Heat capacities of selected cycloalcohols

Thermochimica Acta 596 (2014) 98–108

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Heat capacities of selected cycloalcohols toslav Ru
ži9 Kve cka a, *, Michal Fulem a , Paulo B.P. Serra a , Ondrej Vlk a , Ivan Krakovský b a

Department of Physical Chemistry, Institute of Chemical Technology, Prague, Technická 5, 166 28 Prague 6, Czech Republic Department of Macromolecular Physics, Faculty of Mathematics and Physics, Charles University in Prague, V Holešovi9 ckách 2, 182 00 Praha 2, Czech Republic b

A R T I C L E I N F O

A B S T R A C T

Article history: Received 28 July 2014 Received in revised form 29 September 2014 Accepted 1 October 2014 Available online 7 October 2014

Isobaric heat capacities of selected cycloalcohols (cyclobutanol, CAS RN: 2919-23-5; cyclopentanol, CAS RN: 96-41-3; cyclohexanol, CAS RN: 108-93-0; cycloheptanol, CAS RN: 502-41-0; cyclooctanol CAS RN: 696-71-9) were measured with a highly sensitive Tian–Calvet calorimeter in the temperature range from 254 K to 352 K. Experimental heat capacity data were correlated as a function of temperature. The phase behavior was investigated with a differential scanning calorimeter. Calorimetric measurements were complemented by FTIR spectroscopy for less volatile compounds (cyclohexanol, cycloheptanol, cyclooctanol). The main aim of this work was to fill the gap in reliable heat capacity data for these compounds and to extend the knowledge base required for a better understanding of alcohols self-association. ã 2014 Elsevier B.V. All rights reserved.

Keywords: Alcohols Heat capacity In liquid phase Temperature correlation IR spectroscopy

1. Introduction Heat capacities belong among the fundamental thermophysical properties which are indispensable for evaluation of the variation of thermodynamic properties with temperature. Heat capacity data have a wide field of application in chemical engineering for establishing energy balances, in thermochemistry for calculating changes in reaction enthalpies as well as in evaluation of molecular and supramolecular interactions and structural changes of materials. Liquid heat capacities also serve as one of input data for reliable extrapolation of vapor pressure down to the triple point [1]. Extensive collection of critically assessed heat capacity data was published [2–4] and estimation methods based on this collection were developed [5,6]. The present paper is a continuation of our effort [7] to establish reliable heat capacity data for alcohols as they often exhibit a complex temperature dependence of liquid heat capacity, including inflection points [8], plateau or even maxima [9–13], which is not captured by the existing estimation methods and which leads to biased estimates with higher uncertainties when compared to other classes of compounds. For a better understanding of H-bonding, the stretching mode of O—H bond of cyclohexanol, cycloheptanol, and cyclooctanol was studied as a function of temperature. The phase behavior of cyclooctanol and

* Corresponding author. Tel.: +420 220 444 116.
E-mail address: [email protected] (K. Ruži9 cka). http://dx.doi.org/10.1016/j.tca.2014.10.002 0040-6031/ ã 2014 Elsevier B.V. All rights reserved.

cyclobutanol was studied by DSC as previously published values were ambiguous. 2. Experimental 2.1. Samples description The studied alcohols were of commercial origin and were used as received except drying over 0.4 nm molecular sieves since their purity, as checked by gas–liquid chromatography, was found satisfactory. The samples purity and water content are reported in Table 1. 2.2. Heat capacity measurements A highly sensitive Tian–Calvet calorimeter (Setaram mDSC IIIa) was used for the measurement of heat capacities using either the incremental temperature (step) or continuous method [14]. The two methods should yield identical results assuming that the calorimeter base-line changes linearly with temperature. This was confirmed for the Setaram mDSC IIIa calorimeter and the temperature range from 258 K to 355 K used in this study [15]. The combined expanded uncertainty of the heat capacity measurements is estimated to be Uc(Cp) = 0.01 Cp. A detailed description of the calorimeter and its calibration can be found in a paper by Straka et al. [16]; the measuring procedure was described in detail previously [15,17]. For the correlation of heat capacity data, a polynomial equation was used:




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Table 1 Sample description table. Compound

CAS number

Supplier

Mole fraction puritya

Water mass fraction wH2 0 b

Cyclobutanol Cyclopentanol Cyclohexanol Cycloheptanol Cyclooctanol

2919-23-5 96-41-3 108-93-0 502-41-0 696-71-9

Aldrich Aldrich Aldrich Aldrich Fluka

0.9982 0.9993 0.9996 0.9937 0.9925

2.8  104 1.2  105 4.0  105 1.5  105 1.0  105

a Gas–liquid chromatography analysis by Hewlett-Packard 6890 gas chromatograph equipped with column HP5 cross-linked 5% PHME siloxane, length 30 m, film thickness 0.25 mm, i.d. 0.32 mm, and FID detector. b Carl–Fischer analysis by Metrohm 831.

  n Cp X T i ¼ Aiþ1 100 R i¼0

(1)

