H4兲2SO4 共790663-77-3兲 ⬎98.2
DSC
13
526 共303.2 K兲
Aparicio et al.65
318–368
关C2mim兴Tos 共328090-25-1兲 99.4 共0.033w兲
TC
20
484.2 共318.15 K兲
Yu et al.38
303–358
⬎99.9
DSC
13
328 共303.2 K兲
Paulechka et al.19 Paulechka et al.25
212–370 222–370
关C3mim兴Br 共85100-76-1兲 99.3, 92.5 molb 共0.7w兲 98.7 molb
AC AC
Reference García-Miaja et al.
61–63
3
363
关C2mim兴N共CN兲2 共923019-22-1兲
1.5 0.4
281.4 280.7
a
a, ammonium; h, halides; m, metals; w, water. Mole fraction purity. c Corrected for water content. d Estimated from figure. e Purity according to 1H NMR. f Only the value at T = 298.15 K is reported. g Purity according to liquid chromatography. h Method not stated, probably AC. b
J. Phys. Chem. Ref. Data, Vol. 39, No. 3, 2010
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YAUHENI U. PAULECHKA TABLE 5. Summary of data on heat capacity of 1-butyl-3-methylimidazolium halides
Method
Estimated uncertainty 共%兲
Reported C p共298.15 K兲 共J K−1 mol−1兲
N/A N/A N/A 共 ⬍ 0.02w兲
AC DSC DSC MDSC
1.5 11 12 25
317b 323 276 299 共343.15 K兲
210–370 298–327 298–323
关C4mim兴Br 共85100-77-2兲 99.86, 98.3 molc 共0.14w兲 N/A 共0.03w兲
AC DSC DSC
0.4 11 12
311.4d 317 296
208–300
N/A
AC
1.5
Reference
Temp. range 共K兲
Sample purity w 共impurity contenta兲 共%兲
Yamamuro et al.7 Fredlake et al.31 Zhang et al.36 Holbrey et al.51
230–380 298–327 298–453 343–453
Paulechka et al.19 Fredlake et al.31 Kim et al.43,44 Yamamuro et al.7
关C4mim兴Cl 共79917-90-1兲
关C4mim兴I 共65039-05-6兲
314b
a
a, ammonium; h, halides; m, metals; w, water. Estimated from figure. c Mole fraction purity. d Corrected for water content. b
TABLE 6. Summary of data on heat capacity of 关C4mim兴BF4 共174501-65-6兲 Sample purity w 共impurity contenta兲 共%兲
Temp. range 共K兲
Reference 11
Zhang et al. Paulechka et al.25 Du et al.29 Fredlake et al.31 Yu et al.39,40 Kim et al.43,44 Van Valkenburg et al.49
181–390 189–370 233–313 298–327 303–358 298–323 223–573
Rebelo et al.54
278–333
Sanmamed et al.56 Waliszewski et al.57 García-Miaja et al.62,63 Nieto de Castro et al.66
283–323 283–358 293–318 308–423
N/A ⬎99 N/A 共⬍8 ⫻ 10−4h, ⬍1.8⫻ 10−3a, 0.19w兲 ⬎99.0 共 ⬍ 0.2w兲 共0.02w, 1.3⫻ 10−3h兲 共0.08w, 0.159h, 1.15⫻ 10−3m兲 共0.13w, 0.131h, 0.127m兲c ⬎98, 99.7 mold 共7.5⫻ 10−3w, 共0.8– 1.3兲 ⫻ 10−2h兲 ⬎99 共0.1w兲 共 ⬍ 0.4w兲 共⬍0.13w, ⬍0.055h兲 共⬍0.02w, ⬍5 ⫻ 10−4h兲
Method
Estimated uncertainty 共%兲
AC AC DSC DSC DSC DSC MDSC
7 0.4 20 11 13 12 25
384 367.1 368b 351 368 389 326
TC
0.8
364.7
TC TC TC TC
0.6 0.9 3 3e
366.2 364.8 363 367 共308.16 K兲
a
a, ammonium; h, halides; m, metals; w, water. Only the value at T = 298.15 K is reported. c Not stated which sample was used. d Mole fraction purity. e Below 370 K. b
TABLE 7. Summary of data on heat capacity of 关C4mim兴PF6 共174501-64-5兲
Reference
Temp. range 共K兲
Sample purity w 共impurity contenta兲 共%兲
Method
Estimated uncertainty 共%兲
Triolo et al.9 Kabo et al.17 Kabo et al.17 Fredlake et al.31 Yu et al.39,40 Holbrey et al.51 Troncoso et al.55 Nieto de Castro et al.66
198–210 195–300 300–550 298–327 303–358 303–453 283–323 308–423
共0.0124w, ⬍7 ⫻ 10−4h兲 99.56 molc 共 ⬍ 5 ⫻ 10−3h兲 99.56 molc 共 ⬍ 5 ⫻ 10−3h兲 共 ⬍ 3 ⫻ 10−4h兲 ⬎99.0 共 ⬍ 0.2w兲 共 ⬍ 0.2w兲 ⬎99.8d 共2 ⫻ 10−3h兲 共⬍0.02w, ⬍5 ⫻ 10−4h兲
AC AC DSC DSC DSC MDSC TC TC
4 0.4 5 11 13 25 0.6 3e
a
a, ammonium; h, halides; m, metals; w, water. Figure only is given. c Mole fraction purity. d Purity according to 1H NMR. e Below 370 K. b
J. Phys. Chem. Ref. Data, Vol. 39, No. 3, 2010
Reported C p共298.15 K兲 共J K−1 mol−1兲 b
408.7 398 413 共303.2 K兲 327 共303.15 K兲 407.7 411 共308.16 K兲
Reported C p共298.15 K兲 共J K−1 mol−1兲
HEAT CAPACITY OF IONIC LIQUIDS
033108-11
TABLE 8. Summary of data on heat capacity of 关C4mim兴CF3CO2 共174899-94-6兲
Reference Strechan et al.
