Experimental thermophysical properties and DFT calculations of imidazolium ionic liquids and 2-butanol mixtures

Experimental thermophysical properties and DFT calculations of imidazolium ionic liquids and 2-butanol mixtures

Journal Pre-proof Experimental thermophysical properties and DFT calculations of imidazolium ionic liquids and 2-butanol mixtures Urooj Fatima, Riyazu...

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Journal Pre-proof Experimental thermophysical properties and DFT calculations of imidazolium ionic liquids and 2-butanol mixtures Urooj Fatima, Riyazuddeen, Mohammad Jane Alam, Shabbir Ahmad PII:

S0378-3812(19)30509-6

DOI:

https://doi.org/10.1016/j.fluid.2019.112447

Reference:

FLUID 112447

To appear in:

Fluid Phase Equilibria

Received Date: 17 September 2019 Revised Date:

24 December 2019

Accepted Date: 28 December 2019

Please cite this article as: U. Fatima, Riyazuddeen, M.J. Alam, S. Ahmad, Experimental thermophysical properties and DFT calculations of imidazolium ionic liquids and 2-butanol mixtures, Fluid Phase Equilibria (2020), doi: https://doi.org/10.1016/j.fluid.2019.112447. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier B.V.

Experimental thermophysical properties and DFT calculations of imidazolium ionic liquids and 2-butanol mixtures Urooj Fatimaa, Riyazuddeena*, Mohammad Jane Alamb, Shabbir Ahmadb a

Department of Chemistry and bDepartment of Physics, Aligarh Muslim University, Aligarh

202002, U.P., India. *Corresponding author E-mail: [email protected] Author statements Riyazuddeen: Supervisor, conceptualization, Reviewing and Editing (Experimental), Urooj Fatima: Methodology, Draft preparation (Experimental) Shabbir Ahmad: Conceptualization, Reviewing and Editing (Computational) Mohammad Jane Alam: Methodology, Draft preparation (Computational)

1

2

Experimental thermophysical properties and DFT calculations of imidazolium ionic liquids and 2-butanol mixtures

3

Urooj Fatimaa, Riyazuddeena*, Mohammad Jane Alamb, Shabbir Ahmadb

4

a

5

202002, U.P., India.

6 7

*Corresponding author E-mail: [email protected]

1

Department of Chemistry and bDepartment of Physics, Aligarh Muslim University, Aligarh

8 9

ABSTRACT

10

Thermophysical properties, densities (ρ), speeds of sound (u) and dynamic viscosities (η) of

11

binary

12

([EMIM][CF3SO3])/ 1-ethyl-3-methylimidazolium ethyl sulfate ([EMIM][EtSO4]) (ILs) and 2-

13

butanol have been measured experimentally. The obtained experimental data are further utilized to

14

determine the excess molar volumes (VE), excess molar isentropic compressibilities (ΚsmE) and

15

viscosity deviations (∆η) to gain insight into the molecular interactions of IL-2-butanol mixtures.

16

In order to understanding the model fitting, the derived/excess properties are fitted to the Redlich-

17

Kister polynomial equation. To unravel the effect of anions [CF3SO3] and [EtSO4] on molecular

18

interactions, the Density Functional Theory (DFT) has been performed which provides the in-

19

depth information about interactions in isolated ILs and their mixtures using DFT/D3-B3LYP

20

method. Furthermore, the natural bond orbital (NBO) analysis has been performed to probe all

21

possible interactions between donor-acceptor NBOs. This project aims to provide the

22

experimental data of studied thermophysical properties properties and to obtain the interactional

23

information at the molecular level between ILs having common cation and different anions and

24

the solvent molecules in binary mixtures, which are interpreted in terms of ion-ion, ion-dipole and

25

dipole-dipole interactions.

mixtures

constituting

1-ethyl-3-methylimidazolium

trifluoromethanesulfonate

-

-

26 27

Keywords: 1-ethyl-3-methylimidazolium trifluoromethanesulfonate ([EMIM][CF3SO3]), 1-ethyl-

28

3-methylimidazolium ethylsulfate ([EMIM][EtSO4]), 2-butanol, Thermophysical properties,

29

Density functional theory.

30 31

2

11.

