Excess Thermodynamic and Volumetric Properties of Binary Mixtures containing Ionic Liquid [Bmim][NTf₂]and Dimethyl Carbonate from T = (298.15to 323.15) K

Excess Thermodynamic and Volumetric Properties of Binary Mixtures containing Ionic Liquid [Bmim][NTf₂]and Dimethyl Carbonate from T = (298.15to 323.15) K

N. Bhanu Murthy1, M. Rangacharyulu2, J. Siva Rama Krishna2* 1Department of Physics, Acharya Nagarjuna University, 2Department of Physics, Acharya Nagarjuna University

Abstract – The density (), ultrasonic velocity (u) and refractive index (nD) of the binary mixtures of 1-Butyl 3- Methylimidazolium bis (Trifluoromethylsulfonyl)Imide (Bmim [NTf2]) and dimethyl carbonate (DMC)and those of pure liquids were measured using Anton Paar vibrating tube density and sound velocity meter (DSA 5000 M) and Dr. Kernchen Abbemat (Anton Paar, Austria) refractometer over the whole composition range as a function of temperature between 298.15 and 323.15 K in steps of 5K at atmospheric pressure. From the experimental data, the excess values of

molar volumes ( ), partial molar volume( ), partial molar

polarity is between that of the water and chlorinated organic solvents.

Solvent feature of ionic liquid comes from H- bond donation from cation, H-bond accepting functionality of the anion, and – bonding. ILs are immiscible to non polar organic solvents and can be used in two phase system.

They have applicable electrochemical window. For some ILs it is in the range of ~6V [3]. However

volume at infinite dilution(,), isentropic compressibility ( ), acousticimpedance (ZE), free length ( ), speeds of sound (uE), and deviations in refractive index ( ) were calculated and fitted to a RedlichKister type equation. The

negative values of , , and positive values of ZE, uE,

choice of electrode has some effect on the electrochemical window. Ionic liquids like ammonium, piperidinium, morpholinium with 4 coordinated nitrogen have larger electrochemical window compared to others [3].

In the present work BMIM imide ionic liquid

and indicate the existence of strong interactions between the components.

Keywords: Bmim imide, dimethyl carbonate, Density, ultrasonic velocity, Refractiveindex, excess/deviation parameters, Redlich Kister type equation.

INTRODUCTION

Since Ionic liquids (ILs) have large variety of new applications, a major focus of study is being carried out both at laboratory and industrial scale. The interesting properties such as negligible volatility or non-flammability make them suitable for the replacement of conventional liquids.

The measurement of physical properties is one of the most important research areas involving ILs for the use of them from laboratory level to industrial applications.

Basing on how they attain the charge, Ionic liquids are divided into three types:

(1) protic; (2) aprotic; and (3) zwitter ionic.

Protic ILs are formed by proton-transfer reaction as acid and base as they donate and accept hydrogen bonds making hydrogen bonded network like water [1]. Aprotic ILs consist of imidazolium and pyrrolidium based cations and form inter molecular hydrogen bonds but not as protic ILs.

Polarity is an important parameter to describe nature of a solvent. Ionic liquids are considered to be highly polar but weak as coordinating solvent [2]. Their

was mixed with well known green solvent dimethyl carbonate in different proportions and the density, sound velocity and refractive index were measured for each mixture at six temperatures in steps of 5K from 298.15K to 323.15K.

[Bmim] [NTf2] has many applications such as extracting solvent for the removal of many organic compounds through liquidliquid extraction [4, 5], in chromatography [6] and enzyme catalysis in ionic liquids [7], etc.

Dimethyl carbonate (DMC) can be used as an anti-knocking agent and can possibly (partially) replace MTBE or ethanol as a fuel additive [8]. In addition, DMC can potentially replace dimethyl sulfate and methyl halides in methylation reactions [9]. It may also be suitable to replace phosgene as a carbonylation agent for the production of polycarbonates and urethane polymers [9]. DMC is relatively non toxic, especially in comparison to the mentioned chemicals [10]. It is of great importance to understand the mixing behavior of ILs in dimethyl carbonate and to provide accurate physicochemical data. The thermo acoustic, volumetric and refractive index data of [Bmim][NTf2] with dimethyl carbonate were not reported earlier.

Basing on our preliminary experiments, [Bmim][NTf2] was foun- d to be miscible with dimethyl Carbonate at all proportions. Hence, it is proposed to measure the densities (), speeds of sound(u), refractive

indices (nD) of the binary mixtures of [Bmim][NTf2] with dimethyl carbonate in the temperature range from 298.15 to

Chemicals:

2 EXPERIMENTAL

1. K and over the whole composition range and to estimate their excess/deviation properties for their potential application in industrial processes. On the basis of the measured values the properties such as excess values of molar volumes( ), partial molar volumes , partial molar volumes at infinite dilution (,) , isentropic

   compressibility(), acoustic impedance (ZE), free length ( ), speeds of sound (uE), and deviations in refractive

   index nD for binary mixtures were fitted using Redlich Kister type polynomial equation.

   The ionic liquid, (BMIM imide) or [Bmim][NTf2] , with purity 0.99 in mass fraction was used in this work. It was purchased from Iolitec, GmBH (Germany), while the dimethyl carbonate was supplied by Sigma Aldrich. The IL [Bmim][NTf2] was used without any further purification and dimethyl carbonate was further purified by distillation. The measured density, speed of sound and refractive index of the pure liquids at atmospheric pressure are compared with literature values to verify the purity of liquids under investigation and are presented in table 1. Ever since the concept of hindered internal rotation about single bonds was established, it has been expected that esters of simple carboxylic acids might exist in a conformational equilibrium in their fluid states. Such equilibrium is expected, on theoretical grounds, to involve the two planar conformations for DMC (shown in fig.1d).

