Vapour pressures and heat capacity measurements on the C7–C9 secondary aliphatic alcohols

J. Chem. Thermodynamics 39 (2007) 758–766 www.elsevier.com/locate/jct

Vapour pressures and heat capacity measurements on the C7–C9 secondary aliphatic alcohols Sergey P. Verevkin a

a,*

, Christoph Schick

b

Department of Physical Chemistry, University of Rostock, 18055 Rostock, Germany b Department of Physics, University of Rostock, 18055 Rostock, Germany

Received 29 September 2006; received in revised form 11 October 2006; accepted 12 October 2006 Available online 19 October 2006

Abstract Molar enthalpies of vaporization of secondary C7–C9 alkanols were obtained from the temperature dependence of the vapour pressure measured by the transpiration method. The measured data sets were checked for internal consistency successfully. A large number of the primary experimental results on temperature dependences of vapour pressures of secondary alcohols have been collected from the literature and have been treated uniform in order to derive their vaporization enthalpies at the reference temperature 298.15 K. This collection, together with our experimental results, have helped to ascertain the database for branched aliphatic alcohols. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: Alcohols; Vapour pressure; Transpiration method; Enthalpy of vaporization; Heat capacity

1. Introduction The relationship between the structure of organic compounds and their energetics is one of the fundamental problems of contemporary thermochemistry. The quantitative evaluation of substituent effects in terms of enthalpy of formation or enthalpy of vaporization is one of the possible approaches to the general problem of elucidating how the individual parts of a molecule influence each other. In our previous work, we studied in this context linear [1] and branched tertiary alcohols [2,3]. This work continues this line and is concerned with systematic determination of vaporization enthalpies of secondary 2-, 3-, 4-, and 5-alkanols with chain length of seven, eight, and nine atoms. There are only vaporization enthalpies of secondary butanol, pentanol, and hexanol derivatives available in the literature [3–5]. However, these are short chain alcohols and the general question: is there any enthalpic effect by migration of the hydroxyl group along the alkyl chain – could be answered only after measurements on the other longer (C7–C9) sec*

Corresponding author. Tel.: +49 381 498 6508; fax: +49 381 498 6502. E-mail address: [email protected] (S.P. Verevkin).

0021-9614/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.jct.2006.10.007

ondary alkanols. Some experimental results on vapour pressures are already available in the literature [4–13]. Two experimental methods, ebulliometric and static, were most frequently used (see table 1). In this work, we applied a transpiration method [1]. Static and transpiration methods work in the temperature ranges close to ambient temperatures. Ebulliometric methods due to high boiling temperatures of alcohols were applied at elevated temperatures (from 320 K up to boiling temperatures). In any case, in order to derive enthalpies of vaporization of alcohols at the reference temperature 298.15 K, the knowledge of the heat capacities are required. These values were measured with help of DSC and applied for the adjusting of experimental results to the reference temperature T = 298.15 K. 2. Experimental 2.1. Materials Samples of secondary aliphatic alcohols were commercially available from Aldrich and Fluka and were further purified by fractional distillation in vacuum. The degree of purity was controlled using a Hewlett–Packard gas

TABLE 1 Compilation of enthalpies of vaporization of the secondary C3–C16 alkanols 2-Propanol 2-Butanol 2-Pentanol 2-Hexanol 2-Heptanol

2-Nonanol 2-Decanol 2-Undecanol 2-Dodecanol 2-Tetradecanol 2-Hexadecanol 3-Pentanol 3-Hexanol 3-Heptanol

3-Octanol

3-Nonanol 4-Heptanol

4-Octanol 4-Nonanol 5-Nonanol a b c

Temperature range/K

C C C T E E S T I E S T S T S E S S S S C T E E S I S T S T E E T I T T T

298.15 298.15 298.15 274.5–309.4 357.4–423.0 322.9–431.4 244.0–338.2 274.9–312.2 283.3–353.2 366.3–480.8 253.1–353.2 283.7–329.2 263.1–363.2 285.7–324.2 278.2–378.3 344.2–505.0 283.3–393.2 293.5–393.1 313.1–428.3 343.3–453.2 298.15 278.3–311.5 325.2–429.8 263.7–294.7 275.2–311.2 283.2–353.2 253.2–348.2 288.3–324.2 263.1–363.0 263.1–363.0 320.6–427.4 275.3–311.2 253.2–353.2 288.3–322.3 285.0–324.2 288.6–334.2