Introduction

2

Ionic liquids (ILs), the ionic compounds exhibit low temperature melting point (typically

3

<100°C), mainly comprise of cations and anions where usually the cations are organic moiety

4

while the anions may be the organic or inorganic moiety. These are highly structured liquids

5

where the ionic moieties arrange themselves into polar and non-polar domains, and the structural

6

segregation occurred in each ion may be due to the size of alkyl chain length and their charges [1].

7

These novel solvents, replacement of hazardous and contaminating volatile organic solvents, often

8

termed as green solvents, which are also called as Room Temperature Ionic Liquids (RTILs) as

9

they show their melting point near/below the boiling point of water. These represent the

10

alluring/tempting properties including; their large electrochemical window, almost null vapor

11

pressure,

12

organic/inorganic/organometallic compounds and high thermal/chemical stabilities [2]. The

13

academic and industrial prospects of emerging green RTILs are because of their other unique

14

properties, i.e., they can be tailored by tuning their ionic moieties, the cation/anion for the specific

15

application and therefore, termed as Designer Solvents and Task-Specific Ionic Liquids (TSIL)

16

which lead their suitability for myriad applications. The greener aspect of ILs is also responsible

17

for drawing the attention, which includes their reusability and recyclability without hammering

18

the properties and allowing them to deem a probable contender to eradicate toxin from high-

19

vacuum systems [1]. Switching to RTILs instead of volatile organic solvents show the significant

20

advancement in various fields, including kinetic stability, catalytic ability, and enantio-selectivity;

21

however, the responses for such changes are still unknown [3]. They have numerous applications

22

such as their usage as biocatalysts and novel solvents for organic and inorganic synthesis, catalyst,

23

synthesis of nanomaterials [4], extraction processes, aqueous bio-phasic systems [5] entrainer for

24

liquid-liquid extraction, extractive distillation, solvents for catalytic reaction, solar cell, heat

25

transfer fluid [6] and chemical sensor [7]. Now-a-day a new application of ILs is emerging, i.e.,

26

dissolution of wood components (cellulose, hemicelluloses, and lignin), because these

27

components are insoluble in common solvents which hindered the development of efficient

28

methods for its utilization and analysis. In the wood industry, the commonly employed ILs are

29

imidazolium-based ILs for treatment of wood and its derivatives[8]. The objective of this work is

30

to study the thermophysical properties of ILs and their mixtures because many of them are

31

synthesized without any investigation on thermophysical properties which necessitate their

32

studying. According to a rough estimation, thousands of ILs will be available shortly; therefore, it

33

is necessary to understand the synthetic flexibility and tunability of thermophysical properties of

non-flammability,

large

liquidous

range,

high

solvating

capacity

for

3

1

pure and mixtures of ILs. Therefore, in order to induce the desired properties in ILs and their

2

mixtures, it is necessary to perform the systematic study on the thermophysical properties of IL-

3

systems including the understanding of structure-property relationship, because it provide the

4

information about the stability of the material and also provide the information for designing the

5

technological processes employed

6

(DFT)-based quantum mechanical computational approach has become more efficient to

7

understand the ionic liquid systems[30]. Fernandes et al. [31] reported a systematic study on the

8

relative anion-cation interaction energies of imidazolium-, pyridinium-, pyrrolidinium-, and

9

piperidinium-based ionic liquids by quantum mechanical calculations. Zhixiang Song et al. [32]

10

in industries. Furthermore, the density functional theory

reported the structure of IL and the influence of water molecule by applying DFT.

11

The imidazolium-based ILs are considered to be the versatile class of ILs and furnish the

12

promising application in numerous industries. 1-ethyl-3-methylimidazolium ethylsulfate, soluble

13

in water and alcohols suggesting a large number of applications including their usage as a solvent

14

to desulfurate petrochemical products, it also helps to extract organic chemicals and contaminant

15

gases [6]. From a wide range of molecular solvents, we have opted the 2-butanol because it shows

16

a variety of application in industries. Thus, the present study will help to tailor the properties of

17

ILs, to enhance their industrial applications.

18

In several previous reports [9-27], the thermophysical properties of these concerned ILs were

19

investigated to explaining the change in properties of mixtures. Our research group has reported

20

[28] earlier the effect of nonpolar solvents, DMSO, ACN, 1-butanol and methanol on the

21

properties of [EMIM][CF3SO3].

