Density, Refractive Index, and Sound Velocity for the Binary Mixtures

Article pubs.acs.org/jced

Density, Refractive Index, and Sound Velocity for the Binary Mixtures of Tri‑n‑Butyl Phosphate and n‑Butanol between 303.15 K and 323.15 K M. Nur Hossain,† M. Mehedi Hasan Rocky,‡ and Shamim Akhtar* Department of Chemistry, University of Chittagong, Chittagong 4331, Bangladesh S Supporting Information *

ABSTRACT: Density, ρ, refractive index, nD, and sound velocity, u, have been measured for pure TBP, n-BuOH, and their binary mixtures in the range, 0 ≤ x2 ≤ 1, between (303.15 and 323.15) K at an interval of 5 K. From measured ρ and nD, excess molar volumes, VmE, thermal expansivity, α, excess thermal expansivity, αE, and deviation in refractive index, ΔnD, were calculated. Furthermore, using ρ and u, some derived properties, such as acoustic impedance, z, isentropic compressibility, κs, and their deviations (Δu, Δz, and Δκs), were also calculated. Values of ρ, nD, u, z, and κs were found to correlate with concentration dependent polynomials, whereas the deviations/excess properties were fitted well to Redlich−Kister equations. The variation patterns of the studied properties were discussed with reference to the nature of molecular interactions taking place between the liquids of TBP and nBuOH.

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INTRODUCTION Knowledge of intermolecular interactions among diluents and extractant is of primary importance since it is one of the basic factors which help to design solvent extraction processes with greater efficiency.1 In general, experimental results of density, refractive index, sound velocity, and thermodynamic excess properties are used as tools to understand such intermolecular interactions in liquid systems with diversified structural moieties and/or functional groups.2,3 Recently, tri-n-butyl phosphate (TBP) was used as a versatile extractant for the PUREX process in the nuclear industry and for extraction of numerous rare earths and heavy metals in chemical industries.4−8 TBP is a polar molecule and its extracting power is mainly due to the presence of a phosphoryl group which undergoes specific interactions like self-association and molecular complex formation with diluents or other solutes.1,8 A proper choice of diluents (e.g., dodecane, heptane, chloroform, butanol, etc.) is useful and frequently adopted to increase the solubility of solutes, in changing reaction equilibrium constants, improving workability of the TBP phase, and so forth.9−11 TBP interacts in a complex way which primarily involves cohesive forces or bonding between the solvent and the extracted complex. Hence, thermodynamic studies on the interaction of TBP with polar and nonpolar cosolvents are significant in understanding the mechanism of the extraction process. Because of its importance, many investigators have already devoted themselves to the study of various TBP-dilution systems.12−17 The study of organic systems having phosphates and polar groups also serves as the model for hydrogen-bonded systems in understanding biological processes.18 With this aim, we have chosen n-butanol © XXXX American Chemical Society

(n-BuOH) as a cosolvent. In order to explore the changes in hydrogen boding and self-association structures of this molecule in the presence of TBP, the present work reports on experimental data of density, ρ, refractive index, nD, and sound velocity, u, and their derived properties at different compositions for the binary system of n-BuOH + TBP at T = (303.15, 308.15, 313.15, 318.15, and 323.15) K. Earlier, Liu et al.10 dealt with only molar excess enthalpies of the binary mixtures of [tributyl phosphate + {CH3(CH2)nOH (n = 0 to 3)}] at 298.15 K. Therefore, data on densities, ρ, refractive index, nD, and sound velocity, u, for this particular system are those yet to be reported.

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EXPERIMENTAL SECTION Chemicals. TBP and n-BuOH were used without further purification. Table 1 summarizes their chemical description. Prior to use, both TBP and n-BuOH were stored over 0.4 nm molecular sieves and care was also taken to protect them from contamination by atmospheric moisture. The water content of the n-BuOH was determined as 0.0233 mol·kg−1 by a Karl Fischer Moisture Titrator (Mettler Toledo DL31). Purities were further checked by comparing their measured densities, refractive indices, and sound velocities with the corresponding literature values as shown in Table 2. Mixture Preparation. A set of 21 compositions was prepared by mixing known masses of pure TBP and n-BuOH, Received: April 15, 2015 Accepted: November 4, 2015

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DOI: 10.1021/acs.jced.5b00343 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

Article

Table 1. Specifications of the Pure Liquids component

source

CAS no.

initial purity (mass fraction)

purification method

Tri-n-butyl phosphate (TBP) n-Butanol (n-BuOH)

BDH Aldrich

126−73−8 71−36−3

> 0.99 > 0.99

None None

Table 2. Experimentala Densities, ρ, Refractive Indicesb, nD, and Sound Velocitiesc, u, of Pure Liquids at Various Temperature under Atmospheric Pressure (0.1 MPa) and Their Comparison with Literature Values ρ·10−3/(kg·m−3)

T/K liquid TBP

n-BuOHd

u/(m·s−1)

nD

exptl

lit.

