density, viscosity, refractive index, and speed of sound in binary mixtures of pyridine and...

$: Density, Viscosity, Refractive Index, and Speed of Sound in Binary Mixtures of Pyridine and 1-Alkanols (C6, C7, C8, C10) at 303.15 K$
Chinese Journal of Chemistry, 2008, 26, 2009—2015 Full Paper

* E-mail: [email protected]; [email protected]; Tel.: 0091-11-26981717 Received April 22, 2008; revised June 27, 2008; accepted July 11, 2008.

© 2008 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Density, Viscosity, Refractive Index, and Speed of Sound in Binary Mixtures of Pyridine and 1-Alkanols (C6, C7, C8, C10) at

303.15 K

ALI, Anwar*,a TARIQ, Mohda,b NABI, Firdosaa SHAHJAHANa a Department of Chemistry, Jamia Millia Islamia (Central University), New Delhi –110025, India

b Laoboratory of Molecular Thermodynamic, Instituto de Tecnologia Quimicae Biologia, Universidade de Nova De Lisboa, Oeiras, Portugal

The densities (ρ), viscosities (η), refractive indices (nD), and speeds of sound (u), of binary mixtures of pyridine with 1-hexanol, 1-heptanol, 1-octanol and 1-decanol, including those of pure liquids, were measured over the entire composition range at 303.15 K and atmospheric pressure. From these experimental data, the values of excess molar volumes (VE), deviations in isentropic compressibilities (∆ks), viscosities (∆η), molar refractions (∆Rm), apparent and partial molar volumes (Vφ,2 and 0

,2Vφ ), apparent and partial molar compressibilities (Kφ,2 and 0,2Kφ ), of alkanols

in pyridine and their corresponding deviations (∆V and ∆K) were calculated. The variations of these parameters with composition of the mixtures suggest that the strength of interactions in these mixtures follow the order: 1-hexanol＞1-heptanol＞1-octanol＞1-decanol. All the excess and deviation functions were fitted to Redlich-Kister polynomial equation to determine the fitting coefficients and the standard deviations.

Keywords binary mixture density, viscosity, refractive index, speed of sound, excess function, intermolecular in-teraction

Introduction

Pyridine and its derivatives are an important class of aromatic compounds. They have attracted attention be-cause many alkaloids and natural products contain pyri-dine ring or hydrogenized pyridine ring structures.1 The treatment of pyridine systems is a first step for a better understanding of the pyrrole ring, especially important to model typical binding sites on proteins.2 Alkanols are polar liquids, strongly self-associated by hydrogen bonding to extent of polymerization that may differ de-pending on temperature, chain length, and position of the —OH group.3

To the best of our knowledge, only Dewan et al.4 have measured the excess volumes for mixtures of pyri-dine and 1-alkanol (C1—C10) at 298.15 K, but a com-plete study from a thermodynamic point of view is lacking. Hence, here, we have measured a complete set of properties, viz., densities (ρ), viscosities (η), refrac-tive indices (nD), and speeds of sound (u), in the mix-tures of pyridine and 1-alkanols (C6, C7, C8, C10) at 303.15 K and atmospheric pressure. Using the experi-mental data the corresponding derived values of excess molar volumes (VE), deviations in isentropic compressi-bilities (∆ks), viscosities (∆η) and in molar refraction, ∆Rm, were calculated. All the excess and deviation functions were fitted to Redlich-Kister polynomial equation.5

Experimental

Pyridine and octanol (Acros Organics, purity＞99%); 1-hexanol, 1-heptanol, and 1-decanol (S.D. Fine Chemicals, purities 98.5%, 99.5%, and 99%, respec-tively) were used after purification by the standard methods.6 All the purified chemicals were stored over 0.4 nm molecular sieves to reduce the moisture content, if any, and were degassed before use. Further, the puri-ties of these solvents were ascertained by comparing the measured ρ, η, nD and u values at 303.15 K with the available literature values,7-15 as shown in Table 1. Mixtures were prepared by mass in a dry box13 using a Precisa XB-220 A (Swiss make) electronic balance having an accuracy of ±0.1 mg. The reproducibility in the molar fraction was within ±0.0001.

