Excess Enthalpies in Binary Systems of Isomeric ... - ACS Publications

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Excess Enthalpies in Binary Systems of Isomeric C8 Aliphatic Monoethers with Acetonitrile and Their Description by the COSMO-SAC Model Łukasz Ruszczyński, Mateusz Reda, Marek Królikowski, Marek Gliński, and Tadeusz Hofman* Department of Physical Chemistry, Faculty of Chemistry, Warsaw University of Technology, Noakowskiego 3, 00-664 Warsaw, Poland S Supporting Information *

ABSTRACT: The excess enthalpies at 298.15 and 308.15 K for six binary mixtures of acetonitrile + C8 aliphatic ether {heptyl methyl ether CH3OnC7H15, or ethylhexyl ether C2H5OnC6H13, or pentyl propyl ether nC3H7OnC5H11, or isopentyl propyl ether n C3H7Oi C5H11, or dibutyl ether nC4H9OnC4H9, or butyl isobutyl ether nC4H9OiC4H9} have been determined by isothermal titration calorimetry using the TA Instruments (model TAM III) calorimeter. The possibility of the COSMO-SAC model to account for the thermodynamic differences between these systems has been tested.

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Table 1. Origin and Purities of the Compounds Used

INTRODUCTION This paper is a continuation of our study in which an influence of position isomerism on the thermodynamic properties has been examined.1,2 Its aim mainly concerns checking if a thermodynamic model is able to distinguish between such isomers if some mixture properties are concerned. In light of usual group contribution methods, for example, the most widespread modified UNIFAC model,3 the position isomers are usually recognized as identical leading to the prediction of identical thermodynamic properties. As this strongly disagrees with reality, some patchworks are undertaken as different values of group parameters depending on their environment or a definition of great groups that are sufficiently large to discriminate position isomers. However, such a procedure cannot be regarded as a general solution as it disagrees with the very foundation of the group contribution concept that requires to keep the number of different groups in a level as low as possible.4 Generally, it is rather clear that traditional group contribution methods cannot account properly for this problem and other, more advanced approaches should be applied. Among them the group of the COSMO5,6 models seem to be the most promising as they, at least partly, are based on the quantum mechanical calculations and treat a molecule as a whole thus avoiding the problem of a proper group definition. The possibility of the COSMO-SAC model to distinguish between a few drugs being position isomers has been already proved for the solubility data.7 Our previous results confirmed that liquid−liquid equilibria in the systems containing the C8 isomeric aliphatic monoethers with acetonitrile can be predicted qualitatively by the COSMO-SAC6 model. It was confirmed that the relations between different solubility curves has been properly described and, moreover, the outstanding properties of branched isomers have been explained. © XXXX American Chemical Society

compound name acetonitrile dibutyl ether butyl isobutyl ether heptyl methyl ether ethylhexyl ether pentyl propyl ether isopentyl propyl ether a

source

initial mass final mass fraction purification fraction analysis purity method purity method ≥ 0.999

distillation

0.999

GCa

> 0.99

distillation distillation

0.998 0.990

GC GC

synthesis

distillation

0.997

GC

synthesis synthesis

distillation distillation

0.990 0.999

GC GC

synthesis

distillation

0.995

GC

SigmaAldrich Aldrich synthesis

Gas−liquid chromatography.

There appears a disadvantage, too. The predicted upper critical solution temperatures are about 60 K higher than experimental values, which means that the model exaggerates positive deviations from ideality.2 As this observation concerns only one property (liquid−liquid equilibrium), we decided to examine excess enthalpies for the same systems. In the literature, such data have not been reported and only excess enthalpies for the dibutyl ether + acetonitrile system at 298.15 K were measured.8

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EXPERIMENTAL SECTION Excess enthalpies of mixing for {ether (1) + acetonitrile (2)} solutions were determined according to procedures similar to Received: September 30, 2015 Accepted: December 24, 2015

A

DOI: 10.1021/acs.jced.5b00838 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

Article

Table 2. Experimental Excess Enthalpies in the System of Acetonitrile (1) + Dibutyl Ether nC4H9OnC4H9 (2) at 0.100 MPaa,b x1

