Partial Molar Isentropic Compressions of Selected Cyclic Ethers at

Article pubs.acs.org/jced

Partial Molar Isentropic Compressions of Selected Cyclic Ethers at Infinite Dilution in Water at Temperatures T = (278 to 318) K and Atmospheric Pressure Ivan Cibulka* Department of Physical Chemistry, Institute of Chemical Technology, Technická 5, 166 28 Prague, Czech Republic ABSTRACT: Speed of sound data for dilute aqueous solutions of five cyclic ethers (oxolane, 1,3-dioxolane, oxane, 1,4-dioxane, 1,3,5-trioxane) were obtained using the Anton Paar DSA 5000 sound analyzer in the temperature range from (278.15 to 318.15) K and at atmospheric pressure. Using previously published density data standard molar isentropic compressions were calculated and mutually compared from the point of view of molecular structures. Group contributions were also evaluated and discussed.

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INTRODUCTION Within our systematic study of volumetric properties of various organic solutes in dilute aqueous solutions partial molar volumes at infinite dilution (standard molar volumes) of a group of five cyclic ethers were investigated in ambient1 and extended2 ranges of state parameters. In the course of the measurements in the ambient range T = (278 to 318) K and at atmospheric pressure1 using the vibrating-tube densimeter and sound analyzer, DSA 5000, data on the speed of sound in dilute aqueous solutions of the ethers have been recorded but not published. Recently we have launched a study of acoustic and related properties of organic solutes in dilute aqueous solutions.3−6 The present paper is a contribution to this study. While our previous investigations of acoustic properties concerned solutes derived from aliphatic open chain hydrocarbons, here we present data for the homologous series of solutes comprising one saturated cycle with one or more oxygen heteroatoms.

Table 1. Specifications of Chemical Samples of Solutes. All Samples Were Used as Supplied formula

CAS RN

supplier

C4H8O

109-99-9

C3H6O2

646-06-0

Sigma Aldrich Fluka

C5H10O

142-68-7

C4H8O2

123-91-1

C3H6O3

110-88-3

Sigma Aldrich Sigma Aldrich Sigma Aldrich

> 0.99 > 0.99 0.99b 0.995c > 0.99

a

Declared by the supplier. bAnhydrous. cSupplied over molecular sieve.

the air-bubbles formation had no observable effect was 318 K. All controls, adjustments, and checks were done using manufacturer’s software installed in the device. A computer connected to the densimeter enabled us to read the raw data from the device memory and to perform the consequent evaluation. The experimental procedure is described in detail in one of our previous papers.4 Measurements were performed in an isothermal mode; that is, the measurements of all prepared solution were done at the same particular temperature, then the temperature was changed and the measurements were repeated. Several vials filled with air-saturated pure water were included and distributed in the measured sample set. The samples of water preceded and followed each set of solutions of a particular solute, that is, each set of solutions was “bracketed” by pure water. Reproducibility of these doubled measurements

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EXPERIMENTAL SECTION The specifications of the organic solutes are summarized in Table 1. They were used as obtained from the supplier. Distilled, demineralized (Millipore RQ) water was used as a calibration fluid for the densimeter and for the preparation of solutions. Solutions were prepared by mass using a Precisa 40SM-200A balance (resolution = 10−2 mg, uncertainty = ± 0.1 mg, maximum load 200 g) to determine the mass of the solute and a Precisa 2200C SCS balance (resolution = 10 mg, estimated uncertainty = ± 2·10−2 percent, maximum load, 2.1 kg) to determine the mass of water. The mass of each prepared solution was about 1 kg. Air-saturated water was used for preparation of solutions. The measurements were performed using the sound analyzer incorporated in the Anton Paar device, model DSA 5000, equipped with the autosampler SP-1m (Anton Paar; carousel with 24 vials, 55 cm3 each). The highest temperature at which © 2013 American Chemical Society