Dgl H m ðT av Þ=ðkJ  mol1 Þ

57.8 50.7 51.2 62.8 62.8 64.9 51.2 66.0 66.9 70.8 72.1 74.0 59.5 75.9 80.5 84.0 86.6 59.1 53.0 64.6 60.7 67.0 66.4 66.9 69.6 70.0 51.4 63.2 64.3 66.3 70.7 69.4

C lp =ðJ  mol1  K1 Þ

C gp =ðJ  mol1  K1 Þ

258.75 298.6

158.3 181.1

326.9

204.3

356.3

226.9

386.7c 417.1c

249.8 272.7

447.6c 508.4c 569.2c

295.6 341.4 387.2

286.05 294.6c

158.3 181.1

339.9

204.0

373.6

226.9

306.8

181.1

332.1

204.0

367.8 370.7

226.9 226.9

Dgl H m =ðkJ  mol1 Þb (298 K)

Reference

45.2 ± 0.1 49.7 ± 0.1 53.0 ± 0.4 57.0 ± 0.2 61.5 ± 0.2 59.9 ± 0.6 61.5 ± 0.5 62.1 ± 0.4 67.2 ± 0.4 66.4 ± 0.4 66.9 ± 0.7 67.9 ± 0.3 72.0 ± 0.6 72.9 ± 0.6 77.4 ± 0.9 76.3 80.8 ± 1.0 86.7 ± 1.1 95.4 ± 1.3 103.9 ± 1.3 52.9 ± 0.3 58.6 ± 0.4 61.5 ± 0.9 62.4 ± 0.7 60.3 ± 0.2 69.3 ± 0.8 66.2 ± 0.8 67.9 ± 0.4 71.0 ± 0.8 70.9 ± 0.3 60.3 ± 0.5 62.6 ± 0.6 62.4 ± 0.3 66.5 ± 0.7 67.2 ± 0.5 71.5 ± 0.3 71.4 ± 0.4

[4] [4] [5] [3] [6] [7] [8] This [9] [10] [8] This [8] This [8] [11] [8] [8] [8] [8] [5] [5] [7] [12] [8] [9] [8] This [8] This [7] [13] This [9] This This This

work

work work

work work

S.P. Verevkin, C. Schick / J. Chem. Thermodynamics 39 (2007) 758–766

2-Octanol

Techniquea

work work work work

Technique: E, ebulliometry; I, Isoteniscopic; T, transpiration; S, static method. Calculated using vapour pressure data listed in the original work with help of equations (2) and (3). Value assessed by addition of an appropriate increment [14] C-(H)2(C)2 to the molar heat capacity of 2-nonanol, measured experimentally in this work.

759

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chromatograph 5890 Series II equipped with a flame ionisation detector and a Hewlett–Packard 3390A integrator. The carrier gas (nitrogen) flow was 7.2 dm3 Æ h1. A capillary column HP-5 (stationary phase cross linked 5% Ph Me silicone) was used with a column length of 30 m, an inside diameter of 0.32 mm, and a film thickness of 0.25lm. The standard temperature program of the GC was T = 323 K for 180 s followed by a heating rate of 10 K Æ min1 to T = 523 K. No impurities greater than mass fraction 0.02 could be detected in the samples used for the vapour pressure measurements. 2.2. Vapour pressure measurements Vapour pressures and enthalpies of vaporization of alcohols were determined using the method of transpiration [1] in a saturated N2-stream and applying the Clausius–Clapeyron equation. About 0.5 g of the sample was mixed with glass beads and placed in a thermostatted U-shaped tube having a length of 20 cm and a diameter of 0.5 cm. Glass beads with diameter of 1 mm provide a surface which is sufficient enough for the (vapour + liquid) equilibration. At constant temperature (±0.1 K), a nitrogen stream was passed through the U-tube and the transported amount of gaseous material was collected in a cooling trap. The flow rate of the nitrogen stream was measured using a soap bubble flow meter and optimised in order to reach the saturation equilibrium of the transporting gas at each temperature under study. On the one hand, flow rate of nitrogen stream in the saturation tube should be not too low in order to avoid the transport of material from U-tube due to diffusion. On the other hand, the flow rate should be not too high in order to reach the saturation of the nitrogen stream with the compound. We tested our apparatus at different flow rates of the carrier gas in order to check the lower boundary of the flow below which the contribution of the vapour condensed in the trap by diffusion became comparable with the transpired one. In our apparatus, the contribution due to diffusion was negligible at a flow rate down to 0.45 dm3 Æ h1. The upper limit for our apparatus where the speed of nitrogen could already disturb the equilibration was at a flow rate of 9.0 dm3 Æ h1. Thus, we carried out the experiments in the flow rate interval of (2 to 5) dm3 Æ h1, which has ensured that transporting gas was in saturated equilibrium with the coexisting liquid phase in the saturation tube. The amount of condensed substance was determined by GC analysis using an external standard (hydrocarbon n-CnH2n+2). The saturation vapour pressure psat i at each temperature Ti was calculated from the amount of product collected within a defined period of time, and the small value of the residual vapour pressure at the temperature of condensation was added. The latter was calculated from a linear correlation 1 between ln (psat obtained by iteration. Assuming i ) and T that Dalton‘s law of partial pressures applied to the nitrogen stream saturated with the substance i of interest is valid, values of psat were calculated: i