HE/J·mol−1

run

HE/J·mol−1

x1

0.0599 0.1130 0.1604 0.2031 0.2416 0.3084 0.3644 0.4120 0.4530 0.4886 0.5199 0.5476 0.5722

324.63 548.73 716.95 846.82 945.93 1085.83 1171.00 1222.95 1250.84 1265.43 1270.71 1267.97 1260.33

2 2 2 2 2 2 2 2 2 2 2 2 2

0.5944 0.6143 0.6367 0.6567 0.6745 0.6906 0.7052 0.7185 0.7306 0.7417 0.7520 0.7615 0.7952

0.0591 0.1116 0.1586 0.2008 0.2390 0.3054 0.3612 0.4087 0.4496 0.4852 0.5164 0.5441 0.5688 0.5910

343.04 581.68 758.53 892.93 996.96 1144.46 1233.30 1287.27 1318.13 1333.74 1338.45 1335.61 1328.49 1316.86

2 2 2 2 2 2 2 2 2 2 2 2 2 2

0.6110 0.6335 0.6535 0.6715 0.6877 0.7023 0.7157 0.7177 0.7279 0.7386 0.7391 0.7494 0.7589 0.7607

T = 298.15 K 1249.72 1237.79 1219.91 1200.50 1180.01 1159.30 1137.86 1116.80 1096.17 1075.69 1055.65 1036.25 942.89 T = 308.15 K 1303.23 1283.86 1262.79 1240.81 1218.25 1195.55 1172.85 1159.52 1150.56 1120.38 1128.70 1107.13 1085.96 1073.42

run

x1

HE/J·mol−1

run

2 2 2 2 2 2 2 2 2 2 2 2 1

0.8161 0.8382 0.8615 0.8761 0.8911 0.9068 0.9229 0.9397 0.9512 0.9629 0.9750 0.9873

886.12 819.91 740.50 684.80 622.41 552.26 473.62 385.30 319.63 248.69 171.76 88.02

1 1 1 1 1 1 1 1 1 1 1 1

2 2 2 2 2 2 2 1 2 1 2 2 2 1

0.7842 0.8092 0.8358 0.8526 0.8701 0.8884 0.9074 0.9273 0.9551 0.9696 0.9846 0.9410

1016.69 947.89 863.84 804.31 737.04 659.93 571.22 468.86 308.03 215.12 112.21 392.36

1 1 1 1 1 1 1 1 1 1 1 1

a Run 1: ether added to acetonitrile. Run 2: acetonitrile added to ether. bStandard uncertainties u are u(T) = 0.03 K, u(x1) = 1 × 10−4, u(p) = 0.005 MPa, and the combined expanded uncertainty Uc(HE) = 0.01·HE (with level of confidence = 0.95).

those described previously.9 A thermal activity monitor (TAM) III calorimeter (TA Instruments, U.S.A.), employing a technique called as isothermal titration calorimetry (ITC), was used. The titration cell and the reference cell were placed in the wells of highly stable thermostatic oil bath having volume of 22 dm3. Before the experiment, the temperature of bath was kept constant at T = 298.1500 K or T = 308.1500 K with a stability of ±0.1 mK/24 h. As the temperature slightly varied as an effect of mixing, its standard uncertainty was estimated to be 0.03 K. Two modes of titration were performed during the experiment: ether added to acetonitrile (mode 1) or acetonitrile added to ether (mode 2). Titration experiments were started by placing about 0.4 cm3 of pure substance in the stainless steel titration cell and next immersing it in the thermostatic oil bath and equilibrating for at least 3 h. The experiment was started when the heat flow baseline was recognized as constant with the standard deviation not greater than 100 nW for at least 20 min and the slope less than 50 nW/h. Depending on the required change in the mole fraction, 5.000−50.000 ± 0.001 μL of the second component was injected into the titration cell using the precise syringe pump provided by the manufacturer of the calorimeter. During the experiment, the mixture was stirred with the stirring speed of 100 rpm. The molar amount (required to calculate mole fractions of solution) of the solvent was calculated on the basis of the injected volume with the known density, which was determined in our laboratory using vibrating tube densitometer DMA 4500 M (Anton Paar, Austria) with an actual relative standard uncertainty about 0.001 mainly due to impurities of the compounds. The

property that was measured directly was the difference in heat flow between the titration cell and the reference cell. Summation of the integrals of the individual heat flow peaks gives the total amount of heat effect during the jth injection (δqj). This quantity is readily transformed into total molar excess enthalpy of mixing corresponding to i injections where n1 is the number of moles of solute (acetonitrile in mode 1, or ether in mode 2) and Δn2,j is the number of moles of solvent (ether in mode 1, or acetonitrile in mode 2) injected during the jth titration. i