   Fig1a: Ball and stick model of Bmim NTf2 Fig 1b: 1-Butyl 3-Methylimidazolium cation

   Fig1c: molecular structure of dimethyl carbonate Fig 1d: molecular conformations of dimethyl carbonate

   Table 1: Experimental and literature values of density, velocity and refractive index at temperatures 298.15K to 323.15K

   kgm-3 u ms-1 nD

   T/K	Exp.	Lit.	Exp.	Lit.	Exp.	Lit.
   [Bmim][NTf2] 298.15	1433.72	1433.72[11]	1227.86	1227.86[11]	1.4268	1.4267[11]
   303.15	1428.92	1428.95[11] 1216.77		1216.77[11] 1.4250 1.4252[11]
   308.15	1424.13	1424.18[11] 1205.8		1205.80[11] 1.4230 1.4237[11]

   313.15 1419.36 1419.41[11] 1194.95 1194.95[11] 1.4220 1.4223[11]

   318.15 1414.61 1414.64[11] 1184.23 1184.23[11] 1.4190 1.4208[11]

   323.15 1409.88 1409.87[11] 1173.61 1173.61[11] 1.4180 1.4192[11]

   Dimethyl carbonate

   td>

   1063.43 1063.

   39[12] 1198.87 119	8[16] 1.3664
   1056.82 1056.	35[13] 1177.29 117	7[16] 1.3641
   1050.18 1050.	14 [12] 1155.63 115	5[16] 1.3618
   1043.50 1043.	10[14] 1134.23 113	4[16] 1.3594
   1036.79 1035.	60[15] 1113.09	– 1.3570

   	1.3664[13]
   	1.3652[17]
   	1.3644[17]
   	1.3624[17]
   	1.3622[17]
   	1.3590[17]

   298.15

   303.15

   308.15

   313.15

   318.15

   323.15 1030.04 1028.40[15] 1092.16 – 1.3547

   1. THEORY:

      The experimentally measured values of , u and nD were used to calculate the values of thermodynamic and

      V E 2 x M 1 1

      m i i

      i1 i

      (3)

      acoustical parameters such as molar volume (Vm), intermolecular free length (Lf), isentropic compressibility (kS). The derived excess/deviation parameter values are shown in Table 2.

      The excess/deviation parameters for the above parameters including deviations in refractive index

      VE

      Where is the density of the mixture and Mi, xi and i are the molar mass, mole fraction, and density of the ith component in the mixture, respectively.

      The isentropic compressibility, kS, is computed directly from the measured values of speed of sound and density

      nD, ( m)

      T

      were also calculated by using the following

      using the NewtonLaplace equation:

      equations:

      = 1

      1 = ( ) (4)

      = (1)

      Where Meff is the effective molecular weight (= x1M1 +

      ( )

      = (2)

      2

      x2M2), where M1 and M2 are the molar masses and x1 and x2 are the mole fractions of IL and dimethyl carbonate,

      Excess isentropic compressibility is given

      respectively), and is the density of the medium.

      The speed of sound (u) and the density of the medium ()

      by: k E

      S

      kS xi kSi

      2

      i1

      (5)

      using NewtonLaplace equation give the intermolecular free length as:

      Where, kS is the isentropic compressibility

      The excess intermolecular free length is given by:

      = u2 (2)

      Where, K is a temperature dependent constant equal to

      =

      [11

      + 22

      ] (6)

      (93.875 + 0.375T) x 10-8.

      The excess molar volumes are given by:

      The excess speeds of sound, uE are estimated in binary mixtures using the following expression proposed by Douheret et al. [18]:

      = [11 + 22]

      (7)

      Table 2: The excess parameters of binary mixtures of BMIM imide and dimethyl carbonate.