psat i ¼ mi  R  T a =V  M i ;

V ¼ V N 2 þ V i;

ðV N 2  V i Þ; ð1Þ

1

1

where R = 8.314472 J Æ K Æ mol ; mi is the mass of transported compound, Mi is the molar mass of the compound, and Vi its volume contribution to the gaseous phase. V N 2 is the volume of transporting gas and Ta is the temperature of the soap bubble meter. The volume of the gas V N 2 transferred through the tube was determined from the flow rate and time measurements. The flow rate was maintained constant using a high precision needle valve (Hoke). The accuracy of the volume V N 2 measurements from the flow rate was assessed to be (±0.001 dm3). Data of psat i have been obtained as a function of temperature and were fitted using following equation [1]:   b T g sat R  ln pi ¼ a þ þ Dl C p  ln ; ð2Þ T T0 where a and b are adjustable parameters and Dgl C p is the difference of the molar heat capacities of the gaseous and the liquid phase, respectively. The T0 appearing in equation (2) is an arbitrarily chosen reference temperature (which has been chosen to be 298.15 K). Consequently, from equation (2) the expression for the vaporization enthalpy at temperature T is derived: Dgl H mðT Þ ¼ b þ Dgl C p  T : Dgl C p

C gp

ð3Þ C lp

Values of ¼  have been derived from the experimental isobaric molar heat capacities of liquid, C lp , alcohols measured in this work, and from values of the isobaric molar heat capacities C gp of gaseous alcohols calculated according to a procedure developed by Domalski and Hearing [14]. In order to assess the uncertainty of the vaporization enthalpy, the experimental data were 1 approximated with the linear equation lnðpsat ) i Þ ¼ f (T using the method of least squares. The uncertainty in the enthalpy of vaporization was assumed to be identical with the average deviation of experimental lnðpsat i Þ values from this linear correlation. We have checked the experimental and calculation procedure with measurements of vapour pressures of n-alcohols [1]. It turned out that vapour pressures derived from the transpiration method were reliable within 1% to 3% and their accuracy was governed by reproducibility of the GC analysis. Experimental results: vapour pressures and enthalpies of vaporization Dgl H m of secondary alkanols are presented in table 2. 2.3. Heat capacities from d.s.c.-measurements The thermal behaviour of the alcohols was determined with a Perkin–Elmer Pyris 1 DSC. The heat capacity at T = 298.15 K was obtained by three different methods: (i) normal heating scan at 10 K Æ min1 with the heat capacity determined according to the three curve method; (ii) quasiisothermal rectangular temperature modulation with period 6 min and amplitude 1.5 K [18]; (iii) StepScanä DSC. measurement with step height 3 K and isotherm 3 min.

