Density, Speed of Sound, Refractive Index, and Viscosity of the

Article pubs.acs.org/jced

Density, Speed of Sound, Refractive Index, and Viscosity of the Binary Mixtures of N,N‑dimethylacetamide with Methanol and Ethanol Sahar Mrad,† Carlos Lafuente,‡ Monia Hichri,*,† and Ismail Khattech† ‡

Departamento de Química Física, Facultad de Ciencias, Universidad de Zaragoza, 50009 Zaragoza, Spain Université de Tunis EL Manar, Faculté de Sciences, Département de Chimie, Laboratoire des Matériaux, Crystallochimie et Thermodynamique Appliquée, LR15ES01, 2092 Tunis, Tunisia

†

S Supporting Information *

ABSTRACT: The thermophysical behavior of the binary mixtures N,Ndimethylacetamide + methanol and N,N-dimethylacetamide + ethanol has been studied through the measurement of density, ρ, speed of sound, u, refractive index, nD, and kinematic viscosity, ν, over the entire mole fraction range at the temperatures of 283.15, 298.15 and 313.15 K and at p = 99.0 kPa. Excess volumes, VE, excess isentropic compressibilities,κES , refractive index deviations, ΔnD, and viscosity deviations, Δη, were also calculated and correlated with the Redlich−Kister equation. Both systems present negative excess volumes and excess isentropic compressibilities and positive refractive index deviations in the whole composition range. The viscosity deviations are positive for N,N-dimethylacetamide + methanol and turn to negative for N,N-dimethylacetamide + ethanol. Moreover, both systems behave differently when temperature is raised. The experimental results were interpreted based on strength of specific interactions, size, and shape of molecules.

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INTRODUCTION Application in the fields of chemistry, biology, and industry in general requires an extensive use of liquid mixtures rather than pure liquids because they provide a wide range of desired properties. Therefore, it is interesting to study the variation of their thermophysical properties with several parameters. This enables the determination of deviation and excess properties of mixtures and gives useful information regarding the nature and strength of molecular interactions.1,2 N,N-dimethylacetamide, abbreviated as DMA, is commonly used as solvent in the adhesive industry and in chemical synthesis. It is a dipolar, aprotic solvent but practically unassociated.3,4 On the other hand, alcohols are polar liquids, strongly self-associated through hydrogen bonding.5,6 They enjoy wide industrial and scientific applications. Such mixtures have significance in theoretical and applied areas of research, because amides are a convenient model for investigating peptide and protein interactions.7−10 A review of literature shows that there are some papers reporting thermophysical properties of the two systems under study, such as excess volumes11 at 313.15 K or excess enthalpies12,13 or both,14 densities and viscosities at 303.15 K,15 and densities, refractive indices, and relative permittivities at 298.15 K.16 On the other hand, there is also a work reporting densities and viscosities of the mixture N,N-dimethylacetamide + ethanol17 and finally a study of the vapor−liquid equilibrium of N,N-dimethylacetamide + methanol.18 © XXXX American Chemical Society

In order to obtain more thermophysical information about these mixtures, measurements of densities, ρ, refractive indices, nD, speeds of sound, u, and kinematic viscosities, ν, were carried out at three temperatures 283.15, 298.15, and 313.15 K and at p = 99.0 kPa. From these data, excess volumes VE, excess isentropic compressibilities κES , refractive index deviations ΔnD, and viscosity deviations, Δη, were calculated and correlated as a function of mole fraction of DMA. The behavior of these functions with composition and temperature has been used to explain the nature of the interactions between the components of the mixture.

