J. Chem. Thermodynamics 41 (2009) 1329–1338

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J. Chem. Thermodynamics

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Thermodynamic, transport, and spectroscopic studies for mixtures of isomericbutanediol and N-methyl-2-pyrrolidinone

S.K. Mehta *, Ganga Ram, Rajat Chauhan, K.K. BhasinDepartment of Chemistry and Centre of Advanced Studies in Chemistry, Panjab University, Chandigarh 160 014, India

a r t i c l e i n f o a b s t r a c t

Article history:Received 12 January 2009Received in revised form 4 June 2009Accepted 6 June 2009Available online 11 June 2009

Keywords:Thermodynamic characterizationSpectroscopic measurementsIsomeric butanediolN-methyl-2-pyrrolidinone

0021-9614/$ - see front matter � 2009 Elsevier Ltd. Adoi:10.1016/j.jct.2009.06.006

* Corresponding author. Tel.: +91 172 2534423; faxE-mail address: skmehta@pu.ac.in (S.K. Mehta).

The thermodynamic parameters viz. excess molar volume VE and speed of sound u, transport parameterviscosity g, and spectroscopic parameters viz. IR, 1H, 13C NMR have been measured for the mixtures ofisomeric butanediol (1,2-, 1,3-, 1,4-, and 2,3-butanediol) and N-methyl-2-pyrrolidinone over the wholecomposition range at 308.15 K. The partial molar quantities QE

i , isentropic compressibility KES , viscosity

deviation Dg, deviation in Gibbs free energies of activation for viscous flow g(x), and excess NMRchemical shift dE have been estimated and analyzed. Results show that the interaction between unlikemolecules takes place through hydroxyl groups of isomeric butanediol and �CO group of N-methyl-2-pyrrolidinone. Excellent agreement between thermodynamic and spectroscopic measurements isobserved.

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1. Introduction

Amide association constitutes a simple model system for basepairing in nucleic acids as well as for peptide bond interactionsin polypeptides and proteins. Particularly interesting are cyclicamides (lactams) in which the nitrogen and carbon atoms of thepeptide bond are composed by a ring composed of methylenegroups. Cyclic amides in general are high density, high boilingpoint, and high polarity solvents. They are completely miscibleover the entire composition range with water. 2-Pyrrolidinoneand its methyl derivative, that is, N-methyl-2-pyrrolidinone havebeen used as cosolvent in the petroleum industry to increase theselectivity and solvent power for extracting aromatic hydrocarbonsand have excellent thermal and chemical stability [1–8]. García etal. [1] have determined excess volumes, mixing viscosities, and ex-cess Gibbs free energies of activation of viscous flow of the aqueousbinary mixtures of the amides formamide, N-methylformamide,N,N-dimethylformamide, pyrrolidin-2-one, and N-methyl-2-pyrro-lidinone from density and viscosity measurements. The values ofthese functions point to strong amide–water interaction with theformation of a variety of aggregates, the nature of which dependson the extent of substitution of the amides. George and Sastry [3]reported experimental densities, viscosities, speeds of sound, andrelative permittivities, for three binary mixtures of (water + 2-pyr-rolidinone, +N-methyl-2-pyrrolidinone, and +N-vinyl-2-pyrrolidi-none) over the entire composition range and at differenttemperatures. The analysis revealed that both hydrophobic and

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hydrophilic hydrations are responsible for the complex nature ofthe thermophysical behavior in these mixtures. Densities and vis-cosities for binary mixtures of N-methyl-2-pyrrolidinone withcyclohexane, benzene, toluene, p-xylene, and ethylbenzene at dif-ferent temperatures and atmospheric pressure have been reportedby Yang et al. [7–9]. The molecular interactions between N-methyl-2-pyrrolidinone and aromatic hydrocarbons have been analysed byLiu and coworkers [10]. Recently, Dávila and Trusler [11] reportedthermodynamic properties of mixtures of N-methyl-2-pyrrolidi-none and methanol. It is anticipated that there is a propensity toform hydrogen bonds between each lone pair of electrons on theoxygen atom in the N-methyl-2-pyrrolidinone molecules and amethanol molecule.

Alkanediols are the simplest and model structural units forpolyhydroxy compounds. These compounds play a significant rolein industry due to their wide range of practical applications, suchas antifreezes, coolants, aircraft deicing fluids, heat transfer fluids,hydraulic fluids, solvents, food, flavor and fragrances, pharmaceu-ticals, chemical intermediates, plasticizers, thermoset plastic for-mulations, petroleum, textile, and other industries. The structuraland interactional analysis of alkanediols in water mixtures hasbeen extensively studied [12–18]. Nakanishi et al. [12] obtained ex-cess molar volume of aqueous solutions of different diols and it hasbeen found that the volumetric behavior of a,x-alkanediols is al-most same, although their VE slightly increases with molecularsize. However, if one of –OH group is not located at the end of diolmolecule, the interstitial contribution due to possible cavity occu-pation by methyl group result in a large volume loss. Palepu andcoworkers [16,17] have reported various thermophysical proper-ties of aqueous solutions of isomeric butanediol to study the

1330 S.K. Mehta et al. / J. Chem. Thermodynamics 41 (2009) 1329–1338

influence of change in the relative –OH positions along the alkylchain of isomeric butanediol in water. George and Sastry [18] re-ported densities, viscosities, speed of sound, and relative permit-tivities for water + alkanediols and found that the water moleculewith diols results less overall volume indicating that structure-making effects are prevalent in aqueous solution of diols. Resultsshow that a,x-alkanediols facilitate heteroatomic hydrogen bond-ing between water and diol, whereas, terminal hydrophobic –CH3

groups induced the compression effects in surrounding watermolecules.