298.15

0.97267

303.15

0.96839

308.15

0.96411

313.15

0.95982

318.15

0.95554

323.15 298.15

0.95126 0.80585

303.15

0.80201

308.15

0.79814

0.97519 0.972520 0.9708321 0.9724922 0.96819 0.968220 0.9664621 0.96319 0.963920 0.9620621 0.96119 0.9577721 0.95419 0.9535821 0.9492221 0.8055424 0.8060626 0.80598428 0.801929 0.802032 0.8020326 0.7980825 0.7982524

313.15

0.79422

318.15

0.79028

323.15

0.78629

exptl

lit.

exptl

lit.

1264.4

1.4210

1.420222

1.4190

1.4183d22

1.4171

1.416322

1247.4

124023

1230.5

1.4146

1213.8

1.4131

1197.3 1239.6

1.3948

1.394630 1.395233

1222.7

1.3927

1.393134

1206.3

0.794133 0.7943736 0.7932926 0.79434028 0.790129

1.3907

1.390933

1189.4

1.3875

1.389034

1172.8

0.786229 0.7864336 0.7865526

1.3848

1.386834

1156.7

1239.825 1242.627 1223.031 122433 1224.627 1206.225 1210.1635 1207.627 119033 1189.227

1172.1337 1170.027

a Standard uncertainties (0.68 level of confidence) for T = 0.01 K, ρ = 1.6·10−2 kg·m−3, nD = 2.0·10−5, u = 0.17 m·s−1, κs = 2.4·10−12 Pa−1, z = 24.1 kg· m−2·s−1. bλ of refractometer: 589 nm (Sodium D-line). cWorking frequency: (1 to 2) MHz. dStandard uncertainty of nD = 0.001 for n-BuOH with literature data.

manufacturer was ± 0.001 kg·m−3, ± 0.1 m·s−1, and ± 0.001 K, respectively. Refractive Indices. Refractive index, nD, was measured by using the Abbe Refractometer (Abbe 60/ED), and its temperature was maintained in an electronically controlled thermostatic water bath (Thermo Haake, UK). The stated precision in nD was ± 0.0001 and that of temperature, ± 0.05 K. For all the pure components and mixtures, triplicate measurements were performed and their mean was always taken into consideration.

which were completely miscible over the whole composition range. All the mass measurements were made by an electronic balance (B 204-S, Mettler Toledo) with an uncertainty of 10−7 kg. To avoid any evaporation/contamination, solutions were always kept in airtight glass stoppred bottles and also handled carefully. For the mixtures, the accuracy in mass fraction was estimated as ± 1.0·10−4. Density and Sound Velocity. Density (ρ/kg·m−3) and sound velocity (u/m·s−1) were measured by using an automated density and sound velocity meter (DSA 5000M, Anton Paar, Austria) with an accuracy of ± 0.005 kg·m−3 for density and ± 0.5 m·s−1 for sound velocity. As the ρ and u are extremely sensitive, temperature was controlled up to ± 0.01 K by a built-in solid state thermostat. The stated repeatability for density, sound velocity, and temperature measurement by the

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RESULTS AND DISCUSSION Experimental density, ρ, refractive index, nD, and sound velocity, u, for all the mixtures of n-BuOH + TBP at T = (303.15, 308.15, 313.15, 318.15, and 323.15) K are presented in B



Article

a

Table 3. Experimental Densities, ρ, Refractive Indices, nD, Sound Velocities, u, as Well as Calculated Isentropic Compressibility, κs, and Acoustic Impedance, z, for n-BuOH (1) + TBP (2) System at T = (303.15 to 323.15) K and under Atmospheric Pressure (0.1 MPa) x2

ρ·10−3 kg·m

−3

0.0000 0.0500 0.1002 0.1503 0.2020 0.2502 0.3006 0.3502 0.4000 0.4502 0.5002 0.5506 0.6005 0.6502 0.7002 0.7493 0.8001 0.8507 0.9009 0.9504 1.0000