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TABLE 2 Vapour pressures p and Dgl H m , obtained by the transpiration method T/Ka

m/mgb

V (N2)/dm3c

p/Pad

(pexp  pcalc)/Pa

Dgl H m =ðkJ  mol1 Þ

2-Heptanol; Dgl H m ð298:15 KÞ ¼ ð62:09  0:40Þ kJ  mol1   T =K 97123:0 117:5 lnðp=PaÞ ¼ 363:5 R  RðT =KÞ  R ln 298:15 274.9 276.9 277.2 278.8 279.1 280.7 281.7 283.7 285.5 286.7 288.5 289.7 291.5 292.7 294.4 295.8 297.4 298.6 300.3 301.7 303.2 304.7 306.2 309.2 312.2

0.82 1.28 0.85 1.33 0.87 0.83 1.57 0.98 2.30 0.98 2.33 1.07 2.85 1.02 2.53 1.07 2.87 1.44 2.73 1.76 2.74 2.20 3.05 4.04 3.64

1.66 2.16 1.32 1.89 1.09 0.918 1.68 0.803 1.68 0.602 1.29 0.516 1.21 0.373 0.806 0.287 0.699 0.315 0.538 0.287 0.430 0.287 0.376 0.376 0.269

10.73 12.91 14.02 15.27 17.26 19.61 20.18 26.33 29.43 35.02 38.82 44.49 50.70 58.57 67.19 79.75 87.80 97.72 108.4 131.0 136.1 163.70 173.2 229.3 288.7

0.0 0.2 0.5 0.6 0.9 0.4 1.0 0.7 0.9 1.0 1.3 0.2 1.9 0.1 0.6 3.2 0.1 0.7 3.3 5.7 5.4 4.2 6.3 2.8 4.6

64.82 64.59 64.55 64.36 64.33 64.14 64.02 63.79 63.58 63.44 63.22 63.08 62.87 62.73 62.53 62.37 62.18 62.04 61.84 61.67 61.50 61.32 61.14 60.79 60.44

4-Heptanol; Dgl H m ð298:15 KÞ ¼ ð62:44  0:29Þ kJ  mol1   T =K 99916:5 125:7 lnðp=PaÞ ¼ 375:8 R  RðT =KÞ  R ln 298:15 275.3 278.3 281.3 284.2 287.3 290.3 293.2 296.3 299.2 302.2 305.3 308.2 311.2

1.43 1.60 1.85 1.93 1.91 2.19 2.48 2.86 3.15 3.99 4.22 3.75 4.78

1.96 1.59 1.38 1.06 0.797 0.690 0.611 0.531 0.478 0.451 0.372 0.266 0.266

15.50 21.33 28.47 38.65 50.94 67.15 86.19 114.0 139.8 187.1 240.3 299.1 381.4

0.1 0.1 0.2 0.7 0.2 0.3 0.5 0.5 5.3 1.0 1.5 0.7 4.2

65.32 64.94 64.56 64.20 63.81 63.43 63.07 62.68 62.31 61.94 61.55 61.18 60.80

2-Octanol; Dgl H m ð298:15 KÞ ¼ ð67:92  0:32Þ kJ  mol1   T =K 105514:5 lnðp=PaÞ ¼ 382:7 ðT =KÞ  126:1 R  R R ln 298:15 283.8 288.3 291 293.6 294.2 295.2 297.2 299.4 300.2 302.4 303.2 305.4 306.1 308.4 309.1

0.64 2.99 2.92 1.73 2.68 2.53 2.89 2.70 2.58 3.14 3.28 3.44 3.71 3.68 3.83

1.49 4.73 3.45 1.52 2.36 2.05 1.91 1.37 1.32 1.30 1.28 1.05 1.11 0.857 0.887

8.23 12.09 16.15 21.64 21.62 23.50 28.80 37.52 37.24 45.90 48.84 62.61 63.41 81.73 82.19

0.4 0.3 0.0 0.8 0.4 0.7 0.4 1.8 1.2 0.9 1.4 1.8 1.2 3.1 1.2

69.73 69.16 68.82 68.49 68.42 68.29 68.04 67.76 67.66 67.38 67.28 67.00 66.92 66.63 66.54 (continued on next page)