The densities of liquids and their binary mixtures were measured by using a single-capillary pycnometer made of Borosil glass, having a bulb capacity of 8 cm3. The capillary, with graduated marks, had a uniform bore and could be closed by a well-fitted glass cap. The marks on the pycnometer were calibrated by using con-ductivity water with its density6 995.65 kg•m－3 at 303.15 K. At least three measurements were made and the average of these values was considered in all calcu-lations. The accuracy in density values was ±0.0001 g•cm－3 . Viscosit ies were measured using an

2010 Chin. J. Chem., 2008, Vol. 26, No. 11 ALI et al.


Table 1 Comparison of experimental densities (ρ), viscosities (η), speeds of sound (u), and refractive indices (nD) of pure liquids with literature values at 303.15 K

ρ/(g•cm－3) η/(mPa•s) u/(m•s－1) nD Liquid

Expt. Lit. Expt. Lit. Expt. Lit. Expt. Lit.

Pyridine 0.9731 0.9737a 0.8199b 0.820a 1395.4 1398.6h 1.4990 1.5025a

1-Hexanol 0.8118 0.81212b 0.8114c

3.8068 3.887b 1282.0 1282.0g 1.4120 1.4137c

1-Heptanol 0.8156 0.81529b 0.8157c

5.0270 5.069b 1306.0 1306.0g 1.4190 1.4200c

1-Octanol 0.8205 0.81823b 5.9091 6.100e 6.1023f

1327.5 — 1.4250 1.42562i 1.4250c

1-Decanol 0.8231 0.82285b 0.82306d

9.3420 9.754b 1360.5 — 1.4320 1.43302i 1.4323c

a Ref 7; b Ref 8 ; c Ref 9; d Ref 10; e Ref 11; f Ref 12; g Ref 13; h Ref 14; i Ref 15. Ubbelohde-type suspended level viscometer. It was calibrated using conductivity water. The viscometer containing the test liquid was allowed to stand for about 20 min in a thermostated water bath so that the thermal fluctuations in the viscometer were minimized. An elec-tronic digital stop watch (Racer, Japan) with a readabil-ity of ±0.01 s was used for flow time measurements. At least three or more measurements of flow time for all compositions were made and the results were averaged. As the flow time for water and the sample liquids was longer than 200 s at 298.15 K and the radius of capillary was 0.48 mm, the kinetic energy correction was negligi-ble. The uncertainties in the measured viscosities were not more than ±2×10－3 mPa•s. Experimental details and calibration of the pycnometer/viscometer and data measurements are the same as reported earlier.13,16-18 Refractive indices were measured for the sodium D-line with the help of a thermostatically controlled Abbe re-fractometer (Metrex, India). Its accuracy was checked by measuring the refractive indices of conductivity wa-ter, pure benzene, and carbon tetrachloride at 298.15 K. A minimum of three readings was taken for each com-position, and the average value was considered in all calculations. The uncertainty in measured refractive indices was ±0.0002. Speed of sound was measured using a single-crystal variable-path ultrasonic interfer-ometer (Model M-82, Mittal Enterprises, New Delhi) operating at 3 MHz. The interferometer was calibrated using conductivity water, benzene and toluene at 298.15 K. The other experimental details are the same as re-ported earlier.17,19 The accuracy in speed of sound measurement was not more than ±2 m•s－1. In all the experiments, temperature of the samples was main-tained at 303.15 ±0.01 K using an electronically ther-mostatic water bath (Julabo, Germany).