Alkanediol-amide mixed solvents constitute interesting binaryliquid systems, however fewer experimental data are available[19–21]. As a part of our research program of measuring physico-chemical properties of diols in amides [22–26], we report thermo-dynamic, transport and spectroscopic parameters of isomericbutanediol (BTD) in N-methyl-2-pyrrolidinone (NPY). The resultshave been compared with mixtures of diols in N,N-dimethylform-amide (DMF)/pyrrolidin-2-one (PY)/water and analyzed.

2. Experimental

2.1. Materials

N-methyl-2-pyrrolidinone (NPY; >99 g.c.) and 1,2-butanediol(1,2-BTD; >98 g.c.) obtained from Fluka and 1,3-butanediol(1,3-BTD; >99 g.c.), 1,4-butanediol (1,4-BTD; >99 g.c.) and 2,3-butanediol (2,3-BTD; >98 g.c.) were purchased from Merck.N-methyl-2-pyrrolidinone was dried with CaO and fractionally dis-tilled as described elsewhere [27]. Prior to use, all the chemicalswere stored over molecular sieves to remove any traces of water.The water impurity in the chemicals was as low as <0.005 mol%.The purity of all the chemicals was checked by comparing theirdensities (measured using Anton Paar digital precision densimeterDMA 60) with literature values [3,16] (table 1). This densimeterwas calibrated before and after each set of density measurementsusing the density of water [3] at 308.15 K. The uncertainty indensity measurements was �1 � 10�2 kg �m�3.

2.2. Methods

The binary solutions were prepared by weight with a precision±1 � 10�4 g. Precautions were taken to prevent evaporation. Theestimated uncertainty in the mole fraction was less than±2 � 10�4 g.

TABLE 1Densities (q*), speed of sound (u*), molar isentropic compressibility K�S, viscosities (g*), isob308.15 K.

Component q*/(kg �m�3) q�lit/(kg �m�3) u*/(m � s�1) u�lit/(m � s�1) K�S/(TPa�1

NPY 1019.03 1019.31a 1509.87 1518.4a 41.871,2-BTD 988.25 991.43b 1422.61 1423.6b 45.59

991.42c 1423.8c

1,3-BTD 991.28 994.20b 1496.03 1495.6b 40.98994.42c 1492.1c

1,4-BTD 1003.95 1006.47b 1577.76 1578.5b 35.921006.40c 1588.0c

2,3-BTD 990.72 990.74b 1456.60 1459.0b 43.27992.11c 1440.0c

a Reference [3].b Reference [16].c Reference [18].d Reference [17].e Reference [39].f Derived from density [3].g Derived from density [16].h At 293.15 K ([27]).i At 298.15 K

The measurement of excess molar volume was carried out in acontinuous dilution dilatometer. Known amounts of the two com-ponents of each mixture were confined over mercury in the ab-sence of air in the bulb and the glass tube of the continuousdilution dilatometer. The number of moles of the component 1was calculated from the weight of the component 1 added in themixing bulb and that of component 2 from the length of the mer-cury displaced from the glass tube. The excess molar volume wascalculated from the change in the mercury height in the precali-brated capillary. Volume correction was used for the capillary toget actual volumes. The dilatometer was immersed in a water bathcontrolled to better than ±0.01 K. Temperature control wasachieved using a circulating water bath, regulated to ±0.01 K, usinga proportional temperature controller. The temperature was cali-brated to 308.15 ± 0.01 K with a precision platinum resistancethermometer. Details of the experimental set-up and the measur-ing procedure have been described elsewhere [28]. The resultsfor VE are estimated to be accurate to ±0.002 cm3 �mol�1.

An ultrasonic time intervalometer (UTI-101) from InnovativeInstruments based on the pulse-echo-overlap technique (PET) cou-pled with an oscilloscope was used for the speed of sound mea-surements. The frequency of sound was 2.0 MHz. The cell for thespeed of sound measurements was calibrated with water [29] asa reference. The temperature was maintained by circulating wateraround the double walled cell at 308.15 ± 0.01 K. The uncertaintyin the measurement of ultrasonic velocity was within±2 � 10�2 m � s�1.

Viscosity measurements were made using modified form of Ub-belohde viscometer placed in a water thermostat, the temperatureof which was controlled to ±0.01 K. The flow time of definite vol-ume of liquid through the capillary was measured with an accuratestopwatch with a resolution of 1 � 10�2 s. Viscosity values areuncertain to within the range 0.001 mPa � s.

1H and 13C NMR chemical shifts were observed with the help ofa JEOL AL 300 MHz FT NMR spectrometer operating at 300 MHz. Inorder to determine the chemical shift d for liquid mixtures of NPYand BTD at entire composition range, CDCl3 was used as an exter-nal solvent for all the NMR measurements. The uncertainty in dvalues was estimated to within the range ±0.001 ppm. Perkin El-mer (RX1) FT-IR spectrometer in the frequency range (4400 to350) cm�1 was utilized to record the FT-IR spectra. The uncertaintyin the measurement of wave number m was within �0:1 cm�1. Allthe spectroscopic measurements were carried out at roomtemperature.

aric thermal expansivities ða�pÞ, and molar heat capacities ðC�pÞ for pure components at

�m3 �mol�1) g*/(mPa � s) g�lit/(mPa � s) a�p/(10�4 � K�1) C�p/(J � K�1 �mol�1)

1.668 1.365a 9.118f 166.1h

30.294 29.48d 10.077g 228.8b,i

30.177c

54.236 53.72d 9.326g 218.4b,i

52.500c

47.378 45.24d 8.595g 202.1b,i

44.871c

51.380 49.00d 8.201g 225.8b,i

57.105e

TABLE 2Excess molar volume VE values for {x BTD + (1 � x) NPY} at 308.15 K.

