4304
J. F. MESSERLY, S. S. TODD, AND H. L. FINKE
cates that some of the C-H bond positions in both EC and DMC have bond dissociation energies substantially lower than those of cyclopropane or cyclobutane, but no significant measurements can be made
without experiments on selectively deuterated compounds. Aclcnowledgment. The cooperation of Dr. J. K. Lee and Dr. E. K. C. Lee is deeply appreciated.
LowmTemperature Thermodynamic Properties of n-Propyl- and n-Butylbenzene
by John F. Messerly, Samuel S. Todd, and Herman L. Finke Contribution No. 142 f r o m the Thermodynamics Laboratory of the Bartlesville Petroleum Research Center, Bureau of Mines, U.S. Department of the Interior, Bartlesville, Oklahoma (Received J u l y 16, 1966)
The heat capacities from 12 to 370"K.,heats of fusion, triple points, and purities of n-propylbenzene and n-butylbenzene were measured in an adiabatic calorimeter. Both compounds exhibited monotropism with the metastable crystals melting 2.02' below the stable crystals in the case of n-propylbenzene and 0.16" below the stable crystals in the case of n-butylbenzene. From the calorimetrically measured data the thermodynamic functions (G, H o o ) / T ,(H, - H o o ) / T ,H s - H'o, S,, and Cswere calculated a t selected temperatures for each compound for both the metastable and stable crystals and the liquid phase. For each compound, the entropies a t 298.15"K. in the liquid state calculated by metastable and by stable paths agreed within experimental error, providing another check of the third law of thermodynamics. The entropy increment obtained between n-propyl- and n-butylbenzene is about 0.25 e.u. greater than the constant entropy increment for the normal paraffins from C, to CIa in both the liquid and ideal gas states. This slightly larger increment from n-propyl to n-butyl substitution has been noticed earlier in monoalkyl-substituted cyclopentanes and cyclohexanes. From incomplete measurements on n-decylbenzene, values of the heat of melting and triple point temperature were obtained. Estimates of the entropies of n-decylbenzene at 298.15"K. in the liquid and ideal gas states were made.
Introduction As part of the continuing program of research conducted in this laboratory on the thermodynamic properties of hydrocarbons and related substances, low-temperature calorimetric studies have been made on corresponding members of several homologous series of compounds. From the study of selected members of each series, it has been possible to calculate the effect on the entropy of the liquid for each methylene group added. For the n-paraffins this entropy increment has been found's to be essentially constant for Cs through CI8. For the n-l-olefins this increment was found by McCullough, et U Z . , ~ to be constant from T h e Journal of Physical Chemistry
Cg to C1, but became irregular from CIOto C16 owing to orientation disorder in the crystals. The data of Messerly, et u Z . , ~ on n-alkylcyclopentanes and of Finke, et U Z . , ~ on n-alkylcyclohexanes have shown that the entropy increment from n-propyl to n-butyl is slightly (1) H. L. Finke, M. E. Gross, G. Waddington, and H. M. Huffman, J . Am. Chem. Soc., 76, 333 (1954). (2) Unpublished data, this laboratory. (3) J. P. McCullough, H. L. Finke, M. E. Gross, J. F. Messerly, and G. Waddington, J . Phys. Chem., 61, 289 (1957). (4) J. F. Messerly, 5. S. Todd, and H. L. Finke, ibid., 69, 353 (1965). (5) H. L. Finke, S. S. Todd, and J. F. Messerly, {bid., 69, 2094 (1965).
THERMODYNAMIC PROPERTIES OF %-PROPYLAND WBWTYLBENZENE
4305
Table I: Heat Capacity (cal. deg.-l mole-') T,OK."
Cab
T,
Csb
T,OK."
