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Excess molar enthalpies of mixtures of a cycloalkane and an alkanol
157
7’hermochimicu Acta, 188 (1991) 157-162 Elsevier Science Publishers B.V., Amsterdam
Excess molar enthalpies of mixtures of a cycloalkane and an alkanol T.M. Letcher, J. Mercer-Chalmers
and A.K. Prasad
Department of Chemistry, Rhodes University, Grahamstown 6140 (South Africa) (Received 4 January 1991)
The excess molar enthalpies, HE, for the sixteen mixtures, (cy~lo_C~H,~ +CH,OH) and (cycle-C,H,, + CIHZ/+I OH) with k = 5, 6, 7, 8 and 10 and I = 2 and 3, were measured at 298.15 K. The H,” results are discussed in terms of the size of the cycloalkane ring and the length of the alkanol chain. INTRODUCTION
In the present work, we investigated the excess molar enthalpy (HE) values obtained on mixing a cycloalkane with an alkanol. Our results show the effect on HE of increasing the ring size of the cycloalkane and also the effect of increasing the chain length of the alkanol. We studied the systems (xc-C,H,, + (1 - x)CH,OH) and (xc-C,H,, + (1 - x)C,H,,+,OH) for k = 5, 6, 7, 8 and 10, and 2 = 2 and 3. These mixtures are miscible over the whole concentration range. The Hz values for five of these sixteen systems have been published [l-9] and are compared with our results. EXPERIMENTAL
The purification procedures used [lo-121 and the flow calorimeter (LKB 2107) method for determining HE have been previously described [13]. RESULTS
The H,” results for each of the sixteen systems are given in Table 1 together with the deviations, A, calculated from the smoothing equation A(J mol-‘)
= H,f(J mol-‘)
-x(1
- x) i
A,(1 - 2~)~
(1)
r=O
where x denotes the mole fraction. The coefficients, 2. (x)40-6031/91
/%03.50
A,, are given in Table
0 1991 - Elsevier Science Publishers B.V. All rights reserved
158 TABLE 1 Molar excess enthalpies, H,” for (xC,H,, +(lx)C,H2,+,0H) deviations, A, from eqn. (1) and the coefficients of Table 2 x
HZ
(J
mol-‘)
x
HZ
(J
;:
mol-‘)
x
;:
mol-“)
mol-‘)
at 298.15 K and the
H,”
CJ
(“J
mol-l)
mol-‘)
xc-C,H,, 0.0747 0.1332 0.1953 0.2410 0.3009
+ (1 - x)CH,OH 249.8 - 4.9 375.9 4.0 452.5 1.3 491.4 0.2 526.0 - 2.1
0.3754 0.4072 0.4817 0.5762
556.1 562.0 566.3 553.7
-0.2 -0.7 -0.6 2.7
0.6735 0.7964 0.8523 0.9188
513.6 438.1 375.4 269.5
-0.7 0.7 - 3.7 3.3
xc-C,H,, 0.0639 0.1251 0.1911 0.2398 0.3365
+(1- x)C,H,OH 119.1 - 4.7 210.3 -1.2 297.0 5.9 346.8 2.7 430.9 - 3.9
0.4114 0.4836 0.5732 0.6205
482.8 519.4 538.7 541.0
- 4.3 -0.1 2.2 3.7
0.6659 0.7752 0.8863 0.9493
537.2 497.7 404.S 240.7
3.2 - 9.4 3.6 1.8
0.4839 0.5220 0.5610 0.6198 0.6833
