Heat Capacities and Derived Thermodynamic Functions of 1

From the melting point to 370 K the liquid heat capacities can be represented within the ... error with Cp,l(n,T) ) {-450.41 + 36.4968n + 1.47317T} Jâ...
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90

J. Chem. Eng. Data 2001, 46, 90-97

Heat Capacities and Derived Thermodynamic Functions of 1-Octadecanol, 1-Nonadecanol, 1-Eicosanol, and 1-Docosanol between 10 K and 370 K J. Cees van Miltenburg* and Harry A. J. Oonk Chemical Thermodynamics Group, Debye Institute, Utrecht University, Padualaan 8, 3584-CH Utrecht, The Netherlands

Lourdes Ventola Dpt. Cristallografia, Universitat de Barcelona, C/Marti i Franque`s, S/N-08028 Barcelona, Spain

The molar heat capacities of the linear alcohols 1-octadecanol (C18H38O), 1-nonadecanol (C19H40O), 1-eicosanol (C20H42O), and 1-docosonol (C22H46O) were measured from 10 K to 370 K. The derived absolute entropies were fitted as a function of the carbon number (n) in the linear chain. At 360 K the function is S°(360 K,n) ) {117.52 + 38.328n} J‚K-1‚mol-1. A simple function was found for the heat capacity of the liquids. From the melting point to 370 K the liquid heat capacities can be represented within the measuring error with Cp,l(n,T) ) {-450.41 + 36.4968n + 1.47317T} J‚K-1‚mol-1. The solid-solid phase transition in 1-octadecanol was investigated in more detail, and the relative Gibbs energy curves of both solid phases and the liquid phase are presented.

Introduction The normal 1-substituted alcohols have received far less interest than the n-alkanes. The measurements of thermal properties for the long chain n-alcohols published are limited to DSC measurements1-4 and an adiabatic study of C13 to C16 1-alcohols around room temperature.5 Furthermore, the melting and transition events were studied by X-ray methods,6-8 dielectric measurements,9 and direct visual observation in capillary tubes.10,11 An extensive study of the infrared spectra has been published.12 We are not aware of high-precision low-temperature studies, which may be used to derive entropy values and other thermodynamic properties. Compounds containing long aliphatic chains are interesting from different viewpoints. They form important building blocks in paraffins, hydrocarbons, polyethylene, and glycerides. The physical property behavior of these compounds is due to the presence of long aliphatic chains. A review of the physical properties of these molecules can be found in the Handbook of Lipid Research.13 Another more recent aspect of these substances is their potential application in heat storage materials. The alcohols have the advantage of negligible or no subcooling and are not very chemically aggressive. Mixing of different members of the family allows one to manipulate the optimum working temperature for heat storage. Our group works in this field in cooperation with the universities of Bordeaux and Barcelona, organized in the Re´seau Europe´en sur les Alliages Mole´culaire (REALM). Experimental Section Three compounds were purchased from Fluka Chemica with an estimated purity of better than 98%. The fourth, 1-docosanol was bought from Aldrich with a stated purity * Corresponding author. Fax: +31 302533946. E-mail: miltenb@ chem.uu.nl.

Figure 1. Molar heat capacity of 1-octadecanol around the melting point: O, material as received; b, material after being melted in the calorimeter.

Figure 2. Cooling curve of 1-octadecanol; all four compounds show two thermal events in their cooling curves; A and B indicate the temperatures mentioned in the text.

of 98%. The compounds were used without further purification. The calorimeter used (laboratory-design indication CAL VII) was home-built as a copy of CAL V.14,15 Below 30 K, the reproducibility of the calorimeter is about 1%, between 30 K and 100 K, 0.05-0.1%, and above 100 K, 0.03%. The accuracy of the heat capacity measurements

10.1021/je000048s CCC: $20.00 © 2001 American Chemical Society Published on Web 12/12/2000

Journal of Chemical and Engineering Data, Vol. 46, No. 1, 2001 91 Table 1. Experimental Data Series for n-Octadecanol T K series 1 296.17 296.97 298.37 300.36 303.72 304.50 305.88 307.86 309.84 311.81 313.77 315.74 317.69 319.64 321.58 323.51 325.38 327.16 328.66 329.62 330.06 330.25 330.35 330.42 330.48 330.53 330.57 330.61 330.65 330.69 330.73 330.76 330.79 330.82 330.85 330.87 330.89 330.90 330.92 330.92 330.93 330.92 330.92 330.92 330.92 330.91 330.92 331.24

Cp J‚K-1‚mol-1 476.27 477.89 481.44 486.75 495.54 498.12 502.27 508.78 515.75 523.48 532.13 541.67 552.96 565.97 582.92 609.33 659.88 775.60 1212.90 3329 9002 17524 27636 38122 46830 51849 52878 54121 58022 61894 65679 71048 76858 85769 94521 117629 145169 168908 220591 376370 -823271 -4861643 -895038 -742115 -570578 -1013209 171031 3342

T K 332.61 334.73 336.79 338.77 340.76 342.75 344.74 346.73 348.73 350.72 352.71 354.70 356.69 358.71 series 2 6.42 7.95 9.39 11.15 12.97 15.00 17.24 19.69 22.27 24.98 27.84 30.66 33.14 series 3 5.49 7.26 8.43 10.19 12.35 15.48 15.60 20.88 23.34 26.03 29.03 31.81 series 4 34.02 35.93 40.39 42.48 44.72 47.23 49.74

Cp J‚K-1‚mol-1 695.86 698.87 702.14 705.36 708.33 711.55 714.82 717.70 720.84 723.56 726.72 729.49 732.26 736.25 1.59 2.14 3.25 4.87 7.29 10.55 14.47 19.23 25.02 31.63 38.29 45.46 52.64 0.18 1.69 2.52 4.00 6.23 11.56 11.58 21.79 27.49 34.23 41.18 48.76 55.34 60.73 71.49 78.06 83.99 90.93 97.70

T K 52.28 54.86 57.46 60.09 62.75 65.44 68.15 70.88 73.63 76.40 79.18 81.98 84.80 87.60 90.35 93.03 95.64 98.20 100.70 series 5 95.70 97.40 99.22 101.17 103.11 105.06 107.01 108.96 110.91 112.87 114.83 116.79 118.75 120.71 122.67 124.64 126.60 128.56 130.53 132.50 134.46 136.44 138.40 140.37 142.35 144.32 146.29 148.26 150.24

Table 2. Thermodynamic Properties at Selected Temperatures for n-Octadecanol (M ) 270.4991 g‚mol-1, Φ°m

def )

191.77 194.44 196.94 200.68 203.25 205.98 208.90 211.50 214.17 216.84 219.40 221.97 224.50 227.00 229.47 231.98 234.52 236.79 239.11 241.41 243.84 246.10 248.36 250.62 253.01 255.41 257.57 259.81 262.07