Csb
T,OK."
cs
n9ropylbenzene 11.36 11.99 12.45 13.12 13.65 14.37 14.98 15.78 16.47 17.52 18.16 19.59 20.09 21.87 22.12 24.33 24.44 26.91 27.15 29.90
0,7929 0.9598 1.0515 1.208 1.348 1.525 1.689 1.913 2.090 2.397 2.606 3.024 3.179 3.742 3.811 4.515 4.552 5.312 5.392 6.216
11.45 12.37 13.43 13.59 14.66 14.99 16.07 16.58 17.69 18.49 19.56 20.63 21.72 22.92 24.03 25.31 26.51 27.73 29.25
0.964 1.204 1.493 1.553 1.837 1.939 2.238 2.394 2.736 2.998 3 * 334 3.691 4.040 4.446 4.800 5,222 5.619 5.987 6.448
180.87 186.47 194.80 204.78 204.89 214.57 225.11 235.95
43.689 43.838 44.121 44.531 44.542 45.025 45.614 46.291
CBb
T,
CB
n-But ylbenzene
Stable crystals 30.09 6.283 33.40 7.273 37.04 8.273 40.88 9.267 44.90 10.225 49.67 11.275 b5.10 12.350 65.21 12.366 59.82 13.230 64.77 14.100 70.37 14.980 76.07 15.836 81.. 83 16.724 82.67 17.567 913.60 18.335 917.63 18.828 99.63 19.092 102.89 19.495 105.41 19.825
108.04 113.49 117.10 119.23 122.27 127.76 133.08 138.60 142.22 144.31 146.43 147.82 147.88 149.87 152.13 154.43 158.22 160.79 164.40
20.143 20.812 21.258 21.543 21.924 22.602 23.258 23.938' 24.372' 24.647' 24.906' 25.079' 25.068' 25.359' 25.645' 25, 935c 26.479' 26.829' 27.394'
Metastable crystals 30.44 6.824 383.56 7.763 37.03 8.721 40.81 9.683 45.25 10.723 50.35 11.806 54.57 12.601 585.35 12.750 59.55 13.508 65.25 14.470 71.29 15.372 76.90 16.185 82.59 17.023 86.87 17.492 88.39 17.831 91.10 18.161 96.50 18.820 101.75 19.465
101.81 107.40 107.90 113.32 119.03 124.57 130.29 136.20 141.93 143.96 147.52 151.25 152.83 153.76 155.73 158.31 159.75 160.92
19.452 20.148 20.199 20.876 21.578 22.263 22.951 23.658 24. 356d 24. 556d 25. 044d 25.45@ 25. 727d 25. 86gd 25. 86gd 26. 357d 26. 63gd 26. 631d
310.45 320.98 331.34 341.52 351.54 361.50 370.54
52.465 53.489 54.495 55.476 56.479 57.433 58.362
Liquid 246.19 46.990 256.30 47.726 266.24 48.524 276.02 49.345 285.65 50.188 295.13 51.014 300.12 51.460 304.48 51.902
T,OK."
11.40 12.04 12.52 13.04 13.72 14.16 14.93 15.46 16.25 17.06 17.83 18.72 19.74 20.48 21.93 22.54 24.29 24.79 26.82 27.23 29.45 29.82
0.943 1.106 I . 243 1.380 1.589 1.718 1. ,940 2.103 2.356 2.600 2.845 3.148 3.496 3.756 4.256 4.476 5.086 5.263 5.956 6.106 6.838 6.969
55.25 60.19 65.81 71.47 77.25 83.16 88.45 89.26 93.80 99.49 105.46 111.19
13.937 14.982 16.089 17.093 18.083 19 107 20.027 20.078 20.788 21.598 22.447 23.254
193.81 197.29 205.85 211.83 221.83 231 69 241.42
49.760 49.919 50.356 50.698 51.356 52.051 52.807
I
I
Stable crystals 32.84 7.967 36.34 9.069 40.05 10.149 43.93 11.206 48.54 12.373 54.19 13.647 54.60 13.737 59.64 14.816 65.35 15.963 71.11 16.988 76.88 17.979 82.71 18.991 85.52 19.457 88.26 19.898 90.52 20.211 94.13 20.737 95.76 20.959 101.34 21.755 102.75 21.943 107.21 22.592 108.56 22.773 112.85 23.393
114.16 118.65 124.61 130.37 135.96 140.23 141.40 146.07 147.21 152.26 153.37 155.21 158.28 159.37 161.23 163.12 164.14 167.07 169.33 169.82 176.91
23.569 24.209 25.052 25.891 26.706 27.284 27.483 28.147 28.327" 29.058" 29.256O 29.513' 29. 92g6 30.146" 30,473" 30. 702e 30.900" 31.505* 31. 9046 32,079" 34,640'