Results and discussion

The experimental values of densities (ρ), viscosities (η), refractive indices (nD), and speeds of sound (u), in pure pyridine, 1-hexanol, 1-heptanol, 1-octanol, 1-decanol and in their binary mixtures, over the entire composition range, at 303.15 K and atmospheric pres-

sure, expressed by the molar fraction, x1, of pyridine, are listed in Table 2. From the experimental data (Table 2), the excess molar volumes, VE, deviations in isentropic compressibilities, ∆ks, viscosities, ∆η, and in molar re-fraction, ∆Rm from ideal solution behaviour of the mix-tures were calculated by using the following relations:

E1 1 1 2 2 2 (1/ 1/ ) (1/ 1/ )V x M x Mρ ρ ρ ρ＝－＋－ (1)

s s 1 s1 2 s2 ( )k k k kφ φ∆ ＝－＋ (2)

1 1 2 2( )x xη η η η∆ ＝－＋ (3)

m m 1 m1 2 m2( )R R x R x R∆ ＝－＋ (4)

where φ is the volume fraction, M is the molar mass, and the subscripts 1 and 2 stand for pure components, pyridine and 1-alkanols, respectively, ks and Rm are the isentropic compressibility, and molar refraction, respec-tively, and were calculated by using the following rela-tions:

s 2

1k

u ρ＝ (5)

2D

m 2D

1

2

n MR

n ρ⎛ ⎞⎜ ⎟⎝ ⎠

－＝

＋ (6)

The dipole moments for pyridine20, 1-hexanol21 and 1-octanol21, as given in literature are 2.37, 1.55 and 1.76 D, respectively, while such values for 1-heptanol and 1-decanol are not available in the literature. Closer ex-amination of the physical nature of compressibilities suggested that it should be more appropriate to use volume fraction basis for compressibilities of pure components of solution to estimate ideal behaviour of this property,22 while it is meaningful and physically significant23,24 to calculate ∆Rm, and also VE, by consid-ering ideal behaviour based on the molar fraction basis of pure component properties.

Binary mixture density Chin. J. Chem., 2008 Vol. 26 No. 11 2011


Table 2 Experimental densities (ρ), viscosities (η), speeds of sound (u), and refractive indices (nD) in binary liquid mixtures at 303.15 K

x1 ρ/(g•cm－3) η/(mPa•s) u/(m•s－1) nD

0.0000 0.8118 3.8068 1282.0 1.4120

0.1186 0.8260 3.3402 1292.4 1.4202

0.2448 0.8420 2.7865 1303.6 1.4299

0.3440 0.8566 2.3202 1313.8 1.4386

0.4548 0.8733 1.8900 1325.4 1.4484

0.5250 0.8845 1.6580 1333.2 1.4546

0.6217 0.9004 1.3922 1344.2 1.4630

0.7254 0.9183 1.1980 1356.8 1.4720

0.8440 0.9406 1.0100 1372.5 1.4829

0.9154 0.9548 0.9180 1382.5 1.4899

Pyridine (1)＋1-Hexanol (2)

1.0000 0.9731 0.8199 1395.4 1.4990

0.0000 0.8156 5.0270 1306.0 1.4190

0.1874 0.8349 3.9720 1317.4 1.4304

0.2960 0.8477 3.3240 1325.2 1.4382

0.3751 0.8580 2.8260 1331.4 1.4444

0.4654 0.8707 2.3220 1338.8 1.4518

0.5536 0.8842 1.9020 1346.5 1.4588

0.6340 0.8975 1.5720 1353.8 1.4654

0.7339 0.9155 1.2390 1363.4 1.4738

0.8257 0.9333 1.0486 1373.2 1.4818

0.9186 0.9533 0.8982 1384.4 1.4904

Pyridine (1)＋1-Heptanol (2)

1.0000 0.9731 0.8199 1395.4 1.4990

0.0000 0.8205 5.9091 1327.5 1.4250

0.1524 0.8336 4.7659 1334.0 1.4332

0.2946 0.8478 3.7900 1341.0 1.4420

0.4007 0.8600 2.9890 1346.8 1.4494

0.5206 0.8758 2.2022 1354.0 1.4584

0.6026 0.8881 1.7420 1359.5 1.4648

0.6908 0.9029 1.3220 1366.0 1.4720

0.7752 0.9189 1.0620 1372.8 1.4790

0.8717 0.9398 0.8280 1381.6 1.4876

0.9257 0.9529 0.7988 1387.0 1.4920

Pyridine (1)＋1-Octanol (2)

