Indian Journal of Chemical Technology Vol. !0, January 2003. pp. 21-26

Articles

Molecular interactions in binary liquid mixtures of a-xylene with 1-alkanols at 303.15 K

C L Prabhavathi'*, K Sivakumarb, P Yenkateswarlu & G K Raman Department of Chemistry, S V U College of Engineering, Tirupati 517 502, India

"Controller of Examinations, S P Mahila University, Tirupati 517 502, India

bDepartment of Chemistry, S V Arts College, Tirupati 517 502, India

Received 27 June 2001; revised received 25 September 2002; accepted 19 November 2002

Excess molar volumes (v") and isentropic compressibilities (ks) for binary mixtures of o-xylene with /-propanol, / -butanol and /-pentanol have been measured at 303.15 K. Excess volume exhibits an inversion in sign in all the three bi­nary mixtures. Further, deviation in isentropic compressibility (Ks) from ideal behaviour was also calculated. Ks values ex­hibits an inversion in sign for the binary mixture o-xylene + /-propanol and the quantity is positive over the entire range of composition in the remaining two mixtures. The experimental sound velocity data have been analysed in terms of Free length theory (FLT) and Collision factor theory (CFT ). The measured data is explained on the basis of intermolecular inter­actions between unlike molecules.

A survey of the literature has shown that 0 data for the binary mixtures of benzene with /-alkanols1·2, toluene with /-alkanols3

, xylenes with chlorotolue­nes4, xylene with iso-alcohols5, xylenes with esters6, xylenes with aliphatic hydrocarbons7 have been re­ported. Further, 0 data for a series of 1 -alkanols with xy lenes at 298.15 K were reported earlier8

•9

• The pres­ent work was undertaken by utilizing this data for further study of excess thermodynamic properties at thi s temperature. Also isentropic compressibility data for binary mixtures of benzene with l-alkanols 10 and toluene with /-alkanols 11 were reported earlier. In the present study, excess volumes and isentropic com­pressibilities of the binary mixtures of a-xylene with /-propanol , 1 -butanol and 1 -pentanol have been re­ported. The sound velocity data have been analysed in terms of Free length theory 12 (FLT) and Collision factor theory (CFT) 13

. The theoretical aspects of FL T and CFT have been described in detail by Chowdary and Naidu 14. Further, the present study was under­taken to know the effect of addition of another methyl group in toluene that may influence both the sign and magnitude of excess volume and deviation in isen­tropic compressibility.

Experimental Procedure o-x y lene and 1 -alkanols were purified by the meth-

*For correspondence [E-mail : vcpspmvv@yahoo.com; Fax: (08574)484 17]

ods described by Riddick and Bunger15. The purity of the samples was checked by comparing the densities of the components with those reported in the litera­ture15'16. Densities were determined by using a bicap­illary type pycnometer which offered an accuracy of 2 parts in 105. Excess volumes were measured using the dilatometer of the type described earlier17

• The values of 0 were accurate to 0.003 cm3mor'. Isentropic compressibilities were computed from density and sound speed data using the relation

k U-2 p - l s=

where u is the sound speed and p is the density of the mixture.

The ultrasonic sound speed was measured with a single crystal interferometer at 4 MHz frequency and the data were accurate to ± 0.15 %. All the measure­ments were carried out at constant temperature em­ploying a thermostat that could be maintai ned to± 0.01 K.

Results and Discussion The experimental excess volumes of three binary

mixtures are given in Table 1 and these are graphi­cally represented in Fig. I. 0 values were fitted to an empirical relation proposed by Redlich-Kister18.

0 /cm3mor' =X, (I-X,) [a0+a, (2X,-l) + az (2X,- I )21 ... ( I )

Articles Ind ian J. Chern. Techno l. , January 20o:1

Table I - Mole fraction of a-xylene ( X1) and excess volu me (II') for the bi nary mixtures of o-xy lene with I -alkanols at 303.15 K

Mole fraction (X1) 0tcm3 mor 1 Mole fraction (X1) 0!cm3mor 1 Mole fraction (X1) vEtcm3 mor 1

of o-xylene of o-xy lene of a-xy lene a-xylene+/-propanol a-x ylene+l-butanol a-xy lene+l-pentanol