Metastable crystals 117.08 24.064 123.13 24.916 128.97 25.729 135.19 26.586 141.76 27.501 148.14 28.392 149.99 28.637 153.73 29.221 154.33 29,284 156.01 29.560 157.63 29, 797' 159.51 30,158'
159.64 160.35 161.85 163.12 165.18 165.40 165.44 169.89 171.19 174.49 180.15
30.111' 30. 118' 30.498' 30,710' 30. 937' 31. . 050' 31,152' 31.799' 32. 346' 32.763' 35. 826'
319.52 329.67 340.00 350.16 360.17 370.02
60.486 61.593 62.728 63.842 64.947 66.011
Liquid 260.84 54.472 270.91 55.416 280.81 56.389 290.55 57.366 300.15 58 378 309.92 59.432 I
'
Tis the mean temperature of each heat capacity - - measurement. Csis the heat capacity of the condensed phase under saturation pressure. Values of C, foir the crystals are not corrected for effects of premelting caused by impurities. The temperature increments of these measurements are, in order of increasing temperature, in OK.: ( c ) 5.794, 5.665, 5.633, 5.515, 5.525, 6.654, 5.486, 5.905, 6.455, 6.276, 6.269, 6.086; ( d ) 5.663, 7.413, 5.515, 7.175, 7.031, 5.302, 5.284, 6.951, 6.818, 5.144; (e) 6.255, 6.102, 6.077, 6.105, 5.939, 5.918, 5.929, 6.132, 5.778, 5.765, 6.110, 5.596, 8.595; (f) 5.062, 6.019, 5.834, 4.895, 5.769, 5.914, 4.779, 5.676, 5.844, 4.666, 5.661, 4.548, 6.786. @
Volume 69, Number 12 December 1966
4306
J. F. MESSERLY, S. S. TODD, AND H. L. FINI~E
Table 11: Equations for Heat Capacity of Liquid C, = A
+ BT + C T 2 + DT*, cal. deg.-l mole-'
Compd.
A
B
104c
n-Propylbenxene n-Butylbenzene
58.710 65.158
- 0.22063 - 0.24196
9.2097 10.343
larger than that found for n-alkanes, but the average values obtained on the n-butyl- to n-decyl-substituted compounds agree well with those obtained for the nalkanes and n-l-olefins. The data of Person and PimenteP on the entropies of the n-alkanes from Cs to C16 in the ideal gas state at 298.15"K. have shown the entropy increment per methylene group to be essentially constant. This constant entropy increment has been shown to be the same as the average entropy increment found for the n-alkyl~yclopentanes~ and nalkylcyclohexanes5 from n-butyl to n-decyl. This work was projected as a study of n-propyl-, n-butyl-, and n-decylbenzenes to verify these relationships found for the entropy increment. Although data on n-butylbenzene were available,' the limited range of the data and the unknown purity of the sample made a restudy of this compound desirable. The measurements were completed on n-propyl- and n-butylbenzene, but work had to be abandoned on n-decylbenzene owing to experimental difficulties. (Two sample containers were found to be ruptured after repeated cycling of the vessels through the solid-solid phase transition a t approximately 235°K.) Efforts were made to procure a pure sample of a heavier n-alkylbenzene in order to determine if the average entropy increment beyond n-butyl was the same as in the n-alkylcyclopentanes and -cyclohexanes. A sample of n-dodecylbenzene was obtained, but the purity, as determined, was too low to obtain a reliable value of S29s.15 for this compound.