1.0000 0.9731 0.8199 1395.4 1.4990

0.0000 0.8231 9.3420 1360.5 1.4320

0.1594 0.8343 7.4020 1363.6 1.4394

0.3162 0.8479 5.5862 1367.2 1.4478

0.3936 0.8557 4.6990 1369.4 1.4528

0.4917 0.8670 3.7520 1372.2 1.4590

0.6403 0.8879 2.3920 1377.1 1.4692

0.6877 0.8959 1.9980 1378.9 1.4728

0.7620 0.9098 1.4820 1381.8 1.4784

0.8493 0.9291 1.0433 1385.9 1.4854

0.9598 0.9597 0.7080 1392.6 1.4964

Pyridine (1)＋1-Decanol (2)

1.0000 0.9731 0.8199 1395.4 1.4990

The values of Rm calculated by using Eq. 6 for pure

liquids are listed in Table 3. The values of VE, ∆ks, ∆η and ∆Rm of the binary

mixtures at 303.15 K were fitted to the Redlich-Kister



type polynomial equation:5

( )3

1E1 2 1

1

1 2i

ii

Y x x A x∑－

＝

＝－ (7)

where YE stands for VE/∆ks/∆η/∆Rm. iA 's are the poly-nomial coefficients and 2x is the molar fraction of 1-alkanols. The coefficients iA of Eq. 7, evaluated by using the least squares method along with the standard deviations ( )EYσ calculated using Eq. 8, are given in Table 4.

( )1/ 22E E

exp calE

( )

( )

m

Y Y

Y

m n

σ

⎡ ⎤⎢ ⎥⎢ ⎥⎢ ⎥⎢ ⎥⎣ ⎦

∑ －

＝

－

(8)

where m is the number of experimental data points and n is the number of coefficients considered (n＝3 in the present case). The variations of the values of VE, ∆ks, ∆η and ∆Rm with molar fraction x1 of pyridine at 303.15 K are shown graphically in Figures 1—4.

The VE and ∆ks values can be examined qualitatively by considering the factors which influence these func-tions. In general, these functions depend upon several contributions arising from physical, chemical and struc-tural effects.25-28 The physical contributions comprise of dispersive forces or weak dipole-dipole interactions that lead to positive values of VE and ∆ks. Chemical contri-butions include breaking up of associates present in pure liquids (resulting in positive VE and ∆ks) and specific interactions, like formation of hydrogen bonds, charge

Table 3 Calculated values of molar refraction Rm (m3•mol－1) for binary mixtures at 303.15 K from Eq. (6)

Pyridine (1)＋1-Hexanol (2) Pyridine (1)＋1-Heptanol (2) Pyridine (1)＋1-Octanol (2) Pyridine (1)＋1-Decanol (2)

x1 Rm x1 Rm x1 Rm x1 Rm

0.0000 3.1318 0.0000 3.5980 0.0000 4.0585 0.0000 4.3486

0.1186 3.0478 0.1874 3.3824 0.1524 3.8189 0.1594 4.0579

0.2448 2.9609 0.2960 3.2597 0.2946 3.5943 0.3162 3.7676

0.3440 2.8914 0.3751 3.1692 0.4007 3.4254 0.3936 3.6253

0.4548 2.8126 0.4654 3.0642 0.5206 3.2305 0.4917 3.5038

0.5250 2.7605 0.5536 2.9566 0.6026 3.0936 0.6403 3.1674

0.6217 2.6867 0.6340 2.8569 0.6908 2.9435 0.6877 3.0826

0.7254 2.6053 0.7339 2.7303 0.7752 2.7958 0.7620 2.9355

0.8440 2.5106 0.8257 2.6129 0.8717 2.6242 0.8493 2.7680

0.9154 2.4539 0.9186 2.4923 0.9257 2.5240 0.9598 2.4925

1.0000 2.3868 1.0000 2.3868 1.0000 2.3868 1.0000 －4.0644

Table 4 Redlich-Kister coefficients, Ai and standard deviations, σ for excess and deviation functions of binary mixtures at 303.15 K