x VE/(cm3 �mol�1) x VE/(cm3 �mol�1) x VE/(cm3 �mol�1) x VE/(cm3 �mol�1)

1,2-BTD 1,3-BTD 1,4-BTD 2,3-BTD0.0176 �0.012 0.0003 �0.009 0.0188 �0.032 0.0015 �0.0290.0674 �0.055 0.0047 �0.022 0.0277 �0.043 0.0022 �0.0430.0777 �0.064 0.0143 �0.041 0.0280 �0.061 0.0051 �0.0620.0936 �0.068 0.0217 �0.049 0.0461 �0.071 0.0107 �0.0860.0998 �0.094 0.0334 �0.053 0.0535 �0.083 0.0184 �0.1110.1104 �0.110 0.0387 �0.053 0.0780 �0.097 0.0226 �0.0980.1172 �0.133 0.0472 �0.055 0.0895 �0.108 0.0270 �0.1500.1763 �0.153 0.0616 �0.056 0.1052 �0.113 0.0410 �0.1780.2053 �0.179 0.0780 �0.055 0.1307 �0.126 0.0606 �0.2010.2235 �0.205 0.0895 �0.054 0.1557 �0.142 0.0667 �0.2060.2485 �0.236 0.1097 �0.042 0.1850 �0.150 0.0755 �0.2070.2493 �0.216 0.1237 �0.039 0.2257 �0.164 0.0865 �0.2070.2827 �0.249 0.1608 �0.036 0.2381 �0.166 0.0908 �0.2060.2924 �0.271 0.2074 �0.026 0.2563 �0.172 0.0996 �0.2030.3248 �0.268 0.2146 �0.024 0.2968 �0.184 0.1102 �0.1990.3361 �0.272 0.2387 �0.019 0.3354 �0.188 0.1135 �0.1960.3432 �0.283 0.2487 �0.010 0.3634 �0.196 0.1176 �0.1930.3843 �0.293 0.2949 �0.003 0.3865 �0.198 0.1323 �0.1860.4095 �0.300 0.3052 0.002 0.4046 �0.195 0.1518 �0.1690.4555 �0.302 0.3425 0.011 0.4370 �0.194 0.1734 �0.1540.4806 �0.305 0.3666 0.013 0.4850 �0.184 0.1849 �0.1470.5199 �0.312 0.4208 0.023 0.5355 �0.177 0.2001 �0.1410.5475 �0.307 0.4400 0.031 0.5770 �0.166 0.2086 �0.1360.5748 �0.293 0.4748 0.036 0.6118 �0.154 0.2137 �0.1300.5934 �0.292 0.5171 0.042 0.6265 �0.149 0.2251 �0.1290.6057 �0.285 0.5605 0.048 0.6374 �0.148 0.2329 �0.1210.6300 �0.280 0.5935 0.051 0.6697 �0.143 0.2407 �0.1190.6515 �0.269 0.6201 0.055 0.6863 �0.139 0.2468 �0.1160.6744 �0.256 0.6456 0.052 0.7034 �0.139 0.2543 �0.1110.7069 �0.233 0.6679 0.052 0.7387 �0.132 0.2683 �0.1010.7533 �0.201 0.6845 0.050 0.7746 �0.120 0.2829 �0.0910.8073 �0.162 0.6940 0.047 0.7979 �0.104 0.3050 �0.0750.8614 �0.125 0.7307 0.035 0.8498 �0.088 0.3138 �0.0700.8948 �0.092 0.7566 0.032 0.8771 �0.071 0.3240 �0.0610.9231 �0.079 0.7884 0.026 0.9123 �0.055 0.3341 �0.0520.9466 �0.066 0.8063 0.025 0.9254 �0.051 0.3428 �0.0440.9482 �0.063 0.8357 0.013 0.9672 �0.026 0.3640 �0.0260.9584 �0.061 0.8925 0.002 0.9942 �0.016 0.3792 �0.0090.9652 �0.059 0.9149 0.003 0.3971 0.0100.9776 �0.047 0.9239 0.008 0.3971 0.0100.9798 �0.042 0.9552 0.009 0.4356 0.0250.9912 �0.012 0.9727 0.008 0.4515 0.038

0.9991 0.006 0.4699 0.0550.4898 0.0680.5000 0.1130.5200 0.1360.5465 0.1660.5730 0.1750.5809 0.1780.5957 0.1880.6268 0.1850.6433 0.1820.6625 0.1710.6992 0.1630.7232 0.1530.7456 0.1490.7695 0.1360.7848 0.1300.8011 0.1230.8394 0.1160.8530 0.1040.8777 0.0870.8909 0.0760.9056 0.0710.9116 0.0670.9201 0.0580.9309 0.0530.9421 0.0430.9563 0.035

S.K. Mehta et al. / J. Chem. Thermodynamics 41 (2009) 1329–1338 1331

0.0 0.5 1.0-2.5

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

x

KE S /

TPa

-1m

3 mol

-1

FIGURE 2. Plot of excess isentropic compressibilities KES against mole fraction for x

BTD: d, 1,2-BTD; s, 1,3-BTD; 4, 1,4-BTD; N, 2,3-BTD; +(1 � x) NPY; — fitting withequation (5).

0.0 0.5 1.0-0.4

-0.2

0.0

0.2

x

VE /

cm3 m

ol-1

FIGURE 1. Plot of excess volumes VE against mole fraction for x BTD: d, 1,2-BTD; s,1,3-BTD; 4, 1,4-BTD; N, 2,3-BTD; +(1 � x) NPY; — fitting with equation (5).