22

Knowledge of thermophysical properties and accurate data, of densities and speeds of sound at

23

different temperatures are important for the engineering design of different types of equipment

24

related to liquid flow for the industrial level applications, and the viscosity data provide

25

quantitative information about the mass transfer, fluid transfer, and fluid flow mechanism[33].

26

Study of ILs with common cation [EMIM] having different anions [CF3SO3] /[EtSO4] with 2-

27

butanol shows the exciting results on changing the compositions and temperatures. To the best of

28

our knowledge, we have not found any report in literature on systematic investigation on the

29

thermophysical properties of binary mixtures, [EMIM][CF3SO3] + 2-butanol and [EMIM][EtSO4]

30

+ 2-butanol. The objective of this work is to study systematically the thermophysical properties,

31

densities (ρ), speeds of sound (u) and dynamic viscosities (η) and to investigate the interactions in

32

ILs-2-butanol mixtures. To understand in-depth about the interactions in ILs-2-butanol mixtures,

33

we have studied the excess/derived properties namely excess molar volumes (VE), excess molar

+

-

-

4

,

), and viscosity deviations (∆η). The derived data of VE,

,

1

isentropic compressibilities (

2

and ∆η values have been further correlated to the Redlich-Kister polynomial equation for binary

3

mixtures. The trend of excess and deviation properties have been discussed in terms of ion-ion,

4

ion-dipole, dipole-dipole and hydrogen bonding interactions and packing of components in the

5

studied mixtures. This work also focuses on quantum mechanical calculations, DFT in order to

6

understand the influence of anions [CF3SO3] and [EtSO4] on the nature of interaction and

7

bonding intensities in IL-2-butanol mixtures. For this purpose, the natural bond orbital (NBO’s)

8

analysis was performed.

9

2. Experimental and Computational Studies

10

-

-

2.1. Material and Purification

11

The studied ionic liquids [EMIM][CF3SO3] and [EMIM][EtSO4] were procured from Sigma

12

Aldrich, and 2-butanol was obtained from Chemika-Biochemika-Reagents (Otto), and detailed

13

information about the ILs and the solvent employed are summarized in Table 1. The water content

14

was determined using Karl Fischer Coulometric titrator (C20, Mettler Toledo) electronic digital

15

balance. No further purifications of chemicals were performed. All the binary and ternary

16

mixtures, [EMIM][CF3SO3] + 2-butanol and [EMIM][EtSO4] + 2-butanol were prepared freshly

17

and kept at desired temperature for sometimes to ensure the complete miscibility of the sample.

18

The binary mixtures of different mole fractions were prepared by weighing on a new classic MS

19

Mettler Toledo electronic digital balance with a precision of 1 × 10-4 g. The combined expanded

20

uncertainty in mole fractions of all the prepared samples was estimated less than 2 × 10-4.

21

2.2 Densities and Speeds of Sound Measurements

22

The measurement of ρ, and u of binary mixtures were performed over the whole

23

concentration range, at various temperatures T= (298.15, 303.15, 308.15, 313.15, 318.15 and

24

323.15) K and pressure P=0.1MPa using vibrating tube densimeter (Anton Paar DSA 5000M)

25

having ultrasonic transducer of frequency 3 MHz. For each system, at least three independent

26

measurements were performed using the same experimental conditions with freshly prepared

27

samples. The instrument was calibrated for setting each series of experiment with the triple

28

distilled water and dry air at all the studied temperatures and pressure P =0.1MPa. The combined

29

expanded uncertainties (level of confidence 0.95, k = 2) associated with measurements of densities

30

and speeds of sound were found to be 5 × 10-4 g·cm-3 and 0.5 m·s-1, respectively. The uncertainty

31

in temperature between 298.15 K to 323.15 K was within 0.05 K.