Function A1 A2 A3 σ

VE/(cm3•mol－1) －2.5201 0.7308 0.2500 0.0251

∆η/(mPa•s) －2.3190 0.5221 1.4594 0.0413

∆ks/(T•Pa－1) －83.0040 25.9500 －5.7780 0.0038

Pyridine (1)＋1-Hexanol (2)

∆Rm/(cm3•mol－1) 7.9473 －1.0137 －5.1485 0.0149

VE/(cm3•mol－1) －1.5475 1.0083 －0.2392 0.0245

∆η/(mPa•s) －3.0802 1.5816 0.9125 0.0613

∆ks/(T•Pa－1) －61.0170 29.9010 －0.8500 0.0022

Pyridine (1)＋1-Heptanol (2)

∆Rm/(cm3•mol－1) 11.8550 －1.6182 －7.5198 0.0258

VE/(cm3•mol－1) －0.4010 0.2809 －0.2241 0.0053

∆η/(mPa•s) －4.0719 2.4797 －1.0111 0.1111

∆ks/(T•Pa－1) －40.3280 21.1420 －5.7100 0.0017

Pyridine (1)＋1-Octanol (2)

∆Rm/(cm3•mol－1) 16.5647 －6.3893 －0.7808 0.0204

VE/(cm3•mol－1) －0.2442 0.0956 0.1569 0.0069

∆η/(mPa•s) －5.7813 2.4513 －0.4563 0.1536

∆ks/(T•Pa－1) －26.3690 17.7780 －4.7400 0.0036

Pyridine (1)＋1-Decanol (2)

∆Rm/(cm3•mol－1) 21.7554 －5.8969 －1.8103 0.0553



transfer complexes and other complex forming interac-tions including strong dipole-dipole interactions be-tween the component molecules in the mixture, which lead to the negative values of VE and ∆ks. The structural contributions include the geometrical fitting of mole-cules of two different molecular sizes into each other’s structure,29 resulting in negative VE and ∆ks values.

Figure 1 shows the dependency of excess molar volumes, VE on the composition of pyridine and 1-al-kanol binary mixtures at 303.15 K. The observed VE values exhibit negative deviations over the entire molar fraction range for all the binary systems at 303.15 K. The extent of negative deviations in excess molar vol-umes can be attributed to the strength of hydrogen bonding between the electronegative N atom of pyridine and one lone pair of electrons available for H atom of —OH group of 1-alkanols. As the size of the alkyl group increases from 1-hexanol to 1-decanol the steric hindrance also increases, resulting in decreased interac-tion between pyridine and 1-alkanol molecules. Hence, the strength of interaction between pyridine and 1-alkanol molecules should follow the sequence: 1-hexanol＞1-heptanol＞1-octanol＞1-decanol, which is supported by the extent of negative deviations in VE (Figure 1). In addition to H-bonding, dipole-dipole and dipole-induced dipole interactions were also expected to operate between unlike molecules.

Figure 1 Excess molar volumes, VE vs. molar fraction (x1) for the binary mixtures of pyridine with (•) 1-hexanol, (■) 1-heptanol, (▲) 1-octanol, and (♦) 1-decanol at 303.15 K.

The observed negative values of ∆ks (Figure 2) for all the investigated systems over the entire composition range indicate the presence of strong interaction be-tween the component molecules of the mixtures. Fort and Moore30,31 suggested that negative deviations in ∆ks from the linear dependence on composition indicate the presence of strong interactions between the component molecules in the mixtures. Also, the negative ∆ks values follow the sequence: 1-hexanol＞1-heptanol＞1-octanol

＞1-decanol, which supports the VE behavior. Figure 3 shows that ∆η values are also entirely negative for all the four binary systems and these negative values follow the sequence: 1-decanol ＞ 1-octanol ＞ 1-heptanol ＞1-hexanol over the complete composition range. Nega-tive deviations in ∆η occur where dispersion and di-pole-dipole forces are operative in the systems,16,32 but they may also occur where components are known to interact more strongly,30,31 as in our case. Garcia et al.3 have also suggested similar deviations in ∆η from ideal-ity as the alkyl chain length increases from methanol to decanol for the binary mixtures N-methylpyrrolidine and alkanols (C1—C10) at 298.15 K.