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TABLE 2 (continued) T/Ka

m/mgb

V (N2)/dm3c

p/Pad

(pexp  pcalc)/Pa

Dgl H m =ðkJ  mol1 Þ

311.3 312.2 314.3 315.2 317.3 318.2 320.3 323.2 326.2 329.2

3.51 4.09 4.22 4.09 4.36 3.74 4.06 3.90 3.18 3.60

0.686 0.722 0.617 0.577 0.514 0.413 0.377 0.291 0.189 0.171

97.38 107.8 130.1 134.9 161.4 172.3 204.9 255.0 320.1 400.4

2.7 0.1 2.4 2.3 0.5 1.4 0.7 0.9 3.1 7.1

66.26 66.15 65.88 65.77 65.50 65.39 65.12 64.76 64.38 64.00

3-Octanol; Dgl H m ð298:15 KÞ ¼ ð67:90  0:38Þ kJ  mol1   T =K 108418:1 135:9 lnðp=PaÞ ¼ 394:4 R  RðT =KÞ  R ln 298:15 288.3 291.3 294.2 297.3 300.4 303.2 306.2 309.2 312.2 315.2 318.2 321.2 324.2

2.77 2.08 3.09 2.90 3.58 3.58 4.72 5.03 4.44 4.79 5.33 5.38 5.25

3.35 1.88 2.16 1.45 1.35 1.07 1.07 0.898 0.613 0.531 0.470 0.368 0.286

15.66 20.99 27.09 37.89 50.21 63.46 83.78 105.9 137.0 170.5 214.5 276.8 346.9

0.0 0.1 0.8 0.6 0.8 0.0 1.4 0.2 1.0 2.5 4.5 1.3 2.4

69.24 68.84 68.44 68.02 67.60 67.22 66.81 66.40 66.00 65.59 65.18 64.77 64.37

4-Octanol; Dgl H m ð298:15 KÞ ¼ ð67:17  0:52Þ kJ  mol1   T =K 105358:7 128:1 lnðp=PaÞ ¼ 385:1 R  RðT =KÞ  R ln 298:15 288.3 289.3 294.2 296.5 297.3 298.6 300.4 301.9 302.4 305.2 305.3 307.2 310.3 313.2 316.2 319.2 322.3

3.77 3.02 1.61 2.58 3.22 2.34 3.68 2.80 4.89 5.05 5.20 5.27 5.95 4.43 5.33 5.53 7.64

4.08 2.80 0.988 1.28 1.44 0.967 1.34 0.865 1.46 1.11 1.13 0.988 0.865 0.514 0.494 0.412 0.432

17.69 20.63 31.13 38.56 42.58 46.07 52.42 61.71 63.73 86.40 87.62 101.5 131.0 164.0 205.4 255.5 336.3

0.1 1.0 0.3 0.3 0.7 1.0 2.9 1.5 2.3 2.2 2.7 1.7 2.0 0.8 1.4 5.1 7.3

68.43 68.30 67.67 67.38 67.27 67.11 66.88 66.69 66.62 66.26 66.25 66.01 65.61 65.24 64.85 64.47 64.07

2-Nonanol; Dgl H m ð298:15 KÞ ¼ ð72:87  0:42Þ kJ  mol1   T =K 111453:7 129:4 lnðp=PaÞ ¼ 393:4 R  RðT =KÞ  R ln 298:15 285.7 288.5 288.6 291.4 292.5 294.4 295.6 297.4 298.6 300.3 301.6

0.68 0.55 0.68 0.70 0.84 1.28 1.05 1.65 1.23 1.43 1.44

4.00 2.51 3.02 2.33 2.33 3.15 2.14 2.95 1.86 1.96 1.64

2.93 3.78 3.88 5.18 6.24 6.98 8.42 9.62 11.34 12.51 15.04

0.04 0.12 0.07 0.13 0.29 0.25 0.26 0.15 0.34 0.47 0.33

74.48 74.12 74.11 73.75 73.60 73.36 73.20 72.97 72.81 72.59 72.43

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TABLE 2 (continued) T/Ka

m/mgb

V (N2)/dm3c

p/Pad

(pexp  pcalc)/Pa

Dgl H m =ðkJ  mol1 Þ

303.5 304.4 305.2 306.4 306.4 308.3 309.4 309.5 311.3 312.4 312.4 314.3 315.3 315.4 317.3 318.3 321.2 321.2 324.2

1.94 1.60 2.15 2.00 2.10 2.30 2.26 1.82 2.68 1.89 2.47 2.68 2.59 1.99 3.28 2.07 1.85 3.50 1.71