      x U k *10-10 ZE*10-5 *10-10m n R *10-3 *10-3

      1 s

      m

      m/s m2 N-1 Kg/m2 .s m3/mol m3mol-1

      0.0000	0.0000	0.0000	29 0.0000	8.15K 0.0000	0.0000	0.0000	0.0000
      0.1010	12.8047	-0.5778	0.1030	-0.0236	0.0142	0.0461	0.0461
      0.1945	20.4161	-0.8050	0.1519	-0.0334	0.0198	0.0512	0.0512
      0.2994	22.7964	-0.8617	0.1712	-0.0362	0.0215	0.0429	0.0429
      0.3999	20.7558	-0.8132	0.1678	-0.0344	0.0208	0.0339	0.0339
      0.4976	17.1026	-0.7195	0.1525	-0.0306	0.0190	0.0272	0.0272
      0.5842	13.8382	-0.6168	0.1331	-0.0262	0.0166	0.0222	0.0222
      0.6886	10.3700	-0.4775	0.1051	-0.0204	0.0131	0.0153	0.0153
      0.8014	6.5662	-0.3122	0.0700	-0.0134	0.0087	0.0064	0.0064
      0.8890	3.1392	-0.1757	0.0399	-0.0075	0.0051	0.0005	0.0005
      1.0000	0.0000	0.0000	0.0000	0.0000	0.0000	0.0000	0.0000
      303.15K
      0.0000	0.0000	0.0000	0.0000	0.0000	0.0000	0.0000	0.0000
      0.1010	15.0762	-0.6359	0.1043	-0.0257	0.0147	0.0593	0.0593
      0.1945	23.7000	-0.8837	0.1539	-0.0363	0.0205	0.0793	0.0793
      0.2994	26.5399	-0.9451	0.1737	-0.0394	0.0222	0.0730	0.0730
      0.3999	24.5321	-0.8926	0.1705	-0.0375	0.0214	0.0540	0.0540
      0.4976	20.6386	-0.7907	0.1552	-0.0333	0.0193	0.0352	0.0352
      0.5842	16.9889	-0.6784	0.1356	-0.0286	0.0169	0.0233	0.0233
      0.6886	12.9079	-0.5256	0.1071	-0.0223	0.0133	0.0146	0.0146
      0.8014	8.3429	-0.3443	0.0715	-0.0146	0.0089	0.0071	0.0071
      0.8890	4.2584	-0.1950	0.0409	-0.0083	0.0052	0.0003	0.0003
      1.0000	0.0000	0.0000	0.0000	0.0000	0.0000	0.0000	0.0000
      308.15K
      0.0000	0.0000	0.0000	0.0000	0.0000	0.0000	0.0000	0.0000
      0.1010	17.2744	-0.6989	0.1054	-0.0278	0.0152	0.0752	0.0752
      0.1945	27.0122	-0.9700	0.1559	-0.0394	0.0212	0.1033	0.1033
      0.2994	30.3474	-1.0366	0.1763	-0.0427	0.0229	0.0993	0.0993/p>
      0.3999	28.3119	-0.9790	0.1732	-0.0406	0.0220	0.0764	0.0764
      0.4976	24.0985	-0.8674	0.1577	-0.0361	0.0198	0.0505	0.0505
      0.5842	20.0194	-0.7443	0.1378	-0.0311	0.0172	0.0315	0.0315
      0.6886	15.3092	-0.5766	0.1089	-0.0242	0.0135	0.0167	0.0167
      0.8014	9.9657	-0.3779	0.0728	-0.0159	0.0090	0.0081	0.0081
      0.8890	5.2075	-0.2143	0.0416	-0.0090	0.0053	0.0033	0.0033
      1.0000	0.0000	0.0000	0.0000	0.0000	0.0000	0.0000	0.0000

      313.15K

      0.0000	0.0000	0.0000	0.0000	0.0000	0.0000	0.0000	0.0000
      0.1010	19.3383	-0.7660	0.1064	-0.0301	0.0159	0.1011	0.1011
      0.1945	30.1866	-1.0623	0.1577	-0.0427	0.0220	0.1343	0.1343
      0.2994	34.0354	-1.1349	0.1787	-0.0463	0.0236	0.1295	0.1295
      0.3999	31.9856	-1.0717	0.1757	-0.0441	0.0226	0.1026	0.1026
      0.4976	27.4678	-0.9497	0.1601	-0.0392	0.0203	0.0689	0.0689
      0.5842	22.9806	-0.8150	0.1400	-0.0337	0.0176	0.0407	0.0407
      0.6886	17.6696	-0.6314	0.1107	-0.0263	0.0137	0.0155	0.0155
      0.8014	11.5609	-0.4138	0.0740	-0.0173	0.0091	0.0032	0.0032
      0.8890	6.1230	-0.2348	0.0423	-0.0098	0.0053	0.0023	0.0023
      1.0000	0.0000	0.0000	0.0000	0.0000	0.0000	0.0000	0.0000
      318.15K
      0.0000	0.0000	0.0000	0.0000	0.0000	0.0000	0.0000	0.0000
      0.1010	21.0881	-0.8355	0.1069	-0.0324	0.0166	0.1249	0.1249
      0.1945	33.1742	-1.1605	0.1593	-0.0460	0.0228	0.1669	0.1669
      0.2994	37.6602	-1.2406	0.1810	-0.0500	0.0244	0.1633	0.1633
      0.3999	35.6027	-1.1714	0.1781	-0.0477	0.0233	0.1324	0.1324
      0.4976	30.7489	-1.0376	0.1623	-0.0424	0.0208	0.0917	0.0917
      0.5842	25.8536	-0.8904	0.1420	-0.0365	0.0180	0.0556	0.0556
      0.6886	19.9882	-0.6902	0.1124	-0.0284	0.0140	0.0200	0.0200
      0.8014	13.1508	-0.4527	0.0753	-0.0187	0.0092	-0.0021	-0.0021
      0.8890	7.0069	-0.2567	0.0430	-0.0106	0.0054	-0.0060	-0.0060
      1.0000	0.0000	0.0000	0.0000	0.0000	0.0000	0.0000	0.0000
      323.15K
      0.0000	0.0000	0.0000	0.0000	0.0000	0.0000	0.0000	0.0000
      0.1010	23.0531	-0.9141	0.1078	-0.0351	0.0174	0.1585	0.1585
      0.1945	36.1970	-1.2678	0.1609	-0.0498	0.0237	0.2105	0.2105
      0.2994	41.1885	-1.3542	0.1830	-0.0542	0.0253	0.2070	0.2070
      0.3999	39.1366	-1.2784	0.1804	-0.0516	0.0240	0.1715	0.1715
      0.4976	34.0006	-1.1325	0.1645	-0.0460	0.0215	0.1246	0.1246
      0.5842	28.7112	-0.9719	0.1440	-0.0396	0.0185	0.0821	0.0821
      0.6886	22.2596	-0.7532	0.1140	-0.0308	0.0143	0.0384	0.0384
      0.8014	14.6873	-0.4940	0.0764	-0.0203	0.0094	0.0083	0.0083
      0.8890	7.9013	-0.2804	0.0436	-0.0115	0.0055	-0.0008	-0.0008
      1.0000	0.0000	0.0000	0.0000	0.0000	0.0000	0.0000	0.0000