455.0 478.2 500.7 520.3 521.0
-5.0 -1.9 4.6 7.4 -2.5
0.7215 0.7965 0.8512 0.9183 0.9581
528.4 512.3 480.7 376.4 232.8
2.0 - 5.2 - 3.3 6.6 -0.3
XC-C,H,~ 0.1025 0.174s 0.1806 0.2971 0.3497
+(I - x)~H~CH(O~H~ 192.7 -3.5 0.4137 304.3 -0.1 0.5225 317.0 3.7 0.6040 477.8 2.5 0.6302 539.6 - 1.2 0.7251
604.8 685.9 715.3 715.8 699.6
- 4.2 - 0.9 3.7 2.0 1.8
0.7757 0.8427 0.9183 0.9503
662.8 595.6 419.4 291.2
- 6.7 0.2 2.4 0.8
XC+JI,~ 0.0983 0.1736 0.2558 0.3586 0.4530
241.1 361.5 473.5 570.1 621.5
0.4884 0.5317 0.5844 0.6533
632.0 637.7 639.4 627.5
-2.4 -2.1 2.3 5.6
0.7150 0.8009 0.8619 0.8967
602.5 540.5 475.0 426.2
2.8 - 8.7 - 5.6 9.9
xc-GH,, 0.1436 0.2511 0.3642 0.4157
+(lx)C$H,OH 230.7 - 1.7 356.7 3.2 479.4 -0.9 528.0 - 1.4
0.5543 0.6018 0.6415 0.6935
604.5 619.5 621.3 614.8
-3.8 2.8 3.6 2.7
0.7483 0.8198 0.8936 0.9344
592.3 554.2 451.6 338.2
- 5.0 - 1.5 1.1 1.4
xc-C;,H,, 0.1347 0.2619 0.3557 0.4471
+ (1 - x)~H~~H~OH)~H~ 313.6 - 4.2 0.5536 542.1 10.2 0.5942 663.0 -5.5 0.6251 762.3 - 6.1 0.6895
826.1 836.7 835.3 812.0
- 0.9 4.6 5.4 2.8
0.7455 0.8362 0.8991
766.2 651.4 517.6
-6.1 -7.6 8.4
XC-C~H,~ +(lx)C3H,0H 0.1005 127.2 -2.2 0.1833 200.4 1.0 0.3001 311.7 3.8 0.4070 405.1 -0.7 0.4536 437.5 3.3
f(1- x)C,H,OH 0.7 -1.9 4.2 0.2 - 2.7
159 TABLE 1 (continued) X
H,
(J
mol-‘)
X
i
X
Hi
(J
H,”
A
(J
(J
mol-‘)
mol-‘)
0.5299 0.6003 0.6646 0.6856
660.9 657.6 639.8 630.6
- 3.6 3.2 4.3 2.7
0.7526 0.8369 0.8891 0.9521
592.1 530.3 449.3 265.0
- 6.0 - 1.7 -0.7 5.2
mol-’
mol-‘)
mol-‘)
xc-C,H,, 0.0889 0.1641 0.2447 0.3431 0.4076
+ (1 - x)C,H,OH 243.6 - 2.2 383.4 0.1 499.7 4.0 594.8 - 1.2 635.9 2.1
xc-C,H,, 0.0913 0.1685 0.2519 0.3516
+ (1 - x)C,H,OH 171.6 - 5.2 296.5 4.6 402.8 3.1 503.0 - 3.6
0.4174 0.5438 0.5850 0.6073
557.7 619.2 633.6 636.2
-2.6 -2.1 3.4 3.2
0.6589 0.7026 0.8655 0.9132
636.0 626.7 495.7 407.2
1.8 - 2.4 -9.8 10.1
xc-C,H,, 0.0969 0.1776 0.3191 0.4205
+(l - x)CH,CH(OH)CH, 259.8 0.9 0.5051 440.6 0.4 0.5462 656.4 - 5.5 0.5732 774.6 5.9 0.6003
837.1 860.1 865.0 867.9
2.7 3.3 -1.9 - 4.6
0.6320 0.7298 0.7998 0.9008
865.2 815.2 690.6 388.0
- 7.0 6.3 1.9 - 3.0
xc-C,H,, 0.0793 0.1473 0.2182 0.3047 0.3791
+ (1- x)C,H,OH 237.1 - 1.6 369.4 - 1.7 472.6 3.1 557.2 3.9 596.3 -2.7
0.4362 0.4718 0.5023 0.5632 0.6237
615.0 623.2 624.6 623.4 614.0
- 3.6 -1.4 - 1.6 1.9 5.5
0.7244 0.8065 0.8695 0.9219
575.8 517.3 442.8 345.1
2.2 -6.1 - 5.9 9.7
xc-C,H,, 0.0430 0.1531 0.2314 0.3902 0.4402
+(l - x)C,H,OH 95.5 - 2.0 284.5 -0.5 394.2 2.8 552.7 - 6.0 584.6 -1.8
0.5220 0.5663 0.6095 0.6433 0.7015
617.6 632.2 638.7 637.9 628.2
3.6 1.1 3.3 2.4 -0.2
0.8202 0.8772 0.9151 0.9542
563.4 476.6 395.2 255.3
