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Excess enthalpies of (aniline + an alkane or an alkene) at the temperature 363.15 K
M-3142 J. Chem. Thermodynamics 1995, 27, 939–944
Excess enthalpies of (aniline+an alkane or an alkene) at the temperature 363.15 K Garabed Avedis, Chemistry Department, Faculty of Sciences, Aleppo University, Aleppo, Syria
Ba¨rbel Meents, and Ju¨rgen Gmehling Technische Chemie (FB9) , Universita¨t Oldenburg, Postfach 2503 , D-26111 Oldenburg, Federal Republic of Germany
(Received 15 March 1995) Excess enthalpies for (aniline+pentane or 2-methylpentane or cyclohexane or hexane or octane or decane) as well as of (aniline+cyclohexene or hex-1-ene or oct-1-ene) were measured at the temperature 363.15 K and pressure 1.89 MPa with the help of an isothermal flow calorimeter from Hart Scientific (model 7501). For all the mixtures endothermic mixing was observed. 71995 Academic Press Limited.
1. Introduction Enthalpies of mixing play an important role for understanding the real behavior of liquid mixtures. Experiments H Es are in particular important to obtain reliable temperature-dependent group-interaction parameters. In this paper we present excess enthalpies for (aniline+pentane or 2-methylpentane or cyclohexane or hexane or octane or decane) as well as of (aniline+cyclohexene or hex-1-ene or oct-1-ene) at the temperature T=363.15 K and the pressure p=1.89 MPa. For (aniline+cyclohexane) additional results are available from Onken(1) at T=293.15 K and 318.15 K as well as from Nicolaides and Eckert(2) at T=308.15 K and 323.15 K. Also Nigam et al.(3) reported enthalpies of mixing for (aniline+ cyclohexane) at T=308.15 K. (Aniline+hexane) at T=339.65 K was measured by Campbell et al.(4) For (aniline+an alkene) results are given by Woycicki for (aniline+cyclohexene) at T=308.15 K.(5) The intention of the present paper was to measure additional results to supplement the H Es used(6) and to revise and verify the existing parameters used in the modified UNIFAC model(7) since results for H E at high temperatures are scarce.
2. Experimental Excess enthalpies H E were determined in a flow calorimeter (Hart Scientific, model 7501) at T=363.15 K and p=1.89 MPa using the auxiliary equipment and operating 0021–9614/95/080939+06 $12.00/0
7 1995 Academic Press Limited
940
G. Avedis, B. Meents, and J. Gmehling