1332 S.K. Mehta et al. / J. Chem. Thermodynamics 41 (2009) 1329–1338

3. Results and discussion

3.1. Thermodynamic properties

The experimentally measured excess molar volume VE valuesfor mixtures of NPY and BTD at 308.15 K are summarized in table2 and graphically presented in figure 1. The VE values are negativefor 1,2-BTD and 1,4-BTD and both positive and negative for 1,3-BTD and 2,3-BTD. These results show strong hydrogen bonding be-tween �C@O group of NPY and –OH groups of diols in the case of1,2-BTD and 1,4-BTD. In our earlier reports on 1,4-BTD and 1,2-BTD in PY [22] and DMF [23], it was observed that 1,4-BTD inter-acts more strongly than 1,2-BTD. However, opposite results havebeen obtained in the present work. The large negative VE valuesfor (1,2-BTD + NPY) mixtures than that of (1,4-BTD + NPY) mix-tures may be due to either disruption of more strongly self-associ-ated 1,4-BTD than 1,2-BTD or confinement of two hydroxyl groupsin 1,2-BTD at one end of the diol chain, forming effective hydrogenbonding with NPY. The breaking of self-associated diols results inpositive VE particularly in the case of 1,3-BTD and 2,3-BTD.

A comparative analysis of VE values of BTD in NPY than of samediols in DMF [23] and PY [22] reveals that in lower diol region, vol-

TABLE 3Speed of sound u values for {x BTD + (1 � x) NPY} at 308.15 K.

x u/(m � s�1) x u/(m � s�1)

1,2-BTD 1,3-BTD0.0282 1515.79 0.0282 1499.580.0564 1510.05 0.0582 1496.740.1026 1509.48 0.1089 1496.450.1884 1504.20 0.2015 1491.230.3027 1496.57 0.3004 1488.420.4056 1487.63 0.4043 1487.010.4941 1478.66 0.4985 1484.500.6024 1471.83 0.5972 1482.690.6843 1459.83 0.7036 1481.160.7939 1451.72 0.7980 1482.410.8880 1444.08 0.9029 1485.060.9396 1433.69 0.9400 1488.420.9764 1425.22 0.9796 1488.84

ume loss is significant for 2,3-BTD and 1,3-BTD in NPY. It indicatesthat NPY interacts strongly with the hydroxyl groups of 2,3-BTDand 1,3-BTD in lower diol region than DMF and PY. The volumetricbehavior of BTD in NPY is similar to that of diols in DMF but differ-ent as compared to diols in PY. This may be due to the fact that PYis self-associated (dimer) [30–33], however, DMF and NPY are not.NPY, however, is not self-associated by H-bonding, although likeDMF, a certain degree of association due to dipole–dipole interac-tions is expected. The volumetric behavior of BTD in NPY differsconsiderably from that of the same butanediols in water. For thelatter VE values for each diol show a large negative value and followthe order: 2,3-BTD > 1,3-BTD > 1,2-BTD > 1,4-BTD. The behaviorhas been explained based on hydrophobic hydration and hydrogenbonding ability of diols [16].

The speed of sound u for the NPY + BTD has been listed in table3. Combining speed of sound u with excess volume VE data, one cancalculate the isentropic compressibility jS as

jS ¼ �V�1ð@V=@PÞS ¼ ðqu2Þ�1

¼X

xiVi þ VE� �.

u2X

xiMi

� �¼ V=Mu2; ð1Þ

x u/(m � s�1) x u/(m � s�1)

1,4-BTD 2,3-BTD0.0565 1533.37 0.0282 1544.520.1010 1533.66 0.0534 1524.620.1892 1536.15 0.1001 1531.580.2806 1550.25 0.1968 1520.010.3915 1549.65 0.2949 1496.830.4722 1551.44 0.3939 1485.500.5803 1556.86 0.4746 1477.460.6682 1565.97 0.5881 1469.100.7044 1572.26 0.6925 1461.230.7935 1578.75 0.7916 1454.230.8996 1585.14 0.8948 1448.470.9460 1591.90 0.9431 1445.740.9653 1586.56 0.9730 1439.79

0.0 0.5 1.0-4

-3

-2

-1

0

1

VE 2 /

cm

3 mol

-1

x

VE 1 /

cm

3 mol

-1

0.0 0.5 1.0-1.5

-1.0

-0.5

0.0

0.5

1.0

xFIGURE 3. Plot of Partial molar excess volumes VE

1 and VE2 against mole fraction for x BTD: d, 1,2-BTD; s, 1,3-BTD; 4, 1,4-BTD; N, 2,3-BTD; +(1 � x) NPY.

TABLE 5Excess partial molar volumes VE;1

i and excess partial molar isentropic compressibilities KE;1S;i of {x BTD + (1 � x) NPY} at infinite dilution at 308.15 K.

NPY VE;11 /(cm3 �mol�1) VE;1

2 /(cm3 �mol�1) KE;1S;1 /(TPa�1 �m3 �mol�1) KE;1

S;2 /(TPa�1 �m3 �mol�1)

1,2-BTD �0.911 �1.378 �13.82 �11.551,3-BTD �1.467 �0.614 4.93 8.771,4-BTD �1.606 �1.001 �24.15 �14.762,3-BTD �3.808 0.269 �24.83 13.25

TABLE 4Least-square coefficients of equation (5) and standard deviation r of {x BTD + (1 � x) NPY} at 308.15 K.