chemical name oxolane (tetrahydrofuran, oxacyclopentane) 1,3-dioxolane (1,3dioxacyclopentane) oxane (tetrahydropyran, oxacyclohexane) 1,4-dioxane (1,4dioxacyclohexane) 1,3,5-trioxane (1,3,5trioxacyclohexane)

mass fraction puritya

Received: January 11, 2013 Accepted: March 20, 2013 Published: April 4, 2013 1249

dx.doi.org/10.1021/je301352v | J. Chem. Eng. Data 2013, 58, 1249−1254

Journal of Chemical & Engineering Data

Article

of speed of sound in water was between ± 0.03 m·s−1 at 278.15 K and ± 0.06 m·s−1 at 298.15 K; a significantly larger scatter ± 0.2 m·s−1 was observed at 318.15 K (it is likely that sound waves caused the generation of air microbubbles in the samples). Since values measured for pure water differed slightly from data tabulated by NIST7 (for details see ref 4) the measured differences Δc = c − c1 where c is the speed of sound in the solution and c1 in water (average value obtained from the “bracketing” measurements), respectively, were regarded as direct experimental data. Similarly the differences Δρ = ρ − ρ1 were evaluated from density measurements.1 The values c1(NIST) and ρ1(NIST) were then used for the calculations of speeds of sound, c = Δc(experimental) + c1(NIST), and densities, ρ = Δρ(experimental) + ρ1(NIST), of solutions used for the evaluations of standard molar isentropic compressions (see below). The values c1 and ρ1 extracted from the NIST database7 are summarized in Table 2.

where Vapp m,2 is the apparent molar volume and m2 is the molality of the solute. Based on this definition it is possible to derive3,4 the expression for standard molar isentropic compression KS0,m,2 =

ρ1/kg·m−3

c1/m·s−1

278.15 283.15 288.15 293.15 298.15 308.15 318.15

999.967 999.702 999.103 998.207 997.048 994.033 990.213

1426.17 1447.27 1465.93 1482.35 1496.70 1519.85 1536.45

(ρc)2 − (ρ1c1)2 Δ[(ρc)2 ] = = aK + bK m2 m2 m2

(3)

The values of the coefficients aK,bK were obtained from measured data (Table 3) by using a least-squares method with unit weights and are recorded in Table 4 along with calculated values of K0S,m,2. Uncertainties σ(K0S,m,2) are affected mainly by the uncertainty in the speed of sound which was estimated to be about ± 0.2 m·s−1 at temperatures from (278 to 298) K and ± 0.4 m·s−1 at 318 K.

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DISCUSSION Comparison with Published Data. There is a plenty of data on acoustic properties of binary mixtures (cyclic ether + water) published in the literature. Unfortunately most of them provide values in concentrated region, often in the graphical form only, and thus such data are not suitable for the reliable evaluation of standard molar isentropic compression. The only data on speed of sound in the diluted range found in the literature are those measured by Kiyohara et al.8 for aqueous oxolane at T = 298.15 K. Average deviation between their values of Δc = c − c1 and those measured in this work in the molality range up to 0.3 mol·kg−1 is 0.1 m·s−1 (evaluated from the linear fits of experimental values, c(m2)) which can be regarded as a good agreement. On the other hand, the densities calculated by Kiyohara et al.8 from densities of pure liquid components and the fit of excess volume using the expansion in powers of (1−x)1/2 deviate significantly from our data (analysis was performed using the plot of (ρ − ρ1)/m2 vs m2). Consequently the plot of Δ[(ρc)2] vs m2 exhibits the maximum at about m2 = 0.4 mol·kg−1. Standard molar isentropic compressions evaluated using the method described above (eqs 2 and 3) are 8.3 cm3·mol−1·GPa−1 for data in the molality range up to 0.4 mol·kg−1 and 5.3 cm3·mol−1·GPa−1 for the molality range from (0.4 to 4) mol·kg−1. Our experimental value K0S,m,2 = 6.3 cm3·mol−1·GPa−1 is between these two values and close to the average 6.8 cm3·mol−1·GPa−1. Other relevant data found in the literature are the data measured in the region of higher concentrations of solutes and consequently the extrapolated values are rather unreliable. Dhondge and Ramesh9 presented extrapolated values of standard molar isentropic compression of aqueous oxolane and 1,4-dioxane in the temperature range from (274.15 to 298.15) K. Direct experimental data are reported for T = 279.15 K with the lowest molalities m2 = 2.68 mol·kg−1 and m2 = 1.02 mol·kg−1 for oxolane and 1,4-dioxane, respectively. The values are compared in Table 5. Obviously the deviations between our values and those by Dhondge and Ramesh9 decrease with increasing temperature and the agreement becomes satisfactory at temperatures around 298.15 K. The extrapolation method is, however, unclear. Surprisingly, if the direct experimental data9 at T = 279.15 K in the molality ranges up to 13 mol·kg−1 (aqueous oxolane, three experimental data