23
Temp. range 共K兲
Sample purity w 共impurity contenta兲 共%兲
188–370
99.8, 97.7 mol 共0.2w兲 b
Method
Estimated uncertainty 共%兲
Reported C p共298.15 K兲 共J K−1 mol−1兲
AC
0.4
408.2c
a
a, ammonium; h, halides; m, metals; w, water. Mole fraction purity. c Corrected for water content. b
TABLE 9. Summary of data on heat capacity of 关C4mim兴OTf 共174899-66-2兲
Reference
Temp. range 共K兲
Sample purity w 共impurity contenta兲 共%兲
Paulechka et al.25 Fredlake et al.31 Yu et al.39 Lin et al.41 Diedrichs and Gmehling42 Diedrichs and Gmehling42 Diedrichs and Gmehling42 Ge et al.45 García-Miaja et al.61–63
291–370 298–327 303–358 303–353 315–425 328–413 313–423 293–358 293–318
99.6 molb 共0.28w兲 ⬎98.1 共0.7w兲 ⬎98.1 共0.7w兲 N/A N/A N/A 共0.0681w, ⬍11⫻ 10−4h, 4.24⫻ 10−4m兲 共⬍0.13w, ⬍0.055h兲
Method
Estimated uncertainty 共%兲
Reported C p共298.15 K兲 共J K−1 mol−1兲
AC DSC DSC DSC DSC MDSC TC DSC TC
0.4 11 13 13 5 5 5 12 3
427.7 417 444 共303.2 K兲 c
449 共315.15 K兲 443 共328.15 K兲 448 共313.16 K兲 457 424
a
a, ammonium; h, halides; m, metals; w, water. Mole fraction purity. c Figure only is given, probably same data as in Ref. 39. b
TABLE 10. Summary of data on heat capacity of 关C4mim兴NTf2 共174899-83-3兲
Reference Shimizu et al.15 Blokhin et al.22 Fredlake et al.31 Zhang and Reddy34 Ge et al.45 Holbrey et al.51 Troncoso et al.55
Temp. range 共K兲
Sample purity w 共impurity contenta兲 共%兲
250–300 186–370 298–327 273–473 293–358 293–453 283–328 283–328
99.7 molb 98.5 molb ⬎99 共0.046w兲 共 ⬍ 0.02w兲 共9.6⫻ 10–3w, ⬍5 ⫻ 10−4h, ⬍1 ⫻ 10−4m兲 ⬎98 共0.2w兲 ⬎99.8c 共1.3⫻ 10−2h兲 ⬎99.5 共2 ⫻ 10−3h兲
Method
Estimated uncertainty 共%兲
Reported C p共298.15 K兲 共J K−1 mol−1兲
AC AC DSC DSC DSC MDSC TC TC
0.2 0.4 11 20 12 25 0.6 0.6
565.4 共564.1兲16 565.1 536 456 599 441 567.3 566.5
a
a, ammonium; h, halides; m, metals; w, water. Mole fraction purity. c Purity according to 1H NMR. b
J. Phys. Chem. Ref. Data, Vol. 39, No. 3, 2010
033108-12
YAUHENI U. PAULECHKA TABLE 11. Summary of data on heat capacity of 1-butyl-3-methylimidazolium ILs with various anions
Temp. range 共K兲
Reference
Sample purity w 共impurity contenta兲 共%兲
Method
Estimated uncertainty 共%兲
Reported C p共298.15 K兲 共J K−1 mol−1兲
关C4mim兴CTf3 共731774-32-6兲 Fredlake et al.31
298–327
⬎99
DSC
11
783
关C4mim兴MeSO4 共401788-98-5兲 Fernandez et al.27 Yu et al.
39
García-Miaja et al.61–63
283–373
⬎95 共0.1w, ⬍3 ⫻ 10−3h兲
DSC
40
255
303–358
⬎98.0 共0.9w兲
DSC
13
375 共303.2 K兲
293–318
共⬍0.13w, ⬍0.055h兲
TC
3
416
TC
20
635
DSC
11
643
AC
1
DSC
10
关C4mim兴OctSO4 共445473-58-5兲 Davila et al.64
298–343
⬎95 共⬍0.05w, ⬍0.1h兲
关C4mim兴CH3共OC2H4兲2SO4 共595565-54-1兲 Crosthwaite et al.32
298–338
⬎98 关C4mim兴Tos 共925230-47-3兲
Strechan et al.21 21
Strechan et al.
344–370
96.0 molb
348–470
b
96.0 mol
548.4 共350 K兲
关C4mim兴NO3 共179075-88-8兲 24
Strechan et al.
271–370
98.1 molb
AC
0.4
353.5
0.4
375.7
关C4mim兴N共CN兲2 共448245-52-1兲 25
Paulechka et al.