where R is the molar gas constant (R = 8.314462 J K1 mol1 [18]). Cyclohexanol, cycloheptanol, and cyclooctanol exhibit the solid– liquid phase transition inside the measured temperature range and therefore the heat capacity of solid samples was also determined, albeit in a rather short temperature range. 2.3. Phase behavior The phase behavior of selected alcohols was investigated in the temperature range from 183 K to 303 K using a differential scanning calorimeter TA Q1000 (TA Instruments, USA). The measurements were carried out using continuous method [14] with a heating rate of 2 K min1. Temperature and enthalpy calibration of the device was performed using water, gallium, naphthalene, indium, and tin. The samples were enclosed in the so-called hermetic aluminum pans. Measurements at higher temperatures (up to normal boiling point temperature in order to see qualitatively the shape of heat capacity curve) were attempted after finishing the phase behavior studies. Relatively few experiments were successful and will be reported below. 2.4. FTIR spectroscopy ATR FTIR spectra were collected using a Nicolet 6700 spectrometer equipped with deuterated triglycine sulfate (DTGS) detector, KBr beam splitter, and horizontal micro-ATR Golden Gate unit (SPECAC) with diamond crystal. The thin layers of liquid samples of alcohols were closed between diamond crystal surface and a glass plate separated by teflon spacer of thickness ca 50 mm. The samples were first investigated at room temperature, and then gradually heated from 313 K to 473 K in steps of 20 K. 64 scans with spectral resolution 4 cm1 were coadded at each temperature to achieve a good signal-to-noise ratio. Contribution from residual water vapor present in air to spectra was subtracted using OMNICTM software. To locate the position of O—H stretching bands in spectra corresponding to free and hydrogen-bonded OH groups, 1% (v/v) solution of cyclooctanol in dry CCl4 at 293 K was also measured. This measurement was performed in a cell for liquids closed with ZnSe windows separated by a silicon spacer of thickness of 0.88 mm. 3. Results and discussion 3.1. Heat capacities Experimental heat capacities are listed in Table 2. A summary of performed experiments is presented in Table 3 along with the literature data. Selected data sets given in bold in Table 3 were correlated by Eq. (1) whose parameters are given in Table 4. Data selection was generally based on time of publishing (old data were not considered), purity and water content of samples, and

technique used (the uncertainty of results obtained by adiabatic calorimetry is usually lowest). The smoothed values (e.g. [19,20]) as well as the measurements at single temperature were not considered. The residuals of all data points from the present work from Eq. (1) are smaller than 1% (see Table 2). Note that the parameters in Table 4 represent the recommendation for the liquid phase heat capacities, while for the solid phase heat capacities they serve as a guide for the estimation of uncertainty of heat capacity measurements of cyclooctanol (by comparison of the data for solid cyclohexanol and cycloheptanol with accurate adiabatic measurements [21,22], as described below). In the case of cyclobutanol, the only measurement of heat capacity was reported in a graphical form by McGregor et al. [23]. The comparison with data of this work is therefore not possible. Fig. 1 shows relative deviations of experimental data from Eq. (1) for cyclopentanol. The agreement of the present data with values published by Kabo et al. [24] is very good and also the data from other sources [19,25,26] are in a reasonable agreement. A single data point reported by Conti et al. [27] exhibit deviation higher than 1% for cyclopentanol as well as for cyclohexanol and cycloheptanol. The agreement of our data for liquid cyclohexanol (Fig. 2) and liquid cycloheptanol (Fig 3) with the data published by Adachi et al. [21,22] is very good in the liquid phase but less satisfactory in the crystal I phase (though within combined uncertainties of the two datasets). A possible explanation can be a different thermal history of the samples. While our samples were cooled from room temperature to 255 K using a cooling rate gradually decreasing from 0.3 K min1 to 0.05 K min1 (for details see Supporting information), the Adachi’s samples were cooled to very low temperatures (well below 100 K) prior measurements of crystal I phase. Steele et al. [10] measured the heat capacity of two-phase system at constant volume C IIV of cyclohexanol by a powercompensated DSC up to the critical temperature and converted the data to the heat capacity along saturation curve Csat, which were almost constant over the temperature range from 440 K to 560 K, with a maximum value at 480 K, i.e. well above the normal boiling temperature 433.94 K [10]. Though Csat can be in principle converted to Cp [2,28] using     @V @p (2) C p ¼ C sat þ T @T p @T sat

the variation of volume with temperature at constant pressure ð@V=@TÞp required for such recalculation is not available in the case of cyclohexanol. At temperatures well below the normal boiling point temperature the Cp and Csat are however identical within the experimental uncertainty. Therefore, the values reported by Steele et al. [10] can be directly compared with the data of this work in the overlapping temperature range. The data agree within 1% with our Cp, however their scatter (caused by publishing rounded Csat values in [10]) would somewhat distort the final fit. Note also a short extrapolation used when producing Csat at 300 K in [10] (C IIV were measured from 310 K to 590 K).




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Table 2 Experimental heat capacities of cycloalcohols at p = (100  5) kPa. T/Ka

Cp/(J mol1 K1)b

calc 100  ðC p  C calc p Þ=C p

Cyclobutanol (m = 0.44834 g) Liquid 258.09 258.09 263.20 263.20 268.30 268.30 273.41 273.41 278.51 278.51 283.62 283.62 288.72 288.72 293.83 293.83 298.93 298.93 304.04 304.04 309.14 309.14 314.25 314.25 319.35 319.35 324.46 324.46 329.57 329.57 334.67 334.67 339.77 339.77 344.88 344.88 349.98 355.09

132.4 132.7 134.8 134.7 137.0 137.2 139.4 139.4 141.8 141.8 144.6 144.4 147.4 147.3 150.5 150.2 153.7 153.8 157.0 157.1 160.5 160.5 164.1 164.0 168.0 167.9 171.9 171.6 175.4 175.4 179.4 179.4 183.6 183.1 187.5 187.0 191.6 195.6

0.27 0.01 0.05 0.02 0.11 0.25 0.07 0.06 0.01 0.01 0.02 0.08 0.03 0.10 0.03 0.20 0.01 0.04 0.04 0.03 0.02 0.04 0.01 0.06 0.13 0.04 0.15 0.01 0.01 0.05 0.04 0.02 0.11 0.15 0.04 0.21 0.06 0.02

T/Ka

Cp/(J mol1 K1)b

calc 100  ðC p  C calc p Þ=C p

Cyclopentanol (m = 0.53715 g) Liquid 265.06 265.06 270.00 270.00 275.00 275.00 280.00 280.00 285.00 285.00 290.00 290.00 295.00 295.00 300.00 300.00 305.00 305.00 310.00 310.00 315.00 315.00 320.00 320.00 325.00 325.00 330.00 330.00 335.00 335.00