Two significant difficulties were encountered during the measurements. First, some of the solutes are rather volatile (oxolane, oxane) and thus, to avoid a larger vapor space in the storage flasks, only limited amounts of the prepared solutions were consumed for the measurements.1 Consequently a limited number of data points were obtained. Second, since the ultrasound passing through the solution initiates the formation of bubbles of the air dissolved in the solutions, many measured values of speed of sound were wrong, evidently because of air bubbles. It is likely that the solubility of air in the solutions is lower than that in pure water. This particularly concerns the solutions of 1,3,5-trioxane; the formation of air bubbles made the measurements nearly impossible. Insertion of the vials with freshly degassed water between the samples on the carousel helped to solve this problem (for details see ref 1).

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RESULTS Direct Experimental Data. The measured values of the differences in speed of sound Δc = c − c1 where c and c1 are the speeds of sound in the solution and water, respectively, along with the molalities of organic solutes m2 are recorded in Table 3. Related values of experimental differences in density Δρ = ρ − ρ1 already published1 are recorded in the table, as well. Standard Molar Isentropic Compressions. Partial molar isentropic compression at infinite dilution (standard molar isentropic compression) of the solute 2 is defined as a limiting value of the derivative of standard molar volume Vom,2 with respect to pressure at constant entropy app ⎞ ⎛ ∂V 0 ⎞ ⎛ −∂V m,2 m,2 ⎟⎟ KS0,m,2 = lim ⎜ ⎟ = −⎜⎜ m2 → 0⎝ ∂p ⎠ ⎝ ∂p ⎠S S

(2)

where aK is the adjustable parameter of the fit of experimental values of the differences Δ[(ρc)2] = (ρc)2 − (ρ1c1)2 in the form

Table 2. Values of Density ρ1 and Speed of Sound c1 in Water (NIST)7 Used in Calculations of Standard Molar Isentropic Compression T/K

aK ⎞ 1 ⎛ ⎜ ⎟⎟ M − 2 ⎜ (ρ1c1)2 ⎝ (ρ1c1)2 ⎠

(1) 1250



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Table 3. Experimental Differences in Densitya Δρ = ρ − ρ1 and Speed of Sound Δc = c − c1 Measured for {Oxolane(2) or 1,3Dioxolane(2) or Oxane(2) or 1,4-Dioxane(2), or 1,3,5-Trioxane(2) + Water(1)} at Atmospheric Pressure T = 278.15 K