- 1.8 - 6.3 3.9 5.0
xc-C,H,, 0.0631 0.1371 0.2371 0.3402 0.4458
+ (1 - x)CH,CH(OH)CH, 192.9 - 5.2 0.5287 377.2 2.4 0.5852 558.2 5.4 0.6093 675.3 - 5.6 0.6459 757.1 - 2.6
788.6 796.1 796.8 793.1
0.2 2.1 3.5 4.4
0.7033 0.7828 0.8512 0.9217
767.4 712.9 630.3 430.1
-4.6 - 7.2 5.5 0.3
xc-C,,H,, 0.1168 0.2081 0.3034 0.3523
+ (1- x)C,H,OH 450.2 0.7 367.4 - 1.3 445.6 - 0.5 473.0 1.7
489.6 496.5 490.1 474.3
1.1 -1.3 2.4 1.7
0.6513 0.7512 0.8921 0.9317
450.4 370.9 211.0 117.4
1.5 -1.4 0.7 - 0.5
0.4037 0.4818 0.5362 0.6034
160 TABLE 1 (continued) X
X
H,”
(J
mol-‘)
$
X
HZ
(J
mol-‘)
mol-‘)
0.5350 0.5736 0.6019 0.6575
489.4 494.2 494.0 485.6
- 1.6 0.9 1.8 2.8
XC-C,,,HzO+(l - x)CH,CH(OH)CH3 0.0729 233.1 6.1 0.5037 0.1467 353.2 -6.7 0.5448 0.2172 448.0 -1.1 0.5819 0.3560 593.3 8.7 0.6156 0.4362 638.2 - 1.1
662.2 668.2 670.0 668.9
-4.1 - 4.7 -2.5 1.7
xc-&Hz,, 0.1394 0.2453 0.3465 0.4502
mol-’
+ (1 - x)C3H,0H 246.2 - 2.4 353.7 4.1 420.8 0.1 466.6 -4.2
HE
(J
mol-‘)
mol-‘)
0.7236 0.7850 0.8693 0.9321
460.2 419.9 320.1 223.1
1.5 - 0.7 - 10.0 10.3
0.6512 0.7126 0.8382 0.9301
658.2 636.2 493.3 312.6
1.7 9.9 - 11.9 7.3
TABLE 2 Smoothing coefficients, A,, for xc-C,H,,
+ (1- x)C,H~~+~OH
k
Alkanol
-Jo
-4,
5 5 5 5 6 6 6 7 7 7 8 8 8 10 10 10
CH,OH C,H,OH C,H,OH CH&H(OH)CH, C,H,OH C,H,OH CH,CH(OH)CH, C2HSOH C,H,OH CH,CH(OH)CH, C,H,OH C,H,OH CH,CH(OH)CH, C2HSOH C,H,OH CH,CH(OH)CH,
2262.1 2097.1 1876.2 2699.9 2546.4 2350.1 3223.4 2655.7 2425.1 3324.0 2505.1 2456.4 3125.7 1988.6 1940.8 2661.3
194.0 - 542.5 - 1068.9 - 1149.8 - 324.6 - 1005.1 - 1104.3 - 153.3 - 828.2 - 1307.3 - 24.3 - 719.4 - 590.4 133.5 - 434.6 - 538.8
A2
958.3 507.3 300.3 493.0 495.3 104.3 280.7 643.9 762.7 1437.0 961.5 793.3 1262.9 360.3 507.8 452.4
A3
- 226.7 - 1288.6 - 1407.0 - 1254.6 - 1270.7 - 1197.5 - 1034.4 - 1463.8 - 1331.1 661.1 - 1114.6 - 1372.3 - 1378.6 198.4 - 205.4 - 301.8
A4
1345.0 1582.6 2295.6 1666.8 1876.9 2467.1 1978.1 1935.0 1346.1 - 1402.0 1533.1 1369.4 1197.5 76.0 956.1 1905.9
DISCUSSION
The HE values for five of the sixteen systems investigated here have been published previously. The results of Stokes and Burfitt [l] for cyclopentane plus ethanol and cycloheptane plus ethanol are within 5 J mol-’ of the smoothing curves fitted to our results, except at very low alcohol concentrations. For cyclohexane plus ethanol, our results are within 10 J mol-r, in the worst case, of the results given by Nagata and Kazuma [2] and also by
161
5
6
7
6
9
10
k excess molar enthalpy data, HE(x = OS), for (xc-C,H,, Fig. 1. Interpolated A, C,H,OH; x)C,G,+~OH) as a function of k: o, CH,OH; 0, C,H,OH; CH,CH(OH)CH,.