157.6 157.6 160.7 160.7 164.2 164.2 167.8 167.9 171.6 171.7 175.7 175.9 180.0 180.1 184.3 184.4 188.6 188.7 193.0 193.1 197.4 197.6 201.8 202.0 206.2 206.4 210.5 210.7 215.0 215.1

0.03 0.05 0.04 0.04 0.08 0.05 0.12 0.08 0.15 0.10 0.07 0.00 0.03 0.09 0.04 0.11 0.03 0.11 0.02 0.09 0.01 0.09 0.02 0.08 0.05 0.01 0.12 0.03 0.07 0.03

Table 2 (Continued) T/Ka

Cp/(J mol1 K1)b

calc 100  ðC p  C calc p Þ=C p

Cyclopentanol (m = 0.53715 g) 340.00 340.00 345.00 345.00 350.00 350.00 354.91 355.00 357.78

219.5 219.5 223.8 223.7 228.1 228.0 232.0 232.0 234.1

T/Ka

Cp/(J mol1 K1)b

0.01 0.02 0.03 0.01 0.05 0.01 0.03 0.00 0.02 calc 100  ðC p  C calc p Þ=C p

Cyclohexanol (m = 0.50086 g) Crystal I 261.42c 261.48c 264.00c 264.00c 267.00 267.00 270.00 270.00 273.00d 273.00d 276.00d 276.00d 279.00d 279.00d 282.00d 282.00d 284.50d 284.95d – Liquid 305.05 305.18 310.00 310.00 315.00 315.00 320.00 320.00 325.00 325.00 330.00 330.00 335.00 335.00 340.00 340.00 345.00 345.00 350.00 350.00 355.00 355.00 357.82 357.94

162.6 162.8 164.5 164.7 166.8 167.0 169.1 169.4 171.7 172.0 174.5 174.9 177.4 177.9 180.8 181.4 184.9 184.8

0.02 0.08 0.09 0.04 0.11 0.02 0.04 0.11

218.3 218.6 223.8 224.0 229.6 229.7 235.5 235.3 241.3 241.1 246.7 246.8 252.0 252.2 257.4 257.6 262.8 263.0 268.0 268.0 272.3 272.5 274.7 274.7

0.03 0.06 0.10 0.02 0.08 0.00 0.03 0.03 0.15 0.07 0.10 0.17 0.10 0.15 0.13 0.17 0.17 0.24 0.16 0.19 0.09 0.04 0.26 0.31

T/Ka

Cp/(J mol1 K1)b

calc 100  ðC p  C calc p Þ=C p

Cycloheptanol (m = 0.37573 g) Crystal I 260.59 260.73 262.00 262.00 264.00 264.00 266.00 266.00 268.00d 268.00d 270.00d 270.00d

195.3 195.4 196.4 196.5 198.0 198.1 199.8 199.8 201.8 201.7 204.0 204.0

0.00 0.03 0.02 0.01 0.06 0.01 0.01 0.04




K. Ruži9 cka et al. / Thermochimica Acta 596 (2014) 98–108 Table 2 (Continued) T/Ka

Cp/(J mol1 K1)b

Table 2 (Continued) calc 100  ðC p  C calc p Þ=C p

Cycloheptanol (m = 0.37573 g)

T/Ka

Cp/(J mol1 K1)b

calc 100  ðC p  C calc p Þ=C p

Cyclooctanol (m = 0.28556 g)

271.34d 271.43d – Liquid 286.01 286.13 290.00 290.00 295.00 295.00 300.00 300.00 305.00 305.00 310.00 310.00 315.00 315.00 320.00 320.00 325.00 325.00 330.00 330.00 335.00 335.00 340.00 340.00 345.00 345.00 350.00 350.00 354.82 355.00 357.82

236.1 236.3 240.6 240.6 246.5 246.5 252.3 252.3 258.1 258.2 263.8 263.8 269.4 269.5 274.8 274.9 280.3 280.2 285.3 285.2 289.9 290.0 294.4 294.4 299.2 299.2 303.6 303.6 307.6 307.7 309.7

0.03 0.02 0.09 0.07 0.07 0.05 0.04 0.03 0.02 0.00 0.00 0.01 0.02 0.04 0.02 0.05 0.07 0.06 0.04 0.01 0.06 0.04 0.12 0.12 0.03 0.03 0.04 0.01 0.05 0.05 0.01

T/Ka

Cp/(J mol1 K1)b

calc 100  ðC p  C calc p Þ=C p

205.2 205.4

Cyclooctanol (m = 0.28556 g) Crystal I 261.10c 261.23c 264.00 264.00 267.00 267.00 270.00 270.00 273.00d 273.00d 276.00d 276.00d 279.00d 279.00d 282.00d 282.00d 283.88d 284.25d – Liquid 301.94 302.06 305.00 305.00 310.00 310.00 315.00 315.00 320.00 320.00 325.00 325.00 330.00 330.00 335.00

101

235.9 236.1 238.7 238.8 241.8 241.9 245.1 245.3 248.9 249.0 252.7 252.8 256.9 256.9 261.4 261.5 264.3 265.2

0.02 0.06 0.07 0.01 0.08 0.02 0.02 0.07

295.6 295.8 299.1 299.1 304.6 304.6 310.1 310.0 315.1 315.1 320.2 320.2 325.0 324.9 329.4

0.05 0.03 0.02 0.02 0.01 0.00 0.05 0.03 0.04 0.03 0.07 0.06 0.04 0.02 0.03

335.00 340.00 340.00 345.00 345.00 350.00 350.00 355.00 355.00 357.87 357.94

329.3 333.7 333.7 338.4 338.3 343.0 342.9 347.1 347.0 349.1 349.1

0.05 0.11 0.14 0.03 0.05 0.06 0.03 0.08 0.04 0.01 0.02

a

u(T) = 0.05 K. Uc(Cp) = 0.01 Cp (0.95 level of confidence). Values are reported with one digit more than is justified by the experimental uncertainty to avoid round-off errors in calculations based on these results. c Data point for supercooled crystalline phase I. d Data point not included in fitting the data to Eq. (1) due to the premelting effect. b