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EXPERIMENTAL SECTION

The provenance and purity grade along with the water content of chemicals used in this work are given in Table 1. To determine the water content of these compounds an automatic titrator Crison KF 1S-2B has been used. The experimental values of density, speed of sound, refractive index, and dynamic viscosity of the pure compounds at working temperatures and at p = 99.0 kPa are collected in Table 2. In this table, the corresponding literature values at T = 298.15 K are also reported for comparison.19−34 Received: November 24, 2015 Accepted: June 27, 2016

A

DOI: 10.1021/acs.jced.5b01000 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

Article

thermostat controls the temperature of the sample within ±0.01 K. The uncertainties of both kinematic and dynamic viscosity determinations were estimated to be 0.01 mm2·s−1 and 0.01 mPa·s respectively. Details of calibration of these devices can be found in previous papers.35,36

Table 1. Provenance and Purity of the Liquid Components chemical name

source

N,Ndimethylacetamide methanol

SigmaAldrich SigmaAldrich Acros

ethanol

purity/mass fraction

analysis method

water content/ 106 w (H2O)

0.995

GC

315

0.998

GC

145

0.998

GC

133

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RESULTS AND DISCUSSION The values of density, speed of sound, isentropic compressibility, refractive index, and kinematic and dynamic viscosities have been reported in Table 3. Excess volume was calculated for the mixtures from density ρ measurements at each temperature using the following equation

Binary mixtures of different compositions were prepared by mass, just before the measurement to prevent any alteration in the composition. The samples were kept in airtight stopper glass vials to avoid evaporation. The weighing was done on a Sartorius semimicro balance CP225-D within ±1 × 10−5 g. Taking into account both the uncertainty in the mass determination and the water content of the pure compounds the final estimated uncertainty in the mole fraction was ±1 × 10−3. ρ and u measurements were performed simultaneously by an Anton Paar DSA 5000 densimeter and sound analyzer (operating at around 3 MHz), provided with automatic viscosity correction for density calculation. The temperature in the cell was regulated to ±0.005 K. The uncertainties of ρ and u measurements are, respectively, 0.2 kg·m−3 and 0.5 m·s−1. nD were measured at 589.3 nm sodium wavelength using an automatic refractometer Abbemat-HP DR. Kernchen with an uncertainty of 1 × 10−5. During measurement, the sample temperature is controlled by a Peltier device with a stability of ±0.002 K. Kinematic viscosity, ν, measurements were carried thanks to an Ubbelohde viscosimeter accompanied by a Schoot-Geräte AVS-440 automatic measuring unit, indicating the flow time t of the sample. At least three flow times were taken for each data, kinetic energy corrections were applied. Once density and kinematic viscosity were known, the absolute viscosity η could be calculated using η= ρ·ν. A Schoot-Geräte CT 1150/2

VE =

⎛1

∑ xiMi⎜⎜

⎝ρ

i

−

1⎞ ⎟⎟ ρi ⎠

(1)

where ρ is the density of the mixture and xi, Mi, and ρi are the mole fraction, the molar mass and density of component i, respectively. From experimental data of density and speed of sound, isentropic compressibility, κS, can be calculated, assuming that ultrasonic absorption is negligible using Laplace’s equation, κS = 1/ρu2. Excess isentropic compressibility can be determined according to the following relations

κSE = κS − κSid

(2)

where the ideal isentropic compressibility is given by the expression obtained by Benson and Kiyohara37 κSid =

⎡

∑ φi⎢κS,i + i

⎢⎣

(∑ φα )2 TVi αp,2 i ⎤ ⎥ − T (∑ xiVi ) i i p, i (∑i xiCp, i) Cp, i ⎥⎦ i (3)

with ϕi and xi being, respectively, the volume fraction and the mole faction of component i in the mixture, T is the

Table 2. Thermophysical Properties of Pure Compounds at Several Temperatures and at p = 99.0 kPa and Comparison of Densities, Speeds of Sound, Refractive Indices, and Dynamic Viscosities with Literature Data at T = 298.15 K and at Atmospheric Pressurea ρ/kg·m−3 T/K

exptl

283.15 298.15

950.13 936.29

313.15

922.43

283.15 298.15

800.71 786.61

313.15

772.31

283.15 298.15

797.88 785.06

313.15

772.50

u/m·s−1 lit

936.28b 936.34c

exptl 1516.80 1453.68 1393.35

786.64h 786.70i

1152.66 1104.23 1054.49

785.11h 785.5o

1194.51 1143.17 1092.44

η/mPa·s

nD lit

Cp/J·mol−1·K−1

N,N-Dimethylacetamide 170.70r d 1455.37 172.69r c 1455.91 175.46r Methanol 78.48s j 1104.30 81.01s 1104k 83.99s Ethanol 106.86s 1143h 112.28s 1143.07p 118.55s