T = 283.15 K

T = 288.15 K

T = 293.15 K

T = 298.15 K

m2

Δρ

Δc

Δρ

Δc

Δρ

Δc

Δρ

Δc

Δρ

Δc

m2b

Δρ

Δc

mol·kg−1

kg·m−3

m·s−1

kg·m−3

m·s−1

kg·m−3

m·s−1

kg·m−3

m·s−1

kg·m−3

m·s−1

mol·kg−1

kg·m−3

m·s−1

0.098044 0.166969 0.211230 0.279105 0.333696

−0.333 7.44 −0.545 12.61 −0.671 15.91 −0.841 20.94 −0.986 24.91 T = 278.15 K

−0.360 −0.595 −0.737 −0.929 −1.096 T = 283.15

6.78 11.45 14.48 18.99 22.61 K

−0.434 −0.722 −0.904 −1.160 −1.370 = 298.15 K

4.88 8.24 10.40 13.60 16.15

0.101272 0.150387 0.198708 0.243885 0.304335 T = 308.15 K

−0.387 −0.640 −0.794 −1.012 −1.192 T = 288.15

Oxolane (aq) 6.06 −0.410 5.49 10.29 −0.681 9.27 12.91 −0.849 11.64 16.98 −1.084 15.22 20.16 −1.282 18.08 K T = 293.15 K T

T = 318.15 K

−0.538 2.97 −0.796 4.40 −1.029 5.79 −1.254 7.08 −1.546 8.79 T = 318.15 K

m2

Δρ

Δc

Δρ

Δc

Δρ

Δc

Δρ

Δc

Δρ

Δc

Δρ

Δc

Δρ

Δc

mol·kg−1

kg·m−3

m·s−1

kg·m−3

m·s−1

kg·m−3

m·s−1

kg·m−3

m·s−1

kg·m−3

m·s−1

kg·m−3

m·s−1

kg·m−3

m·s−1

0.059817 0.112042 0.214998 0.316063 0.404999

0.642 1.200 2.294 3.361 4.290

3.35 6.21 11.73 17.00 21.50

0.610 1.139 2.176 3.181 4.055

2.93 5.42 10.24 14.88 18.87

0.578 1.082 2.065 3.021 3.851

2.33 4.24 7.89 11.13 14.15

0.529 0.986 1.879 2.743 3.494

1.99 3.66 6.84 9.77 12.12

0.446 0.829 1.577 2.297 2.922

0.92 1.61 3.08 4.27 5.34

0.051464 0.096776 0.145553 0.193657 0.241570

−0.207 −0.375 −0.542 −0.695 −0.834

5.05 9.46 14.18 18.68 23.16

−0.224 −0.409

4.61 8.58

−0.268 −0.495 −0.731 −0.952 −1.168

3.39 6.31 9.44 12.38 15.37

2.08 3.86 5.74

16.87 20.90

3.78 7.06 10.42 13.77 17.11

−0.317 −0.606 −0.901

−0.768 −0.928

−0.240 −0.440 −0.644 −0.832 −1.013

−1.432

9.46

0.080683 0.080683 0.171566 0.171566 0.242335 0.242335 0.321746 0.321746 0.399113 0.399113

0.746

5.21

3.60

0.592

3.15

0.489

1.72

10.92 10.94 15.30 15.30 20.08 20.06 24.64 24.58

4.55 4.61 9.63 9.60 13.56 13.45 17.85 17.67 21.90 21.75

0.658

1.579 1.579 2.226 2.225 2.945 2.945 3.641 3.641

0.700 0.700 1.483 1.480 2.087 2.085 2.760 2.758 3.412 3.409

1.252 1.251 1.762 1.761 2.326 2.326 2.873 2.873

6.60 6.59 9.20 9.19 12.08 12.06 14.78 14.77

0.049773 0.049773 0.109562 0.109562 0.207301 0.207301 0.303121 0.303121 0.401402 0.401402 0.401402 0.401402