Both solid and liquid heat capacities of cyclooctanol were measured by Sciesinski et al. [35] and by Rute et al. [36] but the data are presented in both cases only in a graphical form, thus not allowing the comparison with our measurements. 3.2. Phase behavior The phase behavior of cycloalcohols in the solid phase is rather complex and was extensively studied by adiabatic calorimetry as well as by other techniques for cyclopentanol (four crystalline phases found [24]), cyclohexanol (three crystalline phases [21]), and cycloheptanol (four crystalline phases [22,38]). On the other hand two rather different temperatures of melting are reported for cyclobutanol and though several sources reported melting and solid–solid transitions of cyclooctanol, there is an ambiguity in the literature data; these two compounds were reinvestigated in the frame of this study. Several experiments were performed with cyclobutanol which was cooled to 183 K by using different scanning rates (from 5 K min1 to 1 K min1), then heated to room temperature by 2 K min1. Non-reproducible exothermic peaks were observed, however after annealing the sample at 183 K for 80 min the peaks appeared at this constant temperature and the only heat effect observed upon heating was that corresponding to the enthalpy of melting. Three final measurements were performed and the I observed values and their standard deviations are DcrI Hm = 1 (7.91  0.04) kJ mol , TcrI ! l = (227.54  0.01) K. From our previous experience, we however estimate the uncertainty of 0.3 kJ mol1 for enthalpy and 0.1 K for temperature, respectively (level of confidence = 0.95). The temperature of fusion was determined as the onset of the fusion peak. The entropy of melting is 34.73 J K1 mol1 or 4.18R, substantially higher than for higher members of the family (cyclopentanol: 0.577R [24]; cyclohexanol: 0.717R [21]; cycloheptanol: 0.688R [22]; cyclooctanol: 0.801R [this work] (see Fig 4)). Dworkin et al. [39] reported a phase transition at 225 K and fusion at 228.4 K with the enthalpy change as a sum of transition and melting 8.53 kJ mol1. McGregor et al. [23] reported their DSC results in a graphical form and mentioned TcrI ! l = 221 K (neither the heat capacities nor the enthalpy of melting is given in [23]). Note that the phase transition near the melting temperature was not observed neither by McGregor et al. [23] nor in this work. In the case of cyclooctanol, five crystalline phases are reported in the literature, however the phases IV and V were reported at elevated pressures exceeding 100 MPa [37,40] and crystal phase III




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Table 3 Overview of the experimental heat capacities of cycloalcohols in the temperature range of the present study. Reference Cyclobutanol (liquid) McGregor et al. [23] This work – Cyclopentanol (liquid) Parks et al. [19] Conti et al. [27] Benson and D’Arcy [26] Kabo et al. [24] Dzida and Goralski [25] This work – Cyclohexanol (crystal I) Kelley [29] Adachi et al. [21] Mayer et al. [20] This work – Cyclohexanol (liquid) Hertz and Bloch[33] Kelley [29] Philip [34] Adachi et al. [21] Petit and Ter Minassian [31] Conti et al. [27] Cáceres-Alonso et al. [32] Mayer et al. [20] Rajagopal and Subrahmanyam [30] Steele et al. [10] This work – Cycloheptanol (cr I) Adachi et al. [22] Rute et al. [36] This work – Cycloheptanol (liquid) Adachi et al. [22] Conti et al. [27] Rute et al. [36] This work – Cyclooctanol (cr I) Andersson and Ross [37]h Sciesinski et al. [35] Rute et al. [36] This work – Cyclooctanol (liquid) Andersson and Ross [37]h Sciesinski et al. [35] Rute et al. [36] This work

Na

(Tmin  Tmax)/K

Uc/%b

Mole fraction purityc

Method

Gd 38

230.0–280.0 258.1–355.1

Nospe 1

0.995 0.9982f

DSC Tian–Calvet

5Sg 1 1 12 73 39

260.0–300.0 298.2 298.2 256.3–302.9 284.1–353.2 265.1–357.8

1.00 Nosp 0.3 0.4 0.15 1

0.998 Nosp 0.99 0.998 0.99 0.9993f

Isoperibol Tian–Calvet Flow (Picker) Adiabatic Tian–Calvet Tian–Calvet

5 11 S 8

260.4–280.0 267.8–297.9 245.0–297.0 261.4–270.0

0.5 Nosp Nosp 1

Nosp 0.99975 Nosp 0.9996f

Isoperibol Adiabatic Adiabatic Tian–Calvet

1 2 1 9 13 1 1 S 3 17 24

289.6 298.1–298.7 305.0 300.1–316.5 298.0–427.7 298.2 298.2 297.9–315.0 298.2–323.2 300.0–620.0 305.1–357.9

Nosp 0.5 Nosp Nosp 1.0 Nosp Nosp Nosp 0.3 1 1

Nosp Nosp Nosp 0.99975 0.99 Nosp Nosp Nosp Nosp 0.999 0.9996f

Isoperibol Isoperibol Isoperibol Adiabatic Tian–Calvet Tian–Calvet Flow (Picker) Adiabatic Adiabatic DSC Tian–Calvet