αp/kK−1

exptl

0.9719 0.9863

1.442726 1.435794

1.0011

1.429006

1.1808 1.2019

1.332821 1.326357

1.2241

1.320130

1.0819 1.0995

1.365294 1.359130

1.1181

1.352755

lit

1.4356e 1.4359f

exptl 1.168 0.930

lit

0.920e 0.937g

0.764

1.32645l 1.32676m

0.677 0.545

0.545k 0.547n

0.444

1.35922l 1.3593q

1.444 1.079

1.082k 1.08p

0.824

a Standard uncertainties u are u(T) = 0.01 K, u(p) = 0.5 kPa, u(x1) = 0.0001, u(u) = 0.5 m·s−1, u(nD) = 1 × 10−5 and the relative expanded uncertainties Ur are Ur(ρ) = 2 × 10−4, Ur(η) = 0.01 with 0.95 level of confidence (k ≈ 2). bReference 19. cReference 20. dReference 21. eReference 22. fReference 23. gReference 24. hReference 25. iReference 26. jReference 27. kReference 28. lReference 29. mReference 30. nReference 31. o Reference 32. pReference 33. qReference 34. rReference 39. sReference 38.

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Table 3. Densities, ρ, Speeds of Sound, u, Isentropic Compressibilities, κS, Refractive Indices, nD, Kinematic Viscosities, ν, and Dynamic Viscosities, η, for the Binary Mixtures N,N-Dimethylacetamide (1) + Alkanol (2) at Several Temperatures and at p = 99.0 kPaa x1

ρ/kg·m−3

0.0000 0.0602 0.1088 0.2079 0.3040 0.4055 0.5011 0.6014 0.7036 0.8030 0.9076 0.9502 1.0000

800.71 823.33 838.65 864.15 883.51 899.79 912.04 922.61 931.65 938.69 945.18 947.54 950.13

0.0000 0.0602 0.1088 0.2079 0.3040 0.4055 0.5011 0.6014 0.7036 0.8030 0.9076 0.9502 1.0000

786.61 809.21 824.55 850.00 869.25 885.57 897.92 908.60 917.77 924.81 931.29 933.67 936.29

0.0000 0.0602 0.1088 0.2079 0.3040 0.4055 0.5011 0.6014 0.7036 0.8030 0.9076 0.9502 1.0000

772.31 794.82 810.12 835.56 854.87 871.24 883.68 894.46 903.69 910.89 917.39 919.78 922.43

0.0000 0.0524 0.1071 0.2064 0.3022 0.4057 0.5032 0.6016 0.7065 0.8013 0.9021 0.9529 1.0000

797.88 811.44 824.49 845.48 863.30 880.34 894.71 907.87 920.68 931.16 941.31 946.06 950.13