NPY A0 A1 A2 A3 A4 r YE (x = 0.5)

1,2-BTDVE/(cm3 �mol�1) �1.248 0.200 0.535 �0.442 �0.457 0.010 �0.315KE

S/(TPa�1 �m3 �mol�1) �5.73 0.85 �0.64 �0.14 �8.25 0.16 �1.44Dg/(mPa � s) �7.964 �13.834 �13.783 �14.987 �13.755 0.191 �2.005g(x)/(J �mol�1) �3506 �2129 2129 351 �3497 27 �884dE/ppm (1H–OH) �0.452 0.099 0.034 �0.306 �0.430 0.004 �0.112dE/ppm (13C–CO) 0.977 �0.227 0.824 �0.943 0.118 0.018 0.240

1,3-BTDVE/(cm3 �mol�1) 0.150 0.214 0.025 0.249 �1.254 0.008 0.036KE

S/(TPa�1 �m3 �mol�1) 2.74 1.04 2.29 1.12 2.48 0.09 0.67Dg/(mPa � s) �12.133 �18.030 �19.274 0.701 17.613 0.705 �3.021g(x)/(J �mol�1) �3566 �183 1131 2310 �975 65 �869dE/ppm (1H–OH) �0.001 0.808 �0.708 �0.624 0.816 0.007 �0.004dE/ppm (13C–CO) 0.584 1.553 �1.488 0.058 �0.002 0.017 0.147

1,4-BTDVE/(cm3 �mol�1) �0.740 0.262 0.033 0.108 �0.701 0.006 �0.186KE

S/(TPa�1 �m3 �mol�1) �5.52 2.09 �4.49 3.94 �16.16 0.16 �1.38Dg/(mPa � s) �4.827 �6.280 3.165 5.875 �0.829 0.033 �1.116g(x)/(J �mol�1) �1439 258 1559 �631 �2463 38 �334dE/ppm (1H–OH) �0.138 0.036 �0.025 �0.046 �0.148 0.003 �0.035dE/ppm (13C–CO) 1.027 �0.584 �0.373 0.076 0.928 0.012 0.256

2,3-BTDVE/(cm3 �mol�1) 0.405 1.228 �0.706 1.034 �1.738 0.021 0.095KE

S/(TPa�1 �m3 �mol�1) �0.49 3.52 �7.31 24.30 �4.03 0.11 �0.14Dg/(mPa � s) �17.318 �30.446 �36.653 �93.662 �82.397 0.658 �4.418g(x)/(J �mol�1) �5855 �3604 �1077 �3320 �2971 84 �1450dE/ppm (1H–OH) �0.184 �0.437 0.082 �0.630 0.076 0.006 �0.045dE/ppm (13C–CO) 0.919 0.247 �1.874 �1.697 4.897 0.020 0.203

S.K. Mehta et al. / J. Chem. Thermodynamics 41 (2009) 1329–1338 1333

TABLE 6Viscosity g values for {x BTD + (1 � x) NPY} at 308.15 K.

x g/(mPa � s) x g/(mPa � s) x g/(mPa � s) x g/(mPa � s)

1,2-BTD 1,3-BTD 1,4-BTD 2,3-BTD0.0282 1.835 0.0282 1.736 0.0277 1.784 0.0282 1.9240.0564 2.019 0.0582 1.864 0.0556 1.943 0.0534 2.0030.1026 2.039 0.1089 2.153 0.1011 2.235 0.1001 2.4050.1884 2.067 0.2015 2.678 0.1982 3.025 0.1968 2.9100.3027 3.253 0.3004 3.197 0.2982 4.088 0.2950 3.3440.4056 3.955 0.4043 4.211 0.4038 5.570 0.3939 4.1590.4941 4.933 0.4985 6.742 0.4943 7.060 0.4746 5.0330.6024 6.647 0.5972 9.628 0.6011 11.076 0.5881 7.2560.6843 8.612 0.7036 14.662 0.7044 16.239 0.6924 8.7580.7939 12.613 0.7980 22.769 0.7935 21.612 0.7916 13.5790.8880 17.954 0.9029 34.773 0.8996 33.430 0.8948 23.2880.9396 22.947 0.9400 43.519 0.9460 39.294 0.9431 32.4530.9764 27.103 0.9796 51.251 0.9650 41.435 0.9730 39.906

FIGURE 5. Plot of viscosity g and excess viscosity Dg against mole fraction for x BTD: d, 1,2-BTD; s, 1,3-BTD; 4, 1,4-BTD; N, 2,3-BTD; +(1 � x) NPY; — fitting with equation(5).

0.0 0.5 1.0-25

-20

-15

-10

-5

0

5

10

KS,

2E / TP

a-1m

3 mol

-1

x

KS,

1E / TP

a-1m

3 mol

-1

0.0 0.5 1.0-15

-10

-5

0

5

10

15

xFIGURE 4. Plot of partial molar excess compressibilities KE

S;1 and KES;2 against mole fraction for x BTD: d, 1,2-BTD; s, 1,3-BTD; 4, 1,4-BTD; N, 2,3-BTD; +(1 � x) NPY.

1334 S.K. Mehta et al. / J. Chem. Thermodynamics 41 (2009) 1329–1338

0.0 0.5 1.0-1800

-1200

-600

0

x

g(x)

/ J

mol

-1

FIGURE 6. Plot of excess Gibbs free energies of activation for viscous flow g(x)against mole fraction for x BTD: d, 1,2-BTD; s, 1,3-BTD; 4, 1,4-BTD; N, 2,3-BTD;+(1 � x) NPY; — fitting with equation (5).

S.K. Mehta et al. / J. Chem. Thermodynamics 41 (2009) 1329–1338 1335

where M is the molar mass of the mixture. Since the u and VE

measurements have not been made on the same samples, the VE

data were extrapolated to the mole fractions of the speed of soundusing least square method.