      Table 3: coefficients (Ai) of RedlichKister polynomial for excess parameters

      VmE(*10-3 m3mol-1)

      RKC/Tem	A0	A1	A2	A3	A4
      298.15	-0.0036	-0.0026	-0.0028	-0.0009	0.0001	0.0000077
      303.15	-0.0038	-0.002	-0.0026	-0.0009	-0.0006	0.0000098
      308.15	-0.004	-0.0029	-0.003	-0.001	-0.0002	0.0000095
      313.15	-0.0042	-0.003	-0.003	-0.0012	-0.0005	0.0000067
      318.15	-0.0044	-0.0032	-0.0032	-0.0012	-0.0004	0.0000095
      323.15	-0.0047	-0.0034	-0.0032	-0.0012	-0.0006	0.0000100
      U ( m/s) 298.15	68.03	78.36	74.73	-14.04	-73.94	0.371650
      303.15	82.14	85.68	78.21	-12.15	-69.26	0.310580
      308.15	95.94	94.37	83.35	-11.4	-69.71	0.320470
      313.15	109.38	102.66	88.66	-11.08	-71.84	0.334690
      318.15	122.46	111.37	95.81	-14.45	-80.72	0.394440
      323.15	135.43	119.26	100.22	-14.41	-81.85	0.409580
      ks(*10-10 m2 N-1)
      298.15	-2.8673	-2.2132	-1.7337	-1.0524	-0.2247	0.001590
      303.15	-3.1512	-2.4128	-1.8744	-1.1771	-0.3334	0.001210
      308.15	-3.457	-2.6435	-2.0486	-1.3062	-0.4018	0.001320
      313.15	-3.7848	-2.8912	-2.2401	-1.4415	-0.4586	0.001510
      318.15	-4.1353	-3.1648	-2.4716	-1.5496	-0.4447	0.002090
      323.15	-4.5136	-3.4515	-2.6897	-1.7165	-0.5302	0.002250
      ZE*10-5 Kg/m2.s
      298.15	0.60805	0.39801	0.26675	0.09804	-0.02633	0.00034
      303.15	0.61872	0.40144	0.26571	0.09555	-0.02112	0.00027
      308.15	0.62867	0.40664	0.26852	0.09212	-0.02618	0.00027
      313.15	0.63825	0.41091	0.27134	0.08990	-0.03208	0.00029
      318.15	0.64721	0.41599	0.27637	0.08149	-0.04611	0.00036
      323.15	0.65590	0.41967	0.27684	0.07797	-0.04860	0.00039
      LfE*10-10m
      298.15	-0.1218	-0.0923	-0.0708	-0.0362	-0.0017	0.000088
      303.15	-0.1327	-0.0997	-0.0758	-0.0400	-0.0043	0.000076
      308.15	-0.1440	-0.1079	-0.0833	-0.0432	-0.0022	0.000085
      313.15	-0.1562	-0.1167	-0.0910	-0.0463	-0.0013	0.000097
      318.15	-0.1690	-0.1263	-0.0969	-0.0485	-0.0018	0.000111
      323.15	-0.1832	-0.1366	-0.1036	-0.0525	-0.0043	0.000126

      298.15	0.0756	0.0476	0.0328	0.0292	0.0183	0.000050
      303.15	0.0772	0.0509	0.0377	0.0285	0.0144	0.000056
      308.15	0.0790	0.0537	0.0393	0.0286	0.0158	0.000070
      313.15	0.0809	0.0567	0.0401	0.0305	0.0200	0.000070
      318.15	0.0831	0.0596	0.0412	0.0328	0.0222	0.000099
      323.15	0.0856	0.0624	0.0432	0.0360	0.0256	0.000129
      Rm*10-3 m3/mol
      298.15	0.1084	0.119	0.1572	0.3123	0.1111	0.00495
      303.15	0.1393	0.3318	0.4637	0.1261	-0.2718	0.00485
      308.15	0.1995	0.4968	0.495	0.0044	-0.2107	0.00479
      313.15	0.2724	0.6919	0.4106	-0.0173	0.0903	0.00385
      318.15	0.3627	0.8606	0.3977	0.0652	0.0984	0.00608
      323.15	0.4934	1.0005	0.4812	0.1594	0.1649	0.00827

      n

      If the difference between the refractive indices of the two components is small then thedeviation in refractive index of binary mixtures containing ILs is given by:

      = [11 + 21] (8)

   2. RESULTS AND DISCUSSION

In the present study, excess molar volume ( ), excess partial molar excess volume ( ) , partial molar excess volume at infinite dilution (,), excess isentropic

compressibility ( ), excess free length ( ), excess

The excess/deviation properties have been fitted to a RedlichKister type polynomial equation given by:

= 12 (2 1) (9)

=0

Where, x1 and x2 are the mole fraction of ionic liquid and dimethyl carbonate, respectively and the Ai are adjustable parameters of the function and are determined using the leastsquares method. In the present investigation the i values ave been taken from 0 to 4. The corresponding standard deviations (YE) have been calculated using the followingexpression:

(YE YE )

acoustic impedance (ZE), excess ultrasonic velocity (uE), and deviations in refractive index () were calculated. The strength of interactions present between the component molecules of the binary mixture under study is indicated by the variations observed in these excess/deviation parameters. Further these variations are effected by the composition, molecular size, shape and temperature. The physical, chemical, and structural contributions [18, 19] influence these thermodynamic parameters.