0.0000 0.0524

785.05 798.44

u/m·s−1

κS/TPa−1

nD

N,N-Dimethylacetamide (1) + methanol (2) T = 283.15 K 1152.66 939.99 1.332821 1204.42 837.28 1.348786 1241.96 773.04 1.359689 1305.60 678.88 1.378028 1353.44 617.89 1.392069 1393.97 571.94 1.404142 1424.83 540.08 1.413314 1450.44 515.21 1.421377 1473.13 494.62 1.428108 1489.18 480.38 1.433693 1505.03 467.09 1.438785 1510.66 462.46 1.440695 1516.80 457.47 1.442726 N,N-Dimethylacetamide (1) + methanol (2) T = 298.15 K 1104.23 1042.61 1.326357 1154.37 927.36 1.342296 1190.66 855.47 1.353187 1250.82 751.96 1.371425 1297.08 683.79 1.385361 1336.00 632.65 1.397369 1365.22 597.53 1.406519 1391.20 568.65 1.414584 1413.52 545.33 1.421314 1429.21 529.36 1.426840 1443.38 515.41 1.431865 1449.24 509.95 1.433783 1453.68 505.42 1.435794 N,N-Dimethylacetamide (1) + methanol (2) T = 313.15 K 1054.49 1164.46 1.320130 1103.11 1033.94 1.335981 1138.11 952.98 1.346800 1196.31 836.24 1.364941 1240.65 759.98 1.378810 1278.33 702.39 1.390754 1306.88 662.57 1.399868 1332.74 629.43 1.407910 1353.05 604.44 1.414597 1370.17 584.77 1.420135 1383.69 569.34 1.425113 1388.92 563.59 1.427006 1393.35 558.40 1.429006 N,N-Dimethylacetamide (1) + ethanol (2) T = 283.15 K 1194.51 878.38 1.365294 1225.32 820.81 1.372458 1254.56 770.60 1.379158 1297.97 702.05 1.390013 1334.90 650.04 1.399246 1369.58 605.59 1.408008 1399.52 570.64 1.415378 1427.29 540.69 1.421959 1454.04 513.74 1.428231 1476.50 492.62 1.433250 1498.33 473.21 1.438261 1508.50 464.50 1.440585 1516.80 457.47 1.442726 N,N-Dimethylacetamide (1) + ethanol (2) T = 298.15 K 1143.17 974.72 1.359130 1172.09 911.67 1.366193 C

ν/mm2·s−1

η/mPa·s

0.846 0.883 0.911 0.962 1.010 1.055 1.093 1.128 1.163 1.190 1.216 1.222 1.230

0.677 0.727 0.764 0.831 0.892 0.949 0.997 1.041 1.083 1.117 1.149 1.158 1.168

0.693 0.725 0.747 0.789 0.828 0.863 0.893 0.921 0.947 0.967 0.982 0.989 0.993

0.545 0.587 0.616 0.671 0.720 0.764 0.802 0.836 0.869 0.894 0.915 0.923 0.930

0.575 0.603 0.623 0.658 0.691 0.722 0.746 0.770 0.792 0.808 0.822 0.827 0.829

0.444 0.479 0.505 0.550 0.591 0.629 0.659 0.689 0.716 0.736 0.754 0.761 0.764

1.810 1.687 1.584 1.453 1.375 1.325 1.297 1.278 1.264 1.257 1.245 1.236 1.230

1.444 1.369 1.306 1.229 1.187 1.166 1.161 1.160 1.164 1.170 1.172 1.169 1.168

1.375 1.300

1.079 1.038



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Table 3. continued x1

ρ/kg·m−3

0.1071 0.2064 0.3022 0.4057 0.5032 0.6016 0.7065 0.8013 0.9021 0.9529 1.0000

811.33 832.09 849.77 866.69 881.01 894.14 906.82 917.35 927.48 932.21 936.29

0.0000 0.0524 0.1071 0.2064 0.3022 0.4057 0.5032 0.6016 0.7065 0.8013 0.9021 0.9529 1.0000

772.50 785.68 798.43 818.91 836.41 853.19 867.42 880.49 893.14 903.56 913.66 918.35 922.43

u/m·s−1

κS/TPa−1

nD

N,N-Dimethylacetamide (1) + ethanol (2) T = 298.15 K 1199.87 856.12 1.372808 1242.53 778.43 1.383513 1277.37 721.22 1.392638 1312.09 670.21 1.401308 1341.04 631.16 1.408629 1367.87 597.73 1.415179 1394.41 567.15 1.421349 1415.67 543.93 1.426396 1437.59 521.70 1.431364 1446.27 512.84 1.433670 1453.68 505.42 1.435794 N,N-Dimethylacetamide (1) + ethanol (2) T = 313.15 K 1092.44 1085.39 1.352755 1120.57 1013.62 1.359742 1147.58 951.04 1.366318 1188.73 864.17 1.376911 1222.57 799.89 1.385976 1256.27 742.66 1.394611 1284.16 699.09 1.401889 1310.45 661.36 1.408433 1336.26 627.04 1.414628 1358.45 599.73 1.419621 1378.54 575.94 1.424595 1386.01 566.84 1.426876 1393.35 558.40 1.429006