0.80201 0.82373 0.84191 0.85735 0.87107 0.88223 0.89253 0.90162 0.90979 0.91729 0.92406 0.93031 0.93599 0.94116 0.94595 0.95033 0.95447 0.95835 0.96193 0.96528 0.96839

0.0000 0.0500 0.1002 0.1503 0.2020 0.2502 0.3006 0.3502 0.4000 0.4502 0.5002 0.5506 0.6005 0.6502 0.7002 0.7493 0.8001 0.8507 0.9009 0.9504 1.0000

0.79814 0.81976 0.83788 0.85327 0.86694 0.87806 0.88834 0.89741 0.90556 0.91305 0.91982 0.92607 0.93173 0.93690 0.94168 0.94606 0.95020 0.95407 0.95764 0.96099 0.96411

0.0000 0.0500 0.1002 0.1503 0.2020 0.2502 0.3006 0.3502 0.4000 0.4502 0.5002 0.5506

0.79422 0.81577 0.83382 0.84917 0.86278 0.87388 0.88413 0.89319 0.90134 0.90881 0.91556 0.92181

nD

κs·1011

u −1

m·s

T = 303.15 K 1.3948 1222.7 1.3978 1223.0 1.4007 1223.3 1.4029 1223.6 1.4048 1223.8 1.4063 1224.3 1.4078 1225.3 1.4092 1226.4 1.4102 1227.6 1.4115 1229.0 1.4125 1230.6 1.4133 1232.3 1.4142 1234.0 1.4151 1235.7 1.4160 1237.3 1.4168 1238.9 1.4176 1240.4 1.4183 1241.9 1.4192 1243.5 1.4201 1245.1 1.4210 1247.4 T = 308.15 K 1.3927 1206.3 1.3958 1206.5 1.3989 1206.7 1.4012 1206.9 1.4031 1207.1 1.4045 1207.5 1.4061 1208.5 1.4074 1209.6 1.4084 1210.8 1.4097 1212.2 1.4107 1213.7 1.4117 1215.4 1.4125 1217.1 1.4134 1218.9 1.4143 1220.5 1.4150 1222.0 1.4158 1223.5 1.4165 1225.1 1.4174 1226.6 1.4182 1228.3 1.4190 1230.5 T = 313.15 K 1.3907 1189.4 1.3940 1189.6 1.3972 1189.8 1.3996 1189.9 1.4015 1190.1 1.4029 1190.4 1.4045 1191.5 1.4058 1192.6 1.4069 1193.8 1.4080 1195.2 1.4090 1196.7 1.4100 1198.5

−1

Pa

z·10−4

x2

−2 −1

kg·m ·s

83.403 81.164 79.372 77.905 76.653 75.621 74.626 73.742 72.937 72.176 71.461 70.785 70.161 69.584 69.053 68.557 68.095 67.655 67.230 66.825 66.365

98.062 100.74 102.99 104.91 106.60 108.01 109.36 110.58 111.69 112.74 113.72 114.64 115.50 116.30 117.04 117.74 118.39 119.02 119.62 120.19 120.80

86.101 83.803 81.963 80.458 79.163 78.109 77.078 76.160 75.325 74.534 73.803 73.100 72.453 71.841 71.289 70.785 70.304 69.836 69.405 68.972 68.503

96.280 98.904 101.11 102.98 104.65 106.03 107.36 108.55 109.65 110.68 111.64 112.56 113.40 114.20 114.93 115.61 116.26 116.88 117.46 118.04 118.63

89.003 86.622 84.719 83.173 81.834 80.754 79.670 78.717 77.848 77.028 76.268 75.524

94.465 97.044 99.208 101.04 102.68 104.03 105.34 106.52 107.60 108.62 109.57 110.48

ρ·10−3 kg·m

−3

0.6005 0.6502 0.7002 0.7493 0.8001 0.8507 0.9009 0.9504 1.0000

0.92747 0.93263 0.93741 0.94178 0.94593 0.94979 0.95336 0.95669 0.95982

0.0000 0.0500 0.1002 0.1503 0.2020 0.2502 0.3006 0.3502 0.4000 0.4502 0.5002 0.5506 0.6005 0.6502 0.7002 0.7493 0.8001 0.8507 0.9009 0.9504 1.0000