235–370
97.9 molb
AC
Fredlake et al.31
298–327
共⬍0.0293h, 0.515w兲
DSC
11
365
关C4mim兴FeCl4 共359845-21-9兲 Yamamuro et al.8
185–305
N/A
AC
1.5
415c
AC
0.4
383.2
关C4mim兴AcO 共284049-75-8兲 Strechan et al.23
207–370
⬎99.5
a
a, ammonium; h, halides; m, metals; w, water. Mole fraction purity. Estimated from figure. d Corrected for water content. b c
4. Trends in Heat Capacity of Ionic Liquids The number of ILs for which reliable data are available is large enough to discuss some general trends in their heat capacities. Molar heat capacity in a homologous series of ILs increases with the number of atoms in the alkyl chain 共Fig. 1兲. The points in Fig. 1 represent the weighted average values calculated from the heat capacities reported in the tables of experimental data. The heat capacities of 关C14mim兴NTf2 and 关C18mim兴NTf2 were extrapolated to T = 298.15 K. A linear trend is observed for the numbers of carbon atoms of n = 3 – 14. Deviations from additivity at n = 2 do not exceed 1.6%. The largest deviation of 3.7% was observed for 关C18mim兴NTf2. The increments per CH2-group, ⌬C p共H → CH3兲, are similar in various homologous series and the J. Phys. Chem. Ref. Data, Vol. 39, No. 3, 2010
weighted average value was calculated to be 32.1⫾ 0.3 J K−1 mol−1 at T = 298.15 K. Similar correlations can be found for other temperatures. The constant value of the increment in different homologous series over a wide range of n confirms the validity of additive procedures toward estimating heat capacity of ILs. It means that not only the increment ⌬C p共H → CH3兲 but also the increments and ⌬C p共关Cat1兴An1 ⌬C p共关Cat1兴An1 → 关Cat1兴An2兲 → 关Cat2兴An1兲, where Cat1 and Cat2 are different cations and An1 and An2 are different anions, are expected to be equal for various Cat1 and An1, respectively. This result was used in the evaluation of uncertainties of the heat capacity data. Different additive procedures for estimation of heat capacities of ILs have been proposed.45,70–72
HEAT CAPACITY OF IONIC LIQUIDS
033108-13
TABLE 12. Summary of data on heat capacity of 1-hexyl-3-methylimidazolium ILs
Temp. range 共K兲
Reference
Sample purity w 共impurity contenta兲 共%兲
Method
Estimated uncertainty 共%兲
Reported C p共298.15 K兲 共J K−1 mol−1兲
关C6mim兴Br 共85100-78-3兲 Crosthwaite et al.32
298–338
共⬍1 ⫻ 10−3h, ⬍2 ⫻ 10−3a兲
DSC
11
344
11
416
关C6mim兴BF4 共244193-50-8兲 298–338
共⬍1 ⫻ 10−3h, ⬍2 ⫻ 10−3a兲
DSC
283–323
⬎99 共0.06w兲
TC
0.6
429.8
283–323
⬎97
TC
0.6
431.0
Waliszewski and Piekarski
283–323
⬎97 共 ⬍ 0.2w兲
TC
0.7
432.0
García-Miaja et al.62,63
293–318
共⬍0.13w, ⬍0.055h兲
TC
3
428
Crosthwaite et al.32 Sanmamed et al.
56
Waliszewski58 59
关C6mim兴PF6 共304680-35-1兲 Holbrey et al.51
303–453
共0.9w兲
MDSC
25
425 共303.15 K兲
关C6mim兴OTf 共460345-16-8兲 Diedrichs and Gmehling42
315–425
N/A
DSC
5
526 共315.15 K兲
42
Diedrichs and Gmehling
328–413
N/A
MDSC
5
519 共328.15 K兲
Diedrichs and Gmehling42
313–423
N/A
TC
5
517 共313.14 K兲
关C6mim兴NTf2 共382150-50-7兲 Shimizu et al.14
272–310
⬎99.5,b,c 99.83 mold 共共2.0− 2.9兲 ⫻ 10−3w兲
AC
0.1
631.6
Blokhin et al.18
188–370
⬎99.5,b,c 99.76 mold 共5 ⫻ 10−4w兲
AC
0.4
629.2
Archer
196–370
⬎99.5
DSC
6
641
Crosthwaite et al.32
298–338
共⬍1 ⫻ 10–3h, ⬍2 ⫻ 10–3a兲
DSC
11
583
42
Diedrichs and Gmehling
320–425
N/A
DSC
5
672 共320.15 K兲
Diedrichs and Gmehling42
323–413
N/A
MDSC
5
680 共323.15 K兲
42
Diedrichs and Gmehling
318–418
N/A
TC
5
668 共318.17 K兲
Ge et al.45
293–358
共2.3⫻ 10–3w, ⬍5 ⫻ 10−4h, ⬍1 ⫻ 10−4m兲
26
53
Bochmann and Hefter
e
323–573
b,c
共 ⬍ 0.02w兲
共1.1⫻ 10 w before measurements, 6.5⫻ 10−2w after measurements兲c −2
DSC TC
12
667 f
0.7