Experimental Section Apparatus and Physical Constants. The low-temperature calorimetric measurements were made with apparatus described by Huffman and co-workers.8 The 1951 International Atomic Weightsg and values of the fundamental physical constantslo were used. Measurements of temperature were made with platinum resistance thermometers calibrated in terms of the International Temperature Scale of 194811 from 90 to 4OO0K., and the provisional scale of the National Bureau of Standards12 from 11 to 90°K. Celsius temperatures were converted to Kelvin temperatures The Journal of Physical Chemistry
1.07~
-
8.8580 -10.108
Range, OK.
Av. dev., oal.
Max. dsv., oal.
180-370 195-380
0.01 0.01
0.02 0.02
by the addition of 273.15°.13 Energy was measured in joules and converted to calories by the relation, 1 cal. = 4.184 (exactly) joules. Measurements of mass, electrical potential, and resistance were made in terms of standard devices calibrated at the National Bureau of Standards. Some of the results in this paper were originally calculated with physical constants and temperatures related to the definition 0" = 273.16"IC Temperatures reported here are in terms of the newer definition,la but only part of the experimental results were recalculated. Numerical inconsistencies less than the precision of the experimental data may have been introduced by this procedure. Materzals. All of the samples used in this study were API Research hydrocarbons.l 4 The samples were frozen in the ampoules as received, and the liquid just above the melting point was examined for traces of ice. In only one sample, n-butylbenzene, was there enough ice present to warrant drying. I n this case the sample was dried with calcium hydride in the liquid phase. Each sample was transferred to the calorimeter without exposure to oxygen or water.
Results Heat Capacities. Both n-propylbenzene
and n-
(6) W. B. Person and G. C. Pimentel, J . Am. Chem. Soc., 7 5 , 532 (1953). (7) H. M. Huffman, G. 9. Parks, and M. Barmore, ibid., 53, 3876 (1931). (8) (a) H. M. Huffman, Chem. Rev., 40,l (1947); (b) H. M. Huffman, S. S. Todd, and G. D. Oliver, J . Am. Chem. Soc., 71, 584 (1949); (c) D. W. Scott, D. R. Douslin, M. E. Gross, G. D. Oliver, and H. M. Huffman, ibid., 74,883 (1952); (d) R. A. Ruehrwein and H. M. Huffman, ibid., 65, 1620 (1943). (9) E. Wichers, ibid., 74, 2447 (1952). (10) F. D. Rossini, F. T. Guoker, Jr., H. L. Johnston, L. Pauling, and G. W. Vinal, ibid., 74, 2699 (1952). (11) €1. F. Stimson, J . Res. Natl. Bur. Std., 42, 209 (1949). (12) H. J. Hopi, and F. G. Brickwedde, ibid., 22, 351 (1939). (13) H. F. Stimson, Am. J . Phys., 2 3 , 614 (1955). (14) These samples of API Research hydrocarbons were made available through the American Petroleum Institute Research Project 44 on the collection, analysis, and calculation of data on properties of hydrocarbons and were purified by the American Petroleum Institute Research Project 6 on the analysis, purification, and properties of
hydrocarbons.
THERMODYNAMIC PROPERTIES OF 12-PROPYLAND WBUTYLBENZENE
Table IV : Melting Point Summaries
Table 111: Triple Point Temperatures, Heats of Fusion, and Cryoscopic Constants
F
AHm, I"
1
Compd.