32

2.3 . Viscosities Measurements

5

1

The measurements of η of all the binary mixtures were performed over the whole concentration

2

range, at various temperatures T= (298.15, 303.15, 308.15, 313.15, 318.15 and 323.15) K and

3

pressure P = 0.1MPa using Anton Paar Lovis 2000 M falling ball automated viscometer. For the

4

determination of viscosities, the capillaries having diameter 1.59 mm(dynamic viscosity range =

5

1-20 mPa·s) and 1.8 mm (dynamic viscosity range = 17-300 mPa·s) were calibrated by standards

6

N-7.5 oil and N-26 oil with standard balls at all temperatures 298.15 K-323.15 K and at pressure

7

0.1 MPa. The combined expanded uncertainties with a level of confidence = 0.95, K=2 associated

8

with measurements of viscosity were found to be Uc(η) (˂ 1 mPa·s) = 0.20 mPa·s, Uc(η) (1-10

9

mPa·s) = 0.50 mPa·s and Uc(η) (11-50 mPa·s) = 0.70 mPa·s, Uc(η) (˂ 50 mPa·s) = 0.90 mPa·s.

10

The temperature was kept constant with a precision of 0.05 K.

11

2.4. DFT Calculation

12

The DFT calculations were carried out on isolated cation, anion, ion pairs and [ion pair + 2-

13

butanol] systems using DFT/B3LYP-D3 method with 6-311++G(d,p) basis set implemented in

14

Gaussian 09 software [34]. The D3 Grimme’s dispersion correction was considered within the

15

B3LYP method for the ion pairs and ion pair + 2-butanol systems. It is found that the B3LYP

16

functional suppresses the self-interaction error upto some extent [30]. Optimized structural

17

parameters and theoretical IR spectrum of the present compounds were obtained using the same

18

method and basis set. The calculated real values of IR frequencies confirm the optimized

19

geometry to minimum energy on potential energy surface. The obtained DFT results were

20

analyzed by Gauss View 5 program [35]. Natural atomic charges, donor-acceptor NBO interaction

21

energies, thermodynamic parameters, dipole moment, molecular polarizability and hyper-

22

polarizability, frontier molecular orbitals energies, HOMO-LUMO gap, and molecular

23

electrostatic potential were computed at the same level of theory. The electrochemical stability of

24

the ion pairs was estimated using the parameters like ionization energy and electron affinity

25

obtained by HOMO-LUMO energy values. The parameter, electrochemical potential window was

26

estimated to define relative chemical stability of ionic liquids. The dispersion correction (D3) was

27

computed and used to estimate the dispersion energy (ED3) similar to interaction energy (∆E)

28

obtained by the supermolecular approach [30, 36]. The HOMO and LUMO energies have also

29

been used to calculate global reactivity descriptors like hardness, softness, chemical potential,

30

electronegativity, the electron affinity, and electrophilicity index of the systems.

31 32

3. Results and Discussion 3.1. Thermophysical Properties

6

1

The densities and speeds of sound are measured experimentally for pure components,

2

[EMIM][CF3SO3], [EMIM][EtSO4], 2-butanol and their binary mixtures; [EMIM][CF3SO3] + 2-

3

butanol and [EMIM][EtSO4] + 2-butanol across the whole composition range at six temperatures,

4

(298.15, 303.15, 308.15, 313.15, 318.15, 323.15) K and pressure, P = 0.1MPa, and the data are

5

listed in Table S1 and S2 of supplementary information, respectively. This study reveals that the

6

change of anions ([CF3SO3] /EtSO4] ) with cation [EMIM] leads to change in density values and

7

the densities of pure [EMIM][CF3SO3] are found to be higher as compared to [EMIM][EtSO4].

8

However, the opposite trend is found for speed of sound values, i.e., u of pure [EMIM][CF3SO3]

9

are found to be smaller as compared to [EMIM][EtSO4].

-

-

+

10

The ρ values of ILs, [EMIM][CF3SO3] and [EMIM][EtSO4] with 2-butanol increase over

11

the entire mole fraction range of ILs, however, it can be observed that these values decrease with

12

increasing temperature for both the studied systems and are depicted in Table S1 (supplementary

13

information). Table S2 of supplementary informations reveals the effect of composition and

14

temperature on speeds of sound (u) for both studied binary mixtures [EMIM]-[CF3SO3]/[EtSO4] +

15

2-butanol. The values of measured u, tend to increase across the IL mole fraction for both the

16

studied binary systems. On the other hand, the speeds of sound with temperature show a

17

decreasing effect on the increase of temperature from 298.15K to 323.15K. The speed of sound

18

provides useful information towards molecular arrangements existing in solution through the

19

compression and decompression process.

