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Excess enthalpies of sulfolane + benzene, + toluene, + p-xylene, and + mesitylene as functions of temperature
M-1554 J. Chem. Thermodynamics 1983, 15, 821-825
Excess enthalpies of sulfolane + benzene, + toluene, + p-xylene, + mesitylene as functions of temperature
and
MIKKO KARVO Department of Chemistry. University of Oulu, SF-90570 Oulu 57, Finland (Received 27 January 1983)
The excess enthalpies of sulfolane + benzene, + toluene, + pxylene, and + mesitylene have been measured with a flow calorimeter at 303.15,313.15,and 323.15K. The HL values as well as the estimated excess heat capacities are positive and increase with increasing hydrocarbon alkylation.
1. Introduction The excess Gibbs energies between 303 and 333 K and the excess enthalpies at 303.15 K of sulfolane + benzene and + toluene have been reported earlier.“, 2, To obtain information about the temperature dependence of HE, similar measurements were undertaken at 313.15 and 323.15 K for the mixtures. In addition the excess enthalpies of sulfolane + p-xylene and + mesitylene were measured, to investigate the influence upon Hz of an increasing number of methyl substituents in the benzene ring.
2. Experimental Sulfolane (E. Merck, zur Synthese) was purified by repeated distillations under vacuum. In the last two or three distillations phosphorus pentoxide was added to the flask for dehydration. t3) The purified sulfolane was used when its melting temperature was 301.55 K or higher.‘3-5’ Benzene, toluene, p-xylene, and mesitylene (all Fluka AG, puriss., p.a.) were distilled at atmospheric pressure through a Vigreux column and then passed through an aluminium oxide column (Fluka AG, chromatography, basic, activity I). The purified aromatic solvents were stored over molecular sieves (British Drug Houses Ltd., type 4A). The densities of the purified samples of sulfolane, benzene, toluene, p-xylene, and mesitylene at 303.15 K were 1.2624,O.86827,0.85760,0.85227, and 0.85681 g. cmb3, 0021-9614/83/090821+05 %02.00/O
0 1983Academic Press Inc. (London) Limited
822
M. KARVO
compared with the literature values 1.2620,(5) 0.86825,@’0.85766,‘6’0.85232,“j’ and 0.8569 g. cm-3,‘6) respectively. The excess enthalpies were determined with an LKB flow microcalorimeter (Model 2107). The experimental procedure has been described earlier.“’ 3. Results The experimental values of HE for the four mixtures are reported in table 1. The excess enthalpies of sulfolane + benzene and + toluene at 303.15 K published earlier are not reproduced in table 1 except some new values for the first pair. These were determined around the local minimum in the Hk against x curve, and they confirm the observed behaviour. The experimental excessenthalpies show that for each binary mixture studied the HE values increase almost linearly with increasing temperature. Therefore it seemed reasonable to use a smoothing function Hr(J.mol-‘)
=x(1-x)
2 ,4,(1-2x)‘+ j=O
i
aj{(7’/K)-303.15j(l
j=O
-2xy
,
(1)
where x denotes the mole fraction, T the temperature, and n (< m) is at its maximum 2. This equation allows the Hz results at different temperatures to be fitted simultaneously. According to @Hf,/aT), = C&,, equation (1) gives the relation: CE,,/(J.K-‘.mol-‘)
=x(1 -x) t agl-2.u)‘, j=O
12)
for the excessheat capacity. The estimates of C’i., represent mean values over the temperature range of the H,!f,measurements. When the coefficients of equation (1) are solved with a least-squares program also giving the standard errors of Aj and aj, it is also possible to determine confidence limits for the calculated CpE,m values. In general the estimation of CF.,, from the temperature dependenceof HE is subject to relatively large error as noted by Fortier and Benson.‘7’ However, when the proposed method was tested with some mixtures for which both Hfi, at several temperatures and the experimental CF.,, values are available in the literature, good,‘*v9)or at least satisfactory, agreement was obtained between the calculated and the measured excessheat capacities. A summary of the coefficients of equation (1) for the representation of the present HE results is given in table 2. The standard errors of the coefficients as well as the standard deviations s(Hf,) of the fits are included. The solid curves in figures 1 and 2 were calculated from (1) and (2) using these coefficient values. The error bars in figure 2 show the uncertainties of CF.,, as calculated from the standard errors of the coefficients aj 4. Discussion The four Hfi, curves in figure 1 show that the excessmolar enthalpies are positive and increase with an increasing number of methyl substituents in the benzene ring.