5 G 8

259.5–276.7 260.0–280.0 260.6–266.0

Nosp Nosp 1

0.99975 >0.99 0.9937f

Adiabatic DSC Tian–Calvet

8 1 G 31

283.2–316.1 298.2 285.0–290.0 286.1–357.8

Nosp Nosp Nosp 1

0.99932 Nosp >0.99 0.9937f

Adiabatic Tian–Calvet DSC Tian–Calvet

G G G 8

280.0–310.0 280.0–290.0 270.0–290.0 261.1–270.0

5 Nosp Nosp 1

0.99 0.99 >0.99 0.9925f

Hot wire Adiabatic DSC Tian–Calvet

G G G 26

325.0–350.0 296.0–300.0 300.0–310.0 301.9–357.9

5 Nosp Nosp 1

0.99 0.99 >0.99 0.9925f

Hot wire Adiabatic DSC Tian–Calvet

a

Number of data points. Uc stands for relative uncertainty in the heat capacity. Molar fraction except the water content, which is quantitatively specified only for measurements of this work (see Table 1) and for cyclopentanol [25] as a 1 104 (mass fraction). d Data presented in a graphical form only. e Nosp stands for not specified. f See Table 1. g Smoothed values. h Measurement at elevated pressure (70 MPa). b c

(Ttran = 220 K) was observed only by Andersson and Ross [37] at pressure 1.3 GPa, reportedly stable after relaxing pressure to 0.1 MPa. Though attempts were made to obtain phase III described in [37] at atmospheric pressure during glassy state investigation [35,36,41], the existence of crystal phase III was not confirmed, despite cooling the sample to T = 100 K. Adiabatic calorimetry has usually a smaller uncertainty than e.g. DSC, however Sciesinski et al. [35] admitted a possible presence of water in their sample. The phase behavior reported by Sciesinski et al. [35] differ

significantly from that reported by Rute et al. [36] or by Tyagi and Murphy [42]. Sciesinski et al. [35] reported a transition from supercooled crystal I to II at about 205 K and a sharp reproducible peak at 255 K (few kelvins below the TcrII ! crI), not observed by any other investigators. Rute et al. [36] and Tyagi and Murphy [42] reported a broad exothermic peak starting below 230 K, but the latter authors claimed this peak disappeared when the sample was annealed at 238 K. To clarify the situation, new DSC measurements were conducted in the frame of the present work. Cyclooctanol was




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Table 4 Parameters of Eq. (1). Compound

Phase

A1

A2

A3

A4

Tmin/K

Tmax/K

Sra

Cyclobutanol Cyclopentanol Cyclohexanol Cyclohexanol Cycloheptanol Cycloheptanol Cyclooctanol Cyclooctanol

Liquid Liquid Crystal I Liquid Crystal I Liquid Crystal I Liquid

65.1806 108.633 4.46374 33.9260 2.56655 55.5889 4.27473 38.0172

53.0410 100.485 9.19093 25.4525 9.99693 57.9475 12.4997 35.2424

17.2298 34.7206 0 1.87623 0 25.5962 0 3.60074

1.57602 3.61154 0 0 0 3.02776 0 0

258.09 256.33 261.10 300.10 260.59 283.20 261.10 301.94

355.09 357.78 270.00 357.94 266.00 357.82 270.00 357.94

0.018 0.021 0.034 0.042 0.014 0.011 0.025 0.012

a

Sr ¼ 100 

8 " # 91=2 calc 2 = n
i

cooled to 183 K using scanning rates from 5 K min1 to 1 K min1, resulting in supercooled crystal phase I (in accordance with [35,36,41], the crystal phase III was not observed during these experiments). Upon heating, the sample was transformed into phase II exhibiting a broad exothermic phase transition I ! II. The event was reproducible, though the reproducibility of the observed onset point temperature and enthalpy of transition was lower than crI 1 in the case of endothermic DcrII Hm and DcrI Hm events (see Table 5). 1 1 DcrI Hm Also (in contrast to endothermic DcrI crII Hm and DcrI Hm events), the temperature of this transition TscI ! crII was depended on heating rate used; at 2 K min1 it started around 224 K and ended at 244 K (see Fig. 5) while at 10 K min1 the event was shifted by about 10 K towards higher temperatures and at 1 K min1 by about 3.5 K towards lower temperatures. Further heating resulted in II ! I phase transition and melting (Table 5). When the sample was cooled again to 183 K, but a subsequent heating was stopped at 255 K and the resulting crystal phase II was cycled between 255 K and 183 K, no phase transition was detected. Heating from 255 K to 283 K produced a II ! I phase transition. Cycling between 270 K and 180 K resulted in exothermic I ! II and endothermic II ! I events, in good agreement with the results obtained by cooling liquid sample (and again rather reproducible). This behavior is exactly the same as reported by Rute et al. [36]. Disappearing of the exothermic II ! I peak reported by Tyagi and Murphy [42] is caused by (unnoticed) I ! II transition when the

[(Fig._2)TD$IG]

2

calc

100(Cp- Cp )/Cp

calc

[(Fig._1)TD$IG]

sample was annealed at 238 K (note a low purity and unknown water content of cyclooctanol in [42]). A sharp reproducible peak at 255 K reported by Sciesinski et al. [35] was not observed in this work and its origin remained unclear; its existence was attributed to presence of water in [35]. Also note a rather sharp onset of endothermic peaks in Fig. 5 for the dry sample, in contrast to statement in [35] “long tail on the low-temperature side (during melting) is not due to impurities, but is typical of plastic crystals”. Influence of water content was investigated experimentally in the present work. Indeed, both temperatures and enthalpies of phase transitions are rather sensitive to water content wH2 0 . We found that exposing a sample for a short time to atmospheric moisture during its handling prior to DSC experiments lead to the depression of TcrI ! l by more than 6 K. The results on the effect of water content on the phase behavior are summarized in Table 6 and Fig. 6 and compared to dry sample in Fig. 5. It should be noted that while TcrI ! l changes smoothly with the water content, TcrII ! crI is almost constant regardless the water content and about 7 K lower than TcrII ! crI for the dry sample. The crI 1 enthalpies DcrII Hm and DcrI Hm evolve more or less linearly with

calc

100(Cp- Cp )/Cp

calc

2

1

0

0

-1 TcrI→l = 299.09 K

-2

260

280

300

320

340

360

T/K

-1

-2

1

260

280

300

320

340

360

T/K Fig. 1. Relative deviations of the experimental heat capacities Cp from the smoothed values C calc obtained from Eq. (1) for cyclopentanol. [TD$INLE] this work, [TD$INLE] p Kabo et al. [24], [TD$INLE] Dzida and Góralski [25], (&) Parks et al. [19], (4) Benson and D’Arcy [26], () Conti et al. [27]. Data sets displayed in color were used in the development of parameters of Eq. (1). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