HiE

=

∑ j = 1 δqj i

n1 + ∑ j = 1 Δn2, j

(1)

The combined uncertainty of the HE data determined in the present study is estimated to be 1%. In order to verify the reliability of the experiment, the test measurements for the systems of cyclohexane + hexane and methanol + water at 298.15 K have been performed. A very good agreement with the literature data has been proved.9

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MATERIALS Acetonitrile (Sigma−Aldrich HPLC) and di-n-butyl ether (Aldrich, purity >0.99) were distilled under normal pressure and stored over freshly dehydrated (400 °C, 6 h) molecular sieves 4A. The other ethers were synthesized by one of us (M.G.) with the details given elsewhere.2 The description of the chemicals and the final purities are given in Table 1 and the NMR spectra for the synthesized compounds are reported in Supporting Information. B



Article

Table 3. Experimental Excess Enthalpies in the System of Acetonitrile (1) + Pentyl Propyl Ether nC3H7OnC5H11 (2) at 0.100 MPaa,b x1

HE/J·mol−1

run

HE/J·mol−1

x1

0.0310 0.0602 0.0876 0.1135 0.1379 0.1830 0.2236 0.2604 0.2938 0.3243 0.3781 0.4240 0.4635 0.5061

171.69 324.37 450.88 558.55 649.82 799.56 914.46 1002.67 1072.89 1127.74 1203.42 1247.15 1271.83 1283.32

2 2 2 2 2 2 2 2 2 2 2 2 2 2

0.5424 0.5738 0.6011 0.6296 0.6542 0.6758 0.6979 0.7171 0.7340 0.7491 0.7625 0.7644 0.7829 0.8022

0.0305 0.0592 0.0863 0.1118 0.1360 0.1806 0.2208 0.2572 0.2904 0.3207 0.3742 0.4199 0.4594 0.5020

178.60 334.38 464.77 574.72 669.87 823.47 941.72 1034.12 1107.02 1163.97 1244.21 1292.27 1319.79 1332.71

2 2 2 2 2 2 2 2 2 2 2 2 2 2

0.5383 0.5697 0.6022 0.6301 0.6543 0.6756 0.6944 0.7137 0.7173 0.7308 0.7382 0.7459 0.7595 0.7603

T = 298.15 K 1282.06 1272.64 1258.14 1236.50 1212.28 1186.42 1155.86 1125.37 1095.86 1066.55 1038.66 1011.97 971.18 923.14 T = 308.15 K 1333.46 1324.83 1307.18 1284.77 1259.41 1232.77 1205.63 1173.91 1156.23 1142.56 1117.35 1112.01 1082.43 1070.68

run

x1

HE/J·mol−1

run

2 2 2 2 2 2 2 2 2 2 2 1 1 1

0.8226 0.8440 0.8666 0.8807 0.8953 0.9104 0.9260 0.9421 0.9531 0.9644 0.9760 0.9879

866.89 799.98 721.49 666.62 605.67 537.26 460.11 372.52 309.84 241.28 167.14 86.64

1 1 1 1 1 1 1 1 1 1 1 1

2 2 2 2 2 2 2 2 1 2 1 2 2 1

0.7838 0.8089 0.8355 0.8524 0.8699 0.8882 0.9072 0.9271 0.9409 0.9695 0.9845 0.9550

1014.07 945.53 861.94 802.75 735.17 658.65 570.41 468.73 392.36 215.35 112.85 308.18

1 1 1 1 1 1 1 1 1 1 1 1

a Run 1: ether added to acetonitrile. Run 2: acetonitrile added to ether. bStandard uncertainties u are u(T) = 0.03 K, u(x1) = 1 × 10−4, u(p) = 0.005 MPa, and the combined expanded uncertainty Uc(HE) = 0.01·HE (with level of confidence = 0.95).