TABLE
X
HE, J.mol-’
1. Experimental
HE, ’
J.mol-’
excess enthalpies
Hfi, ’
J.mol-’
HE, ’
J.mol-’
HZ x
J.mol-’
HE ’
J.mol-’
(1 -x)C,H,O,S + xC,H, 303.15 K 0.7988
7.6
0.7274
5.5
0.6800
6.3
0.6581
8.3
0.6116
14.9
313.15 K 0.0403 0.0956 0.1729 0.2201
12.9 29.2 44.9 50.4
0.2956 0.3677 0.4640 0.5141
53.2 49.1 40.2 37.0
0.5640 0.5868 0.6116
32.6 30.4 24.6
0.6581 0.6858 0.7274
18.7 16.6 15.6
0.7455 0.7988 0.8420
14.5 16.3 18.2
0.9137 0.9638 0.9817
24.8 24.4 18.3
0.0403 0.0956 0.1729
14.0 30.4 47.8
0.2200 0.2956 0.3677
56.2 61.3 59.5
0.4640 0.5141 0.5640
323.15 K 52.4 0.5945 49.0 0.6116 43.0 0.6788
41.4 40.4 34.0
0.7274 0.7936 0.8427
29.0 29.9 30.2
0.9137 0.9638 0.9817
33.3 27.5 16.9
352.4 356.3 338.4
0.7687 301.2 0.8216 265.9 0.9024 196.7
0.9481 0.9787
130.8 70.3
378.9 381.5
0.6851 0.8025
0.9155 0.9560
198.8 124.2
(1 -x)C,H,O,S+xC,H,CH, 16.6 42.2 88.5
0.1451 157.5 0.1911 189.0 0.2651 257.2
0.3275 0.4202 0.4698
313.15 K 298.0 0.5200 332.4 0.6172 348.2 0.6851
0.0676 85.6 0.1620 200.0
0.2651 283.6 0.3275 324.1
0.4202 0.4698
360.6 370.6
0.0168 0.0412 0.0783
323.15 K
0.0682 164.7 0.1693 341.7 0.2326 419.0 0.2704 457.9
0.2958 470.5 0.3393 509.0 0.3847 519.0
0.0703 174.1 0.1429 326.1 0.2326 445.8
0.2958 0.3847
0.0709 181.8 0.1429 360.6 0.2326 484.2
0.2958 556.8 0.3847 621.3
0.5200 0.6172
(1 -x)C,H,O,S+xl,4-C,HdCH,), 303.15 K 0.4332 536.1 0.5817 562.3 0.4830 555.9 0.6042 559.8 0.5321 570.8 0.6583 565.4
380.8 314.8
0.6790 552.3 0.7829 497.3 0.7993 481.4
0.8138 460.0 0.8844 346.3 0.9506 177.4
628.9 617.2
0.7829 0.8138
545.9 507.2
0.8844 0.9506
0.6042 687.9 0.6790 664.3
0.7829 0.8138
581.5 542.1
0.8750 428.0 0.9336 276.9
0.7568 640.9 0.7735 616.1 0.7904 611.0
0.8817 468.2 0.9447 288.4
749.2 721.2
0.7735 0.7904
705.3 679.1
0.8817 0.9447
517.1 300.8
0.5525 864.1 0.6526 850.9
0.7568 0.7904
791.8 742.0
0.8817 0.9447
541.8 301.5
313.15 K 514.1 569.2
0.4332 0.4830
594.4 601.6
0.6042 0.6790
372.6 227.8
323.15 K 0.4332 649.9 0.4830 670.3 (1 -x)C4H,02S 0.0582 241.4 0.0690 264.2 0.1289 405.2
0.1969 474.0 0.2165 495.8 0.2536 534.9
0.0690 255.8 0.1289 425.0 0.2165 571.6
0.2717 0.3570 0.4043
615.9 663.2 697.8
0.0690 289.5 0.1289 488.3 0.2165 627.9
0.2717 0.3570 0.4043
695.2 784.3 807.5
+x1,3,5-C,H,(CH,),
303.15 K 0.2717 543.8 0.5025 653.1 0.3358 589.1 0.6311 659.9 0.4043 611.8 0.6526 650.6 313.15 K 0.4534 704.2 0.6526 0.5025 758.3 0.7568 0.5525 745.1 323.15 K 0.4534 0.5025
819.3 862.5
M. KARVO
824
TABLE 2. Coefficients and standard deviations s{ Hk/(J mol - ‘)] for least squares representations by equation (1). The standard errors of the coefficients are given in parenthesis + xC,H, 113.8 154.8 - 190.6 545.3 690.8 1109.0 5.20 ~ 2.57 3.4