20

Dynamic viscosity is significantly influenced by the intermolecular interactions such as

21

dispersive force, columbic interactions, and hydrogen bonding. The η are experimentally

22

determined for all pure components [EMIM][CF3SO3], [EMIM][EtSO4] and 2-butanol and their

23

binary mixtures [EMIM][CF3SO3] + 2-butanol and [EMIM][EtSO4] + 2-butanol across the whole

24

composition range and at the six temperatures (298.15, 303.15, 308.15, 313.15, 318.15, 323.15) K

25

and at pressure P = 0.1MPa; and the data are given in Table S3 (Supplementary Information). The

26

values of η decrease with an increase of temperature for both the systems, [EMIM][CF3SO3] + 2-

27

butanol and [BMIM][EtSO4] + 2-butanol whereas, the values increase across the concentration

28

range of IL for both the systems. The effect of anion ([CF3SO3] /[EtSO4] ) on viscosities of the

29

mixture lead the larger value of η in the case of [EMIM][EtSO4] + 2-butanol as compared to

30

[EMIM][CF3SO3] + 2-butanol system.

-

-

31

Table S4 (supplementary information) reveals the comparison of our data of ρ, u and η at

32

298.15 K for all studied pure components and the reported data available in the literature [9-

7

1

27,37-47] with the percent deviations and the plots of standard deviation against temperature are

2

also reported in Fig. S1 of supplementary information. It is observed that the measured values of

3

ρ, u and η show good agreement with the literature data with slight deviations. The noticeable

4

deviations are observed for η data as our experimental viscosities are determined by the Anton

5

Paar Lovis 2000M falling ball automated viscometer while the other authors have used the

6

ordinary Ubbelohde viscometer. The inconsiderable deviations observed in density and speed of

7

sound data may be ascribed either to certain unspecified impurities in compounds or owing to the

8

use of different experimental methods.

9 10

3.2 DerivedProperties The VE (excess molar volume),

11

,

(excess molar isentropic compressibility) and -

-

12

∆η (viscosity deviation) values of IL having different anion ([CF3SO3] /EtSO4] ) and cation

13

([EMIM] ) with 2-butanol as a function of the concentration of IL at various temperatures are

14

incorporated in Tables S5-S7 of supplementary information. The values of VE,

15

the studied binary mixtures as a function of the mole fraction of IL are graphed in Figs. 1(a, b)-

16

3(a, b) at different temperatures.

17 18 19

+

,

, and ∆η for

The VE trends reveal the deviations from ideality. The VE are computed for the binary mixtures [EMIM][CF3SO3]/[EMIM][EtSO4] + 2-butanol by using following equation, =∑



(1)

20

where ρ are the densities of mixtures and ρi is the density of pure component i; Mi and xi represent

21

the molar mass and mole fraction of the pure components.

22

As depicted in the Figure 1(a), the VE for the system, [EMIM][CF3SO3] + 2-butanol show negative

23

to positive variations with the minimum negative value at x1 = 0.1092, the positive value starts

24

from x1 = 0.2945 and it increases up to x1 = 0.6907 and then the value again start declining.

25

Furthermore, as shown in Figure 1(b), for the system [EMIM][EtSO4] + 2-butanol, the excess

26

molar volume increases upto x1 = 0.7957 and then start declining. This system shows minima at x1

27

= 0.1032. Moreover, with the increase in temperature, the VE decrease for both the studied binary

28

systems but the deviation from ideality becomes negative with the temperature for

29

[EMIM][CF3SO3] + 2-butanol system. As it can be observed for the case of [EMIM][CF3SO3] +

30

2-butanol, the VE value varies from negative to positive which reveals that the interactions

31

become weaker at higher IL concentration while, for the system[EMIM][EtSO4] + 2-butanol, all

32

the positive values of VE attribute that the interaction between the ion-pair of IL and the solvent is

8

1

weaker as compared to interaction in [EMIM][CF3SO3] + 2-butanol. Thus, on replacing the anion,

2

[CF3SO3] by [EtSO4], the interaction of IL with the alcoholic moiety becomes weak at the lower