Figure 2 Deviations in isentropic compressibilities, ∆ks vs. molar fraction (x1) for the binary mixtures of pyridine with (•) 1-hexanol, (■) 1-heptanol, (▲) 1-octanol, and (♦) 1-decanol at 303.15 K.

Figure 3 Deviations in viscosities, ∆η vs. molar fraction (x1) for the binary mixtures of pyridine with (•) 1-hexanol, (■) 1-heptanol, (▲) 1-octanol, and (♦) 1-decanol at 303.15 K.

The curves in Figure 4 show that for all the systems under study the deviations in molar refraction, ∆Rm, are



positive and tend to become more positive with in-creasing chain length of 1-alkanols over the entire composition range, thereby, showing an opposite trend to that of VE values, which is obvious, as suggested by Brocos and co-workers.23 The decrease in ∆Rm (Figure 4) from 1-hexanol to 1-decanol can be explained by considering the size of the alkyl groups, which, in turn, affects the interaction between pyridine and 1-alkanol molecules in the mixtures. As the size of alkyl group decreases from 1-decanol to 1-hexanol, the steric hin-drance also decreases, resulting in increased strength of H-bonding, dipole-dipole, and dipole-induced dipole interactions between unlike molecules, thereby, making ∆Rm decrease in the order: 1-hexanol＜1-heptanol＜1-octanol＜1-decanol. Our finding is supported by the view23,33 that ∆Rm tends to decrease as the strength of interaction between the component molecules in the mixture increases.

Figure 4 Deviations in molar refraction, ∆Rm vs. molar fraction (x1) for the binary mixtures of pyridine with (•) 1-hexanol, (■) 1-heptanol, (▲) 1-octanol, and (♦) 1-decanol at 303.15 K.

Furthermore, the extent of interactions between the component molecules in a mixture is well reflected in the parameters like apparent molar volume, apparent molar compressibility, partial molar volume and partial molar compressibility.22,34 The apparent molar volumes,

Vφ,2, of 1-hexanol, 1-heptanol, 1-octanol and 1-decanol in pyridine were calculated by using the equation: 22

2* E

,2 2( )V V V xφ ＝＋／ (9)

where 2*V and x2 are the the molar volumes and molar

fractions of 1-hexanol/1-heptanol/1-octanol/1-decanol. The partial molar volumes, ,2Vφ

� of 1-alkanols in pyri-dine at infinite dilution were obtained by the method described earlier.34,35 The deviations in ,2Vφ

� at infinite dilution, ∆V, were calculated by using the equation:34

2*

,2V V Vφ∆ ＝－

� (10)

The values of ,2Vφ� , 2

*V and ∆V are listed in Table 5. It is clear from Table 5 that the values of ∆V are nega-tive i.e., partial molar volumes, ,2Vφ

� of 1-hexanol, 1-heptanol, 1-octanol/1-decanol in pyridine at infinite dilution are smaller than their corresponding molar volumes in the pure state 2

*V . The extent of negative deviations in ∆V obeys the sequence: 1-hexanol＞1-heptanol＞1-octanol＞1-decanol. This suggests the appreciable interaction between the component mole-cules in the mixtures.