1.138 1.138 2.497 2.495 4.691 4.687 6.813 6.811 8.960 8.956

3.13 3.00 6.61 6.45 12.16 11.96 17.25 16.97 22.38 22.35

1.104 1.104 2.422 2.420 4.550 4.546 6.607 6.606 8.694 8.693 8.690 8.690

2.67 2.69 5.70 5.71 10.53 10.53 15.07 15.09 19.56 19.47 19.65 19.65

1.023 1.019 2.233 2.239 4.208

1.75 1.76 3.77 3.90 7.26

6.105 6.091 8.027 8.022

9.85 10.06 12.96 12.99

1,3-Dioxolane (aq) 2.60 0.552 4.81 1.029 9.01 1.966 13.02 2.875 16.43 3.666 Oxane (aq) 4.16 −0.253 7.78 −0.467 11.57 −0.687 15.28 −0.893 18.87 −1.092 1,4-Dioxane (aq) 4.10 0.624

1.393

8.55

1.316

7.48

1.964

12.00

1.856

10.45

2.591

15.64

2.450

13.71

3.209

19.26

3.032

16.88

1.075 1.074 2.352 2.354 4.421 4.423 6.427 6.426 8.450 8.450

1,3,5-Trioxane (aq) 2.50 1.047 2.03 2.48 1.046 2.04 5.24 2.295 4.34 5.16 2.294 4.36 9.45 4.309 8.03 9.40 13.45 6.257 11.51 13.40 17.41 8.230 14.98 17.35 8.229 14.85

1.135

4.85

1.036

3.53

1.598

6.82

1.451

4.94

2.107

8.96

2.597

10.98

2.353

7.88

2.045

1.83

3.844

3.32

5.582

4.72

7.317

6.07

Values of Δρ were taken from data published in ref 1. Standard uncertainties are u(T) = 0.01 K, u(m2) = 3·10−5 mol·kg−1, and the combined expanded uncertainty is Uc(Δρ) = 3·10−3 kg·m−3 and Uc(Δc) = 0.4 m·s−1 at T = 318.15 K, and Uc(Δc) = 0.2 m·s−1 at lower temperatures (level of confidence = 0.95). bSolutions with different composition were measured for oxolane at T = 318.15 K. a

points) and 5.9 mol·kg−1 (aqueous 1,4-dioxane, four experimental data points) were treated using the method described above (eq 3 with the quadratic term was used for oxolane) the values of standard molar isentropic compression were obtained that significantly differ from those presented in the paper9 but are in slightly better agreement with the values measured in this work.

0 Rajashekar et al. 10 reported the value K S,m,2 = 10 3 −1 −1 cm ·mol ·GPa for aqueous 1,4-dioxane at T = 303.15 K. This value is by 3 cm3·mol−1·GPa−1 lower than our value (K0S,m,2 = 13.1 cm3·mol−1·GPa−1) obtained using the second-order polynomial fitted to our data in the experimental temperature range. The extrapolation method employed in this work (eqs 2 and 3) applied to the data10 in the molality range up to 13.6

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Table 4. Coefficients aK, and bK of eq 3, and Standard Molar Isentropic Compressions K0S,m,2, for {Oxolane(2) or 1,3Dioxolane(2) or Oxane(2) or 1,4-Dioxane(2), or 1,3,5-Trioxane(2) + Water(1)}. The Uncertainties σ(K0S,m,2) Represent the Combined Expanded Uncertainties aK·10−12

T K

−4 −2

bK·10−10 −1

kg ·m ·s ·mol 3

−4 −2

K0S,m,2 ± σ(K0S,m,2) −2

kg ·m ·s ·mol 4

278.15 283.15 288.15 293.15 298.15 318.15

0.2033 0.1854 0.1652 0.1488 0.1296 0.0636

278.15 283.15 288.15 293.15 298.15 318.15

0.2651 0.2425 0.2185 0.1970 0.1741 0.0927

Oxolane (aq) −0.225 −0.609 −0.832 −1.505 −1.007 −0.100 Oxane (aq) −1.528 −2.968 −2.766 −3.158 −2.491 −1.240