644 共325 K兲
a
a, ammonium; h, halides; m, metals; w, water. Purity according to 1H NMR. IUPAC sample. d Mole fraction purity. e At p = 10 MPa. f Below 373 K. b c
J. Phys. Chem. Ref. Data, Vol. 39, No. 3, 2010
033108-14
YAUHENI U. PAULECHKA TABLE 13. Summary of data on heat capacity of 1-octyl-3-methylimidazolium ILs Estimated uncertainty 共%兲
Reported C p共298.15 K兲 共J K−1 mol−1兲
Reference
Temp. range 共K兲
Sample purity w 共impurity contenta兲 共%兲
Method
Crosthwaite et al.32
298–338
关C8mim兴Br 共304680-36-2兲 共⬍1 ⫻ 10–3h, ⬍2 ⫻ 10–3a兲
DSC
11
392
Paulechka et al.25 Crosthwaite et al.32 Sanmamed et al.56 Waliszewski58 Waliszewski and Piekarski59
195–370 298–338 283–323 283–323 283–323
关C8mim兴BF4 共244193-52-0兲 99.4 molb 共⬍1 ⫻ 10–3h, ⬍2 ⫻ 10–3a兲 ⬎99 共0.2w兲 ⬎97 ⬎97 共 ⬍ 0.2w兲
AC DSC TC TC TC
0.4 11 0.7 0.6 0.7
497.8 506 500 499.4 498.3
Wu et al.37
298
N/A
DSC
60
851
Diedrichs and Gmehling42 Diedrichs and Gmehling42 Diedrichs and Gmehling42
315–425 328–413 313–423
N/A N/A N/A
DSC MDSC TC
Paulechka et al.20 Crosthwaite et al.32 Ge et al.45 Bochmann and Hefter53
190–370 298–338 293–358 323–573c
关C8mim兴NTf2 共178631-04-4兲 98.6 molb 共⬍1 ⫻ 10−3h, ⬍2 ⫻ 10−3a兲 共3.8⫻ 10−3w, ⬍5 ⫻ 10−4h, ⬍1 ⫻ 10−4m兲 共1.4⫻ 10−2w before measurements, 3.5⫻ 10−2w after measurements兲
AC DSC DSC TC
关C8mim兴PF6 共304680-36-2兲 关C8mim兴OTf 共403842-84-2兲 5 5 5
0.4 11 12 0.7d
a
a, ammonium; h, halides; m, metals; w, water. Mole fraction purity. c At p = 10 MPa. d Below 370 K. b
TABLE 14. Summary of data on heat capacity of disubstituted imidazolium ILs Estimated uncertainty 共%兲
Reported C p共298.15 K兲 共J K−1 mol−1兲
0.4
897.4 共310 K兲
Reference
Temp. range 共K兲
Sample purity w 共impurity contenta兲 共%兲
Paulechka et al.25
309–370
关C14mim兴NTf2 共404001-53-2兲 98.6 molb AC
Zhu et al.35
343–370
关C16mim兴Br 共132361-22-9兲 共 ⬍ 0.05w兲 DSC
Shimizu et al.16
327–345
关C18mim兴NTf2 共404001-51-0兲 共 ⬍ 1w, ⬍0.1h兲 AC
Zhang et al.30
298.15
关C3CNmim兴BF4 共683224-99-9兲 N/A DSC
20
431
Zhang et al.30
298.15
关C3CNmim兴NTf2 共778593-18-3兲 N/A DSC
20
603
Zhang et al.30
298.15
关C3CNmim兴N共CN兲2 共879866-74-7兲 N/A DSC
20
435
Yamamuro et al.8
210–300
N/A
Crosthwaite et al.32
298–338
关C6Fmim兴NTf2 共872672-61-2兲 共⬍1 ⫻ 10–3h, ⬍2 ⫻ 10–3a兲 DSC
Method
20
1.5
902 共343.15 K兲 1052c
关C3CNmim兴FeCl4
a
a, ammonium; h, halides; m, metals; w, water. Mole fraction purity. c Only the extrapolated value at T = 298.15 K is reported. d Estimated from figure. b
J. Phys. Chem. Ref. Data, Vol. 39, No. 3, 2010
AC
1.5
11
431d
725
604 共315.15 K兲 599 共328.15 K兲 588 共313.17 K兲
692.7 654 733 710 共325 K兲
HEAT CAPACITY OF IONIC LIQUIDS
033108-15
TABLE 15. Summary of data on heat capacity of trisubstituted imidazolium ILs Estimated uncertainty 共%兲
Reported C p共298.15 K兲 共J K−1 mol−1兲
DSC
11
493 共309 K兲
关C3mmim兴NTf2 共169051-76-7兲 ⬎99 共0.082w兲 共0.05w, 3.3⫻ 10−3h兲
DSC MDSC
11 25
555 459
330–372
关C4mmim兴BF4 共402846-78-0兲 N/A
DSC
11
375 共330 K兲
Fredlake et al.31
298–327
N/A
DSC
11
434
Crosthwaite et al.32
298–338
关C6mmim兴NTf2 共384347-22-2兲 共⬍1 ⫻ 10−3h, ⬍2 ⫻ 10−3a兲
DSC
11
686
Zhang et al.30
298.15
关C3CNmmim兴Cl 共683225-04-9兲 N/A
DSC
20
282
Zhang et al.30
298.15
关C3CNmmim兴BF4 共683225-07-2兲 N/A
DSC
20
339
Zhang et al.30
298.15
关C3CNmmim兴NTf2 共929285-32-5兲 N/A
DSC
20
715
Zhang et al.30
298.15
关C3CNmmim兴N共CN兲2 共929285-33-6兲 N/A DSC
20
444
Reference
Temp. range 共K兲
Sample purity w 共impurity contenta兲 共%兲
Method
Fredlake et al.31
309–347
关C2mmim兴NTf2 共174899-90-2兲 ⬎99 共0.022w兲
Fredlake et al.31 Van Valkenburg et al.49
298–327 323–663
Fredlake et al.31
关C4mmim兴PF6 共227617-70-1兲
a
a, ammonium; h, halides; m, metals; w, water.