n-Propylbenxene Stable crystals Metastable crystals n-Butylbenzene Stable crystals Metastable crystals
tp,
OIL
cal. mole-1
4 deg.-l
4307
B,
1/F
n-Propylbenzene (impurity
deg.-l
173.59 171.6
2215 f 2" 2031 f 50"
0.03699 0.03470
0.00235 0.00204
185.30 185.14
2682 i 2" 2691 i4"
0.03931 0.03951
0.00289 0.00264
The uncertainty shown here is the maximum deviation from the mean of two or more determinations. a
butylbenzene exhibit monotropism, and in each case the metastable form could be readily obtained and supercooled. Complete measurements of the heat capacities on both metastable and stable crystals from 12°K. to the melting points were obtained for these compounds. The heat capacities of the liquids were measured from just above the melting point to approximately 370°K. Only one of the two crystalline forms of n-butylbenzene, which melt 0.16"K. apart, was reported by Huffman, et al.,7 and by Rossini.I5 The incompleted study on n-decylbenzene showed at least two crystalline polymorphs. The observed values of heat capacity at saturation pressure, C,, are recorded for each compound in Table I. The temperature increments useld in the measurements were small emugh to obviate corrections for nonlinear variation of C, with T . Corrections for the effect of premelting have not been made to these data, but pertinent AT values are included to permit their calculation. The precision uncertainty of the results was, in general, less than O.l%, and above 30°K. the accuracy uncertainty should not exceed 0.2%, except in regions near phase transformations. Near phase changes the data for the solid state is less precise and accurate because of rapid changes of C, with T , slow equilibration, or uncertainties caused by the presence of impurities. Cubic equations in 2' were fitted to the heat capacity of each compound in the liquid state. The constants for these equations are! listed in Table 11,together with values of the deviations from observed data as an estimate of reliability. Heats of Fusion, Triple Point Temperatures, and Purity of Samples. The heats of fusion, AHm, were determined from the heat capacity data and enthalpy measurements made over appropriate temperature
TF,
O K .
=
0.03 mole
0.0988 0.2603 0.5150 0.7466 0.9318 1.0000 Pure
Stable crystals 10.12 173.5123 3.842 173.5575" 173.5719 1,942 173.5775" 1.339 1.073 173.5820 1,000 0
0.1300 0.2542 0.4025 0.8474 1.0000 Pure
Metastable crystals 7.69 171.5100" 3.93 171.5321 2.48 171.5566" 1.18 171.6224b 1.00 0
Twlod,
OK.
%)c
173.5076 173.5575 173.5727 173.5775 173.5796 173.5802 173.5882
171.51 171.54 171.55 171.56 171.57 171.58
n-Butylbenzene (impurity = 0.08 mole %)c 0.0971 0.2459 0.4872 0.6878 0.8912 1.0000 Pure
Stable crystals 10.299 185.0961 4.067 185.2093" 2.053 185.2511 1.454 185,2648 1.122 185.2711" 1.000 0
185.0786 185.2093 185.2516 185.2641 185.2711 185.2737 185.2947
0.3892 0.5928 0.8578 1.0000 Pure
Metastable crystals 2.569 185.0746 1.687 185.0940" 1.166 185.1066' 1.000 0
185.0726 185.0940 185.1066 185.1106 185,1348
n-Decylbenzene (impurity = 0.05 mole %) 0.0880 11.36 258.6699 258.6494 0.2374 4.21 258.7185 258.7147 0.4870 2.05 258,7345" 258.7345 0.6867 1.46 258.7405 258.7399 0.8865 1.13 258,7429" 258.7429 1.0000 1.000 258.7441 Pure 0 258.7532 a Straight lines through these points were extrapolated to I/F = 0 to c a h l a t e triple point temperature. This point was thought to be high owing to the partial transposition to the higher melting (Le., stable) form. The impurities listed are those calculated from the melting point studies on the stable crystals. From the melting point study of the metastable crystals of n-propylbenzene an impurity of 0.03 mole yo was also found; for n-butylbenzene the impurity was estimated at between 0.05 and 0.09 mole %, from a study of the metastable form.
(15) A. F. Forziati, Vir. R. Norris, and F. D. Rossini, J . Res. iliall. Bur. Std., 43, 555 (1949).
Volume 69, Number 12 December 1966
4308
J. F. MESSERLY, S.S.TODD, AND H. L.FINKE
Table V : Thermodynamic Functions for Condensed Phases" -(Gs
T , OK.