procedure described in an earlier paper.(8) Studies of test mixtures indicated that the precision of the results was better than 21 per cent over all the mole-fraction range.(8) The supplier of the chemicals used are summarized in table 1. All liquids were dried over molecular sieves (0.4 nm) and distilled under reduced pressure, prior to their use. The purities of the distilled components were carefully checked by g.c. and Karl-Fischer titration. Mole-fraction purities determined by g.l.c. for all samples exceeded 0.99. TABLE 1. Pure-component specification; x denotes mole-fraction purity Component
102·x
Supplier
aniline pentane 2-methylpentane cyclohexane hexane octane decane cyclohexene hex-1-ene oct-1-ene
q99 q99 q99 q99.7 q99 q99 q99 q99 q97 q98
Gru¨ssing Janssen Chimica Janssen Chimica Scharlau Janssen Chimica Merck Schuchardt Janssen Chimica Janssen Chimica Janssen Chimica Merck Schuchardt
3. Results The experimental values of HmE for all mixtures are listed in table 2. The polynomial form: k
HmE /(J·mol−1 )=x(1−x) s (Ai (2x−1)i,
(1)
i=0
TABLE 2. Experimental excess molar enthalpies HmE at T=363.15 K and p=1.89 MPa x
HmE J·mol−1
x
HmE J·mol−1
0.0313 0.0623 0.1230 0.1822 0.2398 0.2961
379.9 710.0 1214.9 1566.4 1800.2 1952.2
0.3510 0.4046 0.4569 0.5080 0.5579 0.6067
0.0357 0.0707 0.1383 0.2031 0.2653 0.3250
439.5 818.2 1390.9 1776.6 2019.1 2167.2
0.3824 0.4375 0.4906 0.5417 0.5909 0.6384
x
HmE J·mol−1
xC6 H5 NH2+(1−x)CH3(CH2 )3CH3 2048.5 0.6544 1918.3 2101.7 0.7010 1800.6 2112.9 0.7465 1649.6 2074.4 0.7911 1471.8 2082.0 0.8347 1256.7 1994.2 0.8773 1002.2
x
HmE J·mol−1
0.9191 0.9600 0.9801
709.2 375.5 194.4
0.9286 0.9648 0.9826
708.5 371.3 188.8
xC6 H5 NH2+(1−x)CH3CH(CH3 )(CH2 )2CH3 2248.7 2282.5 2275.7 2240.3 2188.1 2093.4
0.6842 0.7285 0.7712 0.8125 0.8525 0.8911
1990.3 1854.0 1692.5 1498.2 1269.9 1008.5
HmE {xC6 H5 NH2+(1−x)Cl Hm }
941
TABLE 2—continued x
HmE J·mol−1
x
HmE J·mol−1
0.0294 0.0586 0.1161
364.8 689.0 1196.8
0.2281 0.3363 0.4407
0.0354 0.0700 0.1372 0.2634
430.2 803.8 1377.6 2023.7
0.3801 0.4882 0.5886 0.6821
0.0648 0.0856 0.1260 0.1649
774.8 989.9 1352.0 1654.0
0.3077 0.4324 0.5424 0.6400
0.0518 0.1008 0.1914 0.2732 0.3475 0.4152
629.7 1163.7 1915.8 2386.0 2662.9 2781.1
0.4772 0.5342 0.5877 0.6354 0.6805 0.7225
0.0276 0.0551 0.1096 0.1635 0.2169 0.2697
237.3 464.8 821.5 1112.7 1321.4 1474.6
0.3219 0.3736 0.4248 0.4754 0.6243 0.5256
0.0339 0.0672 0.1320 0.1945 0.2549
319.6 604.7 1068.9 1407.0 1636.3
0.3133 0.3697 0.4243 0.4771 0.5282
0.0421 0.0828 0.1601 0.2324 0.3002 0.3639
423.4 787.0 1347.9 1743.9 2000.2 2156.4
0.4238 0.4802 0.5336 0.5840 0.6318 0.6771
x
HmE J·mol−1
xC6 H5 NH2+(1−x)c-(CH2 )6 1827.5 0.5417 2190.4 2136.8 0.6394 2018.1 2240.7 0.7339 1719.9