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RESULTS AND DISCUSSION The experimental data for the following systems, acetonitrile + heptyl methyl ether, CH3OnC7H15, or ethylhexyl ether, C2H5OnC6H13, or pentyl propyl ether, nC3H7OnC5H11, or isopentyl propyl ether, nC3H7OiC5H11, or dibutyl ether, n C4H9OnC4H9, or butyl isobutyl ether, nC4H9OiC4H9 at 298.15 and 308.15 K data are shown in Tables 2−7. The densities of pure substances measured at T/K = 288.15, 293.15, 298.15, 303.15, 308.15, 313.15, 318.15, and 323.15 are shown in Supporting Information in Table S1. The data for the acetonitrile + dibutyl ether system at 298.15 K are of special significance in the verification of the method as they were already measured and they are accessible in the literature.8 The new data together with the literature ones are shown in Figure 1. Our data show a very good agreement with the data of Domańska and Letcher8 for mixtures having a molar surplus of acetonitrile. For a remaining part of the concentration range there appear systematic deviations and our values are about 25 J/mol higher. The origin of this shift is not clear, nevertheless, in light of a considerable scattering of the literature data we consider our measurements as more credible. An additional support for this opinion we draw from a perfect correspondence of two separate sets of data (run 1 and run 2) that meet together at the mole fraction of acetonitrile of about 0.8. In a narrow range of concentration, the data given by both runs overlap each other and the residuals between them are of about 0.5%.

The experimental dependencies are slightly unsymmetrical with the maximum values for the concentration of acetonitrile slightly higher than 0.5 (see Figure 2). The curves become less symmetric if the ether group is shifted to the end of an ether molecule. The maximum values of excess enthalpy exceed 1000 J/mol, which confirm high positive deviations from ideality in these systems. The differences between systems with different ethers are significant although for some isomers are relatively not very high. The residual between the highest maximum (for the system with butyl isobutyl ether) and the lowest maximum (for the system with heptyl methyl ether) is about 200 J/mol, that is, about 20% of the overall value. The outstanding properties of the above-mentioned systems were confirmed previously through the determination of the liquid−liquid equilibria in binary mixtures containing C8 aliphatic ether and acetonitrile or nitromethane.1,2 The lowest deviations from ideality were observed for the highly unsymmetrical ethers while the highest ones for the system with butyl isobutyl ether. It is interesting to note that an influence of the position isomerism on the excess enthalpy is more profound for lower amounts of acetonitrile in the mixture. It can be suggested that structural differences between isomeric ethers influence mainly interactions between ether molecules rather than interactions between unlike ones. The excess enthalpies are relatively strongly dependent on temperature. Excess heat capacities are positive and their values estimated at the maximum of excess enthalpy vary between C



Article

Table 4. Experimental Excess Enthalpies in the System of Acetonitrile (1) + Ethyl Hexyl Ether C2H5OnC6H13 (2) at 0.100 MPaa,b x1

HE/J·mol−1

run

HE/J·mol−1

x1

0.0307 0.0596 0.0868 0.1125 0.1368 0.1816 0.2220 0.2586 0.2919 0.3223 0.3759 0.4217 0.4612 0.5038

117.27 254.22 371.23 469.30 554.01 694.15 802.50 886.87 955.18 1009.29 1086.32 1134.04 1161.73 1179.14

2 2 2 2 2 2 2 2 2 2 2 2 2 2

0.5401 0.5715 0.5988 0.6274 0.6521 0.6738 0.6959 0.7006 0.7152 0.7222 0.7322 0.7452 0.7473 0.7608

0.0303 0.0588 0.0857 0.1111 0.1352 0.1795 0.2196 0.2559 0.2889 0.3192 0.3726 0.4182 0.4577 0.5002

139.21 281.37 401.37 504.43 593.74 740.66 854.71 943.69 1014.34 1070.45 1150.67 1199.91 1228.78 1245.99