1.94 1.43 1.70 1.45 1.60 1.39 1.37 1.01 1.26 0.795 1.09 0.992 0.879 0.669 0.935 0.543 0.388 0.708 0.284

17.19 19.28 21.73 23.65 22.51 28.47 28.34 30.83 36.59 40.83 39.07 46.40 50.61 51.09 60.25 65.47 81.88 84.89 103.40

0.43 0.10 1.07 0.56 0.58 1.01 1.98 0.23 0.68 1.27 0.49 0.25 0.23 0.18 0.02 0.02 1.30 1.71 2.50

72.18 72.06 71.96 71.81 71.81 71.56 71.42 71.40 71.17 71.03 71.03 70.78 70.65 70.64 70.40 70.27 69.89 69.89 69.50

3-Nonanol; Dgl H m ð298:15 KÞ ¼ ð70:87  0:26Þ kJ  mol1   T =K 114606:8 146:7 lnðp=PaÞ ¼ 406:6 R  RðT =KÞ  R ln 298:15 285.2 288.3 291.3 294.3 297.3 298.3 300.3 303.3 306.4 309.3 312.3 315.4 318.3 321.2 324.3

0.948 1.108 1.076 1.215 1.525 1.728 1.718 2.156 2.295 2.263 2.124 2.305 1.953 2.070 2.391

4.123 3.585 2.539 2.121 1.972 2.032 1.703 1.554 1.255 0.986 0.717 0.598 0.388 0.329 0.299

3.94 5.30 7.25 9.79 13.21 14.53 17.22 23.69 31.21 39.16 50.53 65.82 85.76 107.45 136.50

0.10 0.05 0.03 0.06 0.00 0.02 0.37 0.44 0.43 0.59 0.91 0.87 1.25 0.97 1.02

72.78 72.32 71.88 71.44 71.00 70.85 70.56 70.12 69.67 69.24 68.80 68.34 67.92 67.49 67.04

4-Nonanol; Dgl H m ð298:15 KÞ ¼ ð71:46  0:28Þ kJ  mol1   T =K 113466:3 140:9 lnðp=PaÞ ¼ 403:1 R  RðT =KÞ  R ln 298:15 285.0 288.2 291.2 294.3 297.3 300.2 303.2 304.3 306.3 309.3 312.2 315.2 318.2 321.2 324.2

0.82 1.18 1.24 1.44 1.60 1.71 2.48 2.41 3.16 2.70 3.41 2.92 3.19 2.80 2.50

3.58 3.55 2.84 2.37 2.01 1.63 1.74 1.57 1.72 1.12 1.06 0.710 0.592 0.414 0.296

3.92 5.68 7.49 10.43 13.56 17.96 24.20 26.21 31.26 40.89 54.62 70.01 91.98 115.3 143.8

0.02 0.19 0.02 0.15 0.26 0.31 0.01 0.59 0.89 1.09 0.61 0.37 2.76 1.68 0.01

73.32 72.87 72.44 72.01 71.58 71.18 70.75 70.60 70.32 69.89 69.48 69.06 68.64 68.22 67.79

5-Nonanol; Dgl H m ð298:15 KÞ ¼ ð71:38  0:40Þ kJ  mol1   T =K 114257:5 143:8 lnðp=PaÞ ¼ 405:6 R  RðT =KÞ  R ln 298:15 288.6 297.5 301.4

0.76 1.24 1.33

2.27 1.59 1.14

5.77 13.42 19.94

0.1 0.5 0.2

72.76 71.48 70.92 (continued on next page)

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TABLE 2 (continued) T/Ka

m/mgb

V (N2)/dm3c

p/Pad

(pexp  pcalc)/Pa

Dgl H m =ðkJ  mol1 Þ

304.4 307.4 310.3 313.3 316.3 319.3 322.3 325.2 328.2 331.2 334.2

1.61 2.04 2.57 3.25 3.31 3.50 3.56 4.45 4.26 5.23 4.33

1.02 0.996 0.971 0.971 0.747 0.622 0.498 0.498 0.397 0.373 0.249

27.03 35.15 45.39 57.42 76.07 96.50 122.7 153.5 184.3 240.6 299.0

0.4 0.2 0.3 0.9 1.1 0.7 1.0 1.1 7.0 1.8 2.4

70.48 70.05 69.64 69.20 68.77 68.34 67.91 67.49 67.06 66.63 66.20

a b c d

Temperature of saturation, N2 gas flow (2.0 to 5.3) dm3 Æ h1. Mass of transferred sample, condensed at T = 243 K. Volume of nitrogen, used to transfer mass m of sample. Vapour pressure at temperature T, calculated from m and the residual vapour pressure at T = 243 K.