x
HmE J·mol−1
0.8254 0.9141 0.9574
1292.3 720.3 376.9
0.9824
186.8
0.9564 0.9712 0.9786
545.8 371.0 279.1
0.9504 0.9759 0.9881
716.0 373.5 188.0
0.9088 0.9546 0.9774
530.4 278.5 137.3
0.8041 0.8455 0.8858 0.9249 0.9630
1243.5 1050.8 827.5 576.8 297.5
0.9392 0.9702 0.9853
599.5 308.2 153.5
xC6 H5 NH2+(1−x)CH3(CH2 )4CH3 2258.9 2298.2 2199.9 2005.7
0.7695 0.8512 0.9279 0.9645
1701.2 1277.1 711.9 372.2
xC6 H5 NH2+(1−x)CH3(CH2 )6CH3 2373.0 2577.3 2550.5 2385.5
0.7273 0.8057 0.8767 0.9412
2109.6 1754.3 1296.9 712.5
xC6 H5 NH2+(1−x)CH3(CH2 )8CH3 2818.3 2790.4 2709.1 2602.8 2473.8 2323.8
0.7618 0.7982 0.8325 0.8647 0.8950 0.9235
2157.9 1974.9 1772.4 1548.2 1300.0 1023.3
xC6 H5 NH2+(1−x)c-(CH2 )2CH:CH(CH2 )2 1588.8 1669.4 1708.5 1711.6 1539.0 1669.2
0.5752 0.6729 0.7210 0.7687 0.8159 0.8626
1623.0 1430.2 1297.5 1138.9 964.9 760.6
xC6 H5 NH2+(1−x)CH3(CH2 )3CH:CH2 1787.8 1886.3 1935.3 1943.0 1930.8
0.5778 0.6258 0.6724 0.7176 0.7615
1877.6 1796.8 1693.5 1568.6 1419.7
xC6 H5 NH2+(1−x)CH3(CH2 )5CH:CH2 2243.7 2263.7 2246.0 2189.9 2098.8 1990.0
0.7202 0.7611 0.8002 0.8373 0.8728 0.9067
1854.7 1699.4 1524.9 1325.6 1106.6 866.0
942
G. Avedis, B. Meents, and J. Gmehling
TABLE 3. Parameters Ai and standard deviations s for representation of excess molar enthalpies at T=363.15 K by equation (1)
xC6 H5 NH2 + (1−x)CH3(CH2 )3CH3 (1−x)CH3CH(CH3 )(CH2 )2CH3 (1−x)c-(CH2 )6 (1−x)CH3(CH2 )4CH3 (1−x)CH3(CH2 )6CH3 (1−x)CH3(CH2 )8CH3 (1−x)c-(CH2 )2CH:CH(CH2 )2 (1−x)CH3(CH2 )3CH:CH2 (1−x)CH3(CH2 )5CH:CH2
A0
A1
A2
A3
8420.7 9101.9 8903.5 9179.7 10332.3 11254.3 6774.2 7771.3 9048.0
−828.3 −1021.4 −1154.9 −1012.0 −1001.3 −992.9 −1092.9 −826.8 −590.9
3306.2 3460.4 2472.5 3224.0 3194.1 2521.4 1034.9 1730.0 1827.5
−807.1
A4
−859.7 1329.0 2673.0 −348.8 809.3
1176.3
s
8.7 4.9 2.7 6.3 4.2 4.0 5.2 4.8 2.4
was used to represent the results. Values of the parameters Ai were determined by the least-square methods and are given together with the standard deviations s in table 3. The number of parameters in equation (1) was chosen for each mixture on the basis of statistical criteria. The experimental and the correlated results are plotted in figures 1 to 3.
FIGURE 1. Excess molar enthalpies HmE at T=363.15 K and p=1.89 MPa for {xC6 H5 NH2+: w ·, (1−x)CH3(CH2 )3CH3 ; Q, (1−x)CH3(CH2 )4CH3 ; r, (1−x)CH3(CH2 )6CH3 ; q, (1−x)CH3(CH2 )8CH3 }.
HmE {xC6 H5 NH2+(1−x)Cl Hm }
943
FIGURE 2. Excess molar enthalpies HmE at T=363.15 K and p=1.89 MPa for {xC6 H5 NH2+: r, (1−x)c-(CH2 )6 ; q, (1−x)CH3CH(CH3 )(CH2 )2CH3 }.