The corresponding molar quantity is given by

KS ¼ �ð@V=@PÞS ¼ VjS ¼ V2=Mu2; ð2Þ

which assumes that dissipative effects are negligible and thatthe hydrodynamic equation of motion can be linearised. The excessmolar isentropic compressibilities KE

S were determined using theequations:

TABLE 7Wave number m values at maximum absorbance of: (a) –OH groups for {x BTD + (1 � x) N

x m/cm�1 x m/cm�1

1,2-BTD 1,3-BTD(a)

0.0282 3443.8 0.0282 3447.40.0564 3443.7 0.0582 3428.20.1026 3444.0 0.1089 3422.30.1884 3447.3 0.2015 3412.00.3027 3403.9 0.3004 3404.00.4056 3400.2 0.4043 3412.00.4941 3389.9 0.4985 3392.20.6024 3392.2 0.5972 3369.70.6843 3389.3 0.7036 3358.10.7939 3365.9 0.7980 3336.30.8880 3349.8 0.9029 3339.50.9396 3349.7 0.9400 3350.80.9764 3342.2 0.9796 3365.1

(b)0.0282 1685.8 0.0282 1685.00.0564 1681.8 0.0582 1685.20.1026 1682.1 0.1089 1681.90.1884 1686.2 0.2015 1670.00.3027 1681.7 0.3004 1670.30.4056 1681.9 0.4043 1670.00.4941 1681.7 0.4985 1670.10.6024 1670.1 0.5972 1670.00.6843 1666.8 0.7036 1671.50.7939 1669.5 0.7980 1670.10.8880 1669.7 0.9029 1668.60.9396 1668.4 0.9400 1654.20.9764 1667.6 0.9796 1653.3

KES ¼ KS � K id

S ; ð3Þ

K idS can be expressed as follows:

K idS ¼

Xi

xi K�S;i þ TðA�p;iÞ2=C�p;i

h i� T

Xi

xiðA�p;iÞ2

,Xi

xiC�p;i

" #; ð4Þ

where C�p;i is the isobaric molar heat capacity, K�S;i is the isentropiccompressibility, xi is the mole fraction, and A�p;i is the product ofmolar volume V�i and thermal expansivity a�p;i for the pure compo-nent i. Figure 2 depicts the graphical representation of the excessmolar isentropic compressibility KE

S At the lower diol mole fractionregion KE

S values increase in the order 2,3-BTD 6 1,4-BTD < 1,2-BTD < 1,3-BTD. However, at the higher diol mole fraction region,the negative KE

S for 1,2-BTD and 1,4-BTD indicates the formationof more compressible isomers with NPY than for 1,3-BTD and 2,3-BTD, both of which show positive KE

S values. The larger negative val-ues of KE

S for aqueous binary mixtures of BTD [16] than the binarymixtures of NPY and BTD indicate that more compressible speciesare being formed for the former.

The excess values of VE and KES have been fitted by the conven-

tional curve fitting strategy for the excess properties of binary mix-tures by using the Redlich–Kister type equation in the form

YE ¼ xð1� xÞX

i

Aið2x� 1Þi; ð5Þ

where YE represents the excess properties. The values for thecoefficient Ai and the standard deviation of the fit for each systemare given in table 4.

The partial molar excess quantities viz. volume VEi and isentro-

pic compressibility KES;i were calculated from the following

equations:

VEi ¼ VE þ ð1� xiÞð@VE=@xiÞ; ð6Þ

KES;i ¼ KE

S þ ð1� xiÞð@KES=@xiÞ: ð7Þ

PY} and (b) �CO group groups for {x BTD + (1 � x) NPY}.

x m/cm�1 x m/cm�1

1,4-BTD 2,3-BTD

0.0277 3443.8 0.0282 3466.00.0556 3428.7 0.0534 3444.00.1011 3409.1 0.1001 3446.20.1982 3403.4 0.1968 3418.10.2982 3393.5 0.2949 3406.80.4038 3397.1 0.3939 3404.00.4943 3385.4 0.4746 3400.90.6011 3366.3 0.5881 3392.10.7044 3346.5 0.6925 3388.00.7935 3339.6 0.7916 3374.10.8996 3343.2 0.8948 3369.20.9460 3363.9 0.9431 3366.90.9653 3324.9 0.9730 3367.2

0.0277 1671.6 0.0282 1681.70.0556 1668.6 0.0534 1681.80.1011 1669.9 0.1001 1674.10.1982 1671.4 0.1968 1674.10.2982 1668.5 0.2949 1673.50.4038 1671.9 0.3939 1667.80.4943 1670.1 0.4746 1667.80.6011 1669.2 0.5881 1670.00.7044 1669.8 0.6925 1669.80.7935 1667.3 0.7916 1667.10.8996 1665.1 0.8948 1657.60.9460 1653.3 0.9431 1660.00.9653 1666.9 0.9730 1657.3

TABLE 913C NMR chemical shift d (ppm) values of �CO groups for {x BTD + (1 � x) NPY}.

x d/10�6 x d/10�6 x d/10�6 x d/10�6

1,2-BTD 1,3-BTD 1,4-BTD 2,3-BTD0.0282 174.131 0.0282 174.045 0.0277 174.161 0.0282 174.2020.0564 174.307 0.1089 174.086 0.0556 174.128 0.1968 174.5850.1026 174.547 0.2015 174.325 0.1011 174.391 0.3939 175.0100.1884 174.699 0.4043 174.956 0.1982 174.894 0.4746 175.1740.3027 174.968 0.4985 175.232 0.2982 174.952 0.5881 175.4130.4056 175.191 0.5972 175.529 0.4038 175.051 0.7916 175.6990.4941 175.373 0.7036 175.735 0.4943 175.434 0.9431 175.9900.6024 175.596 0.7980 175.916 0.6011 175.570 0.9730 175.9820.6843 175.784 0.9029 176.048 0.7044 175.8340.7939 175.949 0.9400 176.106 0.7935 175.9900.8880 176.031 0.9796 176.155 0.8996 176.1880.9396 176.183 0.9460 176.2870.9764 176.238 0.9653 176.303