TABLE 16. Summary of data on heat capacity of monosubstituted pyridinium ILs Estimated uncertainty 共%兲
Reported C p共298.15 K兲 共J K−1 mol−1兲
AC
7
291 共397.31 K兲
AC
7
302 共351.39 K兲
AC
7
383
N/A N/A N/A
DSC MDSC TC
5 5 5
587 共330.15 K兲 604 共328.15 K兲 592 共323.18 K兲
298–338
关C6py兴NTf2 共460983-97-5兲 共⬍1 ⫻ 10–3h, ⬍2 ⫻ 10–3a兲
DSC
11
612
Zhang et al.30
298.15
关C3CNpy兴NTf2 共820972-37-0兲 N/A
DSC
20
632
Zhang et al.30
298.15
关C3CNpy兴N共CN兲2 共929285-34-7兲 N/A
DSC
20
422
Reference
Temp. range 共K兲
Sample purity w 共impurity contenta兲 共%兲
Tong et al.13
395–410
N/A
Tong et al.13
355–395
N/Ab
Zhang et al.12
286–390
N/Ab
Diedrichs and Gmehling42 Diedrichs and Gmehling42 Diedrichs and Gmehling42
330–425 328–418 323–423
Crosthwaite et al.32
Method
关C2py兴Br 共1906-79-2兲 关C3py兴Br 共873-71-2兲 关C4py兴BF4 共203389-28-0兲 关C4py兴NTf2 共187863-42-9兲
a
a, ammonium; h, halides; m, metals; w, water. Impurity content was estimated from the provided data to be ⬎10 mol %.
b
J. Phys. Chem. Ref. Data, Vol. 39, No. 3, 2010
033108-16
YAUHENI U. PAULECHKA TABLE 17. Summary of data on heat capacity of polysubstituted pyridinium ILs Estimated uncertainty 共%兲
Reported C p共298.15 K兲 共J K−1 mol−1兲
Reference
Temp. range 共K兲
Sample purity w 共impurity contenta兲 共%兲
Method
Crosthwaite et al.32
298–338
关C23mpy兴EtSO4 共2073-48-5兲 共⬍1 ⫻ 10−3h, ⬍2 ⫻ 10−3a兲
DSC
11
389
Crosthwaite et al.32 Bandrés et al.46 García-Miaja et al.60
298–338 278–328 293–318
关C43mpy兴BF4 共597581-48-1兲 共⬍1 ⫻ 10−3h, ⬍2 ⫻ 10−3a兲 ⬎99 ⬎99 共 ⬍ 0.12w兲
DSC DSC TC
11 11 3
405 412 388
Crosthwaite et al.32
298–338
关C43mpy兴NTf2 共344790-86-9兲 ⬎99
DSC
11
622
Bandrés et al.46
278–328
关C44mpy兴BF4 共343952-33-0兲 ⬎99
DSC
11
414
Crosthwaite et al.32
298–338
关C63mpy兴Br 共67021-56-1兲 共⬍1 ⫻ 10−3h, ⬍2 ⫻ 10−3a兲
DSC
11
343
Crosthwaite et al.32
298–338
关C63mpy兴NTf2 共547718-92-3兲 共⬍1 ⫻ 10−3h, ⬍2 ⫻ 10−3a兲
DSC
11
624
Bandrés et al.47
278–328
关C83mpy兴BF4 共712355-10-7兲 ⬎98
DSC
11
589
Crosthwaite et al.32
298–338
关C83mpy兴NTf2 共712355-02-7兲 共⬍1 ⫻ 10−3h, ⬍2 ⫻ 10−3a兲
DSC
11
669
Diedrichs and Gmehling42 Diedrichs and Gmehling42 Diedrichs and Gmehling42
315–425 328–413 313–423
关C2apy兴NTf2 共900797-77-5兲 N/A N/A N/A
DSC MDSC TC
5 5 5
603 共315.15 K兲 590 共328.15 K兲 619 共313.12 K兲
Diedrichs and Gmehling42 Diedrichs and Gmehling42 Diedrichs and Gmehling42
315–425 328–413 313–423
关C4apy兴NTf2 共900797-79-7兲 N/A N/A N/A
DSC MDSC TC
5 5 5
673 共315.15 K兲 690 共328.15 K兲 688 共313.13 K兲
Crosthwaite et al.32 Diedrichs and Gmehling42 Diedrichs and Gmehling42 Diedrichs and Gmehling42
298–338 315–425 328–413 313–423
关C6apy兴NTf2 共872672-57-6兲 共⬍1 ⫻ 10−3h, ⬍2 ⫻ 10−3a兲 N/A N/A N/A
DSC DSC MDSC TC
15 5 5 5
628 750 共315.15 K兲 753 共328.15 K兲 731 共313.15 K兲
Crosthwaite et al.32
298–338
关共C2兲2Nic兴EtSO4 共872672-51-0兲 共⬍1 ⫻ 10−3h, ⬍2 ⫻ 10−3a兲
DSC
11
513
Crosthwaite et al.32
298–338
关共C4兲2Nic兴NTf2 共872672-53-2兲 共⬍1 ⫻ 10−3h, ⬍2 ⫻ 10−3a兲
DSC
11
707
Crosthwaite et al.32
298–338
关C6mmpy兴NTf2 共872672-54-3兲 共⬍1 ⫻ 10−3h, ⬍2 ⫻ 10−3a兲
DSC
11
620
Crosthwaite et al.32
298–338
关C6mapy兴NTf2 共872672-59-8兲 共⬍1 ⫻ 10−3h, ⬍2 ⫻ 10−3a兲
DSC
11
725
Crosthwaite et al.32
298–338
关C6C3共C2兲2py兴NTf2 共872672-56-5兲 共⬍1 ⫻ 10−3h, ⬍2 ⫻ 10−3a兲
DSC
11
766
a
a ammonium; h, halides; m, metals; w, water.