C°p,m J‚K-1‚mol-1 3.8 10.55 19.90 31.68 43.66 58.18 70.44 84.76 98.38 111.40 123.55 134.99 145.80 155.97 165.63 174.59 183.20 191.27 198.38 205.90 212.92 226.10 238.49 250.19 261.80 273.27 284.49 295.99 307.91 320.01 332.70 345.74 359.56 374.15 389.51 405.27 423.07 442.53 463.71 483.07 487.88 520.74 581.29 581.2 694.51 707.47 722.83

∆S°m J‚K-1‚mol-1 1.32 4.14 8.41 14.13 20.93 28.67 37.27 46.44 56.07 66.06 76.29 86.63 97.03 107.44 117.82 128.13 138.35 148.47 158.47 168.33 178.07 197.17 215.76 233.87 251.53 268.79 285.69 302.28 318.60 334.70 350.62 366.40 382.07 397.68 413.26 428.84 444.47 460.20 476.10 489.20 492.21 508.70 526.05 546.34 747.16 765.54 786.27

Extrapolated. b Solid. c Liquid.

∆H°m J‚mol-1 9.9 45.7 120.6 250.2 437.6 689.8 1 012 1 402 1 860 2 385 2 973 3 619 4 321 5 076 5 880 6 731 7 625 8 561 9 536 10546 11594 13790 16114 18557 21118 23794 26582 29484 32503 35643 38907 42298 45824 49492 53310 57282 61423 65750 70282 74136 75033 80066 85530 91961 158473 164642 171793

Φ°m J‚K-1‚mol-1 0.33 1.094 2.378 4.126 6.345 8.967 11.96 15.27 18.87 22.70 26.74 30.95 35.30 39.76 44.32 48.94 53.63 58.35 63.11 67.89 72.67 82.26 91.81 101.32 110.74 120.08 129.33 138.48 147.53 156.49 165.35 174.14 182.84 191.46 200.02 208.52 216.97 225.38 233.75 240.55 242.10 250.43 258.77 268.68 268.68 281.30 295.43

T K 152.21 154.19 156.17 158.14 160.12 series 6 162.00 163.58 165.86 168.82 171.77 174.73 177.68 180.64 183.60 186.56 189.53 192.49 195.44 198.40 201.35 204.31 207.28 210.24 213.21 216.17 219.13 222.09 225.06 228.03 230.99 233.96 236.92 239.88 242.85 245.81 248.78 251.75 254.72 257.70 260.67 263.63 266.60 269.56 272.52 275.48 278.45 281.42 284.38

Cp J‚K-1‚mol-1 264.34 266.67 269.00 271.56 273.71 275.69 277.35 279.79 283.21 286.55 289.99 293.31 296.72 300.38 303.74 307.28 310.88 314.44 318.02 321.69 325.55 329.16 333.00 336.90 340.68 344.55 348.64 352.66 356.81 360.95 365.35 369.66 373.97 378.63 383.14 387.73 392.64 396.31 401.47 406.59 411.89 417.00 422.35 428.50 433.74 439.39 445.79 452.32

T K 287.35 290.31 293.28 296.24 299.20 302.16 305.11 308.06 310.99 313.87 316.70 319.47 322.15 324.66 326.83 328.39 329.29 329.76 330.02 330.17 330.28 330.36 330.43 330.50 330.57 330.64 330.71 330.76 330.80 330.83 330.86 330.88 330.89 330.90 330.91 330.91 330.92 330.92 330.94 330.97 331.77 333.78 336.23 338.67 341.10

Cp J‚K-1‚mol-1 458.55 465.13 472.36 479.80 487.32 495.65 504.47 514.29 525.73 539.58 555.88 580.25 624.69 715.87 998.57 1850 3957 7939 13950 21446 29319 35611 38431 37905 36552 39764 45596 57831 73374 99951 117430 153761 204468 266856 480056 758099 760250 362245 169411 61870 1312.63 697.64 701.20 704.87 708.60

Table 3. Melting Experiments of n-Octadecanola experiment

∆T0 S°m - ∆T0 H°m/T)

T K 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 120 130 140 150 160 170 180 190 200 210 220 230 240 250 260 270 280 290 298.15 300 310 320 331.2a,b 331.2a,c 340 350 a

Cp J‚K-1‚mol-1 104.36 111.03 117.50 123.77 129.89 135.98 141.88 147.63 153.24 158.73 164.09 169.24 174.24 179.18 183.77 188.13 192.29 196.31 199.73

1 2 3 4 5 mean value

triple point

∆Hfusion

purity

K

J‚mol-1

%

331.12 331.22 331.16 331.23 331.20

66 873 66 733 66 643 66 601 66 512 66 672 ( 200

98.9 98.2 98.6 98.2 98.8

remarks as received slow heating used in Table 2

a The following linear fits were used for the iterative calculation of the baseline: Cp[solid] ) {-374.29 + 2.88485T} and Cp[liquid] ) {204.82 + 1.47854T} J‚K-1‚mol-1.

was checked with n-heptane and with synthetic sapphire. No deviations larger than 0.2% from the recommended values were found. The compounds were evacuated for about 0.5 h before closing the measuring vessel. A helium pressure of about 1 kPa was admitted before closing in order to promote the heat exchange within the vessel. Measurements were made in the intermittent mode, using stabilization periods of about 600 s and heat input periods of about 500 s. The temperature increase was generally about 2 to 3 K for each measurement. Each compound was first measured from room temperature up to about 360 K. Then a slow, controlled cooling curve was measured by setting the inner adiabatic shield and the wire heater about 10 K below the temperature of the vessel. This resulted in a cooling rate outside the crystallization area of about 4 K‚h-1. Between 5 K and 30 K, stabilization and input periods of about 100 to 150 s were used. Measurements on 1-octadecanol were made with 6.365 g, on 1-nonadecanol with 3.277 g, for 1-eicosanol with 4.2397 g, and for 1-docosanol with 4.6422 g. After completion of the measurements, all data were combined in one file. The data consist of the mean tem-

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Journal of Chemical and Engineering Data, Vol. 46, No. 1, 2001

Table 4. Experimental Data Series for n-Nonadecanol T K series 1 298.06 298.61 299.89 301.89 303.87 305.86 307.85 309.83 311.82 313.79 315.77 317.74 319.71 321.68 323.64 325.60 327.54 329.36 330.40 330.64 330.75 330.84 330.93 331.03 331.17 331.40 331.97 332.92 333.72 334.09 334.26 334.35 334.41 334.46 334.49 334.51 334.52 334.50 334.49 334.54 335.58 337.74 339.95 342.01 344.00 345.98 347.97