278.15 283.15 288.15 293.15 298.15 318.15

0.2697 0.2493 0.2394 0.2140 0.1989 0.1400

1,3,5-Trioxane (aq) −4.192 −3.527 −5.155 −2.966 −2.785 −2.043

−1

aK·10−12

T

−1

cm ·mol ·GPa 3

K

−4 −2

bK·10−10 −1

kg ·m ·s ·mol 3

−13.7 −7.9 −2.3 1.9 6.3 19.3

± ± ± ± ± ±

0.4 0.4 0.4 0.4 0.4 1.0

278.15 283.15 288.15 293.15 298.15 318.15

0.2047 0.1853 0.1701 0.1569 0.1403 0.0815

−21.8 −14.2 −7.3 −1.8 3.6 19.9

± ± ± ± ± ±

0.7 0.7 0.7 0.6 0.6 1.2

278.15 283.15 288.15 293.15 298.15 308.15 318.15

0.2240 0.2021 0.1856 0.1670 0.1506 0.1176 0.0936

−20.9 −13.9 −10.0 −3.5 0.3 12.8

± ± ± ± ± ±

0.6 0.6 0.6 0.6 0.6 0.8

−4 −2

K0S,m,2 ± σ(K0S,m,2) −2

kg ·m ·s ·mol 4

1,3-Dioxolane (aq) −1.914 −1.661 −2.247 −3.382 −2.822 −1.956 1,4-Dioxane (aq) −2.038 −1.438 −2.065 −1.939 −1.778 −1.054 −1.557

cm3·mol−1·GPa−1 −13.1 −6.9 −2.4 1.1 5.0 16.8

± ± ± ± ± ±

0.6 0.5 0.5 0.5 0.5 0.9

−10.8 −4.0 0.8 5.4 9.2 16.0 20.6

± ± ± ± ± ± ±

0.4 0.4 0.4 0.4 0.4 0.4 0.7

Table 5. Comparison of Measured Values of Standard Molar Isentropic Compression at p = 0.1 MPa with the Values Reported by Dhondge and Ramesh9 oxolane

1,4-dioxane

KoS,m,2/cm3·mol−1·GPa−1

KoS,m,2/cm3·mol−1·GPa−1

T/K

ref 9

this work

ref 9

this work

274.15 277.15 279.15

−10.0 −9.0 −8.0 −16.4b −7.0 −5.5 7.7

−18.4a −14.7a −12.4a

−4.5 −3.5 −3.0 −10.4b −2.5 −1.5 9.3

−15.5a −11.6a −9.2a

281.15 283.15 298.15

−10.1a −7.9 6.3

−6.9a −4.0 9.2

a

Obtained by the extrapolation/interpolation using the second order polynomial fitted to the measured values in the experimental temperature range. bEvaluated by the present method (for details see text). Figure 1. Plot of experimental standard molar isentropic compressions K0S,m,2 against temperature T. The lines are to aid the eye. Full lines, five member cycles; dashed lines, six member cycles: ●, oxolane; ○, 1,3-dioxolane; ■, oxane; □, 1,4-dioxane; ▲, 1,3,5-trioxane.

mol·kg−1 (four experimental data points) yielded K0S,m,2 = 16 cm3·mol−1·GPa−1. Dependences of Standard Isentropic Compression on Temperature. Experimental values of standard isentropic compression of aqueous cyclic ethers are plotted against temperature in Figure 1. Obviously the magnitudes of standard molar isentropic compressions are similar, likely due to similar sizes of solute molecules. It can be, however, seen that the slopes of the dependences are related to the ratio between hydrophilic (oxygen) and hydrophobic (methylene groups) parts of the solute molecule. Less hydrophilic solutes exhibit larger slope as can be clearly observed on pairs 1,3-dioxolane/ oxolane and 1,4-dioxane/oxane. It seems likely that this behavior is the general one as it is observed for some other

classes of aqueous solutes (polyols derived from propane,4 branched aliphatic alcohols5). Group Contributions. Present data make possible to evaluate the group contributions to the standard molar isentropic compression. Group additivity scheme analogical to that proposed for standard molar volumes1,2 leads to the formula (KS0,m,2)calc = KS0,m,c + nKS0,m,CH2 + mKS0,m,O + kKS0,m,(OCO) (4) 1252