(11) (37) (58) (149) (67) (135) (0.56) (0.93)
+xC,H,CH, ~ ~~__ 1237.8 -365.3 83.3 817.8 674.1 - 1647.9 17.04 - 7.90 8.0
~~~
(27) (90) (139) (352) (155) (315) (1.5) (2.5)
of Hk
+ x1.4-C,H,(CH&
+.x1,3.5-C,H,(CH,),
2225.8 (15) -315.3 (35) 1358.5 (97) -459.3 (60) -211.0 (129)
2492.8 (33) ~ 595.6 t 55) 2308.7 ( 169) -- 39.2 (90) 912.7 (196)
23.16 -9.79 6. I
(0.84) (1.6)
46.04 PO.95 -31.02 Il.5
(2.1) (2.4) (5.2)
The increments at x = 0.5 and at 323.15 K per CH,-group are 325, 240, and 185 J. mol-r when moving from benzene to mesitylene. The observed behaviour suggeststhat no strong attractions between the sulfolane and aromatic molecule exist; had strong attractions existed the excess enthalpies would have been negative or would at least have decreased with increasing methyl substitution of the benzene molecule.(l”*r ‘) Usually for mixtures of simple non-polar molecules Hk is positive and decreaseswith increasing temperature. For the present mixtures the temperature dependence of Hfi, turned out to be just the opposite: the excess enthalpies increase with increasing temperature. A possible interpretation
FIGURE 1. Excess molar enthalpies for sulfolane + an aromatic hydrocarbon at 323.15 K. A, Benzene; 0. toluene; A, p-xylene; 0, mesitylene. All curves are calculated from equation (1) with coefficients from table 2.
HE FOR SOME SULFOLANE
MIXTURES
AT THREE
TEMPERATURES
825
X
2. Excess mean molar heat capacities for sulfolane + an aromatic hydrocarbon in the range 303 to 323 K as calculated from equation (2) with coefficients from table 2: 1, benzene; 2, toluene; 3, p-xylene; 4, mesitylene. FIGURE
could be that in addition to dispersion forces, sulfolane and an aromatic hydrocarbon interact oia dipole-induced dipole mechanism which decreases in strength with increasing temperature, and thus gives rise to positive excess heat capacities. REFERENCES
1. Karvo, M. J, Chem. ThermodynamicslWJ, 12, 635. 2. Karvo, M. J. Chem. Thermodynamics 1980, 12, 1175. 3. Jannelli, L.; Della Monica, M.; Della Monica, A. Guzz. Chim. ital. 1!%4,94, 552. 4. Benoit, R. L.; Choux, G. Can. J. Chem. 1968,46, 3215. 5. Ashcroft, S. J.; Clayton, A. D.; Sheam, R. B. J. Chem. Eng. Data 1979,24, 195. 6. Timmermans, J. Physico-chemical Constants of Pure Organic Compounds, Vol. 2. Elsevier: Amsterdam. 1965, pp. 97, 100, 113, 124. 7. Fortier, J-L.; Benson, G. C. J. Chem. Thermodynamics 19’77,9, 1181. 8. Van Ness, H. C.; Abbot, M. M. int. DATA Ser., Ser. A. Sel. Data Mixtures 1974, pp. 84, 160. 9. Tanaka, R. J. Chem. Thermodynamics 1932, 14,259. 10. Tamres, M. J. Am. Chem. Sot. 1952,74, 3375. II. McGIashan, M. L.; Stubley, D.; Watts, H. J. Chem. Sot. A 1969, 673.