TABLE 3 Specific heat capacities C lp of the secondary C7–C9 alcohols at T = 298.15 Ka 2-Heptanol 4-Heptanol 2-Octanol 3-Octanol 4-Octanol 2-Nonanol 3-Nonanol 4-Nonanol 5-Nonanol a

C lp scan/(J Æ g1 Æ K1)

C lp iso/(J Æ g1 Æ K1)

C lp step scan/(J Æ g1 Æ K1)

C lp avg ± 2%/(J Æ g1 Æ K1)

2.58 2.64 2.52 2.62 2.57 2.46 2.63 2.61 2.59

2.60 2.66 2.54 2.62 2.58 2.49 2.56 2.53 2.57

2.55 2.61 2.49 2.59 2.51 2.47 2.58 2.52 2.56

2.57 2.64 2.51 2.61 2.55 2.47 2.59 2.55 2.57

For the definition of C lp scan, C lp iso, and C lp step scan, see text.

To allow heat capacity calibration, a sapphire was used with the same temperature profiles. For all measurements, an empty pan run was subtracted and the specific heat capacity was calculated according to standard procedures. The temperature scale of the d.s.c. was calibrated by measuring high-purity indium (T0 = 429.8 K) and zinc (T0 = 692.6 K). The values of C lp at T = 298.15 K measured by the three d.s.c. methods and the averages are presented in tables 1 and 3.

different sources are also in very close agreement as shown in figure 1 for 2-octanol as an example. The correlation of the enthalpies of vaporization with the number of C atoms in the homologues series is a valu14 12 10

3. Results and discussion

lnP/Pa

8

Temperature dependences of vapour pressures of secondary alcohols are reported in table 2. However, except for references [6,9,13], authors did not calculate enthalpies of vaporization from their results. This is the reason we have also treated original experimental results available from the literature [6–13] using equations (2) and (3) and calculated Dgl H m (298.15 K) for comparison with our results. The collection of the available experimental results and derived Dgl H m (298.15 K) for secondary alcohols is presented in table 1. Vapour pressures of 2-alkanols have been measured more frequently than 3-, 4-, or 5-derivatives. Enthalpies of vaporization of secondary alkanols measured by using all possible techniques are remarkably consistent as evident from table 1. Vapour pressures of secondary alkanols from

6 4 2 0 -2 -4 0.002

0.0025

0.003

0.0035

0.004

K/T FIGURE 1. Plot of vapour pressure against reciprocal temperature for the liquid 2-octanol. –, N‘Guimby [8]; – Geisler [9]; n – Ambrose [10]; d – this work.

S.P. Verevkin, C. Schick / J. Chem. Thermodynamics 39 (2007) 758–766

the alkanes [15], aliphatic esters [16], and aliphatic ethers [17]. The plot of Dgl H m (298.15 K) against the number of C-atoms in the alkyl chain for the secondary alcohols is presented in figure 2. The linear trend is observed and the following equation expressed dependence of vaporization enthalpy on number of C-atoms (NC) for 2-alkanols:

110

100

Vaporization enthalpy/(kJ.mol-1)

765

90

Dgl H m ð298:15 KÞ=kJ  mol1 ¼ 30:66 þ 4:61 N C :

80

Enthalpies of vaporization of 3-, 4-, and 5-alkanols are very close to those of 2-alkanols. Graphical presentation of enthalpies of vaporization of secondary 2-, 3-, 4-, and 5-alkanols is given in figure 3. As can be seen, an enthalpic effect of migration of the OH-group along the chain in secondary C5–C9 alkanols is generally negligible within the experimental uncertainties, less than 1 kJ Æ mol1.