+(land A,
Stokes and Adamson [3]. Our results for cyclohexane plus 2-propanol are 10 J mol-’ of the smoothing curves based on the data of Vesely et al. [4] and Nagata et al. [5]. There are four sets of data in the literature for the HE value for (xC,H,, + (1 - x)C,H,OH) [6-91. Our results are within 5 J mol-‘, in the worst case, of the smoothing curve for the data given by Nagata and Kazuma [6] but almost 30 J mol-r higher than the published data of Veseljr and Pick [7,8] and 80 J mol-’ lower than the published data of Belousov et al. [9]. The Hz values for all the sixteen systems discussed here are positive, with HE(maximum) ranging from 490 to 866 J mol-‘. This reflects the breakdown of the hydrogen bonding between the alkanol molecules on mixing with a cycle compound. For each particular alkanol, the value of HE(maximum) or Hi(x = 0.5) increases with increasing cycloalkane carbon number from k = 5 to k = 7 and decreases from k = 7 to k = 10. This can be seen in Fig. 1 where Hi(x = 0.5) has been plotted against k. The concentration of the cycloalkane at which flz(maximum) occurs for a particular alkanol, decreases with increasing cycloalkane carbon number. For example for ethanol systems, H~(maxirnum) occurs at x = 0.61 for k = 5, x = 0.56 for k = 6, x = 0.54 for k = 7, x = 0.51 for k = 8 and x = 0.45 for k = 10. For cyclopentane systems, HE(x = 0.5) decreases with increasing chain length of the I-alkanols from Z= 1 to Z= 3. The same is true for each of the other cycloalkanes for I= 2 and 3. This can be attributed to the decreasing hydrogen bonding between alcohol molecules as I increases from 1 to 3. within
162
The HE(x = 0.5) value for (xc-C,H,, + (1 - x)CH,CH(OH)CH,) is + (1 x)C,H,OH) or (xc-C,H,, + larger than Hi(x = 0.5) for (xc-C,H,, (1 - x)C,H,OH) for k between 5 and 10. This implies a stronger hydrogen bonding between 2-propanol molecules than between ethanol molecules or between l-propanol molecules. This could be due to the inductive effect of the methyl groups of 2-propanol. ACKNOWLEDGEMENTS
The authors wish to thank the FRD (South Africa) and Rhodes University for financial help. REFERENCES 1 2 3 4 5 6 7 8 9 10 11 12 13
R.H. Stokes and C. Burfitt, J. Chem. Thermodyn., 5 (1973) 623. I. Nagata and K. Kazuma, J. Chem. Eng. Data, 22 (1977) 79. R.H. Stokes and M. Adamson, J. Chem. Sot., Faraday Trans. 1, 73 (1977) 1232. F. Vesely, P. Uchytil, M. Zabransky and J. Pick, Collect. Czech. Chem. Commun., 44 (1979) 2869. I. Nagata, K. Fujiwara and Y. Ogasawara, J. Chem. Thermodyn., 10 (1978) 1201. I. Nagata and K. Kazuma, J. Chem. Eng. Data, 22 (1977) 79. F. Vesely and J. Pick, Collect. Czech. Chem. Commun., 32 (1967) 4134. F; Vesely and J. Pick, Collect. Czech. Chem. Commun., 34 (1969) 1854. V.P. Belousov, L.M. Kurtymina and A.A. Kozulyaer, Vestn. Leningr. Univ. Fiz., 10 (1970) 163. T.M. Letcher, J. Chem. Thermodyn., 16 (1984) 805. T.M. Letcher, C. Heyward, S. Wooten and B. Shuttleworth, Fuel, 65 (1986) 891. T.M. Letcher, S. Wooten, B. Shuttleworth and C. Heyward, J. Chem. Thermodyn., 18 (1986) 1037. T.M. Letcher and B.W.H. Scoones, J. Chem. Thermodyn., 14 (1982) 703.