Excess enthalpies of sulfolane + benzene, + toluene, + p-xylene, + mesitylene as functions of temperature
and
MIKKO KARVO Department of Chemistry. University of Oulu, SF-90570 Oulu 57, Finland (Received 27 January 1983)
The excess enthalpies of sulfolane + benzene, + toluene, + pxylene, and + mesitylene have been measured with a flow calorimeter at 303.15,313.15,and 323.15K. The HL values as well as the estimated excess heat capacities are positive and increase with increasing hydrocarbon alkylation.
1. Introduction The excess Gibbs energies between 303 and 333 K and the excess enthalpies at 303.15 K of sulfolane + benzene and + toluene have been reported earlier.“, 2, To obtain information about the temperature dependence of HE, similar measurements were undertaken at 313.15 and 323.15 K for the mixtures. In addition the excess enthalpies of sulfolane + p-xylene and + mesitylene were measured, to investigate the influence upon Hz of an increasing number of methyl substituents in the benzene ring.
2. Experimental Sulfolane (E. Merck, zur Synthese) was purified by repeated distillations under vacuum. In the last two or three distillations phosphorus pentoxide was added to the flask for dehydration. t3) The purified sulfolane was used when its melting temperature was 301.55 K or higher.‘3-5’ Benzene, toluene, p-xylene, and mesitylene (all Fluka AG, puriss., p.a.) were distilled at atmospheric pressure through a Vigreux column and then passed through an aluminium oxide column (Fluka AG, chromatography, basic, activity I). The purified aromatic solvents were stored over molecular sieves (British Drug Houses Ltd., type 4A). The densities of the purified samples of sulfolane, benzene, toluene, p-xylene, and mesitylene at 303.15 K were 1.2624,O.86827,0.85760,0.85227, and 0.85681 g. cmb3, 0021-9614/83/090821+05 %02.00/O
0 1983Academic Press Inc. (London) Limited
822
M. KARVO
compared with the literature values 1.2620,(5) 0.86825,@’0.85766,‘6’0.85232,“j’ and 0.8569 g. cm-3,‘6) respectively. The excess enthalpies were determined with an LKB flow microcalorimeter (Model 2107). The experimental procedure has been described earlier.“’ 3. Results The experimental values of HE for the four mixtures are reported in table 1. The excess enthalpies of sulfolane + benzene and + toluene at 303.15 K published earlier are not reproduced in table 1 except some new values for the first pair. These were determined around the local minimum in the Hk against x curve, and they confirm the observed behaviour. The experimental excessenthalpies show that for each binary mixture studied the HE values increase almost linearly with increasing temperature. Therefore it seemed reasonable to use a smoothing function Hr(J.mol-‘)
=x(1-x)
2 ,4,(1-2x)‘+ j=O
i
aj{(7’/K)-303.15j(l
j=O
-2xy
,
(1)
where x denotes the mole fraction, T the temperature, and n (< m) is at its maximum 2. This equation allows the Hz results at different temperatures to be fitted simultaneously. According to @Hf,/aT), = C&,, equation (1) gives the relation: CE,,/(J.K-‘.mol-‘)
=x(1 -x) t agl-2.u)‘, j=O
12)
for the excessheat capacity. The estimates of C’i., represent mean values over the temperature range of the H,!f,measurements. When the coefficients of equation (1) are solved with a least-squares program also giving the standard errors of Aj and aj, it is also possible to determine confidence limits for the calculated CpE,m values. In general the estimation of CF.,, from the temperature dependenceof HE is subject to relatively large error as noted by Fortier and Benson.‘7’ However, when the proposed method was tested with some mixtures for which both Hfi, at several temperatures and the experimental CF.,, values are available in the literature, good,‘*v9)or at least satisfactory, agreement was obtained between the calculated and the measured excessheat capacities. A summary of the coefficients of equation (1) for the representation of the present HE results is given in table 2. The standard errors of the coefficients as well as the standard deviations s(Hf,) of the fits are included. The solid curves in figures 1 and 2 were calculated from (1) and (2) using these coefficient values. The error bars in figure 2 show the uncertainties of CF.,, as calculated from the standard errors of the coefficients aj 4. Discussion The four Hfi, curves in figure 1 show that the excessmolar enthalpies are positive and increase with an increasing number of methyl substituents in the benzene ring.