TABLE 81H NMR chemical shift d (ppm) values of –OH groups for {x BTD + (1 � x) NPY}.

x d/10�6 x d/10�6 x d/10�6 x d/10�6

1,2-BTD 1,3-BTD 1,4-BTD 2,3-BTD0.1026 4.594 0.0282 4.614 0.0277 4.839 0.0282 4.6020.1884 4.618 0.1089 4.651 0.1011 4.882 0.0534 4.6330.3027 4.679 0.2015 4.674 0.2982 5.005 0.1001 4.6640.4941 4.798 0.3004 4.765 0.4038 5.074 0.1968 4.6850.6024 4.878 0.4043 4.868 0.4943 5.158 0.3939 4.6990.6843 4.946 0.4985 4.984 0.6011 5.216 0.4746 4.7160.7939 5.038 0.5972 5.102 0.7044 5.293 0.5881 4.7240.8880 5.118 0.7036 5.182 0.7935 5.351 0.7916 4.7870.9396 5.170 0.7980 5.248 0.9460 5.474 0.8948 4.8320.9764 5.218 0.9029 5.315 0.9653 5.497 0.9431 4.881

0.9400 5.342

1336 S.K. Mehta et al. / J. Chem. Thermodynamics 41 (2009) 1329–1338

The partial molar volumes VEi shown in figure 3 at the lower diol

mole fraction region increase in the order 2,3-BTD < 1,4-BTD < 1,3-BTD < 1,2-BTD, showing stronger interaction from for 2,3-BTD + NPY than the other isomer. Whereas at the higher diol molefraction region, VE

i vary in the order 1,2-BTD < 1,4-BTD < 1,3-BTD < 2,3-BTD. The negative value of partial molar volumes for1,2-BTD and 1,4-BTD may be taken as sign of strong interactionwith NPY than 2,3-BTD and 1,3-BTD. This trend is similar to as ob-tained for (BTD + DMF) mixtures [23]. The estimated values of par-tial molar quantities at infinite dilution are listed in table 5. Figure

FIGURE 7. Plot of 1H NMR chemical shifts d of hydroxyl protons against mole frac

4 shows the variation of partial molar excess compressibilities KES;i

for the given systems. Negative KES;i values for 1,2-BTD and 1,4-BTD

(figure 4) infer that structure-making effects are dominating inthese systems whereas structure-breaking ability is more promi-nent for 2,3-BTD and 1,3-BTD mixtures, which show positive KE

S;i

values.

3.2. Transport properties

Experimental viscosity data for mixtures of (NPY + BTD) is givenin table 6 and plotted in figure 5. Viscosity deviation Dg of mea-sured values were calculated using the following equation:

Dg ¼ g� expX

xi ln g�i� �

; ð8Þ

where g and g�i are the viscosities of mixture and of pure compo-nent i. Figure 5 shows the variation of viscosity g and Dg valuesfor the binary mixtures of NPY with BTD over the whole composi-tion range at 308.15 K. The Dg values are negative for all the mix-ture and follow the order 2,3-BTD < 1,3-BTD � 1,2-BTD < 1,4-BTD.According to Reed and Taylor [34], negative Dg values denote acharacteristic behavior of liquid systems where dispersion forcesamong the mixing molecules are prevalent, whereas positive Dgvalues are observed in binary mixtures where specific interactions(hydrogen bonding, dipole–dipole, etc.) are dominant. The presentresults show that dispersion forces are responsible for dissociationof self-associated diol molecules and the magnitude of these disper-sion forces are more for 2,3-BTD and 1,3-BTD than 1,2-BTD and 1,4-BTD. A comparative analysis of viscosity deviation Dg with aqueousmixtures of BTD [17], which is positive again infer the strong inter-actions between diols and water than between diols and NPY.

The excess Gibbs free energies of activation for viscous flow g(x)values may also be considered a reliable measure to detect thepresence of interactions between molecules [1,2,7,34,35]. It hasbeen calculated using the equation

gðxÞ ¼ RT ln gV �X

xi ln g�i V�i� �h i

; ð9Þ

where R is the gas constant, T is the absolute temperature, V and V�iare the molar volume of the mixture and that of the pure compo-nents. As shown in figure 6 , the negative values of g(x) also suggestthat dispersion forces are responsible for the breaking of self-association of diols that increases as 1,4-BTD < 1,2-BTD � 1,3-BTD < 2,3-BTD. Both Dg and g(x) values were fitted to equation(5) and parameters are listed in table 4.

tion for x BTD: d, 1,2-BTD; s, 1,3-BTD; 4, 1,4-BTD; N, 2,3-BTD; +(1 � x) NPY.

FIGURE 9. Plot of 13C NMR chemical shifts d of carbonyl group against mole fract

FIGURE 8. Plot of 1H NMR excess chemical shifts dE of hydroxyl protons againstmole fraction for x BTD: d, 1,2-BTD; s, 1,3-BTD; 4, 1,4-BTD; N, 2,3-BTD; +(1 � x)NPY; — fitting with equation (5).

TABLE 10NMR chemical shifts d1i for pure components.