2 2 2 2 2 2 2 2 2 2 2 2 2 2

0.5366 0.5680 0.5954 0.6241 0.6489 0.6707 0.6929 0.7087 0.7123 0.7294 0.7300 0.7446 0.7526 0.7582

T = 298.15 K 1182.65 1179.14 1168.38 1150.78 1130.20 1108.32 1081.40 1065.04 1051.83 1033.01 1024.54 993.85 998.04 972.66 T = 308.15 K 1249.45 1243.66 1231.90 1213.04 1190.92 1167.11 1138.01 1106.59 1108.49 1079.56 1070.68 1051.08 1027.25 1023.39

run

x1

HE/J·mol−1

run

2 2 2 2 2 2 2 1 2 1 2 1 2 2

0.7698 0.7960 0.8241 0.8419 0.8604 0.8799 0.9002 0.9215 0.9514 0.9832 0.9362 0.9670

945.75 886.61 813.10 760.41 699.82 629.84 548.36 453.10 300.46 110.64 380.89 210.90

1 1 1 1 1 1 1 1 1 1 1 1

2 2 2 2 2 2 2 1 2 2 1 2 1 2

0.7767 0.8023 0.8297 0.8470 0.8651 0.8840 0.9037 0.9243 0.9385 0.9531 0.9683 0.9839

974.18 909.43 830.05 773.66 709.32 635.50 550.94 453.19 380.38 300.25 210.30 109.85

1 1 1 1 1 1 1 1 1 1 1 1

Run 1: ether added to acetonitrile. Run 2: acetonitrile added to ether. bStandard uncertainties u are u(T) = 0.03 K, u(x1) = 1 × 10−4, u(p) = 0.005 MPa, and the combined expanded uncertainty Uc(HE) = 0.01·HE (with level of confidence = 0.95). a

Table 5. Experimental Excess Enthalpies in the System of Acetonitrile (1) + Butyl Isobutyl Ether nC4H9OiC4H9 (2) at 0.100 MPaa,b x1 0.0314 0.0610 0.0887 0.1149 0.1396 0.1851 0.2261 0.2631 0.2967 0.3275 0.3815 0.4274 0.4671 0.5097

HE/J·mol−1 190.14 350.90 485.13 599.68 696.81 853.87 975.46 1068.16 1141.56 1196.66 1261.61 1297.60 1319.15 1325.33

run 2 2 2 2 2 2 2 2 2 2 2 2 2 2

HE/J·mol−1

x1 0.5459 0.5772 0.6045 0.6329 0.6575 0.6789 0.7009 0.7183 0.7200 0.7368 0.7392 0.7517 0.7613 0.7650

T = 298.15 K 1320.60 1300.50 1289.44 1261.30 1234.56 1209.18 1179.45 1152.42 1150.40 1120.99 1115.50 1091.00 1069.87 1062.69

run

x1

HE/J·mol−1

run

2 2 2 2 2 2 2 1 2 2 1 2 1 2

0.7847 0.8097 0.8362 0.8530 0.8705 0.8887 0.9077 0.9275 0.9411 0.9552 0.9697 0.9846

1014.58 947.35 865.62 807.06 740.35 662.36 572.56 468.86 391.21 305.40 210.46 105.72

1 1 1 1 1 1 1 1 1 1 1 1


4 and 10 J·K−1·mol−1. Such values are typical for the systems with very strong molecular interactions. The measured data were correlated by the four-parameter Redlich−Kister equation in the form

The number of adjustable parameters guarantees description of the data with standard deviations close to the experimental accuracy. The values of adjusted parameters are given in Table 8. All the measured excess enthalpies were predicted by means of the COSMO-SAC model in the form described by Hsieh et al.6 The σ-profiles for the compounds had been calculated and the details are given in our previous paper.2 Also the determined

i=0

(HE/J·mol−1) = x1x 2 ∑ Ai (x1 − x 2)i 3

(2) D



Article

Table 6. Experimental Excess Enthalpies in the System of Acetonitrile (1) + Isopentyl Propyl Ether nC3H7Oi C5H11 (2) at 0.100 MPaa,b x1