Fig. 2. Relative deviations of the experimental heat capacities Cp from the smoothed values C calc obtained from Eq. (1) for cyclohexanol. Crystalline p phase: [TD$INLE] this work, (f) this work (experimental points affected by premelting effect and excluded from the fit by Eq. (1)), (&) Adachi et al. [21], (......) Mayer et al. [20], [TD$INLE] Kelley [29]. Liquid phase: [TD$INLE] this work, [TD$INLE] Adachi et al. [21], [TD$INLE] Kelley [29], (~) Rajagopal and Subrahmanyam [30] (partially displayed), () Petit and Ter Minassian [31] (partially displayed), [TD$INLE] Caceres-Alonso et al. [32], [TD$INLE] Mayer et al. [20]; ($) Steele et al. [10]. Data reported by Conti et al. [27], Hertz and Bloch [33], Philip [34] are out of scale. Data sets displayed in color were used in the development of parameters of Eq. (1). TcrI ! l = 299.09 K is the fusion temperature reported by Adachi et al. [21]. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)




K. Ruži9 cka et al. / Thermochimica Acta 596 (2014) 98–108

104

[(Fig._3)TD$IG]

[(Fig._5)TD$IG]

2

calc

100(Cp- Cp )/Cp

calc

Heat Flow / W.g

1

0

-1

-2

260

280

300

320

340

crII

[(Fig._4)TD$IG]

4.2 (nC = 4) 0.8

l

0.7

0.6

7

220

8

240

260

280

300

T/K

wH2 0 . The exothermic DscI Hm as well as TscI ! crII does not exhibit any trend with wH2 0 . After finishing the study of phase transitions, the heat capacity measurements were performed at higher temperatures close to the expected temperature of normal boiling point with the aim to see at least qualitatively the evolution of the heat capacity with temperature. Most experiments were unsuccessful due to a leak of samples from the so-called hermetic aluminium pans. The results of a successful experiment during which no leakage of a sample was detected after two successive heatings from room temperature to 473 K arepresented in Fig. 7. As noted previously by a number of authors (e.g. in [41]), the absolute accuracy of heat-flux DSC is usually no better than 5% or even worse despite a careful calibration with recommended reference materials. The absolute scale of the heat capacity measured by DSC was therefore slightly adjusted to fit with the results of independent Tian–Calvet calorimetry with a superior accuracy, according to a common practice [13]. There is an obvious maximum at around 420 K, corresponding to the disintegration of H-bonded aggregates stable at lower

6

cr I → cr II

360

Fig. 3. Relative deviations of the experimental heat capacities Cp from the smoothed values C calc obtained from Eq. (1) for cycloheptanol. Crystalline phase: [TD$INLE] p this work, (f) this work (experimental points affected by premelting effect and excluded from the fit by Eq. (1)), (&) Adachi et al. [22]. Liquid phase: [TD$INLE] this work, [TD$INLE] Adachi et al. [22]. Data reported by Conti et al. [27] are out of scale. Data sets displayed in color were used in the development of parameters of Eq. (1). TcrI ! l = 280.30 K is the fusion temperature reported by Adachi et al. [22]. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

5

cr I → l

0.2

0.0

T/K

4

0.4

cr II → cr I

TcrI→l = 280.30 K

∆ crI S / R

endo

-1

0.6

Fig. 5. Effect of water content on the phase behavior of cycloocta nol. [TD$INLE] wH2 0 = 1 103%, [TD$INLE] the sample exposed to air (wH2 0  0.065% as estimated from depression of TcrI ! l), [TD$INLE] wH2 0 = 0.613%. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

temperatures. This behavior was confirmed by infrared spectroscopy as described in the next section. The sample leakage impaired similar measurements on more volatile cyclohexanol and cycloheptanol despite several attempts undertaken, however up to 450 K no maximum on the heat flow curve was observed. 3.3. Infrared spectroscopy Fig. 8 shows infrared spectrum in O—H stretching region of 1% (v/v) solution of cyclooctanol in CCl4 at 293 K. A sharp band centered at 3620 cm1 is assigned to O—H stretching from free OH groups (monomers). A broader weaker band centered at ca 3500 cm1 is due to OH groups associated in dimers and a broadest weakest band centered at ca 3350 cm1 can be assigned to OH associated in larger multimers. Obviously, the band from OH monomers dominates the spectrum of diluted solution. Fig. 9 shows infrared spectra of cyclohexanol, cycloheptanol, and cyclooctanol obtained at various temperatures. A strong temperature dependence of infrared spectrum of cyclooctanol is observed. Three bands resolved in the diluted solution of cyclooctanol in CCl4 (see Fig. 8) are present in the spectra. At 293 K the broad band centered at ca 3300 cm1 from larger multimers dominates in the spectrum. Temperature has a strong influence on the distribution of OH groups of cyclooctanol molecules among the multimers: with increasing temperature the distribution is shifted in favor of smaller multimers. This is reflected in the FTIR spectra shown in Fig. 9c; the band from dimers becomes stronger than that from larger multimers at T  393 K. At the highest temperature (473 K), the bands from monomers and dimers dominate the spectrum. The situation is rather different in the case of cyclohexanol (Fig. 9a), where the presence of monomers is negligible (the measurements at higher temperatures were unsuccessful due to evaporation of the sample). Recall that according to Steele et al. [10] the maximum on Csat vs. T is present at much higher temperature (480 K). Cycloheptanol (Fig. 9b) represents an intermediate state between the cyclohexanol and cyclooctanol with the apparent but nondominant presence of monomers and dimers.