0.79028 0.81174 0.82973 0.84504 0.85861 0.86968 0.87991 0.88895 0.89708 0.90455 0.91130 0.91755 0.92320 0.92836 0.93313 0.93749 0.94165 0.94550 0.94906 0.95239 0.95554

0.0000 0.0500 0.1002 0.1503 0.2020 0.2502 0.3006 0.3502 0.4000 0.4502 0.5002 0.5506 0.6005 0.6502 0.7002 0.7493 0.8001 0.8507 0.9009 0.9504 1.0000

0.78629 0.80768 0.82561 0.84088 0.85441 0.86545 0.87567 0.88470 0.89283 0.90029 0.90703 0.91328 0.91893 0.92409 0.92885 0.93320 0.93736 0.94122 0.94478 0.94810 0.95126

nD

κs·1011

u −1

m·s

T = 313.15 K 1.4109 1200.3 1.4117 1202.0 1.4125 1203.6 1.4133 1205.2 1.4140 1206.8 1.4148 1208.3 1.4154 1210.0 1.4162 1211.6 1.4171 1213.8 T = 318.15 K 1.3875 1172.8 1.3910 1172.9 1.3944 1173.1 1.3969 1173.2 1.3988 1173.3 1.4004 1173.6 1.4019 1174.6 1.4032 1175.6 1.4044 1177.0 1.4054 1178.4 1.4065 1180.0 1.4075 1181.8 1.4085 1183.5 1.4093 1185.4 1.4101 1187.0 1.4109 1188.6 1.4117 1190.2 1.4124 1191.7 1.4130 1193.4 1.4138 1195.1 1.4146 1197.3 T = 323.15 K 1.3848 1156.7 1.3887 1156.8 1.3921 1156.9 1.3948 1157.0 1.3968 1157.1 1.3984 1157.4 1.3999 1158.2 1.4014 1159.4 1.4025 1160.7 1.4036 1162.2 1.4047 1163.8 1.4058 1165.5 1.4068 1167.4 1.4077 1169.2 1.4085 1170.9 1.4093 1172.5 1.4101 1174.2 1.4109 1175.7 1.4116 1177.4 1.4123 1179.2 1.4131 1181.4

Pa

−1

z·10−4 kg·m−2·s−1

74.838 74.213 73.639 73.103 72.589 72.115 71.643 71.205 70.716

111.32 112.10 112.83 113.50 114.16 114.76 115.36 115.91 116.50

91.997 89.549 87.578 85.976 84.603 83.483 82.372 81.396 80.467 79.613 78.809 78.034 77.334 76.657 76.060 75.503 74.967 74.474 73.983 73.515 73.004

92.684 95.209 97.336 99.140 100.74 102.07 103.35 104.51 105.59 106.59 107.53 108.44 109.26 110.05 110.76 111.43 112.08 112.68 113.26 113.82 114.41

95.055 92.522 90.497 88.838 87.416 86.256 85.132 84.089 83.136 82.235 81.400 80.607 79.851 79.160 78.526 77.947 77.377 76.863 76.352 75.853 75.319

90.950 93.432 95.515 97.290 98.864 100.17 101.42 102.57 103.63 104.63 105.56 106.44 107.28 108.05 108.76 109.42 110.07 110.66 111.24 111.80 112.38

Standard uncertainties (0.68 level of confidence) for T = 0.01 K, ρ = 1.6·10−2 kg·m−3, nD = 2.0·10−5, u = 0.17 m·s−1, κs = 2.4·10−12 Pa−1, and z = 24.1 kg·m−2·s−1. a

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Table 4. Fitting Coefficient, Ai, of Redlich−Kister Equation and Standard Deviation, σ, for Excess Molar Volume, VmE, Deviation in Refractive Index, ΔnD, Sound Velocity, Δu, Isentropic Compressibility, Δκs, and Acoustic Impedance, Δz, for n-BuOH (1) + TBP (2) System at Various Temperatures property VmE·106/(m3·mol−1)

ΔnD

Δu/(m·s−1)

Δκs·1011/(Pa−1)

Δz·10−4/(kg·m−2·s−1)

T/K

Ao

A1

A2

A3

303.15 308.15 313.15 318.15 323.15 303.15 308.15 313.15 318.15 323.15 303.15 308.15 313.15 318.15 323.15 303.15 308.15 313.15 318.15 323.15 303.15 308.15 313.15 318.15 323.15