Cp J‚K-1‚mol-1

T K 349.96 351.94 353.94 355.93 357.92 series 2 6.04 8.02 10.11 11.78 13.72 15.95 18.29 20.76 23.35 26.05 28.90 series 3 6.11 7.66 9.50 11.18 13.14 15.24 17.50 19.92 22.46 25.11 27.90 30.85 series 4 6.11 7.91 9.74 11.50 13.54 15.71 18.01 20.45 23.02 25.69 28.52 series 5 32.19 34.08 36.42 38.74 41.09

493.77 496.47 500.40 505.51 511.60 516.69 522.50 528.56 534.96 542.65 549.86 557.94 566.73 577.16 590.33 608.37 646.59 836.40 7439 25023 37370 40285 37242 30393 21213 10928 3500 2542 5856 15958 30569 47456 68205 101334 133052 177928 -367256 -156428 334341 46982 956.92 739.78 742.91 745.79 750.39 752.56 755.63

Cp J‚K-1‚mol-1 758.48 761.55 764.83 767.20 770.16 1.23 1.77 4.05 6.11 8.94 12.61 17.21 22.19 28.30 35.26 42.05 0.96 1.70 3.32 4.94 7.75 11.24 15.26 20.31 26.16 32.81 39.32 47.22 0.92 1.93 3.55 5.53 8.36 11.94 16.28 21.28 27.36 34.51 40.83 51.86 57.36 63.77 69.20 76.20

T K 43.47 45.89 48.34 50.84 53.37 55.93 58.53 61.16 63.81 66.49 69.20 71.93 74.67 77.44 80.22 83.01 85.82 88.68 91.51 94.28 97.13 100.02 series 6 102.65 104.29 106.58 109.48 112.38 115.27 118.17 121.08 123.99 126.91 129.83 132.76 135.69 138.63 141.56 144.50 147.44 150.38 153.32 156.27 159.22 162.18 165.13 168.09 171.05

Table 5. Thermodynamic Properties at Selected Temperatures for n-Nonadecanol (M ) 284.5260 g‚mol-1, Φ°m

def )

∆T0 S°m - ∆T0 H°m/T)

T K 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 120 130 140 150 160 170 180 190 200 210 220 230 240 250 260 270 280 290 298.15 300 310 320 334.5a,b 340 350 360 370 380 a

C°p,m J‚K-1‚mol-1 3.90 10.88 20.45 32.53 44.90 59.92 72.95 87.53 101.66 115.43 128.26 140.40 151.38 162.04 171.99 181.38 190.55 198.71 206.26 214.84 222.01 235.86 248.89 261.31 273.49 285.22 296.97 308.85 321.35 333.88 347.23 361.12 375.60 391.05 407.08 423.14 440.77 460.36 481.89 500.60 504.96 532.65 575.29 735.27 743.88 759.00 774.30 789.65 804.96

Cp J‚K-1‚mol-1 83.20 90.05 97.03 103.98 110.96 117.96 124.61 131.13 137.65 143.70 149.63 155.57 161.37 166.95 172.41 177.75 182.88 188.07 192.92 197.53 202.21 206.30 211.15 213.75 217.22 221.26 225.43 229.56 233.32 237.34 241.20 245.25 248.68 252.31 256.11 259.60 263.25 266.84 270.25 273.96 277.63 281.00 284.29 287.84 291.41 294.72 298.20

T K 174.01 176.97 179.93 182.89 185.85 188.81 191.77 194.74 197.70 200.67 203.63 206.59 209.56 212.53 215.49 218.46 221.43 224.40 227.36 230.33 233.29 236.26 239.23 242.20 245.17 248.14 251.11 254.08 257.05 260.02 262.98 265.95 268.92 271.88 274.85 277.81 280.78 283.74 286.70 289.66 series 7 291.93 293.55 295.34 297.30 299.26 301.22 303.19

Cp J‚K-1‚mol-1 301.62 305.17 308.77 312.56 316.12 319.90 323.50 327.13 330.92 334.74 338.89 342.67 346.62 350.78 354.77 358.82 363.29 367.30 371.74 376.09 380.63 385.18 389.81 394.70 399.18 404.07 408.83 413.10 417.91 423.17 428.46 433.51 438.73 444.37 450.07 455.73 462.06 468.47 475.09 481.30 484.38 489.64 493.89 498.56 503.27 507.77 514.05

Extrapolated. b Liquid.

∆H°m J‚K-1‚mol-1 9.8 45.3 122.8 254.5 447.6 710.4 1 042 1 444 1 917 2 459 3 069 3 741 4 471 5 255 6 090 6 974 7 904 8 877 9 890 10 944 12 036 14 327 16 752 19 304 21 978 24 772 27 684 30 712 33 864 37 139 40 545 44 086 47 769 51 602 55 592 59 740 64 059 68 563 73 275 77 274 78 204 83 399 88 919 169 791 173 858 181 371 189 038 196 858 204 830

Φ°m J‚K-1‚mol-1 0.326 1.068 2.343 4.132 6.400 9.096 12.18 15.59 19.30 23.25 27.41 31.76 36.26 40.88 45.59 50.39 55.24 60.14 65.07 70.03 75.00 84.95 94.88 104.76 114.57 124.30 133.93 143.45 152.88 162.22 171.46 180.61 189.67 198.67 207.59 216.46 225.27 234.04 242.77 249.86 251.47 260.43 269.11 282.81 291.13 306.05 320.75 335.23 349.51

Cp J‚K-1‚mol-1 519.19 524.83 530.43 536.05 542.71 549.61 557.52 567.19 581.18 591.15 608.25 644.38 816.90 3197 10868 22224 33483 41110 41967 33889 18133 4559 1533 4102 12024 27122 45287 75965 105450 156307 238467 330548 475173 472409 288053 2374 739.51 741.95 745.26 748.94 751.78 754.83 757.63 760.66 763.98 766.71 769.71 772.79

Table 6. Measured Enthalpies of Transition and Melting of n-Nonadecanola series

∆S°m J‚K-1‚mol-1 1.31 4.09 8.49 14.31 21.32 29.39 38.23 47.67 57.63 67.96 78.57 89.32 100.13 110.94 121.72 132.43 143.06 153.58 163.98 174.25 184.42 204.34 223.75 242.65 261.09 279.12 296.77 314.08 331.11 347.91 364.53 381.00 397.37 413.68 429.96 446.23 462.53 478.91 495.44 509.04 512.15 529.46 546.98 790.41 802.47 824.26 845.85 867.28 888.54

T K 305.14 307.10 309.06 311.02 312.97 314.92 316.87 318.83 320.77 322.72 324.66 326.58 328.39 329.61 330.11 330.33 330.45 330.55 330.63 330.73 330.87 331.30 332.39 333.51 334.01 334.21 334.31 334.38 334.42 334.44 334.46 334.48 334.49 334.49 334.50 335.07 336.77 339.06 341.20 343.18 345.17 347.15 349.13 351.12 353.10 355.08 357.07 359.06