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The first term on the right-hand side of the formula is the derivative of so-called covolume with respect to pressure at constant entropy (for a detailed discussion of the covolume see, for example, ref 11). Other terms are related to the methylene group (−CH2−), ether-oxygen atom (−O−), and the structure where two oxygen atoms are in the close vicinity, that is, separated by one methylene group only (−O−C−O−). Respective integers n, m, and k are numbers of the groups/ structures in the solute molecule. Experimental data obtained in this work enable us to evaluate all contributions in eq 4:

Group contributions enable us to predict the standard molar isentropic compression of aqueous 1,3,5-trioxane. Figure 3

KS0,m,CH2 = KS0,m,2(oxane) − KS0,m,2(oxolane)

KS0,m,O = KS0,m,2(1,4‐dioxane) − KS0,m,2(oxolane)

KS0,m,c = KS0,m,2(oxolane) − 4KS0,m,CH2 − KS0,m,O = KS0,m,2(oxane) − 5KS0,m,CH2 − KS0,m,O = KS0,m,2(1,4‐dioxane) − 4KS0,m,CH2 − 2KS0,m,O

and KS0,m,(OCO) = KS0,m,2(1,3‐dioxolane) − 3KS0,m,CH2 − 2KS0,m,O

Figure 3. Comparison of the experimental and predicted values of o of aqueous 1,3,5standard molar isentropic compression KS,m,2 trioxane. The lines are to aid the eye: ▲, experimental (this work); ●, predicted with k = 0; ○, predicted with k = 3.

− KS0,m,c

The plot of the contributions against temperature is shown in Figure 2. The line that represents smoothed values evaluated

presents a comparison of the experimental values with those calculated using the group contribution scheme. Two sets of predicted values are shown in the figure: those without the inclusion of the structural contribution (−O−C−O−), i.e., k = 0 in eq 4, and those that include three structures (−O−C− O−), i.e., k = 3. Obviously, the latter predictions are more close to the experiment but it is clear that three neighboring structures (−O−C−O−) mutually interact and the effect of three structures (−O−C−O−) is overestimated. The optimum value is noninteger k = 2.14 for which the root-mean-square deviation between predicted and experimental values over the entire experimental temperature range reaches its minimum 1.05 cm3·mol−1·GPa−1.

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CONCLUSIONS New data on speed of sound were reported for five aqueous cyclic ethers in dilute region and standard molar isentropic compressions were evaluated. The analysis of the results showed the behavior observed for other classes of aqueous solutes in respect to the hydrophilic/hydrophobic ratio. Group contributions were evaluated using data for four cyclic ethers and tentatively employed for the prediction of the standard molar isentropic compression of 1,3,5-trioxane. A verification of the group additivity scheme requires, however, additional data for other selected cyclic ethers, preferably for those with larger cycles.

Figure 2. Plot of the group and structural contributions KoS,m,group to the standard molar isentropic compression against temperature T. The lines are to aid the eye: ○, covolume; ●, −CH2−; ▲, −O−; Δ, structural (−O−C−O−); dashed line represents the smoothed values evaluated for the group −CH2− from data by Høiland12,13 and Nakajima.14

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AUTHOR INFORMATION

Corresponding Author

*Tel.: +420 220444063. E-mail: [email protected].

for the methylene group from data found in the literature for open-chain aliphatic 1- and 2-alkanols and α,ω-alkanediols12−14 is plotted in the figure for a comparison. Obviously the values obtained from cyclic solutes are close to those for open-chain solutes, however, the contributions of the methylene group incorporated in the cycle are systematically lower.

Funding

Support from the Ministry of Education, Youth and Sports of the Czech Republic (fund MSM6046137307) is acknowledged. Notes

The authors declare no competing financial interest. 1253



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Partial Molar Isentropic Compressions of Selected Cyclic Ethers at

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