1.9839 2.0445 2.0963 2.1569 2.2116 0.0180 0.0192 0.0204 0.0218 0.0231 −42.186 −42.502 −43.364 −44.349 −45.478 3.2378 3.4625 3.7398 4.0703 4.4274 −5.4462 −5.4600 −5.5252 −5.6040 −5.6923

−0.8067 −0.8591 −0.9024 −0.9555 −0.9977 −0.0132 −0.0129 −0.0135 −0.0138 −0.0145 28.638 29.030 29.870 31.497 32.061 −2.0903 −2.2894 −2.5511 −2.9412 −3.2053 3.7021 3.7405 3.8146 3.9636 4.0087

−0.1900 −0.1647 −0.1658 −0.1221 −0.0923 0.0064 0.0083 0.0093 0.0114 0.0136 −8.8215 −8.7657 −8.2276 −8.3519 −8.0830 −0.2703 −0.1978 −0.0137 0.0642 0.1468 −1.0412 −1.0435 −0.9914 −1.0228 −1.0132

0.6689 0.7342 0.7654 0.8551 0.8928 −0.0051 −0.0069 −0.0092 −0.0101 −0.0114 −17.755 −17.085 −17.223 −19.322 −19.606 3.8053 3.8828 4.0894 4.5551 4.7994 −1.9669 −1.9215 −1.9276 −2.1387 −2.1594

κs =

1 1 = 2 uz uρ

(1)

(2)

m

ΔY /Y E = x1x 2 ∑ Ai (x 2 − x1)i

Excess molar volumes, VmE, have been evaluated from experimental ρ by the equation2 ⎛x M x M + x 2M 2 xM ⎞ − ⎜⎜ 1 1 + 2 2 ⎟⎟ VmE = 1 1 ρ ρ2 ⎠ ⎝ ρ1

Here, Ai is the fitting coefficient and m is the degree of polynomial expansion, optimized by using the F test.38,39 The values of fitting coefficients are listed in Table 4 along with standard deviations, σ(YE). σ were calculated as

(3)

1/2 ⎡ E E 2 σ(Y E) = ⎢⎣∑ (Yexp − Ycal ) /(n − p)⎤⎥⎦

(7)

where n represents the number of experimental data points and p the number of coefficients. The variations in VmE, ΔnD, Δu, Δz, and Δκs each as a function of mole fraction x2 of TBP are graphically shown by Figures 1−5. Smooth curves in each case indicate that relevant deviations/excess properties fitted well with the Redlich−Kister equations in the whole range of composition as well as temperature. It has been suggested that excess molar volumes of binary mixtures whether positive or negative are due to several factors that may be divided into chemical, physical, and structural contributions.40 While physical interactions involve mainly dispersion forces giving a positive contribution to VmE, chemical

(4)

where nD represents the refractive index of mixture and nD1 and nD2 are that of the pure components. Considering volume fraction as ϕi = xiVi/∑i2= 1 xiVi, where Vi is the molar volume of the ith component, for all the mixtures values of Δu, Δz, and Δκs have been calculated by following a general equation ΔB = Bm − (ϕ1B1 + ϕ2B2 )

(6)

i=0

where ρ is the density of mixture and x1, M1, ρ1 and x2, M2, ρ2 are the mole fraction, molar mass, and density of pure components 1 and 2, respectively. Also, deviation in refractive index, ΔnD, was calculated using the relationship30 ΔnD = nD − (x1nD1 + x 2nD2)

−1.0043 −1.1027 −1.5644 −1.6435 −1.8434

σ 0.0038 0.0036 0.0028 0.0031 0.0030 0.0001 0.0001 0.0001 0.0001 0.0001 0.0721 0.0749 0.0889 0.0775 0.0686 0.0085 0.0098 0.0129 0.0110 0.0107 0.0060 0.0065 0.0076 0.0065 0.0063

Here, ΔB refers to Δu, Δz, or Δκs; Bm is the respective mixture property; B1 and B2 refer to those for pure components, and ϕ1 and ϕ2 are the corresponding volume fractions. The values of ρ, nD, u, z, and κs were correlated with concentration dependent polynomials, as provided in the associated Supporting Information. Each of the deviations/ excess properties ΔY or YE (VmE, ΔnD, Δu, Δz, or Δκs) of mixtures was fitted by the nonlinear least-squares method to a Redlich−Kister polynomial.17

Table 3. It also contains the values of calculated thermo acoustic properties, e.g., acoustic impedance, z, and isentropic compressibility, κs, as a function of mole fraction of TBP, evaluated from experimental ρ and u using the following equations:16,17

z = uρ

A4

(5) D



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Figure 1. Excess molar volumes, VmE, against the mole fraction of TBP, x2, for the system n-BuOH (1) + TBP (2) at different temperatures (T): ■, 303.15 K; ◇, 308.15 K; ◆, 313.15 K; Δ, 318.15 K; ▲, 323.15 K; + , literature data42 at 303.15 K; solid lines fitted with the Redlich−Kister equation.