(Hs Hoo)/T, Hoc)/T, cal. deg.-1 oal. d e g . 3 mole-' mole-'
-IC.
Hs - H'o, cal. mole-'
8 st
cs
oal. deg.-l oal. deg.-1 mole-1 mole-1
n-Propylbenzene 10 12 14 16 18 20 25 30 35 40 45 50 60 70 80 90 100 110 120 130 140 150 160 170 173.60
0.047 0.080 0.128 0.188 0.262 0.330 0.623 0.961 1.352 1,782 2.242 2,724 3.728 4.761 5.803 6.842 7.871 8.887 9.889 10.874 11.846 12.802 13.745 14.68 15.01
Stable 0.140 0.242 0.376 0.541 0.731 0.942 1.540 2,198 2.884 3.5'72 4.248 4.903 6,140 7.280 8,329 9.312 10.232 11.098 11.924 12.724 13.492 14.241 14.976 15.70 15.96
173.60 180 190 200 210 220 230 240 250 260 270 273.15 280 290 298.15 300 310 320 330 340 350 360 370
15.01 16.06 17.65 19.22 20.73 22.21 23.64 25.04 26.41 27.74 29.04 29.44 30.31 31.56 32.36 32.78 33.99 35.16 36.31 37.45 38.57 39.67 40.75
28.72 29.25 30.02 30.72 31.38 32.00 32.60 33.16 33.71 34.25 34.77 34.94 35.29 35.80 36.22 36.31 36.81 37.32 37.82 38.32 38.82 39.32 39.82
10 12 14
0.055 0,094 0 149
crystals 1.40 2.90 5.27 8.65 13.15 18.83 38.49 65.93 100.93 142,88 191.15 243.16 368.4 509.6 666.3 838.1 1,023.2 1,220.8 1,430.9 1,654.1 1,888.9 2,136.1 2,396.2 2,669.4 2,770.9
Liquid 4,986 5,268 5,403 6,144 6,590 7,040 7,497 7,959 8,428 8,904 9,389 9,543 9,881 10,382 10,798 10,893 11,412 11,941 12,480 13,028 13,587 14,155 14,733 Metastable crystals 0.164 1.64 0,282 3.38 0.437 6.12
T h e Journal of Physical Chemistry
0.187 0.322 0.504 0.729 0.993 1.292 2.163 3.159 4.236 5.354 6.490 7,627 9.868 12,041 14.132 16.154 18.103 19.985 21.813 23.598 25,338 27.043 28.721 30.38 30.97
0.557 0.954 1.428 1.963 2.642 3.147 4.718 6.264 7.719 9.044 10.243 11I343 13.262 14,922 16.439 17.877 19.139 20.385 21,649 22.885 24.100 25.354 26.659 27.976 28.458
43.73 45.31 47,67 49.94 52.11 54.21 56.24 58.20 60.12 61.99 63.81 64.38 65.60 67.36 68.78 69.09 70.80 72.48 74.13 75.77 77.39 78.99 80.57
43.55 43.67 43.95 44.33 44.79 45.32 45.91 46.56 47.26 48.02 48.84 49.11 49.69 50.58 51 32 51.49 52.43 53.38 54.34 55.32 56.31 57.31 58.31
-
fH. \
~
~
H G ~ T ,H V I T , cal. deg.-l cal. deg.-1
!
"
Ha - H'o, cal. mole-'
T , OK.
mole -1
mole-1
16 18 20 25 30 35 40 45 50 60 70 80 90 100 110 120 130 140 150 160 170 171.67
0,219 0.305 0.404 0.711 1.086 1,513 1.979 2.474 2.987 4.050 5,132 6.215 7.289 8.348 9.389 10.412 11.417 12,405 13.375 14.330 15.27 15.42
0.624 0.835 1.067 1.712 2,427 3.143 3.855 4,547 5.214 6.458 7.594 8.635 9.603 10.507 11.357 12.168 12.948 13.702 14.437 15,157 15.87 15.99
171.67 173.60
15.42 15.74
Metastable liquid 27.82 4,775 27.99 4,859
9.98 15.03 21.33 42.80 72.82 110.00 154.19 204.62 260.68 387.5 531.6 690.8 864.3 1,050.7 1,249,3 1,460.1 1,683,2 1,918.3 2,165.5 2,425.1 2,697.6 2,744.3
SB cs , cal. den.-> cal. dee.-l !