3

concentration of [EMIM][EtSO4]. Whereas, as the x1 of IL in [EMIM][CF3SO3] + 2-butanol

4

system raised, it shows higher positive VE value as compare to [EMIM][EtSO4] + 2-butanol. It

5

may be summarized that at a lower concentration of IL, the stronger interactions are found in case

6

of [EMIM][CF3SO3] + 2-butanol and at higher concentration of IL, the [EMIM][EtSO4] + 2-

7

butanol shows stronger interaction between [EMIM][EtSO4] and 2-butanol. The value of VE for

8

[EMIM][CF3SO3] + 2-butanol and [EMIM][EtSO4] + 2-butanol are 0.43198 cm3mol-1 (at x1 =

9

0.3938) and 0.28404 cm3mol-1 (at x1 = 0.3936) respectively. The studied systems have same

10

cation and solvent. The contribution of anion is 0.14797 cm3mol-1. On comparing the VE values

11

[EMIM][CF3SO3] with acetonitrile(ACN) and dimethylsulfoxide (DMSO) from literature [28],

12

the VE is found to be negative over the entire concentration range (x1) at all the focused

13

temperature under atmospheric pressure for both studied systems [EMIM][CF3SO3] +

14

ACN/DMSO while, for IL, [EMIM][EtSO4] with 1-butanol/methanol [29] then again found to be

15

negative over the entire composition range at all the temperatures under pressure P = 0.1 MPa.

16

The relative degree of expansion/contraction of the two liquids on mixing is responsible for the

17

magnitude and sign of VE for a system. Usually, the VE arises from three types of interactions

18

between the components of liquid mixtures, these interactions include (i) Physical interactions (ii)

19

Chemical or specific interactions and (iii) structural contributions. The physical interaction is

20

mainly comprises of dispersive forces or weak dipole-dipole or dipole-induced dipole or ion-ion

21

interactions and resulting in a positive contribution, hereby the contraction and compression of

22

volume the mixtures. However, the chemical/specific interactions, includes the charge transfer

23

complexes, formation of hydrogen bonds complexes and other complexes forming interactions,

24

leading a negative contributions and the last, the structural contribution, occurs due to the

25

difference in shape and size of the molecules present in the mixtures, or due to the

26

accommodation of one component into the interstitial sites of structural network of other

27

components, thereby, reducing the free volume and compressibility of the mixtures and again

28

contributing their results towards negative contributions. The results of the studied binary mixtures

29

show the positive and negative values of VE. The negative values of VE may be due to strong attractive

30

forces between different species i.e., may be the formation of hydrogen bonds take place or may be

31

due to accommodation of 2-butanol molecules in the interstitial sites of molecules of ILs While, the

32

positive values of VE can be ascribed to disruption of order in the solution, i.e. weakening of

33

molecular association (may be due to destruction of hydrogen bond network) or may be due to the

34

specific geometry of the molecules which resist the proximity of constituent molecules.

9

2

,

The values of

1

for studied binary mixtures [EMIM]-[CF3SO3]/[EtSO4] + 2-butanol

have been determined using the following relation

=

,

3 ,

,



4

where

5

compression, respectively.

6

The molar isentropic compression, ,

7

8

and

,

,

=

where Vm is the molar volume and

, is defined as

.

= 1⁄

whereas ideal molar isentropic compression (

11

expression ,

=∑

,

+

.

(3)

is the isentropic compressibility and it can be determined as,

10

12



=



= 1/

9

(2)

are the molar isentropic compression and ideal molar isentropic



=−

,

'

" $ & ! # ( %,# )#

+

⁄ ,

= 1/ .

(4)

) have been calculated using the following

'

"' $ %,' & ()'

+

*+ &' $ %

()*+

,

(5)

, αid, - and Cpid are the molar volume, isobaric thermal expansivity, molar isobaric

13

The

14

expansion, and molar isobaric heat capacity of the ideal mixture. The method of determination of

15

,

, αid, - and Cpid is given in our previous work [51]. The experimental data of molar heat

16

capacities, ./ of [EMIM][CF3SO3], [EMIM][EtSO4] and 2-butanol have been taken from the

17

literature [6, 28, 42, 48,49].