1 7 8 mean value and estimated error

Τtrans

Τfus

∆Htrans + ∆Hfus

K

K

J‚mol-1

331 331 331

334.5 334.5 334.5

72 516 72 319 72 434 72 423 ( 100

a The following linear fits of the heat capacity were used for the iterative calculation of the baseline: Cp[solid] ) {285.92 + 2.63902T} and Cp[liquid] ) {227.63 + 1.5176T} J‚K-1‚mol-1.

peratures, mean heat capacity over the measurement interval, and relative enthalpy values. After calculating starting values for the entropy and enthalpy at 10 K, the data set was interpolated for every degree. The derived properties S°(T) and Φo(T) ) -(H°(T) - TS°(T)) were calculated by numerical integration. The latter function Φo(T) is given, as it is useful for calculating relative stabilities and as it is easier to interpolate. The starting values of S° and H°(T) - H°(0) were calculated assuming that below 10 K the low-temperature limit of the Debye heat capacity function Cp ) RT3 holds. Results and Discussion 1-Octadecanol. The experimental data series are given in Table 1. The derived thermodynamic properties H°(T) - H°(0), S°(T), and Φ°(T) are given in Table 2. All four compounds do not follow the Debye low-temperature limit Cp ) RT3 in the temperature range measured. For obtaining starting values for the numerical integration of Cp/T, leading to S°, we used the fitted values of Cp at 10 K to calculate R, assuming that below 10 K the Debye limit holds. Between 10 K and just below the melting point, no

Journal of Chemical and Engineering Data, Vol. 46, No. 1, 2001 93 Table 7. Experimental Data Series for n-Eicosanol T

Cp

T

Cp

T

Cp

T

Cp

T

Cp

K

J‚K-1‚mol-1

K

J‚K-1‚mol-1

K

J‚K-1‚mol-1

K

J‚K-1‚mol-1

K

J‚K-1‚mol-1

18.57 20.84 23.13 25.49 27.96 30.29 series 3 8.14 9.97 11.49 13.35 15.31 17.38 19.58 21.86 24.18 26.58 28.98 31.14 32.98 series 4 6.78 8.63 10.58 12.41 14.58 16.92 19.36 21.94 24.63 27.33 29.77 31.80 33.56 series 5 35.01 36.33 37.86 39.63 41.38 43.11 44.86 46.62 48.39 50.17 51.97 53.77 55.59 57.41 59.25 61.10 62.95 64.82 66.69 68.57 70.46 72.35 74.25 76.16 78.07

18.83 23.72 29.39 35.97 41.84 48.31

80.00 81.96 83.86 85.76 87.69 89.62 91.55 93.49 95.43 97.37 99.32 101.05 101.93 103.36 105.33 107.28 109.24 111.20 113.16 115.12 117.08 119.05 121.01 122.98 124.95 126.92 128.89 130.86 132.84 134.81 136.78 138.76 140.73 142.71 144.69 146.67 148.64 150.62 152.60 154.58 156.56 158.55 160.53 162.51 164.49 166.47 168.46 170.44 172.43 174.41 176.40 178.38 180.37 182.35 184.34 186.32 188.31 190.30 192.28 194.27

180.43 183.09 188.67 192.44 196.13 199.57 203.15 206.51 209.82 213.17 216.10 221.38 221.46 223.41 226.39 229.71 232.54 235.55 238.45 241.23 244.18 246.70 249.41 252.24 254.90 257.91 260.30 262.96 265.40 268.26 270.58 273.17 275.76 278.17 281.04 283.28 285.77 288.19 290.79 293.51 296.09 299.08 301.21 303.27 305.82 308.16 310.61 313.05 315.47 318.22 320.54 323.05 325.59 328.10 331.01 333.46 336.14 338.66 341.64 344.20

196.25 198.24 200.23 202.21 204.20 206.19 208.17 210.16 212.15 214.13 216.12 218.11 220.09 222.07 224.05 226.03 228.02 230.00 231.99 233.98 235.96 237.94 239.92 241.90 243.89 245.87 247.85 249.84 251.82 253.80 255.78 257.77 259.75 261.74 263.72 265.70 267.69 269.67 271.65 273.64 275.62 277.60 279.59 281.57 283.55 285.53 287.50 289.48 series 6 290.72 291.17 292.38 294.33 296.27 298.22 300.17 302.12 304.07 306.02 307.97

346.98 349.82 352.38 355.52 358.00 360.95 363.77 366.52 369.63 372.22 375.10 377.96 380.83 384.12 386.81 389.71 392.75 395.90 399.36 402.12 405.61 408.77 412.14 415.65 418.70 422.26 425.70 429.35 433.00 435.79 438.83 442.76 446.90 450.69 455.28 458.95 462.95 467.15 471.61 475.83 480.10 484.67 489.61 495.21 500.83 506.11 511.81 517.92

309.92 311.87 313.82 315.77 317.73 319.68 321.62 323.54 325.44 327.30 329.11 330.76 332.15 333.26 334.10 334.72 335.17 335.51 335.77 335.97 336.13 336.26 336.37 336.46 336.56 336.68 336.81 336.96 337.10 337.21 337.29 337.36 337.41 337.45 337.49 337.52 337.55 337.58 337.62 338.21 339.79 341.80 343.79 345.78 347.76 349.75 351.73 353.71 355.68 357.65 359.61 361.57 363.52 365.48 367.43 369.38 371.32

594.34 605.04 616.96 629.93 647.04 668.29 698.55 734.59 786.19 856.66 983.25 1227 1657 2354 3398 4864 6800 9249 12264 15892 20009 24352 27929 29331 27573 23378 18616 18300 23342 30509 39170 49113 60100 72558 86862 94001 89777 95989 78093 1847 780.06 782.58 786.29 788.77 792.08 794.69 797.67 800.73 802.90 806.01 808.43 811.15 814.58 816.18 818.86 821.32 822.98

series 1 295.86 297.11 299.09 301.07 303.05 305.02 306.99 308.96 310.92 312.87 314.82 316.77 318.71 320.64 322.57 324.48 326.38 328.24 330.03 331.70 333.16 334.26 334.98 335.44 335.75 335.97 336.15 336.29 336.42 336.53 336.63 336.73 336.84 336.97 337.10 337.23 337.32 337.40 337.46 337.51 337.53 337.55 337.57 337.59 337.74 339.00 341.22 343.31 345.30 347.29 349.28 351.27 353.26 355.25 series 2 9.78 12.29 14.65 16.43

518.89 524.56 530.51 537.75 546.37 554.28 563.46 573.17 583.72 596.09 608.17 620.89 635.10 651.05 670.46 695.70 732.86 794.81 909.58 1127 1671 2938 5121 8233 11909 15694 19533 23338 27137 30494 32000 30317 26011 22688 22853 28669 37815 47645 55983 86703 297406 128287 138920 436103 9946 778.30 781.21 784.95 787.43 790.48 793.43 796.09 799.32 801.89 4.45 7.23 11.03 14.42