4. Discussion The HmE values shown in the figures 1 to 3 are positive at all mole fractions. The large positive excess molar enthalpies for [xC6 H5 NH2+(1−x){c-(CH2)6 or CH3 (CH2 )n−2 CH3 or CH3 CH(CH3 )(CH2 )2 CH3 }] arise mainly from the breaking of self-association interactions between the C6 H5 NH2 molecules, known to be associated in the pure state through hydrogen bonding. Spectroscopic studies indicate that while one of the Hs of the –NH2 group of aniline forms a strong hydrogen bond, the second H in the –NH2 group interacts weakly with the p electrons of the adjacent aniline molecules,(9) and the addition of an alkane cause a rupture of the hydrogen-bonded network in the aniline.(10) The positive excess enthalpies of [xC6 H5 NH2+(1−x){c-(CH2 )2CH:CH(CH2 )2 or CH3(CH2 )n−3CH:CH2 }] are thought to be the result of the decreasing p–p interactions in the alkene in addition to the dissociation of aniline molecules and possible interactions of the p bond in the olefin molecule not only with the free electron pair on the N atom but also with the H atom in the –NH2 group and with the isovalently conjugated bonds in the aniline ring.(5, 9, 11) Preliminary calculations showed that
944
G. Avedis, B. Meents, and J. Gmehling
FIGURE 3. Excess molar enthalpies HmE at T=363.15 K and p=1.89 MPa for {xC6 H5 NH2+: q, (1−x)c-(CH2 )2CH:CH(CH2 )2 ; r, (1−x)CH3(CH2 )3CH:CH2 ; Q, (1−x)CH3(CH2 )5CH:CH2 }.
the predictions of the modified UNIFAC model with existing binary parameters(7) were only fair at high temperatures for the mixtures studied. Therefore they should be revised. G. Avedis is grateful to Deutscher Akademischer Austauschdienst (DAAD) for financial support and to M. Schu¨tte for technical assistance. REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11.
Onken, U. Z. Physik. Chem. Neue Folge 1962, 33, 162. Nicolaides, G. L.; Eckert, C. A. J. Chem. Eng. Data 1978, 23, 152. Nigam, R. K.; Singh, P. P.; Singh, K. C. Thermochimica Acta 1980, 35, 1. Campbell, A. N.; Kartzmark, E. M. Can J. Chem. 1969, 47, 619. Woycicki, W. J. Chem. Thermodynamics 1986, 18, 317. Gmehling, J.; Christensen, C.; Holderbaum, Th.; Rasmussen, P.; Weidlich, U. Heats of Mixing Data Collection; 4 parts. DECHEMA Chemistry Data Series: Frankfurt, starting 1984. Gmehling, J.; Li, J.; Schiller, M. Ind. Eng. Chem. Res. 1993, 32, 178. Gmehling, J. J. Chem. Eng. Data 1993, 38, 143. Wolff, H.; Mathias, D. J. Phys. Chem. 1979, 77, 2081. Chowdarv, M. C.; Krishnan, V. R. Indian J. Chem. 1976, 14, 377. Kehiaian, H.; Sosnkowska-Kehiaian, K. Trans. Faraday Soc. 1966, 62, 835.
Excess enthalpies of (aniline+an alkane or an alkene) at the temperature 363.15 K Garabed Avedis, Chemistry Department, Faculty of Sciences, Aleppo University, Aleppo, Syria
Ba¨rbel Meents, and Ju¨rgen Gmehling Technische Chemie (FB9) , Universita¨t Oldenburg, Postfach 2503 , D-26111 Oldenburg, Federal Republic of Germany
(Received 15 March 1995) Excess enthalpies for (aniline+pentane or 2-methylpentane or cyclohexane or hexane or octane or decane) as well as of (aniline+cyclohexene or hex-1-ene or oct-1-ene) were measured at the temperature 363.15 K and pressure 1.89 MPa with the help of an isothermal flow calorimeter from Hart Scientific (model 7501). For all the mixtures endothermic mixing was observed. 71995 Academic Press Limited.