Component d1i =10�6 –OH 1H NMR d1i =10�6 �CO 13C NMR

NPY 174.0221,2-BTD 5.2591,3-BTD 5.3721,4-BTD 5.5272,3-BTD 4.948

TABLE 11NMR chemical shifts d1i values for {isomeric butanediols + NPY} at infinite dilution.

Mixture d1i =10�6 –OH 1H NMR d1i =10�6 �CO 13C NMR

NPY + 1,2-BTD 4.568 176.268NPY + 1,3-BTD 4.606 176.185NPY + 1,4-BTD 4.830 176.361NPY + 2,3-BTD 4.572 176.007

S.K. Mehta et al. / J. Chem. Thermodynamics 41 (2009) 1329–1338 1337

3.3. Spectroscopic Parameters

IR measurements for mixtures of (BTD + NPY) over the entirecomposition range have also been carried out. The shift in wavenumber m appears for hydroxyl groups of BTD and �CO group ofNPY. This trend is similar to (BTD + DMF) [23], but differ in com-parison to (BTD + PY) [22] mixtures where the change in m valuesof CO group of PY was very small and non-specific. The results indi-cate that the interactions are taking place through both –OH and�CO groups. The wave number m at maximum absorbance of the–OH and the �CO stretching frequencies for mixtures of diols inNPY over the whole composition range is listed in table 7.

NMR can provide meaningful physical information about struc-tural and molecular interactions [22–26,34–38]. The 1H and 13CNMR chemical shifts d for the mixtures of (BTD + NPY) show a sig-nificant change in d values for –OH protons of BTD and �CO carbonof NPY as a function of mole fraction of diol. However, not muchchange in d values is seen for –CHn proton and carbon of NPYand diols. The NMR chemical shift d data of 1H and 13C NMR aretabulated in table 8 and 9, respectively. Excess NMR chemical shift,dE, has been estimated from the additivity rule, i.e.:

dE ¼ d� ðx1d11 þ x2d

12 Þ; ð10Þ

where d11 and d12 are the chemical shifts of diols and NPY at infinitedilution concentration, respectively. The d E values were also fittedto equation (5) to obtain the values of coefficient Ai and the stan-dard deviation (table 4).

3.3.1. Chemical shift of –OH groupsThe d values of hydroxyl protons are shown graphically as a

function of mole fraction of diols in figure 7. Hydroxyl protons shiftdownfield with the addition of diol in NPY indicating the formationof C@O� � �H–O hydrogen bonding. The d11 values for hydroxyl pro-tons are measured experimentally and the values are listed in table10. Whereas d12 values for the same protons have been estimatedby extrapolation of d values for the –OH protons to infinite dilution(figure 7). Table 11 lists the estimated values. The dE values are pre-sented graphically in figure 8 and follow the order 2,3-BTD < 1,3-BTD < 1,4-BTD < 1,2-BTD.

3.3.2. Chemical shift of �C@O groupThe variation of 13C NMR chemical shifts values for mixtures of

BTD in NPY is depicted in figure 9. With addition of diol, d of the�CO group shifts downfield over the whole composition range thatagain confirm the formation of C@O� � �H–O hydrogen bonding. Thed12 values for the �CO group are experimentally measured and the

ion for x BTD: d, 1,2-BTD; s, 1,3-BTD; 4, 1,4-BTD; N, 2,3-BTD; +(1 � x) NPY.

FIGURE 10. Plot of 13C NMR excess chemical shifts dE of carbonyl group againstmole fraction for x BTD: d, 1,2-BTD; s, 1,3-BTD; 4, 1,4-BTD; N, 2,3-BTD; +(1 � x)NPY; — fitting with equation (5).

TABLE 12Mole fractions corresponding to the maxima/minima of excess molar volume VE andexcess chemical shifts dE.

NPY VE/(cm3 �mol�1) dE/10�6 –OH 1H NMR dE/10�6 �CO 13C NMR

1,2-BTD 0.4731 0.4904 0.4731 a

1,3-BTD 0.6404 0.6404 a 0.6404 a

1,4-BTD 0.3981 0.4250 0.40772,3-BTD 0.4746 a 0.4746 a 0.4746

a The mole fractions at the transition points since these systems show S-shapebehavior.

1338 S.K. Mehta et al. / J. Chem. Thermodynamics 41 (2009) 1329–1338

values are listed in table 10. However d 11 values for the �COgroup have been estimated by extrapolation of d values of �COgroup to infinite dilution (figure 9) and the estimated values aretabulated in table 11. The dE values are shown in figure 10 and in-creases in the order 2,3-BTD < 1,3-BTD < 1,4-BTD < 1,2-BTD.

Comparison of NMR measurements with excess molar volumedata shows interesting correlation (table 12). The maximum/min-imum values of 1H and 13C NMR excess chemical shift dE and excessmolar volume V are positioned at about the same mole fraction forall the mixtures. It may be concluded that carbonyl group of NPYand hydroxyl groups of BTD are the two active sites of interactionsin (BTD + NPY) mixtures whereas in (BTD + PY) systems [22], hy-droxyl groups of BTD is the only active site of interactions.

4. Conclusions

Strong interactions between NPY and BTD mixtures have beenanalyzed by their thermodynamic and transport properties. Theposition of hydroxyl groups caused a noticeable effect on thermo-physical properties. 1,2-BTD and 1,4-BTD interacts more effectively

with NPY than 1,3-BTD and 2,3-BTD. On the basis of spectroscopicmeasurements, it is concluded that these interactions are throughthe �C@O group of NPY and the –OH groups of the diols. The re-sults obtained from spectroscopic measurements correlate withthe thermodynamic and transport studies.

Acknowledgement

The authors wish to thank the UGC (India) for financialassistance.

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JCT 08-454