J. Phys. Chem. Ref. Data, Vol. 39, No. 3, 2010
HEAT CAPACITY OF IONIC LIQUIDS
033108-17
TABLE 18. Summary of data on heat capacity of ammonium ILs Sample purity w 共impurity contenta兲 共%兲
Estimated uncertainty 共%兲
Reported C p共298.15 K兲 共J K−1 mol−1兲
Reference
Temp. range 共K兲
Paulechka et al.25
277–370
Gardas et al.52
293–363
关共C4兲3mN兴Ser 共4.1⫻ 10−3w兲
MDSC
15
635
Gardas et al.52
293–363
关共C4兲3mN兴Thr 共4.9⫻ 10−3w兲
MDSC
15
753
Gardas et al.52
293–363
关共C4兲3mN兴Lys 共4.3⫻ 10−3w兲
MDSC
15
824
Gardas et al.52
293–363
关共C4兲3mN兴Tau 共4.8⫻ 10−3w兲
MDSC
15
827
Crosthwaite et al.32
298–338
DSC
11
1325
Nockermann et al.69
303
indirect
20
436
Domanska and Bogel-Łukashik67
383–430
关C2OHC3mmN兴Br 共13186-62-4兲 共0.021w兲
TC
13
371 共382.50 K兲
Domanska and Bogel-Łukashik67
410–438
关C2OHC4mmN兴Br 共28508-15-8兲 共0.027w兲
TC
13
383 共409.71 K兲
Domanska and Bogel-Łukashik67
386–403
关C2OHC6mmN兴Br 共219787-58-3兲 共0.030w兲
TC
13
465 共386.41 K兲
298–338
关cpma兴MeSO4 共872672-63-4兲 ⬎98
DSC
11
1066
Method
关C4mmmN兴NTf2 共258273-75-5兲 99.8 molb
关共C4兲4N兴Doc 共663955-05-3兲 N/A 关C2OHC1mmN兴NTf2 共174899-86-6兲 共⬍0.025h, 2.5⫻ 10−3w兲
AC
0.4
559.3
c
Crosthwaite et al.32 a
a, ammonium; h, halides; m, metals; w, water. Mole fraction purity. c CASRN corresponds to N-关2-关2-共2-hydroxyethoxy兲ethoxy兴ethyl兴-N-关2-共2-hydroxyethoxy兲ethyl兴-N-methyl-1-tridecanaminium methyl sulfate. b
TABLE 19. Summary of data on heat capacity of phosphonium ILs
Reference
Temp. range 共K兲
Sample purity w 共impurity contenta兲 共%兲
Gardas et al.52
293–363
共5.3⫻ 10−3w兲
Gardas et al.52
293–363
共5.1⫻ 10−3w兲
Gardas et al.52
293–363
共4.5⫻ 10−3w兲
Gardas et al.52
293–363
共5.0⫻ 10−3w兲
Gardas et al.52
293–363
共5.0⫻ 10−3w兲
Gardas et al.52
293–363
共5.1⫻ 10−3w兲
Gardas et al.52
293–363
共6.4⫻ 10−3w兲
Ge et al.45
293–358
关共C6兲3C14P兴NTf2 共460092-03-9兲 共9.5⫻ 10−3w, ⬍5 ⫻ 10−4h, ⬍1 ⫻ 10−4m兲
Method
Estimated uncertainty 共%兲
Reported C p共298.15 K兲 共J K−1 mol−1兲
MDSC
15
749
MDSC
15
844
MDSC
15
747
MDSC
15
961
MDSC
15
920
MDSC
15
997
MDSC
15
995
DSC
12
1366
关共C4兲4P兴Ser 共899795-70-1兲 关共C4兲4P兴Pro 共899795-76-7兲 关共C4兲4P兴Val 共899795-72-3兲 关共C4兲4P兴Thr 共899795-77-8兲 关共C4兲4P兴Cys 共899795-83-6兲 关共C4兲4P兴Lys 共899795-74-5兲 关共C4兲4P兴Tau
a
a, ammonium; h, halides; m, metals; w, water. J. Phys. Chem. Ref. Data, Vol. 39, No. 3, 2010
033108-18
YAUHENI U. PAULECHKA TABLE 20. Summary of data on heat capacity of pyrrolidinium and piperidinium ILs Estimated uncertainty 共%兲
Reported C p共298.15 K兲 共J K−1 mol−1兲
1.1
554.0
AC DSC DSC
0.4 5c 12
588.0 606 629
关C4mprl兴FAP 共851856-47-8兲 共1.32⫻ 10−2w, ⬍10−2h兲
DSC
12
769
关C3mpip兴NTf2 共608140-12-1兲 共 ⬍ 0.5w兲
DSC
5c
607
Reference
Temp. range 共K兲
Sample purity w 共impurity contenta兲 共%兲
Method
Waliszewski et al.57
283–358
关C3mprl兴NTf2 共223437-05-6兲 共 ⬍ 0.4w兲
TC
Paulechka et al.25 Jagadeeswara Rao et al.28 Ge et al.45
236–370 298–520 293–353
关C4mprl兴NTf2 共223437-11-4兲 99.8 molb 共 ⬍ 0.5w兲 共2.0⫻ 10−3w, ⬍5 ⫻ 10–4h, ⬍1 ⫻ 10−4m兲
Ge et al.45
293–358
Jagadeeswara Rao et al.28
298–520
a
a, ammonium; h, halides; m, metals; w, water. Mole fraction purity. c Below 370 K. b
Volumic heat capacity of ILs at a given temperature remains constant25,71 and deviations from the average value do not exceed ⫾5%.25 The temperature dependence of 共C p / V兲 over the temperature range of 258– 370 K was described by the equation25
5. Establishment of Recommended Values After completion of the evaluation procedure, the experimental data were fitted to the equations
3
共C p/V兲/J K−1 mol−1 = 1.951 + 8.33 ⫻ 10−4共T/K兲,
共1兲
where T is the absolute temperature. A method for prediction of IL heat capacity from molecular volumes of the ions was proposed in Ref. 73.