18

As Fig. 2(a-b) reveals that the values of

,

of both the systems, [EMIM][CF3SO3] + 2-

19

butanol and [EMIM][EtSO4] + 2-butanol are negative over the whole range of compositions at

20

studied temperatures as a function of IL concentration and at pressure, P = 0.1MPa, and the values

21

show increasing trend with increasing temperatures. Similarly the values of

22

[EMIM][CF3SO3] + 2-butanol and [EMIM][EtSO4] + 2-butanol are 49.22 1015

23

(at x1 = 0.3938) and 68.87 1015

,

,

,

for

/m3·mol-1·Pa-1

/m3·mol-1·Pa-1 (at x1 = 0.3936) respectively, The studied

24

systems have same cation and solvent. The contribution of anion is 19.65 1015

25

The comparison of

26

be negative for both the studied systems but the negative devition from ideality is of lesser extent

27

in contrast to [EMIM][CF3SO3] + 2-butanol system. However, on comparison of [EMIM][EtSO4]

28

+ 1-butanol/methanol [29] with [EMIM][EtSO4] + 2-butanol suggest that although the

,

,

of [EMIM][CF3SO3] with ACN/DSMO [28] reveals the

/m3·mol-1·Pa-1. ,

is found to

,

were

10

1

found to be negative for [EMIM][EtSO4] + 1-butanol/methanol but of much lesser magnitude for

2

[EMIM][EtSO4] + 2-butanol. The trend of variation of

3

behavior in the system and the obtained data reveals that both the systems are less compressible

4

than the corresponding ideal mixtures and this may be due to the strong interaction between the

5

components of the mixtures which lead to contraction in free volumes and thereby become the

6

cause of reduction in compressibility at all temperatures. It also help to elucidate the interstitial

7

accommodation of 2-butanol molecules in two different IL with same cation, these tend to

8

decrease the free volume in the mixture as compared to those of pure components due to

9

disruption of ILs assemblies on the addition of 2-butanol. On comparison, the larger negative ,

,

help to interpret the compressibility

10

values of

are found in [EMIM][EtSO4] + 2-butanol system, which may be attributed to the

11

existence of strong forces of attraction between the solvents molecules. The less negative values

12

for [EMIM][CF3SO3] + 2-butanol may be due to the weak molecular association, i.e., may be held

13

by weaker forces either by ion-dipole, dipole-dipole or dipole induced dipole forces of attraction.

14 15

The viscosity deviations for the considered binary mixtures [EMIM][CF3SO3] + 2-butanol

16

and [EMIM][EtSO4] + 2-butanol have been evaluated from the viscosity data of pure and binary

17

mixtures using the following expression

18

∆2 = 2 − ∑

2

(6)

19

where ηi and η are the dynamic viscosity of pure component i and of binary mixtures,

20

respectively, while, xi is the mole fraction of the pure component i.

21

The study of plots in Fig 3(a-b) shows that for ∆η for both the systems are found negative for the

22

complete composition range, at all investigated temperatures and atmospheric pressure, P =

23

0.1MPa. The ∆η decreases and then increases with increasing concentration of IL for both studied

24

systems. However, on the other hand for both studied mixtures, the negative value of ∆η decreases

25

with temperature, i.e., moves toward the positive magnitude. Viscosity deviations can be

26

explained in terms of the different factors, i.e., the shape and size of the molecule and the specific

27

molecular interactions. It is noticed that this increase or decrease in values of ∆2 with the rise of

28

temperature may be due to the presence of specific molecular interaction or maybe because of size

29

as well as the shape of the molecules. Since both the systems show negative deviations and

30

[EMIM][CF3SO3] + 2-butanol is having less negative values of ∆η as compared to

31

[EMIM][EtSO4] + 2-butanol suggesting the existance of strong ion-dipole interactions between

32

the IL and solvent molecules is compared with [EMIM][CF3SO3] + 2-butanol system. Similarly,

11

1

the values of ∆η or [EMIM][CF3SO3] + 2-butanol and [EMIM][EtSO4] + 2-butanol are -11.65

2

mPa·s (at x1 = 0.3938) and -25.41 mPa·s (at x1 = 0.3936) respectively, The studied systems have

3

same cation and solvent. The contribution of anion is -13.76 mPa·s. Again the comparison of ∆2