HE/J·mol−1

run

x1

0.0312 0.0606 0.0882 0.1142 0.1388 0.1841 0.2249 0.2618

146.23 290.01 408.27 509.27 601.64 746.06 854.04 938.09

2 2 2 2 2 2 2 2

0.3259 0.3798 0.4258 0.4654 0.5079 0.5442 0.5756 0.6028

0.0302 0.0586 0.0854 0.1107 0.1347 0.1789 0.2188 0.2551 0.2881 0.3183 0.3716 0.4172 0.4567 0.4992

172.90 330.24 459.90 569.60 662.35 815.27 932.75 1023.72 1094.95 1149.69 1226.35 1272.01 1297.45 1309.92

2 2 2 2 2 2 2 2 2 2 2 2 2 2

0.5356 0.5670 0.5944 0.6231 0.6480 0.6698 0.6920 0.7115 0.7146 0.7286 0.7356 0.7438 0.7574 0.7579

HE/J·mol−1 T = 298.15 K 1059.82 1132.90 1173.83 1197.42 1207.75 1208.43 1202.00 1188.92 T = 308.15 K 1308.91 1299.38 1284.29 1261.69 1236.36 1209.39 1177.19 1145.30 1126.15 1113.73 1087.13 1083.01 1053.03 1041.54

run

x1

HE/J·mol−1

run

2 2 2 2 2 2 2 2

0.6559 0.6774 0.6994 0.7186 0.7355 0.7504 0.7638

1146.74 1123.73 1095.05 1065.33 1039.65 1009.60 980.96

2 2 2 2 2 2 2

2 2 2 2 2 2 2 2 1 2 1 2 2 1

0.7816 0.8068 0.8337 0.8507 0.8684 0.8869 0.9061 0.9263 0.9401 0.9544 0.9691 0.9843

985.70 918.02 835.03 776.50 709.72 633.68 545.87 445.61 370.56 288.34 198.15 97.76

1 1 1 1 1 1 1 1 1 1 1 1

Standard uncertainties u are u(T) = 0.03 K, u(x1) = 1 × 10−4, u(p) = 0.005 MPa, and the combined expanded uncertainty Uc(HE) = 0.01·HE (with level of confidence = 0.95). aRun 1: ether added to acetonitrile. Run 2: acetonitrile added to ether. b

Table 7. Experimental Excess Enthalpies in the System of Acetonitrile (1) + Heptyl Methyl Ether CH3OnC7H15 (2) at 0.100 MPaa,b x1

HE/J·mol−1

run

x1

0.0307 0.0595 0.0867 0.1123 0.1366 0.1813 0.2216 0.2582 0.2914 0.3218 0.3754 0.4212 0.4607 0.5033

121.93 239.87 341.60 429.61 506.45 633.10 730.39 810.19 873.09 924.58 999.51 1047.97 1077.80 1098.67

2 2 2 2 2 2 2 2 2 2 2 2 2 2

0.5396 0.5710 0.5983 0.6269 0.6517 0.6733 0.6955 0.7111 0.7148 0.7318 0.7322 0.7469 0.7547 0.7604

0.0304 0.0590 0.0859 0.1114 0.1354 0.1799 0.2200 0.2563 0.2894 0.3197 0.3732 0.4188 0.4583 0.5008

134.59 251.76 353.59 442.81 521.39 653.25 756.83 839.94 905.77 960.09 1038.18 1088.67 1120.30 1141.99

2 2 2 2 2 2 2 2 2 2 2 2 2 2

0.5372 0.5686 0.5960 0.6246 0.6494 0.6712 0.6934 0.6998 0.7128 0.7215 0.7299 0.7446 0.7451 0.7586

HE/J·mol−1 T = 298.15 K 1106.62 1106.42 1099.11 1085.72 1069.51 1050.71 1027.65 999.40 1003.47 979.57 969.51 955.96 932.69 932.89 T = 308.15 K 1150.08 1149.07 1141.55 1127.29 1109.88 1090.30 1065.91 1067.72 1040.92 1035.68 1015.72 996.50 990.59 965.99

run

x1

HE/J·mol−1

run

2 2 2 2 2 2 2 1 2 2 1 2 1 2

0.7786 0.8041 0.8313 0.8485 0.8664 0.8851 0.9047 0.9251 0.9391 0.9536 0.9686 0.9841