7’hermochimicu Acta, 188 (1991) 157-162 Elsevier Science Publishers B.V., Amsterdam
Excess molar enthalpies of mixtures of a cycloalkane and an alkanol T.M. Letcher, J. Mercer-Chalmers
and A.K. Prasad
Department of Chemistry, Rhodes University, Grahamstown 6140 (South Africa) (Received 4 January 1991)
The excess molar enthalpies, HE, for the sixteen mixtures, (cy~lo_C~H,~ +CH,OH) and (cycle-C,H,, + CIHZ/+I OH) with k = 5, 6, 7, 8 and 10 and I = 2 and 3, were measured at 298.15 K. The H,” results are discussed in terms of the size of the cycloalkane ring and the length of the alkanol chain. INTRODUCTION
In the present work, we investigated the excess molar enthalpy (HE) values obtained on mixing a cycloalkane with an alkanol. Our results show the effect on HE of increasing the ring size of the cycloalkane and also the effect of increasing the chain length of the alkanol. We studied the systems (xc-C,H,, + (1 - x)CH,OH) and (xc-C,H,, + (1 - x)C,H,,+,OH) for k = 5, 6, 7, 8 and 10, and 2 = 2 and 3. These mixtures are miscible over the whole concentration range. The Hz values for five of these sixteen systems have been published [l-9] and are compared with our results. EXPERIMENTAL
The purification procedures used [lo-121 and the flow calorimeter (LKB 2107) method for determining HE have been previously described [13]. RESULTS
The H,” results for each of the sixteen systems are given in Table 1 together with the deviations, A, calculated from the smoothing equation A(J mol-‘)
= H,f(J mol-‘)
-x(1
- x) i
A,(1 - 2~)~
(1)
r=O
where x denotes the mole fraction. The coefficients, 2. (x)40-6031/91
/%03.50
A,, are given in Table
0 1991 - Elsevier Science Publishers B.V. All rights reserved
158 TABLE 1 Molar excess enthalpies, H,” for (xC,H,, +(lx)C,H2,+,0H) deviations, A, from eqn. (1) and the coefficients of Table 2 x
HZ
(J
mol-‘)
x
HZ
(J
;:
mol-‘)
x
;:
mol-“)
mol-‘)
at 298.15 K and the
H,”
CJ
(“J
mol-l)
mol-‘)
xc-C,H,, 0.0747 0.1332 0.1953 0.2410 0.3009
+ (1 - x)CH,OH 249.8 - 4.9 375.9 4.0 452.5 1.3 491.4 0.2 526.0 - 2.1
0.3754 0.4072 0.4817 0.5762
556.1 562.0 566.3 553.7
-0.2 -0.7 -0.6 2.7
0.6735 0.7964 0.8523 0.9188
513.6 438.1 375.4 269.5
-0.7 0.7 - 3.7 3.3
xc-C,H,, 0.0639 0.1251 0.1911 0.2398 0.3365
+(1- x)C,H,OH 119.1 - 4.7 210.3 -1.2 297.0 5.9 346.8 2.7 430.9 - 3.9
0.4114 0.4836 0.5732 0.6205
482.8 519.4 538.7 541.0
- 4.3 -0.1 2.2 3.7
0.6659 0.7752 0.8863 0.9493
537.2 497.7 404.S 240.7
3.2 - 9.4 3.6 1.8
0.4839 0.5220 0.5610 0.6198 0.6833
455.0 478.2 500.7 520.3 521.0
-5.0 -1.9 4.6 7.4 -2.5
0.7215 0.7965 0.8512 0.9183 0.9581