C p = 兺 Ai i=0
冋兺 n
i=1
J. Phys. Chem. Ref. Data, Vol. 39, No. 3, 2010
i T . 100 K
共2兲
The Ai parameters of Eq. 共2兲 were found by the weighted least-squares method. The number of terms in Eq. 共2兲 was adjusted in such a way as to have all Ai parameters statistically significant. If the water content in a sample was reported as a definite value, the original heat capacity values were corrected for it. It was assumed that, at a low concentration of water, the specific heat capacity of a sample is a sum of specific heat capacities of individual components multiplied by their mass fractions. The recommended values were derived for those 23 ILs whose data had the uncertainty no greater than 2.5% 共Table 21兲. Deviations of experimental values from smoothed curves are presented in Figs. 2–15. The standard deviation s was calculated according to the equation
s=
FIG. 1. Heat capacity of ILs at T = 298.15 K: 共⫹兲 关Cnmim兴Br; 共〫兲 关Cnmim兴BF4; 共쎲兲 关Cnmim兴NTf2; 共Δ兲 关Cnmprl兴NTf2.
冉 冊
共Csm,i − Cexp,i兲2 n−m
册
1/2
,
共3兲
where n is the number of experimental points for the compound used in regression, m is the number of Ai parameters in Eq. 共2兲, the subscripts “exp” and “sm” are used for experimental and smoothed values, respectively.
HEAT CAPACITY OF IONIC LIQUIDS
033108-19
TABLE 21. Coefficients of recommended polynomials for heat capacity of ILs
Compound 关C2mim兴Br 关C2mim兴BF4 关C2mim兴NTf2 关C2mim兴EtSO4 关C3mim兴Br 关C4mim兴Br 关C4mim兴BF4 关C4mim兴PF6 关C4mim兴CF3CO2 关C4mim兴OTf 关C4mim兴NTf2 关C4mim兴Tos 关C4mim兴AcO 关C4mim兴NO3 关C4mim兴N共CN兲2 关C6mim兴BF4 关C6mim兴NTf2 关C8mim兴BF4 关C8mim兴NTf2 关C14mim兴NTf2 关C4mmmN兴NTf2 关C3mprl兴NTf2 关C4mprl兴NTf2
Temp. range 共K兲
A0
A1
347–370 283–358 260–370 190–290 290–370 222–370 225–370 189–370 190–323 192–370 291–370 186–370 342–370 207–332 332–370 271–370 235–370 283–323 188–370 195–250 250–370 188–370 309–370 277–370 283–358 236–370
133.15 181.90 365.26 512.31 348.91 280.09 259.99 397.57 384.57 428.88 298.27 529.92 280.48 514.78 223.02 316.26 407.17 275.68 657.59 1496.9 399.76 774.65 595.19 380.95 356.21 273.86
37.626 41.368 47.317 −214.62 −19.751 −48.376 −1.9623 −99.008 −94.482 −104.23 34.912 −61.634 76.638 −205.50 53.174 −10.207 −87.610 52.102 −152.29 −1261.8 8.0572 −206.21 97.500 59.829 66.345 186.92
A2
90.117 10.422 21.610 6.4366 40.947 52.522 47.235 2.8501 34.880
A3
−11.005 −1.7802 −3.7652 −6.1006 −4.8977 −3.4251
77.720
−7.9148
7.6536 35.761
−3.3246
71.677 501.32 8.3628 86.014
−41.998
FIG. 2. Deviation of experimental heat capacities from Eq. 共2兲 for 关C2mim兴BF4: 共〫兲 Ref. 38; 共Δ兲 Ref. 56; 共⫹兲 Ref. 57. Data from Refs. 49 and 50 are not shown due to high deviation.