ν/mm2·s−1

η/mPa·s

1.236 1.149 1.097 1.063 1.041 1.030 1.021 1.015 1.004 0.998 0.993

1.003 0.956 0.932 0.921 0.917 0.921 0.926 0.931 0.931 0.931 0.930

1.066 1.022 0.983 0.929 0.896 0.875 0.861 0.854 0.849 0.844 0.837 0.833 0.829

0.824 0.803 0.785 0.761 0.749 0.746 0.747 0.752 0.758 0.762 0.764 0.765 0.764

a Standard uncertainties u are u(T) = 0.01 K, u(p) = 0.5 kPa, u(x1) = 0.0001, u(u) = 0.5 m·s−1, u(nD) = 1 × 10−5 and the relative expanded uncertainties Ur are Ur(ρ) = 2 × 10−4, Ur(η) = 0.01 with 0.95 level of confidence (k ≈ 2).

Table 4. Adjusted Parameters and Standard Deviations, σ(Q), for Fitting Equation function

VE × 106/m3·mol−1

κES /TPa−1

ΔnD

Δη/mPa·s

VE × 106/m3·mol−1

κES /TPa−1

ΔnD

Δη/mPa·s

T/K 283.15 298.15 313.15 283.15 298.15 313.15 283.15 298.15 313.15 283.15 298.15 313.15 283.15 298.15 313.15 283.15 298.15 313.15 283.15 298.15 313.15 283.15 298.15 313.15

A0

A1

A2

N,N-Dimethylacetamide (1) + methanol (2) −2.0759 0.6722 −0.2882 −2.1139 0.5884 −0.3645 −2.1395 0.5701 −0.3905 −254.77 237.77 −210.82 −285.27 254.30 −251.32 −321.34 286.37 −291.84 0.017298 0.003076 0.001154 0.017615 0.002670 0.001916 0.017788 0.002618 0.002125 0.293 −0.025 0.041 0.256 −0.018 0.035 0.220 −0.018 0.041 N,N-Dimethylacetamide (1) + ethanol (2) −0.9871 0.4661 −0.5949 −0.9470 0.4410 −0.5866 −0.9126 0.3700 −0.5843 −195.24 137.20 −126.83 −217.26 148.13 −135.28 −245.20 162.17 −161.44 0.009846 0.000241 0.000385 0.009438 0.000289 0.000513 0.009068 0.000462 0.000774 −0.587 0.508 −0.196 −0.347 0.315 −0.079 −0.188 0.192 −0.024

temperature and Vi, αp,i, Cp,i, and κS,i are the molar volume, the isobaric expansibility, the molar heat capacity at constant

A3

σ(Q)

0.3782 0.5838 0.5905 138.32 170.03 196.44 −0.003652 −0.003097 −0.002729

0.0052 0.0053 0.0042 0.66 0.89 1.02 0.000038 0.000065 0.000043 0.001 0.001 0.001

−0.023

0.0979 78.80 69.02 80.98 −0.003857 −0.003837 −0.003938 0.061 −0.028

0.0021 0.0024 0.0025 0.60 0.63 0.66 0.000025 0.000023 0.000024 0.001 0.001 0.001

pressure, and the isentropic compressibility of pure component i. Isobaric expansibility has been calculated from our D



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Figure 2. Excess isentropic compressibilities, κES , for N,N-dimethylacetamide (1) + alkanol (2) as a function of mole fraction, x1: □, methanol at T = 283.15 K; ○, methanol at T = 298.15 K; Δ, methanol at T = 313.15 K; ■, ethanol at T = 283.15 K; ●, ethanol at T = 298.15 K; ▲, ethanol at T = 313.15 K; , eq 10.