9

nC / K Fig. 4. Dimensionless entropy of fusion DS/R as a function of a number of carbon atoms nC in the studied cycloalcohols. Odd–even effect can be observed also for 1 TcrI ! l and DcrI Hm .

3.4. General trends in liquid heat capacities of cyclic alcohols In Fig. 10, the comparison of molar and specific heat capacity for cyclobutanol, cyclopentanol, cyclohexanol, cycloheptanol, and cyclooctanol is shown. It can be seen that the liquid heat capacity




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105

Table 5 Overview of cyclooctanol phase transitions at atmospheric pressure obtained by calorimetry. Reference

TscI ! crII/K

Dworkin et al. [39] Edelmann and Würflinger [40] Sciesinski et al. [35] Tyagi and Murphy [42] Tyagi and Murphy [42] Rute et al. [36] this workh

a

Nosp Nosp >190 <230d Nospd <230e 224.6  0.5

1 TcrII ! crI/K DcrII scI Hm =kJ mol

1 TcrI ! l/K DcrI crII Hm =kJ mol

D1crI Hm =kJ mol1 Mole fraction purity Method

Nosp Nosp Nosp 1.3 Nosp Nospf 1.55  0.10

1.690 2.67 2.12  0.05 1.15 1.89 2.05 2.12  0.01

1.792 2.04 2.06  0.01 1.4 1.46 1.97 1.91  0.02

246.5 264.0  0.5 261.3 258.2 258.2 264.1 263.56  0.01

283.8 297.5  0.5 295.0 294e 294e 297.1 296.78  0.07

>0.99b 0.998c 0.99c 0.95c 0.95c >0.99g 0.9925b,i

DSC DTA Adiabatic DSC DSC DSC DSC

a

Nosp stands for not specified. Stored over molecular sieves. Neither water content nor drying mentioned. d Tyagi and Murphy [42] observed a broad exothermic I ! II phase transition for non-annealed sample only (see text). e TcrI ! l determined as a top of the peak instead as a peak onset. f Broad exothermic I ! II peak similar to that observed in this work was observed, but reported in a graphical form only. g Commercial sample purified by sublimation and crystallization, handled under dry Ar. h Values are tabulated as average of three measurements along with standard deviations; from our previous experience, we however estimate the uncertainty of 0.3 kJ mol1 for enthalpy and 0.1 K for temperature, respectively (level of confidence = 0.95). Values were determined at p = (100  5) kPa. i Water mass fraction 1.0  105 (see Table 1), handled in a dry box. b c

Table 6 Influence of water content on phase transitions of cyclooctanol at p = (100  5) kPa. Water mass fractiona 5

1.0  10 Exposed to moist air 1.41 103 2.71 103 3.81 103 5.05  103 6.13  103

TscI ! crII/K b

224.6  0.5 220.6  0.2 220.3  0.9 219.8  0.7 223.7  0.5 222.0  0.2 225.0  4.0

1 DcrII scI Hm =kJ mol

TcrII ! crI/K

1.55 1.74 1.72 1.73 1.70 1.75 1.60

263.56 257.0 255.9 255.4 255.8 255.7 255.7

      

0.10 0.05 0.04 0.05 0.11 0.04 0.10

      

1 DcrI crII Hm =kJ mol

0.01 0.1 0.1 0.3 0.1 0.1 0.2

2.12 1.98 2.19 2.44 2.75 3.05 3.19

      

0.01 0.01 0.03 0.04 0.01 0.02 0.01

TcrI ! l/K 296.78 290.4 281.3 275.6 271.0 267.8 265.9

      

DIcrI Hm =kJ mol1 0.07 0.1 0.9 0.3 0.3 0.1 0.5

1.91 1.61 1.45 1.09 0.82 0.57 0.36

      

0.02 0.01 0.10 0.02 0.02 0.01 0.02

a

Carl–Fischer analysis by Metrohm 831. Mean and standard deviation of four determinations for the dry sample and average of two determinations for the moist samples; these figures reflect rather reproducibility than uncertainty, which is estimated to be 0.1 K for temperatures and 0.3 kJ mol1 for enthalpies. b

3.5. Comparison with estimation methods for liquid heat capacity As reasoned in our previous paper [7], only two estimation methods [5,6], which are based on the same database of critically evaluated heat capacity data and provide comparable results

[(Fig._7)TD$IG]

(overall average relative uncertainty of both methods is 1.2%), are considered for comparison with our experimental results. These methods differ by definition of the group contributions and
structural corrections segments. While Zábranský and Ruži9 cka [5] utilized a second-order group contribution method with the notation introduced by Benson et al. [43], Kolská et al. [6] followed a three-level approach developed by Marrero and Gani [44]. Comparison is discouraging (Fig. 11), the deviation being comparable to the case of cyclohexylalcohols reported previously [7] and much higher than average relative uncertainty of both

[(Fig._6)TD$IG] 4

300

3.0

Ttran / K

2.8

-1 -1

cp / (J K g )

2.6

-1

290

∆tranHm / (kJ mol )

increases with molar weight as expected, however, when expressed as the specific heat capacity cp, there is an apparent difference between the lower and higher members of the series, which starts to diminish at higher temperatures.

3

280 2 270 1

260

2.4 250

2.2

300

350

400

450

500

T/K Fig. 7. Specific heat capacity of cyclooctanol. (*) Setaram mDSC IIIa, (adjusted; for numerical values see Table S1 in Supporting information).

]ENIL $DT[ TA Q1000

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0

wH 2O / % Fig. 6. Transition temperatures Ttran and enthalpies DtranHm as a function of water crI content wH2 0 in cyclooctanol samples. [TD$INLE] TcrII ! crI, [TD$INLE] DcrII Hm , [TD$INLE] 1 TcrI ! l, [TD$INLE] DcrI Hm . (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)




K. Ruži9 cka et al. / Thermochimica Acta 596 (2014) 98–108

106

[(Fig._8)TD$IG]

[(Fig._9)TD$IG] n=1

absorbance / a.u.

adsorbance / a.u.