1. Introduction Enthalpies of mixing play an important role for understanding the real behavior of liquid mixtures. Experiments H Es are in particular important to obtain reliable temperature-dependent group-interaction parameters. In this paper we present excess enthalpies for (aniline+pentane or 2-methylpentane or cyclohexane or hexane or octane or decane) as well as of (aniline+cyclohexene or hex-1-ene or oct-1-ene) at the temperature T=363.15 K and the pressure p=1.89 MPa. For (aniline+cyclohexane) additional results are available from Onken(1) at T=293.15 K and 318.15 K as well as from Nicolaides and Eckert(2) at T=308.15 K and 323.15 K. Also Nigam et al.(3) reported enthalpies of mixing for (aniline+ cyclohexane) at T=308.15 K. (Aniline+hexane) at T=339.65 K was measured by Campbell et al.(4) For (aniline+an alkene) results are given by Woycicki for (aniline+cyclohexene) at T=308.15 K.(5) The intention of the present paper was to measure additional results to supplement the H Es used(6) and to revise and verify the existing parameters used in the modified UNIFAC model(7) since results for H E at high temperatures are scarce.
2. Experimental Excess enthalpies H E were determined in a flow calorimeter (Hart Scientific, model 7501) at T=363.15 K and p=1.89 MPa using the auxiliary equipment and operating 0021–9614/95/080939+06 $12.00/0
7 1995 Academic Press Limited
940
G. Avedis, B. Meents, and J. Gmehling
procedure described in an earlier paper.(8) Studies of test mixtures indicated that the precision of the results was better than 21 per cent over all the mole-fraction range.(8) The supplier of the chemicals used are summarized in table 1. All liquids were dried over molecular sieves (0.4 nm) and distilled under reduced pressure, prior to their use. The purities of the distilled components were carefully checked by g.c. and Karl-Fischer titration. Mole-fraction purities determined by g.l.c. for all samples exceeded 0.99. TABLE 1. Pure-component specification; x denotes mole-fraction purity Component
102·x
Supplier
aniline pentane 2-methylpentane cyclohexane hexane octane decane cyclohexene hex-1-ene oct-1-ene
q99 q99 q99 q99.7 q99 q99 q99 q99 q97 q98
Gru¨ssing Janssen Chimica Janssen Chimica Scharlau Janssen Chimica Merck Schuchardt Janssen Chimica Janssen Chimica Janssen Chimica Merck Schuchardt
3. Results The experimental values of HmE for all mixtures are listed in table 2. The polynomial form: k
HmE /(J·mol−1 )=x(1−x) s (Ai (2x−1)i,
(1)
i=0
TABLE 2. Experimental excess molar enthalpies HmE at T=363.15 K and p=1.89 MPa x
HmE J·mol−1
x
HmE J·mol−1
0.0313 0.0623 0.1230 0.1822 0.2398 0.2961
379.9 710.0 1214.9 1566.4 1800.2 1952.2
0.3510 0.4046 0.4569 0.5080 0.5579 0.6067
0.0357 0.0707 0.1383 0.2031 0.2653 0.3250
439.5 818.2 1390.9 1776.6 2019.1 2167.2
0.3824 0.4375 0.4906 0.5417 0.5909 0.6384