TABLE
X
HE, J.mol-’
1. Experimental
HE, ’
J.mol-’
excess enthalpies
Hfi, ’
J.mol-’
HE, ’
J.mol-’
HZ x
J.mol-’
HE ’
J.mol-’
(1 -x)C,H,O,S + xC,H, 303.15 K 0.7988
7.6
0.7274
5.5
0.6800
6.3
0.6581
8.3
0.6116
14.9
313.15 K 0.0403 0.0956 0.1729 0.2201
12.9 29.2 44.9 50.4
0.2956 0.3677 0.4640 0.5141
53.2 49.1 40.2 37.0
0.5640 0.5868 0.6116
32.6 30.4 24.6
0.6581 0.6858 0.7274
18.7 16.6 15.6
0.7455 0.7988 0.8420
14.5 16.3 18.2
0.9137 0.9638 0.9817
24.8 24.4 18.3
0.0403 0.0956 0.1729
14.0 30.4 47.8
0.2200 0.2956 0.3677
56.2 61.3 59.5
0.4640 0.5141 0.5640
323.15 K 52.4 0.5945 49.0 0.6116 43.0 0.6788
41.4 40.4 34.0
0.7274 0.7936 0.8427
29.0 29.9 30.2
0.9137 0.9638 0.9817
33.3 27.5 16.9
352.4 356.3 338.4
0.7687 301.2 0.8216 265.9 0.9024 196.7
0.9481 0.9787
130.8 70.3
378.9 381.5
0.6851 0.8025
0.9155 0.9560
198.8 124.2
(1 -x)C,H,O,S+xC,H,CH, 16.6 42.2 88.5
0.1451 157.5 0.1911 189.0 0.2651 257.2
0.3275 0.4202 0.4698
313.15 K 298.0 0.5200 332.4 0.6172 348.2 0.6851
0.0676 85.6 0.1620 200.0
0.2651 283.6 0.3275 324.1
0.4202 0.4698
360.6 370.6
0.0168 0.0412 0.0783
323.15 K
0.0682 164.7 0.1693 341.7 0.2326 419.0 0.2704 457.9
0.2958 470.5 0.3393 509.0 0.3847 519.0
0.0703 174.1 0.1429 326.1 0.2326 445.8
0.2958 0.3847
0.0709 181.8 0.1429 360.6 0.2326 484.2
0.2958 556.8 0.3847 621.3
0.5200 0.6172
(1 -x)C,H,O,S+xl,4-C,HdCH,), 303.15 K 0.4332 536.1 0.5817 562.3 0.4830 555.9 0.6042 559.8 0.5321 570.8 0.6583 565.4
380.8 314.8
0.6790 552.3 0.7829 497.3 0.7993 481.4
0.8138 460.0 0.8844 346.3 0.9506 177.4
628.9 617.2
0.7829 0.8138
545.9 507.2
0.8844 0.9506
0.6042 687.9 0.6790 664.3
0.7829 0.8138
581.5 542.1
0.8750 428.0 0.9336 276.9
0.7568 640.9 0.7735 616.1 0.7904 611.0
0.8817 468.2 0.9447 288.4
749.2 721.2
0.7735 0.7904
705.3 679.1
0.8817 0.9447
517.1 300.8
0.5525 864.1 0.6526 850.9
0.7568 0.7904
791.8 742.0
0.8817 0.9447
541.8 301.5
313.15 K 514.1 569.2
0.4332 0.4830
594.4 601.6
0.6042 0.6790
372.6 227.8
323.15 K 0.4332 649.9 0.4830 670.3 (1 -x)C4H,02S 0.0582 241.4 0.0690 264.2 0.1289 405.2
0.1969 474.0 0.2165 495.8 0.2536 534.9
0.0690 255.8 0.1289 425.0 0.2165 571.6
0.2717 0.3570 0.4043
615.9 663.2 697.8
0.0690 289.5 0.1289 488.3 0.2165 627.9
0.2717 0.3570 0.4043
695.2 784.3 807.5
+x1,3,5-C,H,(CH,),
303.15 K 0.2717 543.8 0.5025 653.1 0.3358 589.1 0.6311 659.9 0.4043 611.8 0.6526 650.6 313.15 K 0.4534 704.2 0.6526 0.5025 758.3 0.7568 0.5525 745.1 323.15 K 0.4534 0.5025
819.3 862.5
M. KARVO
824
TABLE 2. Coefficients and standard deviations s{ Hk/(J mol - ‘)] for least squares representations by equation (1). The standard errors of the coefficients are given in parenthesis + xC,H, 113.8 154.8 - 190.6 545.3 690.8 1109.0 5.20 ~ 2.57 3.4