Excess molar volumes for binary mixture of [Bmim][NTf2] and dimethyl carbonate as a function of composition from 298.15 to 328.15 K are shown in Fig. 1. The contraction in the volume of the mixture can be attributed to the formation of hydrogen bonds between the ionic liquid [Bmim][NTf2] and dimethyl carbonate.

(YE) = { exp cal } (10)

The values of become more negative with

mn

where m is the total number of experimental points and n is the number of coefficients in eq.(22). The calculated values of the coefficients Ai along with the standard deviations, (YE)are given in Table 4.

increase in temperature. This is due to the fitting of smaller dimethyl carbonate molecules into the voids created by larger IL molecules leading to decrease in volume of the mixture to a greater extent, which results in more negative

values with increase in temperature.

0.0001

mole fraction of BMIM imide

-0.0001 0.0

0.2

0.4

0.6

0.8

1.0

-0.0003

-0.0005

-0.0007

-0.0009

-0.0011

-0.0013

-0.0015

298.15K

303.15K

308.15K

313.15K

318.15K

323.15K

Excess molar volume (10-3m3 mol-1)

Fig. 2: Plots of excess molar volume () against mole fraction (x1) for binary mixtures of [Bmim][NTf2] and Dimethyl carbonate at temperature T and atmospheric pressure.

The strength of interaction follows the order:

Where and are the molar volumes of pure

1 2

(323.15>318.15>313.15>308.15>303.15>298.15) K. The

properties of partial molar volumes reflect the existing molecular interactions in the system. The contribution of a

components of [Bmim][NTf2] and dimethyl carbonate respectively. Differentiating the RedlichKister equation

for , we get the derivatives ( ) mentioned in the

component of a mixture to the overall volume of the

x1

,

solution is interpreted in terms of Partial molar volume. Therefore, the partial molar volume is a function of composition of the mixture. The partial molar volumes

equations (11) and (12) are obtained by, which leads to the following equations for ,1, ,2:

4

of component 1[Bmim][NTf ] and of component

,1 = + 2 (2 1) 4

,1

2 ,2

1 2

2 2 ()(

)1

2 (dimethyl carbonate) in the mixtures over the entire range of composition have been calculated by using the following equations:

=0

1 2

=1

2 1

(13)

Table 5: Partial molar volumes (,1, ,2 against

,1 = + + (

)

(11)

mole fraction x ) for [Bmim][NTf ] and dimethyl

1

2 x1

, 1 2

carbonate mixtures at temperature T and atmospheric pressure:

,2 = + ( )

(12)

2 1 x1

,

298.15K 303.15K 308.15K 313.15K 318.15K 323.15K

x Vm,1 Vm,2 Vm,1 Vm,2 Vm,1 Vm,2 Vm,1 Vm,2 Vm,1 Vm,2 Vm,1 Vm,2

10-6m3mol-1 10-6m3mol-1 10-6m3mol-1 10-6m3mol-1 10-6m3mol-1 10-6m3mol-1

0.0000	289.6753	84.7069	290.2161	85.2368	291.2702	85.7760	291.9740	86.3250	292.8900	86.8837	293.5233	87.4529
0.1010	290.2420	84.6762	291.1750	85.2028	291.9834	85.7437	292.8723	86.2926	293.7347	86.8498	294.6158	87.4143
0.1945	290.6148	84.6124	291.5405	85.1476	292.3743	85.6794	293.2657	86.2320	294.1386	86.7855	295.0418	87.3498
0.2994	290.8308	84.5448	291.6912	85.0939	292.5899	85.6092	293.4643	86.1628	294.3464	86.7156	295.2249	87.2847
0.3999	290.9022	84.5086	291.7564	85.0518	292.6748	85.5623	293.5584	86.1056	294.4357	86.6634	295.3081	87.2316
0.4976	290.9488	84.4698	291.8400	84.9801	292.7461	85.5024	293.6519	86.0263	294.5253	86.5876	295.4128	87.1422
0.5842	291.0535	84.3426	291.9794	84.8107	292.8752	85.3458	293.7956	85.8518	294.6780	86.4023	295.5851	86.9330
0.6886	291.3290	83.8449	292.2725	84.2660	293.1807	84.7881	294.1064	85.2746	295.0197	85.7743	295.9474	86.2606
0.8014	291.8079	82.3974	292.7519	82.7678	293.7003	83.1984	294.6341	83.6283	295.5920	84.0091	296.5409	84.4086
0.8890	292.2160	80.1124	293.1728	80.3718	294.1495	80.6678	295.1071	80.9382	296.0906	81.1889	297.0620	81.4444
1.0000	292.4976	74.8593	293.4814	74.6123	294.4675	74.7296	295.4569	74.3886	296.4490	74.4948	297.4435	74.3206

4

2 1

,2 = + 2 (2 1)

=0

4

1

+ 222 ()(2

which represents the contraction of volume on mixing [Bmim][NTf2] with dimethyl carbonate at all the temperatures under study.