Figure 1. Excess volumes, VE, for N,N-dimethylacetamide (1) + alkanol (2) as a function of mole fraction, x1: □, methanol at T = 283.15 K; ○, methanol at T = 298.15 K; Δ, methanol at T = 313.15 K; ■, ethanol at T = 283.15 K; ●, ethanol at T = 298.15 K; ▲, ethanol at T = 313.15 K; , eq 10.

equation have been determined using the least-square method, and they are listed in Table 4 along with the standard deviation σ(Q). Our VE results for both systems at T = 298.15 and 313.15 K are in good agreement with those published by Zielkiewicz11 and Oba et al.14 with the average deviation being5.7%. With respect to densities and refractive indices for the two systems at T = 298.15 K measured by Ritzoulis and Fidantsi,16 the average deviations are, respectively, 0.25 and 0.19%. Finally, in accordance with the VE and Δη results for the mixture DMA + ethanol at T = 298.15 K reported by Ali and Nain17 not being good, especially for excess volumes with an average deviation equal to 26%, the average deviation for viscosity deviations is lower with this deviation being 11%. The variation of excess volume with mole fraction of DMA is presented in Figure 1. Negative VE values over the entire range of composition and for all temperatures investigated are obtained in both systems. The magnitude of VE follows the sequence in absolute value of methanol > ethanol. For DMA + methanol, VE curves are nearly symmetrical with a minimum around x1 ≈ 0.4. We note that in this mixture a rise in temperature leads to more negative VE values. For DMA + ethanol, the corresponding curves are slightly shifted to the region rich in alcohol and the minimum occurs at approximately x1 ≈ 0.36. VE values tend to become less negative with increasing temperature. Such results indicate that mixing process lead to a contraction in volume and reflect the existence of strong interactions. Negative deviation from ideal

experimental density values, and molar heat capacity values were taken from literature.38,39 The values of all these properties are presented in Table 2. Refractive index deviation in terms of volume fraction, ϕi, is given by this expression40,41

ΔnD = nD −

∑ φinD,i i

(4)

where, nD and nD,i are the refractive index of the mixture, and the refractive index of component i, respectively. Viscosity deviation in terms of mole fraction, xi, was calculated using the following relation Δη = η −

∑ xiηi i

(5)

where, η and η i are the dynamic viscosity of the mixture, and the dynamic viscosity of the component i, respectively. All these calculated excess or deviation properties can be found in the Supporting Information. A Redlich−Kister polynomial equation42 was applied in order to correlate the calculated excess and deviations properties of the binary mixtures with composition Q = y1y2 ∑ Ai (y1 − y2 )i i

(6)

Q refers to V , ΔnD, or Δη, and yi is the mole fraction, xi, or volume fraction, ϕi. The values of coefficients Ai in the above E

κES ,

E



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Figure 3. Refractive index deviations, ΔnD, for N,N-dimethylacetamide (1) + alkanol (2) as a function of volume fraction, ϕ1: □, methanol at T = 283.15 K; ○, methanol at T = 298.15 K; Δ, methanol at T = 313.15 K; ■, ethanol at T = 283.15 K; ●, ethanol at T = 298.15 K; ▲, ethanol at T = 313.15 K; , eq 10.

Figure 4. Viscosity deviations, Δη, for N,N-dimethylacetamide (1) + alkanol (2) as a function of mole fraction, x1: □, methanol at T = 283.15 K; ○, methanol at T = 298.15 K; Δ, methanol at T = 313.15 K; ■, ethanol at T = 283.15 K; ●, ethanol at T = 298.15 K; ▲, ethanol at T = 313.15 K; , eq 10.