The apparent molar compressibilities, Kφ,2, of 1-alkanols in pyridine were calculated using the relation:34

* E,2 2 s 2( )K K K xφ ＝＋／ (11)

where KsE[＝(ksV)E] is the excess molar compressibility

of the mixture; *2K is the molar isentropic compressi-

bility of pure 1-alkanols. The partial molar compressi-bilities, ,2Vφ

� , of 1-alkanols in pyridine were obtained by using the method described elsewhere.34,35 The de-viations in ,2Kφ

� , at infinite dilution, ∆K, were obtained by using the relation:22

2*

,2K K Kφ∆ ＝－

� (12)

The values of ,2Kφ� , 2

*K and ∆K are also included in Table 5. The partial molar compressibilities, ,2Kφ

� , of 1-alkanols in pyridine at infinite dilution, characterizes the compressibilities of their molecules in the mixture, whereas, molar isentropic compressibilities, 2

*K , of pure components 1-alkanols can be considered as partial molar isentropic compressibilities of these molecules when dissolved in itself. Mehta and Chauhan35 analyzed the deviations in ∆K in terms of structural and geometrical

Table 5 Values of ,2Vφ� , 2

*V , ∆V, ,2Kφ� , 2

*K and ∆K for the binary liquid mixtures at 303.15 K

,2Vφ� /

(10－5 m3•mol－1) 2*V /

(10－5 m3•mol－1) ∆V/

(10－5 m3•mol－1) ,2Kφ� /

(10－14 m5•N－1•mol－1) 2*K /

(10－14 m5•N－1•mol－1) ∆K/

(10－14 m5•N－1•mol－1) Pyridine (1)＋ 1-Hexanol (2)

12.3386 12.5868 －0.2481 8.4089 9.4339 －1.0250

Pyridine (1)＋ 1-Heptanol (2)

14.0499 14.2472 －0.1972 9.3630 10.2420 －0.8785

Pyridine (1)＋ 1-Octanol (2)

15.8031 15.8720 －0.0689 10.3337 10.9770 －0.6432

Pyridine (1)＋ 1-Decanol (2)

19.1975 19.2297 －0.0322 12.1207 12.6219 －0.5012



compressibilities. The breaking up of the associated structures (on mixing) leads to the structural compressi-bility whereas the geometrical compressibility is due to the simultaneous compression of molecules resulting from specific interactions. The former causes an expan-sion whereas the latter leads to contraction in volume. It is worth to mention that all the values of ∆K (Table 5) for the four binary mixtures studied are negative and these negative values follow the order: 1-hexanol＞1-heptanol＞1-octanol＞1-decanol. Negative values of ∆K are indicative of significant interactions between the component molecules in the mixtures, that is, the geo-metrical compressibility factor (due to H-bonds, dipole- dipole and dipole-induced dipole interactions between pyridine and 1-alkanols molecules) dominates over the structural compressibility factor (breaking up of associ-ated structures of component molecules). We, thus, con-clude that the behaviour of VE, ∆ks, ∆η, ∆Rm, ∆V and ∆K supports each other for the systems under study.

Conclusion

In the present investigation we have measured the densities, viscosities, refractive indices and speeds of sound in the binary mixtures of pyridine and 1-hexanol/1-heptanol/1-octanol/1-decanol over the whole composition range at 303.15 K. The negative deviations in VE values over the entire composition range for all the binary systems suggest the presence of strong interactions between pyridine and 1-alkanol molecules and that the strength of interaction follows the order: 1-hexanol ＞ 1-heptanol ＞ 1-octanol ＞

1-decanol. The ∆ks values are also negative, indicating the presence of strong interactions between the compo-nent molecules of the mixtures, thereby, supporting the behaviour of VE. The observed negative values of ∆η for all the binary systems follow the trend: 1-decanol＞1-octanol＞1-heptanol＞1-hexanol. The positive devia-tion in ∆Rm was found to increase with increase in the chain length of 1-alkanols over the entire composition range. The observed decrease in the magnitude of ∆Rm indicates that the strength of interactions between the component molecules increases in the mixtures. The negative values of ∆V and also of ∆K for 1-alkanols in pyridine over the entire composition range for all the binary mixtures clearly suggest the presence of signifi-cant interactions between the component molecules. Therefore, it is concluded that all the parameters derived from the density, viscosity, refractive index and speed of sound are in good agreement with each other.

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density, viscosity, refractive index, and speed of sound in binary mixtures of pyridine and...

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