The variation of excess partial molar volumes of

=1

[Bmim][NTf2] and (dimethyl carbonate) are

)1 (14)

,1

,2

1

Using the above equations, have been

represented in Figures 3 and 4 respectively, in the

temperature range from 298.15 to 323.15K. Inspection of

evaluated using:

,1

,2

these figures not only reveals the existence of strong forces between the unlike molecules but also supports the

,1 1

= ,1 (15)

= ,2 (16)

deductions drawn from excess molar volume. The partial molar volumes and excess partial molar volumes of

[Bmim][NTf ] at infinite dilution,( ) and ( ), are

,2

The values of

2

and

are presented in Table 5 for all

2

given by:

,

,1

,2

,1

,2

= 0 + 1 + 2 + 3 + =

the systems. From this table, we observe that the values of

,1

,1 1

,1

and ,2

for both the components in the mixtures are

(17)

lower than their individual molar volumes in the pure state,

The data of and (,) are presented in Table 6 at

conclude that with increasing temperature, strong

,1 ,1

1.0

0.8

0.6

0.4

0.2

0.0

-0.0005

0.0000

,1

298.15K to 323.15K in steps of 5 K. From this table, the values of (,) are found to be negative and become more negative with increasing temperature. Hence we can

interactions increase among the unlike molecules of the mixtures. This supports the existing strong molecular interactions that were observed with the variation of .

0.0005

Molefraction of BMIM imide

298.15K

303.15K

308.15K

313.15K

318.15K

323.15K

-0.0020

-0.0040

-0.0060

-0.0080

-0.0100

1.0

0.8

0.6

0.4

0.2

0.0

0.0000

-0.0035

-0.0040

298.15K

303.15K

308.15K

313.15K

318.15K

323.15K

-0.0010

-0.0015

-0.0020

-0.0025

-0.0030

excess partial molar volume-2 (10-3m3

excess partial molar volume-1 (10- 3m3 mol-1)

mol )

-1

,1

Fig. 3: Plots of excess partial molar volume ( ) against mole fraction x1 for [Bmim][NTf2] and Dimethyl carbonate mixtures at temperature T and atmospheric pressure

Molefraction of BMIM imide

-0.0120

-0.0140

,2

Fig. 4: Plots of excess partial molar volume ( ) against mole fraction (x1) for [Bmim][NTf2] and dimethyl carbonate mixtures at temperature T and atmospheric pressure

Table 6: Partial ( ) and excess partial molar volumes (( )) at infinite dilution for [Bmim][NTf2] (1) Dimethyl

,1 ,1

carbonate(2) mixtures at temperature T and atmospheric pressure

T/K		,		,
	10-6m3mol-1	10-6m3mol-1	10-6m3mol-1	10-6m3mol-1
298.15	289.68	-2.82	74.86	-9.85
303.15	290.22	-3.27	74.61	-10.62
308.15	291.27	-3.2	74.73	-11.05
313.15	291.97	-3.48	74.39	-11.94
318.15	292.89	-3.56	74.49	-12.39
323.15	293.52	-3.92	74.32	-13.13

,1

,1

,2

,2

1.0

0.8

0.6

0.4

0.2

0.0

0.00

Mole fraction of BMIM imide

Deviation in isentropic compressibility

(10-10m2 N-1)

In Fig. 4, the values for this system are found to be negative in the whole composition range at all investigated temperatures. The negative values are attributed to the strong attractive interactions between the molecules of the

components [20]. In the present study, the negative values can be attributed to a closer approach of unlike molecules and a stronger interaction between components of mixtures at all temperatures. This supports the inference drawn from .

-0.20

-0.40

-0.60

-0.80 298.15K

303.15K

-1.00 308.15K

313.15K

-1.20 318.15K

-1.40 323.15K

Fig. 4: Plots of excess isentropic compressibility () against mole fraction (x1) for [Bmim][NTf2] and dimethyl carbonates mixtures at temperature T and atmospheric pressure

In the present study, the negative were observed. The trend of values (Fig. 5) is similar to that

among the components of a mixture cause the formation of molecular aggregates and more compact structures due to

of

at all temperatures under study. The specific

which the ultrasonic velocity increases leading to positive

uE. On the other hand, if the structure-breaking factor

interactions between unlike molecules in the liquid mixture lead to negative values of . The structural readjustments in the liquid mixture towards a less compressible phase of

fluid and closer packing of molecules [20] also contribute to negative .

Figure 6 shows that ZE is positive for the systems at all the temperatures under study. Specific acoustic impedance is a parameter that depends on the molecular packing of the mixture. The positive values of ZE indicate the presence of strong interactions between the component molecules [18].

From the figure 7 the uE values are found to be positive over the entire range of composition at all investigated temperatures. This indicates the increasing strength of interaction between component molecules of binary liquid mixtures. In general, strong interactions

predominates, it leads to expansion of the liquid mixture, and hence the ultrasonic velocity decreases resulting in negative uE [20]. The positive values of uE in the present system indicate much stronger interactions between the molecules [21].

Fig.8 shows that the values of are positive over the entire range of compositions at a given temperature. The variation of refractive index deviations with the mole fraction of IL shows the reverse trend to

[22]. This further supports the presence of strong interactions between component molecules in study.

Generally, the cohesive forces (attraction forces) or dispersive forces between the molecules of a mixture cannot be easily assessed by any theory.