The variation of refractive index deviation as a function of volume fraction of DMA is presented in Figure 3. Refractive index deviation for both systems is positive and their plots are quite symmetric, ΔnD values follow the order of methanol > ethanol. As we have already mentioned, there is a contraction in the volume of the mixture, and this decrease of the intermolecular distance leads to increase iof the refractive index due to an enhancement of the London dispersion forces.46,47 An opposite behavior with temperature is seen for both systems under study; for DMA + methanol, ΔnD increases with temperature, indicating that the light propagates at lower velocity when temperature increases, while for DMA + ethanol, ΔnD decreases when temperature rises and consequently the light propagates at higher velocity. It is worth mentioning that ΔnD behavior is opposite to VE behavior as Nakata and Sakurai48 and Brocos et al.49 showed in their works. Figure 4 shows the variation of viscosity deviation with mole fraction of DMA. Viscosity deviations are slightly positive for DMA + methanol and turn to negative for DMA + ethanol. It is remarked that magnitude of Δη for both systems decreases in absolute value and tends toward zero as the temperatures increases. According to Fort and Moore,50 positive Δη may occur if there are strong specific interactions such as hydrogen bonding, causing complex formation. On the other hand, Δη tends to become less positive and increasingly negative as the strength of the interaction between unlike molecules decreases. Negative Δη is obtained for systems involving dispersion forces, and it may due to the differences in size and shape of

behavior can be explained by two main factors. First, one consists on the predominance of attractive forces in the mixture, such as charge transfer, dipole−dipole, and hydrogen bonding interactions, leading to complex formation between unlike molecules, which is responsible for negative contributions. In addition, some specific acid−base interaction can be assumed in the case of amide alcohol mixture.43 The second factor is related to the attribution of more favorable packing and geometrical fitting of smaller molecules into the voids of larger ones.44 In Figure 2, the behavior of excess isentropic compressibility with mole fraction of DMA is shown. Negative κES values observed indicate the presence of significant interactions leading to a decrease in the compressibility of the mixture. The magnitude of κES follows the order in absolute value of methanol > ethanol. This indicates that interactions between DMA and methanol are stronger than those between DMA and ethanol molecules. Asymmetry is more marked in the κES curves, which is due to differences in size and shape of molecules. According to Fort and Moore,45 negative values of κES are obtained for mixtures involving hydrogen bonding, and the corresponding values could be large if one component is associated in pure state, which is the case for both systems. As it can be seen from curves, the effect of temperature is more obvious for κES comparing to VE, and the same behavior is obtained from both binary mixtures; as a consequence of rising temperature, the κES values become more negative. F



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compounds. As it was suggested by Pikkarainen15 for the interpretation of Δη, the predominance of interactions between unlike molecules over the dissociation effects is more pronounced for DMA + methanol than for DMA + ethanol.

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CONCLUSIONS In this paper, ρ, nD, u, ν, and η at several temperatures and at p = 99.0 kPa were reported for the binary mixtures N,Ndimethylacetamide + methanol and N,N-dimethylacetamide + ethanol. The results obtained for VE, κES , ΔnD, and Δη support the fact that the addition of DMA to the alcohol molecules disturbs their association and breaks up the hydrogen bonding formed at the pure state. Because of the high ability for proton accepting, DMA and free hydroxyl groups of alcohol are attracted leading to complex formation between unlike molecules. Comparison of the thermophysical properties for each binary system confirms that interactions occurring in DMA + methanol are stronger than those present in DMA + ethanol. Generally, the sign and magnitude of excess properties or property deviations could inform one about the strength of interactions in mixtures, but these properties alone are not enough to give explicit structural information. In this respect, spectroscopic techniques could be of great assistance.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jced.5b01000. Calculated excess volumes and excess compressibilities along with refractive index deviations and viscosity deviations can be found in Table 1 S1. (PDF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Tel. +0021698559305. Fax: +0021671247921. Funding

C. Lafuente is grateful for financial assistance from Diputación General de Aragón and Fondo Social Europeo “Construyendo Europa desde Aragón”. S. Mrad, M. Hichri, and I. Khattech gratefully acknowledge the financial assistance from ‘“Ministère de l”Enseignement Supérieur et de la Recherche Scientifique de la Tunisie’’ Notes

The authors declare no competing financial interest.

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REFERENCES

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Density, Speed of Sound, Refractive Index, and Viscosity of the

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