887.77 832.40 763.41 713.93 656.99 590.86 514.04 424.12 355.87 279.54 194.11 98.14

1 1 1 1 1 1 1 1 1 1 1 1

2 2 2 2 2 2 2 1 2 2 1 2 1 2

0.7692 0.7954 0.8236 0.8414 0.8600 0.8795 0.8999 0.9212 0.9360 0.9512 0.9669 0.9832

948.35 889.13 815.49 762.69 701.97 631.81 550.11 454.58 382.16 301.47 211.63 111.03

1 1 1 1 1 1 1 1 1 1 1 1


E



Article

Table 8. Values of the Redlich-Kister Coefficients Adjusted to the Experimental Excess Enthalpies Data CH3CN (1) + n

C4H9OnC4H9 n C3H7OnC5H11 C2H5OnC6H13 CH3OnC7H15 n C4H9OiC4H9 n C3H7OiC5H11

5046 5098 4752 4390 5284 4827

C4H9OnC4H9 C3H7OnC5H11 C2H5OnC6H13 CH3OnC7H15 n C3H7OiC5H11

5313 5293 4996 4546 5237

n

Figure 1. Excess enthalpies for the system acetonitrile (1) + dibutyl ether at 298.15 K. (Δ), the data of Domańska and Letcher;8 this work: (○), run 1 (ether added to acetonitrile); (●), run 2 (acetonitrile added to ether).

a

A0

A1

A2

T = 298.15 K 396.6 1495 265.0 1461 322.2 833.0 670.9 1043 243.7 1621 281.6 1309 T = 308.15 K 303.0 1578 317.8 1528 348.1 1031 734.3 1173 293.2 1243

A3

σa

283.2 487.7 1071 536.3 307.3 872.3

4.3 6.5 8.8 3.8 6.0 4.4

323.1 379.3 735.5 420.6 26.57

5.4 5.6 4.9 2.7 5.6

σ = [Σ(HE,exp − HE,calc )2/n]1/2 i i

Table 9. Values of Excess Enthalpies at Equimolar Composition at 298.15 K Divided by That of Acetonitrile + Heptyl Methyl Ethera,b CH3CN (1) + n

n

C4H9O C4H9 n C3H7OnC5H11 C2H5OnC6H13 CH3OnC7H15 n C4H9OiC4H9 n C3H7OiC5H11

experimentalb

COSMO-SAC

mod. UNIFAC

1.15 1.16 1.08 1 1.20 1.10

1.03 1.03 1.02 1 1.17 1.01

1.26 1.26 1.26 1 1.26 1.26

a Experimental data and predicted by the COSMO-SAC and modified UNIFAC models. bCalculated using the Redlich−Kister equation adjusted to the experimental data.

ones. The lowest excess enthalpy (for the acetonitrile + heptyl methyl system) was taken as the reference value. The advantages and shortcomings of both models are clearly visible. The COSMO-SAC model properly predicts the outstanding character of butyl isobutyl ether while the modified UNIFAC also properly assumes that heptyl methyl ether possesses significantly different properties. But both models practically equate remaining ethers what disagrees with experiment. The modified UNIFAC model gives equimolar excess enthalpies equal to 1257 and 1574 J·mol−1 for the heptyl methyl ether and remaining ethers, respectively. These values are closer to the experimental data than those predicted by the COSMO-SAC model. As the COSMO-SAC model better accounts for differences between liquid−liquid equilibria,2 it may be suggested that its main deficiency lies in the oversimplifications included in the formulation of intermolecular interactions. The influence of temperature is predicted correctly with an average increase of the excess enthalpy at equimolar composition close to 4 J·K−1·mol−1.

Figure 2. Excess enthalpies for the system acetonitrile (1) + C8 ether at 298.15 K. Symbols denote experimental points for acetonitrile + the following ether: (●, 6), butyl isobutyl, nC4H9OiC4H9; (○, 5), dibutyl, n C4H9OnC4H9; (▲, 4), pentyl propyl, nC3H7OnC5H11; (Δ, 2), propyl isopentyl, nC3H7OiC5H11; (□, 3), ethylhexyl, C2H5OnC6H13; (◇, 1), heptyl methyl, CH3OnC7H15. Dashed lines represent values calculated by the Redlich−Kister equation with the parameters taken from Table 8. Solid lines were calculated by the COSMO-SAC model with dotted parts corresponding to the predicted miscibility gaps.