2.99 4.44 6.19 8.90 12.37 16.25 20.89 26.20 32.17 38.67 44.75 50.87 56.94 1.81 3.27 4.90 7.45 10.95 15.26 20.39 26.49 33.46 40.51 46.85 53.07 58.75 63.77 67.12 70.80 76.15 81.41 86.71 92.01 97.28 102.48 107.65 112.73 118.04 123.43 128.30 133.18 137.93 142.65 147.15 151.87 156.18 160.55 164.82 168.88 172.69 175.32

phase transitions were observed. In the melt the molar heat capacity reaches very high values, and near the end of the melting process when the remaining solid starts to float in the liquid formed, which enhances the distribution of impurities, even negative values for the heat capacity are found. However, this has no influence on the calculation of the enthalpy of fusion. For this calculation, the enthalpy function is used and this function increases with every heat input. In Figure 1 the molar heat capacity in the vicinity of the melting point is given. The first melting experiment showed a very small shoulder; this effect is more pronounced in the once-melted material. The occurrence of a phase transition in the long chain alcohols has been reported, as discussed in the Introduction. The observed effect is attributed to a solid-solid transition, in which the crystalline form is changed into a crystal with rotational disorder. We follow the often-used notation, the β- and γ-forms, which are stable at low temperatures, transform into the R-form at the transition points close to the melting points. On cooling, the compound crystallizes in the R-form. The R f γ transition (in the case of n-octadecanol) does

517.30 519.39 525.48 532.47 539.17 545.42 551.71 558.59 567.52 574.90 584.55

show a significant subcooling. The cooling curve (see the Experimental Section) is given in Figure 2. For all four alcohols the subcooling of the liquid f R phase is very small. The temperatures of the freezing process were taken at the point A (see Figure 2) and are given in Table 13. Subcooling ranged from 0.2 K to 0.5 K. The liquid f R and R f γ transitions are clearly separated. The R f γ transition is a solid-solid phase transition which involves nucleation and which is consequently subcooled. The amount of subcooling depends on the cooling rate. Closer inspection of the thermal plateau (indicated by B in Figure 2) and repeating the cooling curve at different cooling rates showed that what looked to be a first-order phase transition is a balance between the heat liberated by the transition process and the heat removed by the cooling. In Table 3 a summary of the melting experiments is given. The enthalpy of fusion was calculated by taking the enthalpy increment between 300 K and 340 K. The Cp functions of the liquid and the solid used for the calculation of the baseline are also given in Table 3. The calculation was performed in an iterative way, the contribution of the liquid formed being

94

Journal of Chemical and Engineering Data, Vol. 46, No. 1, 2001

Table 8. Thermodynamic Properties at Selected Temperatures for n-Eicosanol (M ) 298.55 g‚mol-1, Φ°m def )

∆T0 S°m- ∆T0 H°m/T) T

C°p,m

∆S°m

∆H°m

Φ°m

K

J‚K-1‚mol-1

J‚K-1‚mol-1

J‚K-1‚mol-1

J‚K-1‚mol-1

10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 120 130 140 150 160 170 180 190 200 210 220 230 240 250 260 270 280 290 298.15 300 310 320 330 338.2a,b 338.2a,c 340 350 360

4.45 11.74 21.84 34.55 47.50 63.74 77.25 92.44 107.16 121.75 135.13 147.59 159.48 170.42 180.43 190.95 200.27 209.09 218.08 225.88 233.71 248.00 261.80 274.80 287.42 300.66 312.50 325.12 338.27 352.08 366.29 380.70 395.89 412.28 429.64 447.40 467.87 490.77 517.70 545.19 551.16 594.75 672.60 1096 699.6 778.2 780.31 795.06 808.95

1.51 4.66 9.43 15.67 23.01 31.44 40.81 50.79 61.30 72.19 83.36 94.68 106.06 117.44 128.72 139.95 151.13 162.21 173.14 184.00 194.69 215.65 236.06 255.93 275.33 294.30 312.88 331.10 349.03 366.74 384.26 401.64 418.89 436.09 453.26 470.44 487.71 505.12 522.84 537.56 540.95 559.69 579.62 604.37 617.62 835.56 839.70 862.54 885.13

11.3 51.1 135.0 275.9 478.3 752.5 1 104 1 529 2 028 2 600 3 242 3 950 4 718 5 543 6 417 7 343 8 322 9 346 10 413 11 526 12 676 15 086 17 636 20 319 23 131 26 072 29 136 32 324 35 642 39 094 42 687 46 422 50 305 54 346 58 554 62 934 67 510 72 300 77 348 81 678 82 692 88 407 94 688 102 741 106 788 180 494 181 898 189 775 197 797

0.380 1.258 2.679 4.629 7.069 9.933 13.20 16.82 20.74 24.92 29.32 33.91 38.66 43.53 48.50 53.55 58.66 63.82 69.00 74.22 79.45 89.93 100.39 110.80 121.12 131.35 141.49 151.52 161.44 171.26 180.99 190.63 200.18 209.65 219.05 228.39 237.67 246.91 256.12 263.61 265.31 274.50 283.72 293.04 301.86 301.86 304.71 320.32 335.70

a

b

c

Extrapolated. Solid. Liquid.

calculated after each measurement and used in the new calculation until a stable value was obtained. A maximum of three iterations were needed. The sum of the enthalpy of fusion and of transition was found to be (66 672 ( 200) J‚mol-1. This is the mean value of four melting experiments; the uncertainty given is two times the standard deviation. It seems that in the compound as received, being stored for a long time at room temperature, lattice defects have healed, resulting in a larger enthalpy of fusion. The difference is within the uncertainty, and it cannot be confirmed by an outlier test that the first melting experiment is different from the following experiments. However, the same effect was observed with all four alcohols. Recent measurements on n-heptadecanol showed the same effect, but with this compound the difference in enthalpy of the solid state between the sample as received and after melting amounted to 1000 J‚mol-1, which is a significant difference. The temperature of fusion was (331.2 ( 0.1) K, the stated uncertainty is larger than can be expected in adiabatic calorimetry. This is caused by the occurrence of the phase transition in the melting region, which also prohibits the usual purity calculation. An attempt was made to separate the transition and the melting effect. The sample was melted and cooled to 328 K (see Figure 2). At

Figure 3. (a) Relative Gibbs energy curves of n-octadecanol around the transition and melting point: 1, compound first cooled to 100 K; b, compound cooled to 328 K; the region around the transition and melting point is given in part b. (b) Enlarged view of the transition region; the symbols are the same as in part a.