i
mole-'
mole-'
0.843 1.140 1.471 2,423 3.513 4.656 5.834 7.021 8.201 10.508 12,726 14.850 16.892 18.855 20.746 22.580 24.365 26.107 27.812 29.487 31.14 31.41
2.224 2.830 3.471 5,138 6.715 8.156 9.490 10.667 11.734 13.585 15.195 16.641 18.029 19.247 20.474 21.695 22.911 24.108 25.334 26.606 27.882 28.098
43.24 43.73
43.50 43.55
0.226 0 386 0.597 0.859 1.163 1.503 2.491 3.614 4.822 6.076 7.348 8.623 11.137 13.580 15.936 18,215 20.411 22,532 24.593 26.602 28.568 30.50 32.40 34.28 36.17 37.19
0.669 1.115 1.662 2.275 2.903 3.583 5.331 7.035 8.655 10.135 11.486 12.713 14.893 16.797 18.524 20.153 21.553 22.990 24.399 25.821 27.258 28.683 30.17 31.89 34.46 35.96
n-Butylbenzene
0.219 0.376 0.586
I
0.651 1.105 1.. 644
10 12 14 16 18 20 25 30 35 40 45 50 60 70 80 90 100 110 120 130 140 150 160 170 180 185.30
0.087 0.098 0.153 0.225 0.312 0.413 0.728 1,113 1.557 2.043 2.561 3.103 4.234 5.396 6.567 7.735 8.894 10,037 11.165 12.275 13.369 14.45 15.51 16.56 17.60 18.14
Stable crystals 0.169 1.69 0,288 3.46 0.444 6.22 0.634 10.15 0.851 15.32 1,090 21.80 1.763 44.08 2.501 75 02 3.265 114.29 4.033 161.33 4.787 215.43 5.520 275.98 414.2 6.903 8.184 572.9 9.369 749.5 943.2 10.480 11.517 1,151.7 12.495 1,374.4 13.428 1,611.4 14.327 1,862.5 15.199 2,127.9 16.05 2,407.6 16.89 2,701.8 17.72 3,012 18.57 3,343 19.05 3,530
I
4309
THERMODYNAMIC PROPERTIES OF %-PROPYLAND n-BUTYLBENZENE
-
T , OK.
-(Gn H'o) T . cal. deg.-' mole-'
("8
-
H'o? / T . cal. deg.-' mole-1
Hs - H'o, cal. mole->
Liquid 33.52 6,212 33.92 6,444 34.71 6,942 35.46 7,446 36.16 7,955 36.83 8,470 37.47 8,993 38.10 9,524 38.71 10,064 39.30 10,612 39.49 10,787 39.90 11,171 40.48 11,739 40.95 12,209 41.06 12,317 41.63 12,906 42.21 13,506 42.78 14,117 43.35 14,739 43.92 15,371 44.49 16,015 45.05 16,670 45.62 17,335
185.30 190 200 210 220 230 240 260 260 270 273.15 280 290 298.15 300 310 320 330 340 350 360 370 380
18.14 18.98 20.75 22.45 24.12 25.74 27.33 28.87 30.37 31.85 32.31 33.28 34.69 35.82 36.08 37.44 38.76 40.07 41.36 42.62 43.86 45.10 46.30
10 12 14 16 18 20 25 30 35 40 45 50 60 70 80 90 100 110 120 130 140 150 160 170 180 185.14
0.056 0.097 0.153 0.225 0.312 0.414 0.729 1.115 1.560 2.046 2.566 3.110 4.243 5.407 6.582 7.754 8.916 10.063 11.194 12.308 13.406 14.48 15.55 16.60 17.64 18.17
11.550 12.535 13.472 14.372 15.241 16.09 16.92 17.74 18.57 18.90
185.14 185.30
18.17 18.19
Metastable liquid 33.53 6,208 33.55 6,216
Metastable 0.170 0.289 0.446 0.636 0.853 1.093 1.767 2.506 3.271 4.041 4.798 5.533 6.923 8.209 9.395 10.506
crystals 1.70 3.47 6.24 10.17 15.36 21.85 44.18 75.17 114.50 161.65 215.90 276.64 415.4 574.6 751.6 945.5 1,155.0 1,378.8 1,616.6 1,868.4 2,133.8 2,413.2 2,707.1 3,016 3.342 3,517
S., Cs oal. deg.-l cal. deg.-1 I
mole-'
mole-'
51.66 52.90 55.46 57.91 60.28 62.57 64.80 66.97 69.08 71.15 71.80 73.18 75.1.7 76.77 77.14 79.07 80.97 82.85 84.71 86.54 88.35 90.15 91.92