528.4 512.3 480.7 376.4 232.8
2.0 - 5.2 - 3.3 6.6 -0.3
XC-C,H,~ 0.1025 0.174s 0.1806 0.2971 0.3497
+(I - x)~H~CH(O~H~ 192.7 -3.5 0.4137 304.3 -0.1 0.5225 317.0 3.7 0.6040 477.8 2.5 0.6302 539.6 - 1.2 0.7251
604.8 685.9 715.3 715.8 699.6
- 4.2 - 0.9 3.7 2.0 1.8
0.7757 0.8427 0.9183 0.9503
662.8 595.6 419.4 291.2
- 6.7 0.2 2.4 0.8
XC+JI,~ 0.0983 0.1736 0.2558 0.3586 0.4530
241.1 361.5 473.5 570.1 621.5
0.4884 0.5317 0.5844 0.6533
632.0 637.7 639.4 627.5
-2.4 -2.1 2.3 5.6
0.7150 0.8009 0.8619 0.8967
602.5 540.5 475.0 426.2
2.8 - 8.7 - 5.6 9.9
xc-GH,, 0.1436 0.2511 0.3642 0.4157
+(lx)C$H,OH 230.7 - 1.7 356.7 3.2 479.4 -0.9 528.0 - 1.4
0.5543 0.6018 0.6415 0.6935
604.5 619.5 621.3 614.8
-3.8 2.8 3.6 2.7
0.7483 0.8198 0.8936 0.9344
592.3 554.2 451.6 338.2
- 5.0 - 1.5 1.1 1.4
xc-C;,H,, 0.1347 0.2619 0.3557 0.4471
+ (1 - x)~H~~H~OH)~H~ 313.6 - 4.2 0.5536 542.1 10.2 0.5942 663.0 -5.5 0.6251 762.3 - 6.1 0.6895
826.1 836.7 835.3 812.0
- 0.9 4.6 5.4 2.8
0.7455 0.8362 0.8991
766.2 651.4 517.6
-6.1 -7.6 8.4
XC-C~H,~ +(lx)C3H,0H 0.1005 127.2 -2.2 0.1833 200.4 1.0 0.3001 311.7 3.8 0.4070 405.1 -0.7 0.4536 437.5 3.3
f(1- x)C,H,OH 0.7 -1.9 4.2 0.2 - 2.7
159 TABLE 1 (continued) X
H,
(J
mol-‘)
X
i
X
Hi
(J
H,”
A
(J
(J
mol-‘)
mol-‘)
0.5299 0.6003 0.6646 0.6856
660.9 657.6 639.8 630.6
- 3.6 3.2 4.3 2.7
0.7526 0.8369 0.8891 0.9521
592.1 530.3 449.3 265.0
- 6.0 - 1.7 -0.7 5.2
mol-’
mol-‘)
mol-‘)
xc-C,H,, 0.0889 0.1641 0.2447 0.3431 0.4076
+ (1 - x)C,H,OH 243.6 - 2.2 383.4 0.1 499.7 4.0 594.8 - 1.2 635.9 2.1
xc-C,H,, 0.0913 0.1685 0.2519 0.3516
+ (1 - x)C,H,OH 171.6 - 5.2 296.5 4.6 402.8 3.1 503.0 - 3.6
0.4174 0.5438 0.5850 0.6073
557.7 619.2 633.6 636.2
-2.6 -2.1 3.4 3.2
0.6589 0.7026 0.8655 0.9132
636.0 626.7 495.7 407.2
1.8 - 2.4 -9.8 10.1
xc-C,H,, 0.0969 0.1776 0.3191 0.4205
+(l - x)CH,CH(OH)CH, 259.8 0.9 0.5051 440.6 0.4 0.5462 656.4 - 5.5 0.5732 774.6 5.9 0.6003
837.1 860.1 865.0 867.9
2.7 3.3 -1.9 - 4.6
0.6320 0.7298 0.7998 0.9008
865.2 815.2 690.6 388.0
- 7.0 6.3 1.9 - 3.0
xc-C,H,, 0.0793 0.1473 0.2182 0.3047 0.3791
+ (1- x)C,H,OH 237.1 - 1.6 369.4 - 1.7 472.6 3.1 557.2 3.9 596.3 -2.7
0.4362 0.4718 0.5023 0.5632 0.6237
615.0 623.2 624.6 623.4 614.0
- 3.6 -1.4 - 1.6 1.9 5.5
0.7244 0.8065 0.8695 0.9219
575.8 517.3 442.8 345.1
2.2 -6.1 - 5.9 9.7
xc-C,H,, 0.0430 0.1531 0.2314 0.3902 0.4402
+(l - x)C,H,OH 95.5 - 2.0 284.5 -0.5 394.2 2.8 552.7 - 6.0 584.6 -1.8
0.5220 0.5663 0.6095 0.6433 0.7015
617.6 632.2 638.7 637.9 628.2
3.6 1.1 3.3 2.4 -0.2
0.8202 0.8772 0.9151 0.9542
563.4 476.6 395.2 255.3
- 1.8 - 6.3 3.9 5.0