Mole fraction of BMIM imide

0.000

0.0

0.2

0.4

0.6

0.8

1.0

-0.010

-0.020

-0.030

-0.040

-0.050

298.15K

303.15K

308.15K

313.15K

318.15K

323.15K

-0.060

298.15K

303.15K

308.15K

313.15K

318.15K

323.15K

0.20

0.18

0.16

0.14

0.12

0.10

0.08

0.06

0.04

0.02

0.00

excess Free length (0A)

excess Acoustic impedance (106Kg/m2

.s)

Fig. 5: Plots of excess free length (LEf) against mole fraction (x1) for [Bmim][NTf2] and Dimethyl carbonate mixtures at temperature T and atmospheric pressure

0.0 0.2 0.4 0.6 0.8 1.0

Mole fraction of BMIM imide

deviation in speed of sound (m/s)

Fig. 6: Plots of excess acoustic impedance (ZE) against mole fraction (x1) for [Bmim][NTf2 (1) dimethyl carbonate (2) mixtures at temperature T and atmospheric pressure

45.00

40.00

35.00

30.00

25.00

20.00

15.00

10.00

5.00

0.00

298.15K

303.15K

308.15K

313.15K

318.15K

323.15K

0.0 0.2 0.4 0.6 0.8 1.0

Mole fraction of BMIM imide

Fig. 7: Plots of excess ultrasonic speed of sounds (uE) against mole frction (x1) for [Bmim][NTf2]

0.030

0.025

0.020

298.15K

303.15K

308.15K

313.15K

318.15K

323.15K

0.0

0.2

0.4

0.6

0.8

1.0

Mole fraction of BMIM imide

0.015

0.010

0.005

0.000

deviation in refractive index

Fig. 8: Plots of deviation in refractive index () against mole fraction (x1) for [Bmim][NTf2] and Dimethyl carbonate mixtures at temperature T and atmospheric pressure

The electronic structure of the aromatic cations reflect the unique properties of imidazolium cations. The delocalized 3-center-4-electron configuration are contained in the electronic structure of these salts across the N1C2 N3 moiety, a double bond between C4 and C5 at the opposite side of the ring, and a weak delocalization in the central region [23]. Almost the same charge is carried by the hydrogen atoms C2H, C4H, and C5H, but carbon C2 is positively charged owing to the electron deficit in the

C=N bond. On the other hand C4 and C5 are practically

temperature, strong interactions increase among the unlike molecules of the mixtures. This supports the existing strong molecular interactions that were observed with the variation of .

• In the present study, the negative values can be attributed to a closer approach of unlike molecules and a stronger interaction between components of mixtures over the entire range of composition at all temperatures under study.

• The negative were observed. The trend of values

  neutral. The properties of these ionic liquids arise from the resulting acidity of the hydrogen atoms. The hydrogen on the C2 carbon (C2H) has been shown to bind specifically with solute molecules.

  The hydrogen bonds play an important role in the stability and miscibility of the binary liquid mixtures of [Bmim][NTf2] (1) and dimethyl carbonate(2). The nature of interaction of dimethyl carbonate molecules with the cation is different from that of anion. The characteristic groups which interact with dimethyl carbonate molecules are the CH groups in the imidazolium ring and oxygen atoms in the anion. The complete miscibility and solvation of cations and anions in the ionic liquid is due to sufficient hydrogen bonding interactions of dimethyl carbonate with [Bmim][NTf2]. Hence, the remarkable contraction in the volume of the mixture can be attributed to the hydrogen bonds between the ionic liquid [Bmim][NTf2] (1) dimethyl carbonate (2).

  5 CONCLUSION

• From the experimental data, parameters such as ,

  (Fig. 5) is similar to that of at all temperatures under study.

• ZE is positive for the systems at all the temperatures under study. The positive values of ZE indicate the presence of strong interactions between the component molecules.

• Similarly the positive values of uE indicate much stronger interactions between the molecules.

• The positive values of at a given temperature over the entire composition range indicate the strong interactions between the component molecules

• Finally it may be concluded that the observed negative values of , , , and positive values of ZE, uE, clearly indicate the dominance of strong attractive forces.

  ACKNOWLEDGEMENTS:

  One of the authors (NBM) thanks Acharya Nagarjuna University authorities for providing the UGC-BSR meritorious fellowship.

  , , ZE, uE,

  , have been evaluated. The excess

  REFERENCES:

  and deviation properties have been fitted to Redlich Kister type polynomial and the corresponding standard deviations were in good agreement with the experimental value.

• The values of become more negative with increase in temperature.

  ,1

• The values of (,) are found to be negative and

become more negative with increasing temperature. Hence we can conclude that with increasing

1. J.S.Wilkes, properties of ionic liquid solvents for catalysis J.mol.catal.A; chem. 214 (2004) 11-17.

2. U.Doman´ska, A.Marciniak; Measurements of activity coefficients at infinite dilution of aromatic and aliphatic hydrocarbons, alcohols, and water in the new ionic liquid [EMIM][SCN] using GLC, J. Chem. Thermodynamics 40 (2008) 860866.

3. M.Galinski, A.Lewandowski, I Stepniak; ionic liquids as electrolyte; ElectrochimicaActa 51 (2006) 55675580

4. S.Dai, Y. H. Ju and C. E. Barnes , Solvent extraction of strontium nitrate by a crown ether using room-temperature ionic liquids, J. Chem. Soc., Dalton Trans., 1999, 1201-1202.