70

60

50

40 0

1

2

3

4

5

6

7

8

9

10 11 12 13 14 15 16 17

Nc FIGURE 2. Plot of experimental vaporization enthalpies Dgl H m (298.15 K) of secondary alcohols against the number of carbon atoms in the compound. s 2-alkanols; 3-alkanols; n - 4-alkanols.

able test to check the internal consistency of the experimental results. Vaporization enthalpies Dgl H m appear to be a good linear function of the number of carbon atoms in

4. Conclusion This investigation was undertaken to establish a consistent set of vapour pressures and vaporization enthalpies of secondary C5–C9 alkanols in the temperature range possibly close to the ambient temperatures. We collected from the literature a large number of the primary experimental results on temperature dependences of vapour pressures, treated them uniformly in order to derive vaporization

OH -0.1

OH

53.0

52.9

OH +1.6

OH 58.6

57.0

OH +0.3

OH

62.4

62.1 -1.8

OH 60.3

OH

OH

OH

67.9

OH

67.9

67.2

OH

72.9

OH

70.9

71.5

OH

71.4

FIGURE 3. Graphical presentation of enthalpies of vaporization Dgl H m (298.15 K) of the secondary alcohols (in kJ Æ mol1) from table 2. Study of the enthalpic effect of migration of the OH-group along the chain in secondary C5–C9 alkanols.

766

S.P. Verevkin, C. Schick / J. Chem. Thermodynamics 39 (2007) 758–766

enthalpies at the reference temperature 298.15 K, and checked the experimental results for the internal consistency. This collection together with the our results helps to ascertain data base for branched aliphatic alcohols. Consistent results from this compilation, together with the critical surveys reported in our recent studies [1–3], have encouraged the re-evaluation of the Benson-type increments for calculation of thermochemical properties of the aliphatic alcohols [19]. Acknowledgement S.V. acknowledges gratefully a financial support from the Research Training Group ‘‘New Methods for Sustainability in Catalysis and Technique’’ of German Science Foundation (DFG). References [1] D. Kulikov, S.P. Verevkin, A. Heintz, Fluid Phase Equilib. 192 (2001) 187–207. [2] S.P. Verevkin, Struct. Chem. 9 (1998) 375–382. [3] D. Kulikov, S.P. Verevkin, A. Heintz, J. Chem. Eng. Data 46 (2001) 1593–1600.

[4] I. Wadso, Acta Chem. Scand. 20 (1966) 536–544. [5] K.G. McCurdy, K.J. Laidler, Can. J. Chem. 41 (1963) 1867–1871. [6] M.M. Brazhnikov, A.I. Andreevskii, A.I. Satschek, A.D. Peschenko, Zh. Prikl. Khim. (Leningrad) 48 (1975) 2181–2185. [7] L.H. Thomas, R. Meatyard, J. Chem. Soc. (1963) 1986–1995. [8] J. N’Guimbi, C. Berro, I. Mokbel, E. Rauzy, J. Jose, Fluid Phase Equilib. 162 (1999) 143–158. [9] G. Geiseler, J. Fruwert, R. Huttig, Chem. Ber. 99 (1966) 1594– 1601. [10] D. Ambrose, B. Ghiassee, J. Chem. Thermodyn. 22 (1990) 307–311. [11] D.R. Stull, Ind. Eng. Chem. 39 (1947) 517–540. [12] L.H. Thomas, R. Meatyard, H. Smith, G.H. Davies, J. Chem. Eng. Data 24 (1979) 159–161. [13] S. Cabani, C. Conti, V. Mollica, L. Lepori, J. Chem. Soc. Faraday Trans. 1 (Lond.) 71 (1975) 1943–1954. [14] E.S. Domalski, E.D. Hearing, J. Phys. Chem. Ref. Data 22 (1993) 805–1159. [15] J.S. Chickos, J.A. Wilson, J. Chem. Eng. Data 42 (1997) 190– 197. [16] S.P. Verevkin, D. Wandschneider, A. Heintz, J. Chem. Eng. Data 45 (2000) 618–625. [17] S.P. Verevkin, E.L. Krasnykh, T.V. Vasiltsova, A. Heintz, J. Chem. Eng. Data 48 (2003) 591–599. [18] M. Merzlyakov, Thermochim. Acta 377 (2001) 193–204. [19] G.N. Roganov, P.N. Pisarev, V.N. Emel’yanenko, S.P. Verevkin, J. Chem. Eng. Data 50 (2005) 1114–1124.

JCT 06-255