49.41 49.60 50.05 50.59 51.23 51.93 52.69 53.52 54.40 5t5.33 55.63 56.31 57.31 58.16 58.36 59 I44 60.54 61.63 62.73 63.83 64.93 66.01 67.12
0,226 0.386 0.599 0.861 1.165 1.507 2.496 3.621 4.831 6,087 7.364 8.643 11.166 13.616 15.977 18.260 20.466 22,598 24.666 26.680 28.647 30.57 32.47 34.34 36.21 37.16
0.675 1,117 1.666 2,277 2.912 3.590 5.340 7.043 8.674 10,161 11.520 12.757 14.944 16.838 18.563 20.196 21.671 23.087 24.476 25.860 27.240 28.641 30.18 31.69 33.49 34.47
51.70 51.74
49.40 49.41
a The values tabulated are the Gibbs energy function, enthalpy function, enthalpy, entropy, and heat capacity of the condensed phase a t saturation pressure.
-
intervals that included the triple point temperature. Corrections to A H m for the effect of premelting- caused by impurities were applied to each measurement. For n-propylbenzene and n-butylbenzene, measurements were also made for the heat of fusion of the metastable phase. The large uncertainty in the heat of fusion of the metastable crystalline form of n-propylbenzene is probably caused by difficulties in securing pure metastable crystals owing to partial transposition to the stable phase if crystallization is too slow and to incomplete crystallization if it is too rapidly cooled. The values of AHin listed in Table 111 represent the average of two or more measurements for each form of each compound. (An approximate value of 7790 cal. mole-1 was found for the heat of fusion of ndecylbenzene.) The triple point temperature and sample purity for each compound were determined from studies of the equilibrium melting temperature as a function of the fraction of sample melted.l6 The melting point data for both stable and metastable crystals are summarized in Table IV. Also listed in Table IV is a melting point study of n-decylbenzene. I n all cases the equilibrium temperatures, TF, were plotted as functions of 1 / ~ , the reciprocal of the fraction of the total sample in the liquid state. The triple point temperatures, T,, were determined by linear extrapolations to the zero value of 1 / ~ . If the impurities form ideal solutions in the liquid phase and are insoluble in the solid phase, the relation between mole fraction of total impurity, Nz*, and melting point depression, AT = T,, - TF,is''
-In (1 - Nz) = A A T ( ~+ BAT
+ . . .)
(1)
where N2 = N Z * / ~ .The cryoscopic constants, A 1= A H m / R T t p z and B = l / X t p - ACm/2AHm, were calculated from the values of A H m and T,, in Table V, and values of ACm, the difference between the heat capacities of the compound in the solid and liquid states at the triple point, were obtained from data in Table V (discussed in the following section). Values of A and B are included in Table 111. Impurity values given in Table IV were calculated using eq. 1 in its simplified form (for Nz*