(a)

n=2 3700

3600

3500

n >=3 3400

3300

3200

3100

3700

3000

3600

3500

3400

3300

3200

3100

wavenumber / cm

-1

wavenumber / cm

Fig. 8. ATR-FTIR spectrum in O—H stretching region of 1% (v/v) solution of cyclooctanol in dry CCl4. Bands from free OH groups (n = 1), OH groups associated in dimers (n = 2) and larger multimers (n  3) are resolved.

(b)

adsorbance / a.u.

estimation methods [5,6]. This failure of currently available estimation methods is logical as the above mentioned methodologies [43,44] do not include the complex influence of hydrogen bonding. It seems to be obvious that any traditional group-contribution method will be unsuccessful when applied for alcohols. This holds certainly true not only for heat capacities but for any other property influenced by H-bonding (densities, viscosities, vapor pressures, etc.)

3700

3600

4. Conclusion

3500

3400

3300

3200

wavenumber / cm

3100

3000

-1

(c)

absorbance / a.u.

The liquid molar heat capacities of five selected alcohols (cyclobutanol, cyclopentanol, cyclohexanol, cycloheptanol, and cyclooctanol) were measured using the Tian–Calvet calorimeter (Setaram mDSC IIIa) in the temperature range from 254 K to 352 K. The solid state heat capacities were also determined for cyclohexanol, cycloheptanol, and cyclooctanol as they exhibit the solid–liquid phase transition in the studied temperature range. For cyclobutanol and cyclooctanol, no literature data are available for comparison according to the authors’ knowledge. For the remaining three cycloalcohols, the data measured in this work represent the extension of the temperature range where reliable data are available (surprisingly, a high proportion of the literature calorimetric data was presented in a graphical form only). The temperature dependence of selected heat capacity values was represented by a polynomial equation. In contrast to values for the liquid phase, polynomials for heat capacity of solid phase (cyclohexanol, cycloheptanol, and cyclooctanol) should not be taken as a recommendation, as the nature of crystalline state is not known with certainty (see Supporting information). Above the melting point temperature, the heat capacities were monotonously increasing with temperature in the temperature range studied using the Tian–Calvet calorimetry, i.e. no maxima or minima were detected. Despite such a relatively simple behaviour, the estimation methods are not capable to yield the estimates with reasonable accuracy. Moreover, the DSC study of the least volatile compound (cyclooctanol) showed a maximum on the heat capacity curve at around 420 K, a phenomenon which is not captured by any estimation method. The change of a relative proportion of presumed aggregates in favor of lower ones with increasing temperature observed by infrared spectroscopic measurements is in agreement with the observed maximum on the temperature dependence of the heat capacity.

3000

-1

3700

3600

3500

3400

3300

3200

wavenumber / cm

3100

3000

-1

Fig. 9. ATR-FTIR spectra of cyclohexanol (a), cycloheptanol (b), and cyclooctanol (c) in O—H stretching region obtained at various temperatures. [TD$INLE] room temperature (298.15 K for cyclohexanol, 297.15 K for cycloheptanol, and 293.15 K for cyclooctanol), [TD$INLE] 313 K, [TD$INLE] 333 K, [TD$INLE] 353 K, [TD$INLE] 373 K, [TD$INLE] 393 K, [TD$INLE] 413 K, [TD$INLE] 433 K, [TD$INLE] 453 K, [TD$INLE] 473 K. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

For cyclobutanol and cyclooctanol, the phase transitions were investigated separately by the TA Q1000 calorimeter as nonconclusive data were found in the literature. The discrepancies in the literature data could be due to the presence of water; this influence was studied in detail for cyclooctanol. The calorimetric and spectroscopic measurements are being performed for another group of alcohols with the aim to better understand complex association behavior of alcohols.




K. Ruži9 cka et al. / Thermochimica Acta 596 (2014) 98–108

[(Fig._10)TD$IG]

Acknowledgements

(a)

300

Paulo B.P. Serra acknowledges financial support from Specific University Research (MSMT No. 20/2014). We thank M. Straka for performing preliminary measurements of heat capacities.

250

Appendix A. Supplementary data

200

Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.tca.2014.10.002.

150

References

-1

-1

Cp / (J K mol )

350

107

240

260

280

300

320

340

360

320

340

360

T/K (b)

-1 -1

cp / (J K g )

2.8

2.4

2.0

1.6 240

260

280

300

T/K Fig. 10. Molar (a) and specific (b) heat capacities of studied cycloalcohols. [TD$INLE] cyclobutanol, [TD$INLE] cyclopentanol, [TD$INLE] cyclohexanol. [TD$INLE] cycloheptanol, [TD$INLE] cyclooctanol. Values are calculated by Eq. (1) with parameters from Table 4. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

[(Fig._1)TD$IG]

5

calc

100(Cp -Cp )/Cp

calc

10

est

0 -5 -10 -15

260

280

300

320

340

360

T/K Fig. 11. Relative deviations of the liquid heat capacity estimated by the methods
Zábranský and Ru ži9 cka [5] and Kolská et al. [6] C est from the smoothed data of p this work C calc (calculated by Eq. (1) with the parameters from Table 4). p [TD$INLE] cyclobutanol [5], [TD$INLE] cyclobutanol [6], [TD$INLE] cyclopentanol [5], [TD$INLE] cyclopentanol [6], [TD$INLE] cyclohexanol [5], [TD$INLE] cyclohexanol [6], [TD$INLE] cycloheptanol [5], [TD$INLE] cycloheptanol [6], [TD$INLE] cyclooctanol [5], [TD$INLE] cyclooctanol [6]. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)




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