xc-C,H,, 0.0631 0.1371 0.2371 0.3402 0.4458
+ (1 - x)CH,CH(OH)CH, 192.9 - 5.2 0.5287 377.2 2.4 0.5852 558.2 5.4 0.6093 675.3 - 5.6 0.6459 757.1 - 2.6
788.6 796.1 796.8 793.1
0.2 2.1 3.5 4.4
0.7033 0.7828 0.8512 0.9217
767.4 712.9 630.3 430.1
-4.6 - 7.2 5.5 0.3
xc-C,,H,, 0.1168 0.2081 0.3034 0.3523
+ (1- x)C,H,OH 450.2 0.7 367.4 - 1.3 445.6 - 0.5 473.0 1.7
489.6 496.5 490.1 474.3
1.1 -1.3 2.4 1.7
0.6513 0.7512 0.8921 0.9317
450.4 370.9 211.0 117.4
1.5 -1.4 0.7 - 0.5
0.4037 0.4818 0.5362 0.6034
160 TABLE 1 (continued) X
X
H,”
(J
mol-‘)
$
X
HZ
(J
mol-‘)
mol-‘)
0.5350 0.5736 0.6019 0.6575
489.4 494.2 494.0 485.6
- 1.6 0.9 1.8 2.8
XC-C,,,HzO+(l - x)CH,CH(OH)CH3 0.0729 233.1 6.1 0.5037 0.1467 353.2 -6.7 0.5448 0.2172 448.0 -1.1 0.5819 0.3560 593.3 8.7 0.6156 0.4362 638.2 - 1.1
662.2 668.2 670.0 668.9
-4.1 - 4.7 -2.5 1.7
xc-&Hz,, 0.1394 0.2453 0.3465 0.4502
mol-’
+ (1 - x)C3H,0H 246.2 - 2.4 353.7 4.1 420.8 0.1 466.6 -4.2
HE
(J
mol-‘)
mol-‘)
0.7236 0.7850 0.8693 0.9321
460.2 419.9 320.1 223.1
1.5 - 0.7 - 10.0 10.3
0.6512 0.7126 0.8382 0.9301
658.2 636.2 493.3 312.6
1.7 9.9 - 11.9 7.3
TABLE 2 Smoothing coefficients, A,, for xc-C,H,,
+ (1- x)C,H~~+~OH
k
Alkanol
-Jo
-4,
5 5 5 5 6 6 6 7 7 7 8 8 8 10 10 10
CH,OH C,H,OH C,H,OH CH&H(OH)CH, C,H,OH C,H,OH CH,CH(OH)CH, C2HSOH C,H,OH CH,CH(OH)CH, C,H,OH C,H,OH CH,CH(OH)CH, C2HSOH C,H,OH CH,CH(OH)CH,
2262.1 2097.1 1876.2 2699.9 2546.4 2350.1 3223.4 2655.7 2425.1 3324.0 2505.1 2456.4 3125.7 1988.6 1940.8 2661.3
194.0 - 542.5 - 1068.9 - 1149.8 - 324.6 - 1005.1 - 1104.3 - 153.3 - 828.2 - 1307.3 - 24.3 - 719.4 - 590.4 133.5 - 434.6 - 538.8
A2
958.3 507.3 300.3 493.0 495.3 104.3 280.7 643.9 762.7 1437.0 961.5 793.3 1262.9 360.3 507.8 452.4
A3
- 226.7 - 1288.6 - 1407.0 - 1254.6 - 1270.7 - 1197.5 - 1034.4 - 1463.8 - 1331.1 661.1 - 1114.6 - 1372.3 - 1378.6 198.4 - 205.4 - 301.8
A4
1345.0 1582.6 2295.6 1666.8 1876.9 2467.1 1978.1 1935.0 1346.1 - 1402.0 1533.1 1369.4 1197.5 76.0 956.1 1905.9
DISCUSSION
The HE values for five of the sixteen systems investigated here have been published previously. The results of Stokes and Burfitt [l] for cyclopentane plus ethanol and cycloheptane plus ethanol are within 5 J mol-’ of the smoothing curves fitted to our results, except at very low alcohol concentrations. For cyclohexane plus ethanol, our results are within 10 J mol-r, in the worst case, of the results given by Nagata and Kazuma [2] and also by
161
5
6
7
6
9
10
k excess molar enthalpy data, HE(x = OS), for (xc-C,H,, Fig. 1. Interpolated A, C,H,OH; x)C,G,+~OH) as a function of k: o, CH,OH; 0, C,H,OH; CH,CH(OH)CH,.