x
HmE J·mol−1
xC6 H5 NH2+(1−x)CH3(CH2 )3CH3 2048.5 0.6544 1918.3 2101.7 0.7010 1800.6 2112.9 0.7465 1649.6 2074.4 0.7911 1471.8 2082.0 0.8347 1256.7 1994.2 0.8773 1002.2
x
HmE J·mol−1
0.9191 0.9600 0.9801
709.2 375.5 194.4
0.9286 0.9648 0.9826
708.5 371.3 188.8
xC6 H5 NH2+(1−x)CH3CH(CH3 )(CH2 )2CH3 2248.7 2282.5 2275.7 2240.3 2188.1 2093.4
0.6842 0.7285 0.7712 0.8125 0.8525 0.8911
1990.3 1854.0 1692.5 1498.2 1269.9 1008.5
HmE {xC6 H5 NH2+(1−x)Cl Hm }
941
TABLE 2—continued x
HmE J·mol−1
x
HmE J·mol−1
0.0294 0.0586 0.1161
364.8 689.0 1196.8
0.2281 0.3363 0.4407
0.0354 0.0700 0.1372 0.2634
430.2 803.8 1377.6 2023.7
0.3801 0.4882 0.5886 0.6821
0.0648 0.0856 0.1260 0.1649
774.8 989.9 1352.0 1654.0
0.3077 0.4324 0.5424 0.6400
0.0518 0.1008 0.1914 0.2732 0.3475 0.4152
629.7 1163.7 1915.8 2386.0 2662.9 2781.1
0.4772 0.5342 0.5877 0.6354 0.6805 0.7225
0.0276 0.0551 0.1096 0.1635 0.2169 0.2697
237.3 464.8 821.5 1112.7 1321.4 1474.6
0.3219 0.3736 0.4248 0.4754 0.6243 0.5256
0.0339 0.0672 0.1320 0.1945 0.2549
319.6 604.7 1068.9 1407.0 1636.3
0.3133 0.3697 0.4243 0.4771 0.5282
0.0421 0.0828 0.1601 0.2324 0.3002 0.3639
423.4 787.0 1347.9 1743.9 2000.2 2156.4
0.4238 0.4802 0.5336 0.5840 0.6318 0.6771
x
HmE J·mol−1
xC6 H5 NH2+(1−x)c-(CH2 )6 1827.5 0.5417 2190.4 2136.8 0.6394 2018.1 2240.7 0.7339 1719.9
x
HmE J·mol−1
0.8254 0.9141 0.9574
1292.3 720.3 376.9
0.9824
186.8
0.9564 0.9712 0.9786
545.8 371.0 279.1
0.9504 0.9759 0.9881
716.0 373.5 188.0
0.9088 0.9546 0.9774
530.4 278.5 137.3
0.8041 0.8455 0.8858 0.9249 0.9630
1243.5 1050.8 827.5 576.8 297.5
0.9392 0.9702 0.9853
599.5 308.2 153.5
xC6 H5 NH2+(1−x)CH3(CH2 )4CH3 2258.9 2298.2 2199.9 2005.7
0.7695 0.8512 0.9279 0.9645
1701.2 1277.1 711.9 372.2
xC6 H5 NH2+(1−x)CH3(CH2 )6CH3 2373.0 2577.3 2550.5 2385.5
0.7273 0.8057 0.8767 0.9412
2109.6 1754.3 1296.9 712.5
xC6 H5 NH2+(1−x)CH3(CH2 )8CH3 2818.3 2790.4 2709.1 2602.8 2473.8 2323.8
0.7618 0.7982 0.8325 0.8647 0.8950 0.9235
2157.9 1974.9 1772.4 1548.2 1300.0 1023.3
xC6 H5 NH2+(1−x)c-(CH2 )2CH:CH(CH2 )2 1588.8 1669.4 1708.5 1711.6 1539.0 1669.2
0.5752 0.6729 0.7210 0.7687 0.8159 0.8626
1623.0 1430.2 1297.5 1138.9 964.9 760.6
xC6 H5 NH2+(1−x)CH3(CH2 )3CH:CH2 1787.8 1886.3 1935.3 1943.0 1930.8
0.5778 0.6258 0.6724 0.7176 0.7615
1877.6 1796.8 1693.5 1568.6 1419.7
xC6 H5 NH2+(1−x)CH3(CH2 )5CH:CH2 2243.7 2263.7 2246.0 2189.9 2098.8 1990.0
0.7202 0.7611 0.8002 0.8373 0.8728 0.9067
1854.7 1699.4 1524.9 1325.6 1106.6 866.0
942
G. Avedis, B. Meents, and J. Gmehling
TABLE 3. Parameters Ai and standard deviations s for representation of excess molar enthalpies at T=363.15 K by equation (1)
xC6 H5 NH2 + (1−x)CH3(CH2 )3CH3 (1−x)CH3CH(CH3 )(CH2 )2CH3 (1−x)c-(CH2 )6 (1−x)CH3(CH2 )4CH3 (1−x)CH3(CH2 )6CH3 (1−x)CH3(CH2 )8CH3 (1−x)c-(CH2 )2CH:CH(CH2 )2 (1−x)CH3(CH2 )3CH:CH2 (1−x)CH3(CH2 )5CH:CH2
A0
A1
A2
A3