Figure 4. Enthalpy curve of 1-nonadecanol around the melting point; the crystal-rotator transition between 330 K and 331.5 K changes with the thermal history of the sample: ∆, compound as received; +, compound after being melted and slowly cooled; b, compound after being equilibrated at 332 K for 24 h. Table 9. Melting Experiments of n-Eicosanola experiment 1 2 3 mean value

triple point

∆Hfus

K

J‚mol-1

338.1 338.2 338.2

73 968 73 482 73 706

remarks as received used in Table 8

73 719 ( 200

a The following linear fits were used for the iterative calculation of the baseline: Cp[solid] ) {-598.07 + 3.8370T} and Cp[liquid] ) {310.04 + 1.38521T} J‚K-1‚mol-1.

this temperature only the liquid f R transition has taken place. From 328 K, set measurements were made up to temperatures in the liquid phase. The molar heat capacities in the (metastable) R-phase were very high. Between 328 K and 330 K the values increased from 1000 to 2000 J‚K-1.mol-1. This makes it very difficult to calculate the enthalpy of the R f liquid transition. The difference in enthalpy between the R and the γ phase at 328 K, calculated after matching the enthalpy in the liquid phase, was 25 600 J‚K-1‚mol-1. Accepting this value as the γ f R enthalpy of transition, thus ignoring the heat capacity contribution, the enthalpy of fusion of the R phase is 41 072

Journal of Chemical and Engineering Data, Vol. 46, No. 1, 2001 95 Table 10. Experimental Data Series for n-Docosanol T

Cp

T

Cp

T

Cp

T

Cp

T

Cp

K

J‚K-1‚mol-1

K

J‚K-1‚mol-1

K

J‚K-1‚mol-1

K

J‚K-1‚mol-1

K

J‚K-1‚mol-1

series 1 296.30 298.36 301.19 304.01 306.80 309.57 312.32 315.05 317.76 320.45 323.11 325.76 328.38 330.97 333.52 336.00 338.30 340.26 341.62 342.35 342.73 342.96 343.12 343.23 343.31 343.36 343.41 343.46 343.50 343.54 343.57 343.60 343.62 343.64 343.66 343.67 343.68 343.70 343.72 343.76 344.50 346.38 348.71 351.03 353.35 355.67

564.01 570.12 578.80 587.73 597.02 606.84 616.97 627.29 638.53 650.17 662.51 676.88 694.27 716.13 746.90 806.19 984.55 1446 3157 7276 13008 19841 28576 42225 62840 85106 79785 78818 91328 106619 124827 153361 187971 250216 325526 318848 234220 196166 154618 69503 1932 862.90 865.14 868.52 872.26 876.03

357.98 360.28 series 2 5.46 7.96 10.53 11.91 13.78 15.59 17.49 19.64 21.88 24.20 26.61 29.11 series 3 6.98 8.98 10.62 12.25 14.21 16.00 17.94 20.12 22.36 24.71 27.14 29.66 series 4 32.25 34.72 36.86 38.76 40.48 42.14 43.83 45.54 47.27 49.01 50.77 52.54 54.32 56.12 57.93 59.75 61.58 63.41

879.57 883.20

65.26 67.12 68.98 70.85 72.73 74.62 76.51 78.41 80.32 82.23 84.14 86.06 87.98 89.90 91.83 93.76 95.70 97.63 99.57 series 5 106.35 109.93 113.42 116.85 120.21 123.52 126.77 129.97 133.13 136.24 139.31 142.34 145.35 148.32 151.27 154.21 157.15 160.08 163.02 165.97 168.91 171.85 174.80 177.75 180.70 183.65 186.60

160.24 164.92 169.67 174.53 179.06 184.08 188.66 192.96 197.46 201.41 205.41 209.34 213.68 217.48 221.28 223.95 228.53 232.36 235.99

189.56 192.51 195.46 198.41 201.37 204.32 207.28 210.23 213.19 216.15 219.10 222.06 225.02 227.97 230.93 233.88 236.84 239.80 242.75 245.71 248.67 251.62 254.58 257.53 260.49 263.45 266.40 269.36 272.32 275.28 278.24 281.19 284.14 287.07 289.98 292.87 295.74 298.59 series 6 268.58 270.83 273.43 276.38 279.33 282.28 285.23 288.18

366.95 371.12 375.56 379.85 384.41 388.63 393.06 397.61 402.07 406.79 411.48 416.03 420.88 425.87 430.63 435.55 440.66 445.90 451.10 456.42 461.75 467.18 472.72 478.41 484.23 490.20 496.25 501.94 508.70 514.85 521.53 528.46 535.35 542.67 550.25 558.04 566.10 573.42

291.13 294.07 297.02 299.97 302.91 305.85 308.80 311.74 314.69 317.63 320.57 323.51 326.44 329.36 332.26 335.11 337.85 340.19 341.76 342.56 342.94 343.16 343.29 343.38 343.45 343.51 343.56 343.60 343.63 343.65 343.67 343.69 343.71 343.74 343.78 344.89 347.47 350.48 353.47 356.45 359.43 362.40 365.36 368.31 371.25

553.77 562.12 570.47 579.47 589.11 598.60 608.87 618.06 627.04 637.21 649.18 662.56 678.59 699.34 729.87 786.21 931.97 1508 3746 9262 17842 30107 46643 69267 71341 92401 122013 151663 187689 231870 269040 252897 213052 166636 79277 1530 864.08 868.92 873.71 878.34 882.69 887.04 891.39 895.29 899.04

0.80 2.42 4.64 5.41 9.34 12.67 16.68 21.68 27.26 33.61 40.53 48.12 1.10 3.05 4.81 6.06 10.02 13.52 17.65 22.80 28.57 35.08 41.97 49.82 58.11 66.14 73.02 79.23 85.04 90.59 95.84 101.44 106.98 112.56 117.90 123.42 128.75 134.43 139.45 144.75 149.76 155.13

J‚K-1‚mol-1. The relative Gibbs energy curves were calculated for the measurement from the γ f R f liquid and the R f liquid measurements. The enthalpy and the entropy of the three data sets were matched at 350 K. The result is plotted in Figure 3a. The transition from the γ f R phase is very close to the melting point of the R phase. In Figure 3b an enlarged view of the transition region is given. Using the extrapolated Gibbs energy curves (the lines in Figure 3a), we found TγfR ) 330.60 K and TRfliquid ) 330.93 K. This latter value corresponds to the melting point (see Table 1); this indicates that the extrapolation of the Gibbs energy curves can be used. As this extrapolation is based on measurements relatively far from the melting point, the influence of impurities in the sample is expected to be small. The triple point (331.2 K) was estimated from the plot of the reciprocal of the melted fraction against the equilibrium temperatures. 1-Nonadecanol. The experimental data are given in Table 4, the derived thermodynamic properties are given in Table 5, and the enthalpy of transition and of melting is given in Table 6. The separation of the crystal-rotator transition and the rotator-liquid transition is about 4 K. The molar heat capacity between these transitions is very high and resembles the behavior in n-nonadecane.16 Since it is not clear which baseline to use when trying to separate these transitions, the sum of them is given. The transition temperature shifted slightly to lower temperatures when the sample had been melted before. We stabilized the sample at 332 K, between the transition and the melting point for 24 h and recooled. The different enthalpy curves