Figure 4. Deviations in acoustic impedance, Δz, against the mole fraction of TBP, x2, for the system, n-BuOH (1) + TBP (2) at different temperatures (T): ■, 303.15 K; ◇, 308.15 K; ◆, 313.15 K; △, 318.15 K; ▲, 323.15 K; solid lines fitted by Redlich−Kister equation.

Figure 2. Deviations in refractive index, ΔnD, against the mole fraction of TBP, x2, for the system of n-BuOH (1) + TBP (2) at different temperatures (T): ■, 303.15 K; ◇, 308.15 K; ◆, 313.15 K; △, 318.15 K; ▲, 323.15 K; solid lines fitted to the Redlich−Kister equation.

Figure 5. Deviations in isentropic compressibility, Δκs, against the mole fraction of TBP, x2, for the system n-BuOH (1) + TBP (2) at different temperatures (T): ■, 303.15 K; ◇, 308.15 K; ◆, 313.15 K; △, 318.15 K; ▲, 323.15 K; solid curves calculated with Redlich−Kister equation.

ment,16,41 its admixture with n-BuOH would mutually induce dissociation of their hydrogen-bonded structures, and subsequently, formation of new PO···HO type H-bonds between the oxygen atom of the >PO group of TBP and the hydrogen of the −OH group of n-BuOH. The experimental positive VmE thus obviously leads to suggest that, within mixtures the interaction leading to a new H-bond between TBP and n-BuOH is rather weaker than the total interactions of TBP−TBP and n-BuOH−n-BuOH. This is also in support of earlier studies of excess molar enthalpies of TBP + alkanols;10,11 volumetric and compressibility studies on TBP + 1-octanol, 1decanol, and isodecanol;17 and excess molar volumes of TBP + n-alkanol and n-alkanol + n-alkane systems.42 The second factor is due to physical intermolecular forces among which the dispersion force is the main to contribute. As physical intermolecular forces are usually weak, the sign of VmE values may be positive or negative.21 Because of high dipole moments, the effect is likely to be greater in the case of alcohols. Here, addition of TBP into n-BuOH can initially disrupt its dipole−dipole forces. Also, declustering of TBP in the presence of n-BuOH followed by considerable dispersion of one into the other has probably favored an overall volume expansion. The third factor is related to structural characteristics arising from the geometrical fitting of one component into the structure of the other. The positive excess molar volumes

Figure 3. Deviations in sound velocity, Δu, against the mole fraction of TBP, x2, for the system n-BuOH (1) + TBP (2) at different temperatures (T): ■, 303.15 K; ◇, 308.15 K; ◆, 313.15 K; △, 318.15 K; ▲, 323.15 K; solid lines fitted to the Redlich−Kister equation.

or specific interactions rather lead to negative VmE, i.e., decrease in volume. The third factor, on the other hand, exhibits either of them depending on specific situations. In general, the first factor comprises of specific forces between molecules, such as dipole−dipole, dipole−induced dipole, hydrogen-bonding, charge-transfer, etc. Usually, breaking up of hydrogen bonds gives rise to positive excess molar volumes and vice versa.12,21 As TBP is a mild self-associated liquid remaining in either a wood-pile or head−tail arrangeE



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Table 5. Thermal Expansivities, α, and Excess Thermal Expansivities, αE, for the System of n-BuOH (1) + TBP (2) at Different Molar Fractions x2