(11) (37) (58) (149) (67) (135) (0.56) (0.93)
+xC,H,CH, ~ ~~__ 1237.8 -365.3 83.3 817.8 674.1 - 1647.9 17.04 - 7.90 8.0
~~~
(27) (90) (139) (352) (155) (315) (1.5) (2.5)
of Hk
+ x1.4-C,H,(CH&
+.x1,3.5-C,H,(CH,),
2225.8 (15) -315.3 (35) 1358.5 (97) -459.3 (60) -211.0 (129)
2492.8 (33) ~ 595.6 t 55) 2308.7 ( 169) -- 39.2 (90) 912.7 (196)
23.16 -9.79 6. I
(0.84) (1.6)
46.04 PO.95 -31.02 Il.5
(2.1) (2.4) (5.2)
The increments at x = 0.5 and at 323.15 K per CH,-group are 325, 240, and 185 J. mol-r when moving from benzene to mesitylene. The observed behaviour suggeststhat no strong attractions between the sulfolane and aromatic molecule exist; had strong attractions existed the excess enthalpies would have been negative or would at least have decreased with increasing methyl substitution of the benzene molecule.(l”*r ‘) Usually for mixtures of simple non-polar molecules Hk is positive and decreaseswith increasing temperature. For the present mixtures the temperature dependence of Hfi, turned out to be just the opposite: the excess enthalpies increase with increasing temperature. A possible interpretation
FIGURE 1. Excess molar enthalpies for sulfolane + an aromatic hydrocarbon at 323.15 K. A, Benzene; 0. toluene; A, p-xylene; 0, mesitylene. All curves are calculated from equation (1) with coefficients from table 2.
HE FOR SOME SULFOLANE
MIXTURES
AT THREE
TEMPERATURES
825
X
2. Excess mean molar heat capacities for sulfolane + an aromatic hydrocarbon in the range 303 to 323 K as calculated from equation (2) with coefficients from table 2: 1, benzene; 2, toluene; 3, p-xylene; 4, mesitylene. FIGURE
could be that in addition to dispersion forces, sulfolane and an aromatic hydrocarbon interact oia dipole-induced dipole mechanism which decreases in strength with increasing temperature, and thus gives rise to positive excess heat capacities. REFERENCES
1. Karvo, M. J, Chem. ThermodynamicslWJ, 12, 635. 2. Karvo, M. J. Chem. Thermodynamics 1980, 12, 1175. 3. Jannelli, L.; Della Monica, M.; Della Monica, A. Guzz. Chim. ital. 1!%4,94, 552. 4. Benoit, R. L.; Choux, G. Can. J. Chem. 1968,46, 3215. 5. Ashcroft, S. J.; Clayton, A. D.; Sheam, R. B. J. Chem. Eng. Data 1979,24, 195. 6. Timmermans, J. Physico-chemical Constants of Pure Organic Compounds, Vol. 2. Elsevier: Amsterdam. 1965, pp. 97, 100, 113, 124. 7. Fortier, J-L.; Benson, G. C. J. Chem. Thermodynamics 19’77,9, 1181. 8. Van Ness, H. C.; Abbot, M. M. int. DATA Ser., Ser. A. Sel. Data Mixtures 1974, pp. 84, 160. 9. Tanaka, R. J. Chem. Thermodynamics 1932, 14,259. 10. Tamres, M. J. Am. Chem. Sot. 1952,74, 3375. II. McGIashan, M. L.; Stubley, D.; Watts, H. J. Chem. Sot. A 1969, 673.