+(land A,
Stokes and Adamson [3]. Our results for cyclohexane plus 2-propanol are 10 J mol-’ of the smoothing curves based on the data of Vesely et al. [4] and Nagata et al. [5]. There are four sets of data in the literature for the HE value for (xC,H,, + (1 - x)C,H,OH) [6-91. Our results are within 5 J mol-‘, in the worst case, of the smoothing curve for the data given by Nagata and Kazuma [6] but almost 30 J mol-r higher than the published data of Veseljr and Pick [7,8] and 80 J mol-’ lower than the published data of Belousov et al. [9]. The Hz values for all the sixteen systems discussed here are positive, with HE(maximum) ranging from 490 to 866 J mol-‘. This reflects the breakdown of the hydrogen bonding between the alkanol molecules on mixing with a cycle compound. For each particular alkanol, the value of HE(maximum) or Hi(x = 0.5) increases with increasing cycloalkane carbon number from k = 5 to k = 7 and decreases from k = 7 to k = 10. This can be seen in Fig. 1 where Hi(x = 0.5) has been plotted against k. The concentration of the cycloalkane at which flz(maximum) occurs for a particular alkanol, decreases with increasing cycloalkane carbon number. For example for ethanol systems, H~(maxirnum) occurs at x = 0.61 for k = 5, x = 0.56 for k = 6, x = 0.54 for k = 7, x = 0.51 for k = 8 and x = 0.45 for k = 10. For cyclopentane systems, HE(x = 0.5) decreases with increasing chain length of the I-alkanols from Z= 1 to Z= 3. The same is true for each of the other cycloalkanes for I= 2 and 3. This can be attributed to the decreasing hydrogen bonding between alcohol molecules as I increases from 1 to 3. within
162
The HE(x = 0.5) value for (xc-C,H,, + (1 - x)CH,CH(OH)CH,) is + (1 x)C,H,OH) or (xc-C,H,, + larger than Hi(x = 0.5) for (xc-C,H,, (1 - x)C,H,OH) for k between 5 and 10. This implies a stronger hydrogen bonding between 2-propanol molecules than between ethanol molecules or between l-propanol molecules. This could be due to the inductive effect of the methyl groups of 2-propanol. ACKNOWLEDGEMENTS
The authors wish to thank the FRD (South Africa) and Rhodes University for financial help. REFERENCES 1 2 3 4 5 6 7 8 9 10 11 12 13
R.H. Stokes and C. Burfitt, J. Chem. Thermodyn., 5 (1973) 623. I. Nagata and K. Kazuma, J. Chem. Eng. Data, 22 (1977) 79. R.H. Stokes and M. Adamson, J. Chem. Sot., Faraday Trans. 1, 73 (1977) 1232. F. Vesely, P. Uchytil, M. Zabransky and J. Pick, Collect. Czech. Chem. Commun., 44 (1979) 2869. I. Nagata, K. Fujiwara and Y. Ogasawara, J. Chem. Thermodyn., 10 (1978) 1201. I. Nagata and K. Kazuma, J. Chem. Eng. Data, 22 (1977) 79. F. Vesely and J. Pick, Collect. Czech. Chem. Commun., 32 (1967) 4134. F; Vesely and J. Pick, Collect. Czech. Chem. Commun., 34 (1969) 1854. V.P. Belousov, L.M. Kurtymina and A.A. Kozulyaer, Vestn. Leningr. Univ. Fiz., 10 (1970) 163. T.M. Letcher, J. Chem. Thermodyn., 16 (1984) 805. T.M. Letcher, C. Heyward, S. Wooten and B. Shuttleworth, Fuel, 65 (1986) 891. T.M. Letcher, S. Wooten, B. Shuttleworth and C. Heyward, J. Chem. Thermodyn., 18 (1986) 1037. T.M. Letcher and B.W.H. Scoones, J. Chem. Thermodyn., 14 (1982) 703.