α·104/K−1

αE·104/K−1

x2

α·104/K−1

αE·104/K−1

x2

α·104/K−1

αE·104/K−1

0.0000 0.0500 0.1002 0.1503 0.2020 0.2502 0.3006

9.8975 9.8371 9.7752 9.6973 9.6555 9.5992 9.5353

0.0000 −0.0118 −0.0249 −0.0540 −0.0455 −0.0549 −0.0698

0.3502 0.4000 0.4502 0.5002 0.5506 0.6005 0.6502

9.4722 9.4087 9.3533 9.3018 9.2387 9.1974 9.1529

−0.0847 −0.0997 −0.1063 −0.1092 −0.1232 −0.1160 −0.1122

0.7002 0.7493 0.8001 0.8507 0.9009 0.9504 1.0000

9.1212 9.0959 9.0433 9.0191 8.9958 8.9812 8.9247

−0.0952 −0.0727 −0.0759 −0.0509 −0.0253 0.0082 0.0000

323.15) K. From measured ρ, nD, and u derived properties, such as α, z, κs as well as VmE, αE, ΔnD, Δu, Δz, and Δκs were calculated. All the deviations/excess properties showed fairly good fittings to the Redlich−Kister type equations. VmE, Δκs, and ΔnD were positive and their variation patterns were also similar, but the signs were opposite for Δu and Δz. It has been concluded that, declustering of self-associated structures, decreased dipole−dipole interactions, unfavorable packing of n-BuOH with TBP, etc. have recognizable influence on the studied properties for the n-BuOH + TBP system.

however indicate that there may be a significant effect due to the steric hindrance. When associated alkanol species (dimers or oligomers) interact with larger associated TBP molecules, steric hindrance must have to be conquered not only by Hbonding, but also by dipole−dipole interaction.11 The larger the alkanol molecules, the more difficult it is to associate with the TBP. So, association with TBP is not favorable for n-BuOH mainly due to poor geometrical fitting between the longer nbutyl chain of n-BuOH and also the alkyl groups of the tributyl “umbrella” of TBP, which ultimately leads to positive VmE in the whole range of composition. Perhaps the mixing behavior does not change significantly with temperature. Nonetheless, at higher temperatures interaction is weakened at least by breaking up of additional forces and ultimately leads to greater volume expansion. The deviation in VmE is also found to increase slightly with temperature (Figure 1). Hence, at increasing temperatures the observed δVmE/δT values were also positive. The average isobaric thermal expansivities, α, of pure liquids and their mixtures were calculated as in the literature2 and excess thermal expansivities, αE, of mixtures were obtained by following the equation: α E = α − (x1α1 + x 2α2)

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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.5b00343. Coefficients of polynomial fitting of ρ, nD, u, z, and κs (Table S1). Plots of density, refractive index, sound velocity, acoustic impedance and isentropic compressibility against mole fraction for n-BuOH + TBP system (Figure S1). (PDF)

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(8)

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Tel.: +880 1712090205; fax: +880 31 726310.

The data of α and αE as presented in Table 5 were almost all negative in the whole range of composition. Again, the sign of αE reveals that, structural effect has a negative role in expansion. It may therefore be related to the so-called molecular packing or geometric fitting between TBP and n-BuOH, which also appears to be less favorable at higher temperatures at least within the studied range. Figures 2−5 exhibit that, at all temperatures where ΔnD and Δκs are positive, values of Δu and Δz are negative for n-BuOH + TBP over the whole range of composition. Positive ΔnD revealed that, in spite of volume expansion the passage of light through the mixtures rather faces hindrance. Positive Δκs on the other hand indicates that in the entire range mixtures of nBuOH + TBP are more compressible compared to ideal mixtures. Earlier, Δκs has been considered as the resultant of several opposing effects.43 Thus, it can be suggested that factors like declustering of self-associated structures in presence of each other, weaker form of cross-H bonding, unfavorable packing of n-BuOH due to steric hindrance by bulkier n-butyl moieties of TBP, and so forthall might be responsible for the positive Δκs in the mixtures n-BuOH + TBP.

Present Addresses †

Department of Chemistry, Lakehead University, Thunder Bay, Ontario P7B 5E1, Canada. ‡ Department of Natural Science, Port City International University, Chittagong, Bangladesh. Funding

The authors gratefully acknowledge the financial support from the Ministry of Science, Information and Communication Technology, Government of the People’s Republic of Bangladesh and also from the Third World Academy of Science, Trieste, Italy. Notes

The authors declare no competing financial interest.

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REFERENCES

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CONCLUSION The present work reports the experimental data of density, ρ, refractive index, nD, and sound velocity, u, and their derived properties at different compositions for the binary system of nBuOH + TBP at T = (303.15, 308.15, 313.15, 318.15, and F



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Density, Refractive Index, and Sound Velocity for the Binary Mixtures

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