0.0684 -0.010 0.0525 -0.006 0.0626 -0.013

0.0917 -0.014 0.086 1 -0.010 0.0947 -0.018

0.1120 -0.018 0.1029 -0.01 1 0.1286 -0.021

0.1826 -0.030 0. 1319 -0.0 14 0. 1850 0.022

0.2106 -0.034 0.200 1 -0.0 18 0.2229 -0.021

0.2529 -0.039 0.2670 -0.0 17 0.2831 -0.014

0.3175 -0.042 0.356 1 -0.008 0.3307 -0.07

0.4219 -0.035 0.4250 0.005 0.4206 0.017

0.5010 -0.019 0.5045 0.027 0.4999 0.032

0.6511 0.026 0.5656 0.046 0.5736 0.051

0.7217 0.047 0.6566 0.073 0.6329 0.064

0.8029 0.062 0.7284 0.089 0.7082 0.076

0.8719 0.061 0.8168 0.095 0.7857 0.079

0.932Q 0.044 0.8979 O.D75 0.8 122 0.078

0.9511 0.035 0.9206 0.064 0.8839 0.063

Table 2 - Standard deviation and values of constants from the Redlich-Kister equation , Eq. (I) and Hwang el a/. equation , Eq. (2)

System

o-xylene +/ -propanol

o-xylene + 1 -butanol

o-xylene +1 -pentanol

ao

-0.0771

0.1024

0. 1318

CIJ

0.4942

0.5920

0.5225

Eq. (I)

Cl ]

cm3 mor 1

0.4680

0.3869

0. 1301

where a0. a 1 and a 2 are adjustable parameters and X1 is the mole fraction of o-xylene. The values of parame­ters are obtained by the least-square method. Further, v'" results were alsa fitted to the semi-empirical equa­tion proposed by Hwang et a/ 19

•

V /cm3mor 1 = Xt Xz [bo+bt Xt 3 + bz Xz3] ... (2)

where X1 and X2 represent mole fractions of o-xylene and 1-alkanol and b0 , b 1• and b2 are constants. The computation of ' b' coefficients in the above equation was desctibed earlier20

"2 1

. The values of the two sets of constants are given in Table 2 along with standard deviations. The standard deviation values given in Table 2 point out that the equation of Hwang et al. also represents precisely the 0 data. Data for density (p), computed from measured excess volumes and experimental sound velocity data (u), are included· in columns 2 and 3 of Table 3. Isentropic compressibi-

22

Eq. (2)

a(0) bo bl be a (\IE)

cm3 mor 1

0.000 -0.2332 1.2124 0.0357 0.002

0.000 -0.0266 1.2205 -0.1 g89 O.Oo:l

0.001 0.0884 0.7954 -0.4486 0.002

lity, ks and the deviation in isentropic compress ibility, Ks are also included in columns 4 and 5 of Table 3. The deviation in isentropic compressibi lity, K5, va lues are graphically represented in Fig. 2. ks and Ks were calculated using the-relations,

k U·2 p · l s=

P = ( Xt Mt + Xz Mz )I(V1+ VO) Ks = k,- (</Jt Kst + ¢z Ksz)

</Jt = Xt Vt 01( Xt Vt 0+Xz Vz 0)

V1° = X1 V1° +Xz Vz0 and <Pt = 1-¢2

(J)

(4)

(5)

(6)

where X, M and VO denote the mole fraction, molec u­lar weight, molar volume of the mixture and Ks, Ks1

and Ks2 denote compressibi li ties of the mixtures and the components I and 2 respectively. Ks represents the deviation in isentropic compressibility from ideal

Prabhavathi et al.: Molecular interactions in binary liquid mixtures of a-xylene wi th l-alkanols at 303.15K Articles

Table 3 - Volume fracti on (¢1) of a-xylene, density (p), sound velocity (u), isentropic compressibility (ks) and deviation in isentropic compressibility (Ks) of a-xylene with /-alkanols at 303. 15 K

1/JJ p 11 ks Ks

gm/cc m/s TPa - I TPa - I

a-xylene+ / -propanol

0.0000 0.79601 1192 884 0.1058 0.804 11 1211 848 -II 0.1400 0.80673 1215 839 - 12 0.1690 0.80896 12 18 833 - II 0.2648 0.81631 1225 816 -6 0.3007 0.81906 1227 811 -2 0.3530 0.82306 1229 804 3 0.4285 0.82878 1234 793 10 0.5405 0.83717 1242 774 18 0.618 1 0.84288 125 1 758 20 0.7505 0.85252 1272 725 IH 0.8070 0.85662 128 1 711 18 0.8678 0.86112 1292 696 17 0.9165 0.86481 1309 675 7 0.9573 0.86803 1319 662 4 0.9691 0.86899 1322 658 3 1.0000 0.87158 1330 649