σ-profiles can be found therein. The results at 298.15 K are shown in Figure 2. As the model for all the systems overestimate deviations from ideality, it predicts an existence of miscibility gaps that actually appear but at temperatures of about (10−50) K lower.2 Therefore, the prediction can be recognized as qualitative only. The model predicts excess enthalpy for the system with butyl isobutyl ether considerably higher than for the remaining systems. It partly agrees with reality although observed differences between experimental excess enthalpies are uniform. The relative values of excess enthalpies at equimolar composition at 298.15 K predicted by the COSMO-SAC and the modified UNIFAC3 models are shown in Table 9 against the experimental

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CONCLUSIONS The excess enthalpies measured at 298.15 and 308.15 K for the systems containing C8 aliphatic monoethers and acetonitrile confirmed very high deviations from ideality with the maximum values greater than 1000 J/mol. Significant differences between excess enthalpies for these systems were found although relatively lower than observed for the liquid−liquid equilibria. The values of measured enthalpies are the lowest for the system with heptyl methyl ether and the highest one for butyl isobutyl ether giving the maximum residual of about 200 J/mol. Relatively F



Article

high-temperature influence on excess enthalpies was observed. The COSMO-SAC model is able to predict the measured data only qualitatively, considerably overestimating excess enthalpies but properly describing differences between the systems and estimating the temperature influence.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jced.5b00838. NMR spectra of synthesized ethers, densities of pure C8 ethers and acetonitrile at 0.100 MPa, and additional references. (PDF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Tel: +48 22 234 7475. Fax: +48 22 628 27 41. Funding

This work was financially supported by Faculty of Chemistry, Warsaw University of Technology. Notes

The authors declare no competing financial interest.

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REFERENCES

(1) Hofman, T.; Reda, M.; Gliński, M. Liquid−liquid Equilibrium in Binary Systems of Isomeric C8 Aliphatic Monoethers with Nitromethane. Fluid Phase Equilib. 2013, 356, 271−276. (2) Reda, M.; Ruszczyński, Ł.; Gliński, M.; Hofman, T. (Liquid+liquid) Equilibrium in Binary Systems of Isomeric C8 Aliphatic Monoethers with Acetonitrile and Its Interpretation by the COSMO-SAC Model. J. Chem. Thermodyn. 2015, 85, 42−48. (3) Weidlich, U.; Gmehling, J. A Modified UNIFAC Model. 1. Prediction of VLE, hE, and and γ∞. Ind. Eng. Chem. Res. 1987, 26, 1372− 1381. (4) Kehiaian, H. V. Group Contribution Methods for Liquid Mixtures: A Critical Review. Fluid Phase Equilib. 1983, 13, 243−252. (5) Klamt, A.; Eckert, F. COSMO-RS: A Novel and Efficient Method for the a Priori Prediction of Thermophysical Data of Liquids. Fluid Phase Equilib. 2000, 172, 43−72. (6) Hsieh, C.-M.; Sandler, S. I.; Lin, S.-T. Improvements of COSMOSAC for Vapor−liquid and Liquid−liquid Equilibrium Predictions. Fluid Phase Equilib. 2010, 297, 90−97. (7) Hsieh, C.-M.; Wang, S.; Lin, S.-T.; Sandler, S. I. A Predictive Model for the Solubility and Octanol−Water Partition Coefficient of Pharmaceuticals. J. Chem. Eng. Data 2011, 56, 936−945. (8) Letcher, T. M.; Domańska, U. The Excess Enthalpies of (acetonitrile + an Ether) at the Temperature 298.15 K. J. Chem. Thermodyn. 1994, 26, 75−84. (9) Domańska, U.; Zawadzki, M.; Paduszyński, K.; Królikowski, M. Perturbed-Chain SAFT as a Versatile Tool for Thermodynamic Modeling of Binary Mixtures Containing Isoquinolinium Ionic Liquids. J. Phys. Chem. B 2012, 116, 8191−8200.

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