5. Jairton Dupont ,Roberto F. de Souza , and Paulo A. Z. SuarezIonic Liquid (Molten Salt) Phase Organometallic Catalysis Chem. Rev., 2002, 102 (10), pp 36673692 ;

6. Jared L. Anderson and Daniel W. Armstrong, High- Stability Ionic Liquids-A New Glass of Stationary Phases for Gas chromatography, Anal. Chem.75(18):4851-8, 2OO3.

7. UdoKragl, Marrit Eckstein, Nicole Kaftzik Enzyme catalysis in ionic liquids Current Opinion in Biotechnology,Volume 13, Issue 6, 1 December 2002, Pages 565571

8. Sandeep Singh, Ashwani Kumar, S. K. Mahla , Gurpreet Singh Batth, Experimental Study On Emission Analysis Of Oxygenated Fuels Dimethyl Carbonate (Dmc) And Dibutyl Maleate (Dbm) In A Ci Engine, International Journal of Research in Engineering and Technology, Volume: 02 Issue: 10 | Oct-2013, Available @ http://www.ijret.org

9. Sanyogita Sharma, S. C. Ameta, V. K. Sharma, Use of Dimethyl Carbonate (DMC) as Methylating Agent under Microwave Irradiation-A Green Chemical Approach, Proceedings of the World Congress on Engineering and Computer Science 2010 Vol IIWCECS 2010, October 20-22, 2010, San Francisco, USA.

10. MaurizioSilva, Green approach to highly selective brasses; reaction of dimethyl carbonate over both zeolites and base catalysis, pure and appl. Chem. Vol.79, No.11 pp 1855-1867, 2007

11. T. Srinivasa Krishnaa, Anil K. Nain, S. Chentilnath, D. Punyaseshudu, B. Munibhadrayya J. Chem. Thermodynamics 101 (2016) 103114.

12. J. M. Pardo, C. A. Tovar, C. A. Cerdeiri na, E. Carballo, and

    L. Roman´aJ. Chem. Thermodynamics 1999, 31, 787796

13. Rodríguez, A.; Canosa, J.; Tojo, J. Physical Properties of Binary Mixtures (Dimethyl Carbonate + Alcohols) at Several Temperatures. J.Chem. Eng. Data 2001, 46, 14761486.

14. Esther Romano, JoseL.Trenzado, Emilio Gonzalez, Jose S Matos, Luisa Segade, Eulogio Jimenez, Thermophysical properties of four binary dimethyl carbonate+ 1-alcohol systems at 288.15-313.15K, Fluid phase Equlibria 211 (2003) 219-40.

15. Mehrdad Moosavi, Ahmad Motahari, Amir Vahid, Vahideh Akbar, Abbas Ali Rostami, and Abdollah Omrani, Densities, Viscosities, and Refractive Indices of Dimethyl Carbonate + 1-Hexanol/1-Octanol Binary Mixtures at Different Temperatures, J. Chem. Eng. Data, DOI:10.1021/acs.jced.5b00830.

16. Gérard Douhéret, Pierre Lajoie, Michael I. Davis, Jose Luis Ratliff, Juan Ulloa and HaraldHøiland, volumetric properties of binary mixtures of water with methoxy(ethoxy)n ethanols J. Chem. Soc., Faraday Trans., 1995,91, 2291-2298, DOI: 10.1039/FT9959102291

17. Ana B. Pereiro, Ana Rodr´guez, Jose Canosa, and Jose Tojo, Density, Viscosity, and Speed of Sound of Dialkyl Carbonates with Cyclopentane and Methyl Cyclohexane at Several Temperatures, J. Chem. Eng. Data 2004, 49, 1392- 1399

18. Douheret, G., Davis, M.I., Reis, J.C.R., Blandamer, M.J.: Isentropic compressibilitiesexperimental origin and the quest for their rigorous estimation in thermodynamically ideal liquid mixtures. Chem-Phys Chem 2, 148161 (2001)

19. Reddy, M.S., Nayeem, S.M., Raju, K.T.S.S., Babu, B.H.: The study of solutesolvent interactions in 1-ethyl-3- methylimidazolium tetrafluoroborate and 2-methoyethanol from density, speed of sound, and refractive index

    measurements. J. Therm. Anal. Calorim. (2016). doi:10.1007/s10973-015-5205-9

20. Sunkara, G.R., Tadavarthi, M.M., Tadekoru, V.K., Tadikonda, S.K., Bezawada, S.R.: Density, refractiveindex, and speed of sound of the binary mixture of 1-butyl-3- methylimidazolium tetrafluoroborate and n-vinyl-2- pyrrolidinone from T = (298.15 to 323.15) K at atmospheric pressure. J. Chem. Eng.Data 60, 886894 (2015)

21. Nayeem, S.M, Kondiah, Sreekanth.K, Rao.D.K; thermoacoustic, volumetric and viscometric investigations in binary liquid system of benzene with benzyl benzoate at T=308.15, 313.15 and 318.15K. J.Thermody. (2014). Doi.10.1155/2014/487403.

22. Ali, A., Nabi, F., Tariq, M.: Volumetric, viscometric, ultrasonic, and refractive index properties of liquid mixtures of benzene with industrially important monomers at different temperatures. Int.J. Thermophys. 30, 464474 (2009)

23. Hunt, P.A., Kirchner, B., Welton, T.: Characterizing the electronic structure of ionic liquids: an examination of the 1- butyl-3-methylimidazolium chloride ion pair. Chem. Eur. J. 12, 67626775 (2006)