a-xy lene+ /-butanol

0.0000 0.80201 1232 821 0.0680 0.80679 1235 812 3 0.1104 0.80978 1237 807 5 0.1312 0.81124 1239 805 7 0.1668 0.81373 1244 800 8 0.2479 0.81940 1248 788 10 0.3243 0.82471 1248 778 13 0.4215 0.83140 1256 763 15 0.4935 0.83631 1259 754 18 0.5729 0.84165 1265 743 21 0.63 17 0.84560 1268 731 19 0.7158 0.85125 1284 713 16 0.7794 0.85556 1291 701 15 0.8545 0.86076 1302 685 12 0.9205 0.86551 1312 671 9 0.9305 0.8664 1317 665 6 1.0000 0.87158 1330 649

a-xylene+ / -pentanol

0.0000 0.80760 1270 768 0.0693 0.812 13 1271 762 2 0.1045 0.81442 1270 761 6 0.1414 0.81680 1270 759 8 0.2021 0.82069 1272 753 9 0.2425 0.82327 1273 750 II 0.3059 0.82727 1275 744 13 0.3554 0.83039 1275 741 16 0.4475 0.83611 1279 731 17 0.5273 0.84110 1281 724 19 0.6002 0.84563 1285 716 20 0.6580 0.84923 1291 707 18

(Crmtd)

23

Articles Indian J. Chern. Techno!., January 2003

Table 3 - Volume fraction {(/)1) of o-xylene, density {p), sound velocity (u), isentropic compressibility (k,) and deviation in isent ropic compressibility (Ks) of o-xylene with 1-alkanols at 303.15 K-Contd

1/JI p

gm/cc

0.7303 0.85378 0.8036 0.85844 0.8283 0.86004 0.8947 0.86439 1.0000 0.87158

Table 4 - Values of parameters co. c1 and c2 for Eq. (7) and the standard deviation a( Ks) at 303.15 K

System co c 1 c2 a (Ks)

TPa·1

o-xy lene + / -propanol 63.068 144.083 -108.391 2

o-xy lene + / -butanol 70.172 33.082 4.347

o-xy lene + /-pentanol 76.310 9.506 -30.809

Table 5 - Experimental and predicted sound velocity data for the binary mixtures of o-xylene with / -alkanols at 303.15 K

Mole fraction UEXP UfLT ucFT of o-xy lene (X 1) mls m/s m/s

a-xylene +/-propanol

0.0684 1211 1201 1214 0.0917 1215 1205 1218 0. 11 20 1218 1208 1222 0.1826 1225 1219 1235 0.2106 1227 1224 1240 0.2509 1229 1230 1247 0.3175 1234 1240 1257 0.4219 1242 1256 1271 0.5010 125 1 1267 1281 0.65 11 1272 1287 1299 0.72 17 128 1 1297 1306 O.lW29 1292 1307 1314 0.8719 1309 1315 1320 0.9329 1319 1322 1325 0.9511 1322 1324 1326

o-xylene +/-butanol

0.0525 1235 1238 1236 0.0861 1237 1244 1241 0.1029 1237 1243 1243 0.1319 1239 1246 1246 0.2001 1244 1253 1254 0.2670 1248 1260 1262 0.3561 1256 1269 1272 0.4250 1259 1276 1279 0.5045 1265 1284 1287 0.5656 1260 1289 1293 0.6566 1284 1298 1302 0.7284 1291 1305 1308 0.8168 1302 1313 1315 0.8979 1312 1321 1322 0.9206 1317 1323 1324

24

fJ ks K s m/s TPa - l TPa - I

1297 696 16 1307 682 II 1310 678 9 1317 667 6 1330 649

Table 5 - Experimental and predicted sound velocity data for the binary mixtures of o-xylene with 1-alkanols at 303.15 K- Co11 td

Mole fraction UEXP UFLT UCI·T

of o-xylene (X 1) m/s m/s m/s

a-xylene+ / -pentanol

0.0626 1271 1262 1264 0.0947 1270 1264 1267 0.1286 1270 1267 1269 0.1850 1272 1271 1273 0.2229 1273 1274 1276 0.2831 1275 1278 128 1 0.3307 1275 128 1 1284 0.4206 1279 1288 129 1 0.4999 1281 1294 1296 0.5736 1285 1299 1301 0.6329 129 1 1303 1306 0.7082 1297 1309 1311 0.7857 1307 13 15 1316 0.8122 1310 1317 1318 0.8839 1317 1322 1322

value which is assumed to be additive in terms of vol­ume fraction . t/J1 and t/J 2 denote the volume fractions of the components 1 and 2 respectively and pis the den­sity of the mixture. The values of isentropic com­pressibilities are accurate to ± 2 TPa· ' .