−7.8960 −64.188 −8.7461
4.9105
s 共J K−1 mol−1兲
C p共298.15 K兲 共J K−1 mol−1兲
0.31 3.5 1.9 0.09 3.5 0.15 0.45 1.3 0.37 0.28 0.14 1.0 0.46 0.10 0.16 0.18 0.10 0.98 1.5 0.15 0.58 0.22 0.59 0.30 0.10 0.17
264.8共350 K兲 305.2 506.3 382.7 280.8 311.4 366.6 408.1 408.2 427.7 565.4 548.7共350 K兲 383.2 353.9 375.7 431.0 631.4 498.1 692.6 897.4共310 K兲 559.3 554.0 588.0
Ref. 19 56 and 57 16, 20, and 57 25 25 and 48 25 19 25, 54, 56, and 57 17 and 55 23 25 15, 22, and 55 21 23 23 24 25 56, 58, and 59 14 and 18 25 25, 56, 58, and 59 20 25 25 57 25
FIG. 3. Deviation of experimental heat capacities from Eq. 共2兲 for 关C2mim兴NTf2: 共䊊兲 Ref. 8; 共Δ兲 Ref. 16; 共⫹兲 Ref. 20; 共-·-兲 Ref. 31; 共⫻兲 Ref. 45; 共〫兲 Ref. 57. J. Phys. Chem. Ref. Data, Vol. 39, No. 3, 2010
033108-20
YAUHENI U. PAULECHKA
FIG. 4. Deviation of experimental heat capacities from Eq. 共2兲 for 关C2mim兴EtSO4: 共•兲 Ref. 10; 共䉮兲 Ref. 25; 共⫹兲 Ref. 33; 共⫻兲 Ref. 45; 共씲兲 Ref. 48; 共〫兲 Refs. 61–63; 共-·-兲 Ref. 68; 共- -兲 extrapolated recommended polynomial curve. Data from Refs. 27 and 38 are not shown due to high deviation.
FIG. 5. Deviation of experimental heat capacities from Eq. 共2兲 for 关C4mim兴Br: 共Δ兲 Ref. 19; 共-·-兲 Ref. 31; 共⫹兲 Refs. 43 and 44.
FIG. 6. Deviation of experimental heat capacities from Eq. 共2兲 for 关C4mim兴BF4: 共쎲兲 Ref. 11; 共䉱兲 Ref. 25; 共䊊兲 Ref. 29; 共-··-兲 Ref. 31; 共Δ兲 Refs. 39 and 40; 共씲兲 Ref. 54; 共䉮兲 Ref. 56; 共〫兲 Ref. 57; 共⫻兲 Refs. 62 and 63; 共⫹兲 Ref. 66; 共- -兲 extrapolated recommended polynomial curve. Data from Refs. 43, 44, and 49, are not shown due to high deviation. J. Phys. Chem. Ref. Data, Vol. 39, No. 3, 2010
FIG. 7. Deviation of experimental heat capacities from Eq. 共2兲 for 关C4mim兴PF6: 共씲兲 Ref. 17 共AC兲; 共-·-兲 Ref. 17 共DSC兲; 共-··-兲 Ref. 31; 共䊊兲 Refs. 39 and 40; 共⫹兲 Ref. 55; 共Δ兲 Ref. 66; 共⫻兲 共- -兲 extrapolated recommended polynomial curve. Data from Ref. 51 are not shown due to high deviation.
FIG. 8. Deviation of experimental heat capacities from Eq. 共2兲 for 关C4mim兴OTf: 共䉱兲 Ref. 25; 共-·-兲 Ref. 31; 共쎲兲 Ref. 39; 共⫹兲 Ref. 42; 共〫兲 Ref. 45; 共Δ兲 Refs. 61–63; 共--兲 extrapolated recommended polynomial curve.
FIG. 9. Deviation of experimental heat capacities from Eq. 共2兲 for 关C4mim兴NTf2: 共-·-兲 Ref. 15; 共Δ兲 Ref. 16; 共⫹兲 Ref. 22; 共-··-兲 Ref. 31; 共⫻兲 Ref. 45; 共〫兲 Ref. 55. Data from Refs. 34 and 51 are not shown due to high deviation.
HEAT CAPACITY OF IONIC LIQUIDS
FIG. 10. Deviation of experimental heat capacities from Eq. 共2兲 for 关C4mim兴N共CN兲2: 共⫹兲 Ref. 25; 共-·-兲 Ref. 31.
FIG. 11. Deviation of experimental heat capacities from Eq. 共2兲 for 关C6mim兴BF4: 共-·-兲 Ref. 32; 共씲兲 Ref. 56; 共䉱兲 Ref. 58; 共Δ兲 Ref. 59; 共䊊兲 Refs. 62 and 63.
FIG. 12. Deviation of experimental heat capacities from Eq. 共2兲 for 关C6mim兴NTf2: 共䊊兲 Ref. 14; 共⫹兲 Ref. 18; 共Δ兲 Ref. 26; 共-·-兲 Ref. 32; 共䉱兲 Ref. 42; 共씲兲 Ref. 45; 共⫻兲 Ref. 53; 共--兲 extrapolated recommended polynomial curve.
033108-21
FIG. 13. Deviation of experimental heat capacities from Eq. 共2兲 for 关C8mim兴BF4: 共⫹兲 Ref. 25; 共-·-兲 Ref. 32; 共Δ兲 Ref. 56; 共䉱兲 Ref. 58; 共䊊兲 Ref. 59.
FIG. 14. Deviation of experimental heat capacities from Eq. 共2兲 for 关C8mim兴NTf2: 共Δ兲 Ref. 20; 共-·-兲 Ref. 32; 共⫹兲 Ref. 45; 共⫻兲 Ref. 53.
FIG. 15. Deviation of experimental heat capacities from Eq. 共2兲 for 关C4mprl兴NTf2: 共Δ兲 Ref. 25; 共〫兲 Ref. 28; 共⫹兲 Ref. 45. J. Phys. Chem. Ref. Data, Vol. 39, No. 3, 2010
033108-22
YAUHENI U. PAULECHKA
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