247.64 253.55 259.18 264.65 269.80 274.82 279.71 284.47 289.01 293.25 297.60 301.79 305.99 310.07 314.06 318.11 322.05 326.01 330.07 334.04 338.13 342.18 346.29 350.31 354.51 358.47 362.76

499.63 504.74 510.94 517.37 524.25 531.43 538.97 546.53

are given in Figure 4. The stabilization at 332 K resulted in a shift of the transition temperature roughly between the two other curves. This also confirms the idea that storage of the material at room temperature can lead to a slightly different enthalpy of the solid phase. The cooling curve from the liquid phase will be discussed later on. 1-Eicosanol. The experimental data are given in Table 7, the derived thermodynamic properties are given in Table 8, and the melting experiments are given in Table 9. Like the molar heat capacity curve of 1-octadecanol, a small shoulder was observed in the melting curve at about 1 K below the end melting point. The position of the maximum of this effect shifted about 0.2 K to lower temperatures in a sample which had recently been melted. The melting experiments given in Table 9 include this effect. The controlled cooling curve gave two well-separated transitions. This will be discussed in a later section. 1-Docosanol. The experimental data are given in Table 10, the derived thermodynamic properties are given in Table 11, and the melting data are given in Table 12. No solid-solid phase transitions were observed. In the melt only one measuring point could indicate a small transition. Plotting the equilibrium temperatures in the melt versus the reciprocal of the melted fraction does result in a straight line. This indicates that the impurities form a eutectic system with the main component. From these curves the purity and the triple-point temperature given in Table 12 were calculated. Cooling Behavior. All four compounds do show two events on cooling. A cooling curve of 1-octadecanol is given

96

Journal of Chemical and Engineering Data, Vol. 46, No. 1, 2001

Table 11. Thermodynamic Properties at Selected Temperatures for n-Docosanol (M ) 326.61 g‚mol-1, Φ°m

def )

Table 13. Comparison of the Experimental and Literature Data

∆T0 H°m/T)

compd

T

C°p,m

∆S°m

∆H°m

Φ°m

K

J‚K-1‚mol-1

J‚K-1‚mol-1

J‚K-1‚mol-1

J‚K-1‚mol-1

10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 120 130 140 150 160 170 180 190 200 210 220 230 240 250 260 270 280 290 298.15 300 310 320 330 340 343.92a,b 343.92a,c 350 360

3.92 11.50 22.51 35.92 50.89 67.03 83.43 99.69 115.59 130.89 145.46 159.57 172.31 185.03 196.76 207.17 217.67 226.92 236.75 245.38 253.67 269.48 284.50 298.56 312.34 325.90 339.63 353.51 367.58 382.30 397.26 412.87 429.13 446.26 464.18 483.25 503.16 525.79 550.31 572.58 579.57 612.67 646.74 704.84 1453 681 859.46 868.15 883.53

1.310 4.055 8.833 15.29 23.13 32.12 42.05 52.82 64.16 75.89 87.91 100.11 112.40 124.72 137.03 149.27 161.42 173.43 185.33 197.09 208.69 231.43 253.60 275.19 296.26 316.85 337.02 356.83 376.31 395.54 414.55 433.39 452.10 470.71 489.29 507.87 526.48 545.18 564.05 579.62 583.22 602.76 622.71 643.40 669.20 674.9 925.36 935.51 960.19

9.8 44.9 129.2 275.1 491.1 783.4 1 156 1 614 2 153 2 769 3 461 4 223 5 053 5 946 6 900 7 910 8 972 10 083 11 243 12 449 13 696 16 311 19 081 21 996 25 051 28 242 31 569 35 035 38 640 42 388 46 286 50 335 54 545 58 920 63 472 68 208 73 140 78 284 83 662 88 239 89 316 95 276 101 563 108 287 116 941 118 753 204 892 208 423 217 184

0.330 1.057 2.369 4.286 6.761 9.732 13.14 16.95 21.10 25.54 30.24 35.14 40.22 45.44 50.78 56.22 61.72 67.29 72.89 78.53 84.18 95.51 106.82 118.08 129.26 140.34 151.32 162.19 172.95 183.60 194.14 204.59 214.94 225.21 235.41 245.53 255.59 265.60 275.56 283.66 285.50 295.42 305.33 315.26 325.25 329.61 329.61 340.02 356.90

a

Extrapolated. b Solid. c Liquid.

Table 12. Melting Experiments of n-Docosanola experiment 1 2 3 4 mean value

triple point

∆Hfus

purity

K

J‚mol-1

%

343.92 343.92 343.90 343.92

86 072 85 964 86 071 86 139

98.3 98.3 98.3 98.4

86 062 ( 100

98.3

remarks as received used in Table 8

a The following linear fits were used for the iterative calculation of the baseline: Cp[solid] ) {-150.62 + 2.418T} and Cp[liquid] ) {352.18 + 1.475T} J‚K-1‚mol-1.

in Figure 2. The temperatures indicated by A and B in the figure are the maximum values measured on each plateau. In Table 13 these values are given. The maximum difference in the solid-liquid and liquid-solid transitions is 0.5 K. One should however be cautious to consider this as subcooling, as different solid phases are involved. 1-Docosanol might melt from the γ phase, and it does crystallize in the R phase. This can account for the difference in the melting and crystallization temperatures. In the case of the nalkanes the subcooling is smaller for compounds with comparable chain lengths; for n-nonadecane we measured only 0.1 K or less.16 The subcooling of the rotator-crystal phase transition is much larger. It ranges between 5 and

Ttrans

Tfus

K

K

331.65 331.65 331 331.75 330.15 331.55 330.85 331.95 325.1a 330.49a a 326.1 330.7a 330.60 331.2 nonadecanol 335.15 334.65 335.15 324.55 334.2 326.3a 334.0a 331 334.5 eicosanol 338.15 335.05 338.05 337.65 343.55 338.15 331.45a 337.58a a 329.7 337.3a 338.2 docosanol 340.15 345.15 343.95 348.05 343.65 336.65a 343.1a a 339.8 343.2a 343.92

∆Htrans ∆Hfus ∆Htrans + ∆Hfus J‚mol-1 J‚mol-1

J‚mol-1

18 828 39 162 26 000 43 000

57 990 69 000

22 300 37 300

59 600

25 600 41 072

66 672

23 800 42 600

66 400

octadecanol

328.45 330 327.85 325.15 330.25

a

72 423 13 933 41 840

62 073

24 400 45 700

70 100

17 238 46 568

63 806

26 200 51 040

77 240

73 719

86 062

ref 10 4 3 8 7 9 11 12 1 this work this work 7 11 12 1 this work this work 7 9 4 12 1 this work this work 7 4 12 1 this work this work

Cooling.