8420.7 9101.9 8903.5 9179.7 10332.3 11254.3 6774.2 7771.3 9048.0
−828.3 −1021.4 −1154.9 −1012.0 −1001.3 −992.9 −1092.9 −826.8 −590.9
3306.2 3460.4 2472.5 3224.0 3194.1 2521.4 1034.9 1730.0 1827.5
−807.1
A4
−859.7 1329.0 2673.0 −348.8 809.3
1176.3
s
8.7 4.9 2.7 6.3 4.2 4.0 5.2 4.8 2.4
was used to represent the results. Values of the parameters Ai were determined by the least-square methods and are given together with the standard deviations s in table 3. The number of parameters in equation (1) was chosen for each mixture on the basis of statistical criteria. The experimental and the correlated results are plotted in figures 1 to 3.
FIGURE 1. Excess molar enthalpies HmE at T=363.15 K and p=1.89 MPa for {xC6 H5 NH2+: w ·, (1−x)CH3(CH2 )3CH3 ; Q, (1−x)CH3(CH2 )4CH3 ; r, (1−x)CH3(CH2 )6CH3 ; q, (1−x)CH3(CH2 )8CH3 }.
HmE {xC6 H5 NH2+(1−x)Cl Hm }
943
FIGURE 2. Excess molar enthalpies HmE at T=363.15 K and p=1.89 MPa for {xC6 H5 NH2+: r, (1−x)c-(CH2 )6 ; q, (1−x)CH3CH(CH3 )(CH2 )2CH3 }.
4. Discussion The HmE values shown in the figures 1 to 3 are positive at all mole fractions. The large positive excess molar enthalpies for [xC6 H5 NH2+(1−x){c-(CH2)6 or CH3 (CH2 )n−2 CH3 or CH3 CH(CH3 )(CH2 )2 CH3 }] arise mainly from the breaking of self-association interactions between the C6 H5 NH2 molecules, known to be associated in the pure state through hydrogen bonding. Spectroscopic studies indicate that while one of the Hs of the –NH2 group of aniline forms a strong hydrogen bond, the second H in the –NH2 group interacts weakly with the p electrons of the adjacent aniline molecules,(9) and the addition of an alkane cause a rupture of the hydrogen-bonded network in the aniline.(10) The positive excess enthalpies of [xC6 H5 NH2+(1−x){c-(CH2 )2CH:CH(CH2 )2 or CH3(CH2 )n−3CH:CH2 }] are thought to be the result of the decreasing p–p interactions in the alkene in addition to the dissociation of aniline molecules and possible interactions of the p bond in the olefin molecule not only with the free electron pair on the N atom but also with the H atom in the –NH2 group and with the isovalently conjugated bonds in the aniline ring.(5, 9, 11) Preliminary calculations showed that
944
G. Avedis, B. Meents, and J. Gmehling
FIGURE 3. Excess molar enthalpies HmE at T=363.15 K and p=1.89 MPa for {xC6 H5 NH2+: q, (1−x)c-(CH2 )2CH:CH(CH2 )2 ; r, (1−x)CH3(CH2 )3CH:CH2 ; Q, (1−x)CH3(CH2 )5CH:CH2 }.
the predictions of the modified UNIFAC model with existing binary parameters(7) were only fair at high temperatures for the mixtures studied. Therefore they should be revised. G. Avedis is grateful to Deutscher Akademischer Austauschdienst (DAAD) for financial support and to M. Schu¨tte for technical assistance. REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11.
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