The dependence of Ks on volume fraction is ex­pressed by an empirical equation.

.. . (7)

where c0, c 1 and c2 are adjustable parameters. These values are calculated by the method of least squares and are given in Table 4 along with standard deviation cr ( Ks).

The sound velocity data predicted in terms of Free , length theory (FL T) and Collision factor theory (CFT) are given along with the experimental results in col­umns 3 and 4 of Table 5. The methods and the details of calculations are discussed earlier22

.

The values of molar volume (V m). molar volume at absolute zero (V0}, available volume (Va). free length (Lr), surface area (Y}, collision factor (S), average ra-

Prabhavathi eta/.: Molecu lar interactions in binary liquid mixtures of a-xy lene with /-alkanols at 303. 15K Articles

Table 6 - Calculated values of molar volume (V,), molar volume at absolute zero ( V0), molar ava ilable volume (Va), free length (Lr) sur­face area ( Y) . colli sion factor (S), average molecular radius ( r ) and actual volume of molecules per mole (B) of pure liquid components at

303. 15 K

Component

o-xy lene

/ -propanol

/ -butanol

/ -pentanol

·~ 0 E

"' E u

~ >

0 -10

VIII Va v" cm3 mor 1

12 1.8 12 100.055 21.757

75.537 58.852 16.685

92. 146 73.028 19.1 35

109. 148 87.682 21.466

c>--<:> : 1- propanol

- ·. 1- butanol >e---X : 1- p<Zntanol

Fig. !- Mole fracti on of a-xy lone versus VE/cm-3mol- 1

LJ Ao

0.5082

0.5945

0.5738

0.5587

dius of the molecules per mole (r) , actual volume of the molecules per mole (B) of pure components are given in Table 6. These data were taken from the lit­erature2'"24.

The vE data which is presented in Table I can be explained on the basi s of two opposing contributions namely, (i) a positive term from the rupture of a lka­nol -a lkanol hydrogen bonds and physical dipole­dipole interactions between alkanol monomers and polymers and (ii) a negative term from the formation of OH----n elec tron hydrogen-bonded complexes; changes of free vo lume and interstitial accommoda­tion .

y s cm3 mor 1

85.622 1.7143

56.131 1.7277

66.957 1.7185

76.925 1.7024

20

10

r

Ao

2.860

2.345

2.539

2.714

B

cm3 mor 1

59.06

32.77

41.32

50.47

o--o : 1 -propanol _ , !-butanol x-x: 1-P<Zntanol

-20~--~~--~~--~~--~~--~ 0 0·2 0 ·4 0·6 0 ·8 1·0

Fig. 2- Yolume fraction of a-xy lene versus Ks/TPa- 1

An examination of results in Fig. I points out that vE data for binary mixtures of a-xylene with 1-propanol, } -butanol and 1-pentanol exhibit an in ver­sion in sign. This suggests that factors (i) and (ii) compete with each other in all the three binary mi x­tures. Further, vE curves for all mixtures are wave­shaped; negative value at lower mole fraction (X1 ) of a -xylene and positive at higher X1• This is due to fac­tor (i) contributions being relatively important at hi gh value of x~. where the effect of the breaking of alka­nol-alkanol H-bonds is relatively very large. At lower mole fraction of a -xylene, X1, the dissociation of the alkanol is of less importance and the balance is essen­tially dependent on the negative contributions. How­ever, v£ values for mixtures of a-xy lene with 1 pro­panol, 1 -butanol and 1 -pentanol are algebraically smaller than those for mixtures of toluene with same alkanols. This shows that the addition of another methyl group in toluene has influenced the sign and magnitude of v£.

An observation of Fig. 2 shows that Ks is positi ve for mixtures of a-xylene+ }-butanol and a -xyl ene +1-pentanol and the quantity exhibits an inversion in sign

25

Articles

in the mixture of a-xylene +/-propanol. The experi­mental values of Ks may be attributed to the relative strength of effects which influenced the free space defined by Jacobson25

. Thi s suggests that positive values of Ks arise due to breaking of hydrogen bonds in se lf-associated alkanols and physical dipole-dipole interactions between alcohol monomers and mul­timers. The negative Ks values are due to changes of

free volume in real mixtures and the presence of 7t

electrons in a-xylene resulting in the formation of weak intermolecular complexes26

. The experimental Ks va lues in Table 3 suggest that the factor which is responsible for positive values is dominant in the bi­nary mixtures of a-xylene +/-butanol and a-xylene+ J -pentano l. On the other hands both the factors com­pete with each other in varying degrees in the mixture of a-xy lene +/-propanol.

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