7 K, and whereas the crystallization temperatures measured by Sirota1 are in accord with our measurements, the transition temperatures differ up to 3 K. Since the cooling rates were comparable in both works, the cause of the difference could be the material of the measuring vessels. This would indicate that the transition is triggered by nonhomogeneous nucleation. Entropy at 360 K and 298.15 K. We fitted the entropy S°(360 K) for the four components in the liquid phase to a function of the form S° ) a0 + a1n, where n is the number of carbon atoms in the chain. The value of S°(360 K) ) 806.83 J‚K-1‚mol-1 of 1-octadecanol was calculated by extrapolation from 350 K using the fit for the liquid phase (see later discussion). The fit obtained is S°(360 K,n) ) {117.52 + 38.328n} J‚K-1‚mol-1, with a correlation coefficient of 0.999 93. The maximum deviation from the fit is found for 1-nonadecanol and is 0.11%, which is within the expected accuracy. The increment in entropy with n can be compared with the value given for the n-alkanes. The fit at 298.15 K of these compounds gives a value of 32.32 J‚K-1‚mol-1.17 When we extrapolate the entropy of the alcohols to a hypothetical liquid state at 298.15 K, by using the fit of the heat capacity of the liquid phases as described later on, we find S°(298.15,n) ) {111.31 + 31.448n} J‚K-1‚mol-1. The maximum deviation in this fit is 0.18% for 1-docosanol. The dependence of S° on n is close to the value found for the n-alkanes. Heat Capacity of the Liquid Phase. We have combined all collected heat capacity data of the liquid phase of the four compounds in a file consisting of temperaturenumber of carbon atoms-heat capacity triplets. With these data a fit was made, starting with the model Cp ) a0 + a1n + a2nT + a3T. The program Exel with the Solver option was used for the fitting procedure. This model allows for a change in temperature dependence of the heat capacity of the liquids with the carbon number. However, it proved to be possible to fit the data set to within the experimental error and with the same error as in the aforementioned fit, with the more simple function Cp ) a0 + a1n + a2T. A total number of 157 data points were used, giving the

Journal of Chemical and Engineering Data, Vol. 46, No. 1, 2001 97 function Cp ) {-450.41 + 36.4968n + 1.47317T} J‚K-1‚mol-1. The standard deviation of this fit is 0.7 J‚K-1‚mol-1, which corresponds to a relative deviation of about 0.1%. This fit shows that the heat capacity of the liquids of the four alcohols has the same temperature dependence. No explanation has been made at the time of this writing. Acknowledgment The authors wish to thank the students Edwin de Heer (Utrecht University) and Cathal Brennan (Trinity College, Dublin) for assisting in the measurements. Literature Cited (1) Sirota, E. B.; Wu, X. Z. The Rotator Phase of Neat and Hydrated 1-Alcohols. J. Chem. Phys. 1996, 105, 7763-773. (2) Yamamoto, T.; Nozaki, K.; Hara, T. X-ray and Thermal Studies of Normal Higher Alcohols C17H35OH, C18H37OH, and Their Mixtures. J. Chem. Phys. 1990, 92, 631-641. (3) Reuter, J.; Wu¨rflinger, A. Differential Thermal Analysis of LongChain n-Alcohols Under High Pressure. Ber. Bunsen-Ges. Phys. Chem. 1995, 99, 1247-1251. (4) Kuchal, Y. K.; Shukla, R. N.; Biswas, A. B. Differential Thermal Analysis of n-Long Chain Alcohols and Corresponding Alkoxy Ethanols. Thermochim. Acta 1979, 31, 61-70. (5) Mosselman, C.; Mourik, J.; Dekker, H. Enthalpies of Phase Change and Heat Capacities of Some Long-chain Alcohols. Adiabatic Semi-Microcalorimeter for Studies of Polymorphism. J. Chem. Thermodyn. 1974, 6, 477-487. (6) Hoffman, J. D.; Smyth, C. P. Molecular Rotation in the Solid Forms of Some Long-Chain Alcohols. J. Am. Chem. Soc. 1949, 71, 431-439.

(7) Tanaka, K.; Seto, T.; Hayashida, T. Phase Transformation of n-Higher Alcohols. (I) Bulletin Institute Chemical Research Kyoto University 1958, 35 123-139. (8) Kolp, D. G.; Lutton, E. S. The Polymorphism of n-Hexadecanol and n-Octadecanol. J. Am. Chem. Soc. 1951, 73, 5593-5595. (9) Pradhan, S. D.; Katti, S. S.; Kulkarni, S. B. Dielectric Properties of n-Long Chain Alcohols, Alkoxyethanols and Alkoxypropanols. Ind. J. Chem. 1970, 8, 632-637. (10) Smith, J. C. Higher Aliphatic Compounds. Part I. The Systems Ethyl Pamitate-Ethyl Stearate and Hexadecyl Alcohol-Octadecyl Alcohol. J. Chem. Soc. 1931, 802-807. (11) Gaikwad, B. R.; Subrahmanyam, V. V. R. Melting Behaviour of Fatty Alcohols and Their Binary Blends. J. Ind. Chem. Soc. 1985, LXII, 513-515. (12) Tasumi, M.; Shimanouchi, T.; Watanabe, A.; Goto, R. Infrared Spectra of Normal Alcohols-I. Spectrochim. Acta 1964, 20, 629666. (13) Small. D. M. Handbook of Lipid Research 4, The Physical Chemistry of Lipids; Plenum Press: New York, 1988. (14) van Miltenburg, J. C.; van den Berg, G. J. K.; van Bommel, M. J. Construction of an Adiabatic Calorimeter. Measurement of the Molar Heat Capacity of Synthetic Sapphire and of n-Heptane. J. Chem. Thermodyn. 1987, 19, 1129-1137. (15) van Miltenburg, J. C.; van Genderen, A. C. G.; van den Berg, G. J. K. Design Improvements in Adiabatic Calorimetry. The Heat Capacity of Cholesterol Between 10 and 425 K. Thermochim. Acta 1998, 319, 151-162. (16) van Miltenburg, J. C.; Oonk, H. A. J.; Metivaud, V. Heat Capacities and Derived Thermodynamic Functions of n-Nonadecane and n-Eicosane Between 10 K and 390 K. J. Chem. Eng. Data 1999, 44, 715-720. (17) Messerly, J. F.; Guthrie, G. B.; Todd, S.; Finke, H. L. LowTemperature Thermal Data for n-Pentane, n-Heptadecane, and n-Octadecane. J. Chem. Eng. Data 1967, 12, 338-346. Received for review February 8, 2000. Accepted October 24, 2000.

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