4

of [EMIM][CF3SO3] + ACN/DMSO [28] suggest that the ∆2 determined for the systems

5

[EMIM][CF3SO3] + ACN/DMSO are negative and no marked deviation is found in ∆2 values for

6

[EMIM][CF3SO3] + 2-butanol. Whereas, for [EMIM][EtSO4], the comparison of [EMIM][EtSO4]

7

+ 1-butanol/methanol [29] with [EMIM][EtSO4] + 2-butanol suggest that the values are again

8

negative and these systems shows pronounced deviations in contrast to [EMIM][EtSO4] + 2-

9

butanol. This trend to this, it may be due to the compactness of molecules by the occupation of

10

solvent molecules into the voids of the IL.

11

3.3. Application of Redlich-Kister Polynomial Equation Eventually the obtained data of VE,

12

-

,

+

and ∆ƞ for the same cationic ([EMIM] )

-

13

and different anionic ([CF3SO3] /[EtSO4] ) IL system with 2-butanol as a function of the

14

concentration of IL at all investigated temperatures and pressure have been fitted to the following

15

Redlich-Kister polynomial equation [50]

$ ∑5 6 4

3 =

16



&

(7)

17

where Y represents VE,

18

referred to as the adjustable parameter, and xi is the mole fraction of components. The optimum

19

numbers of ai coefficients have been determined from an examination of values of standard

20

deviations. The standard deviation, σ has been calculated using the following equation

21

7 = !∑

5

,

9:)

$8*

5

and ∆ƞ. ai can be obtained by least square method analysis and is

8*;<= &

,

/

(8)

22

where Yi refers to the molar properties of the components, n is the number of experimental data

23

points and m is the number of coefficients of the Redlich-Kister equation; and the coefficients of

24

Redlich-Kister polynomial equation are depicted in Table 2 for the studied excess/derived

25

properties.

26

The

VE,

,

and

∆η

of

all

the

binary

mixtures

containing

27

[EMIM][CF3SO3]/[EMIM][EtSO4] with 2-butanol are displayed in Figs.1-3 and the Redlich-

28

Kister polynomial equation fits data well in it. Also, the Redlich-Kister equations are help to

29

provide the estimation of coefficient and standard errors.

12

1

3.4. Density Functional Theory

2

The optimized geometries of the cation [EMIM]+, anions [CF3SO3] and [EtSO4] , ionic liquid,

3

[EMIM][CF3SO3] and [EMIM][EtSO4] and ionic liquid-solvent systems, [EMIM][CF3SO3] + 2-

4

butanol and

5

intermolecular distances in Figs. 4 and 5. Some selected structural parameters of these geometries

6

are summarized in Table S8 and S9 (supplementary information). The shift in bond lengths and

7

bond angles of [EMIM+], [CF3SO3] and [EtSO4] have been observed due to interactions

8

presented in ionic liquids and ionic liquid + solvent systems. The minimum self-consistent field

9

molecular energies and some important molecular parameters like dipole moment, polarizability,

10

hyper-polarizability, thermodynamic parameters, HOMO-LUMO energies gap, interaction energy

11

and electrochemical potential window (EW) are tabulated in Table S10 (supplementary

12

information). It is found that the calculated thermodynamic functions (heat capacity, entropy, and

13

enthalpy) of molecules rise rapidly with increasing temperature within low-temperature range

14

while these functions rise less rapidly (almost constant) with temperature in the high-temperature

15

range [51]. These parameters are important as they are related to the physical properties like

16

density, speed of sound, and the viscosity [52]. Electrochemical stabilities of the ion-pairs have

17

been estimated by electrochemical potential window using the parameters, ionization energy and

18

electron affinity obtained by HOMO-LUMO energies. The cathodic and anodic stability are

19

correlated by LUMO (~electron affinity) and HOMO (~ionization potential) energies [30]. These

20

parameters are determined for electrochemical applications of studied ionic liquids,

21

[EMIM][CF3SO3] and [EMIM][EtSO4]. B3LYP-D3 method is used to estimate the interaction

22

energies using dispersion energy values. The molecular electronic energies and interactional

23

energies for the both [EMIM][CF3SO3], [EMIM][EtSO4] and mixture of ionic liquid and solvent,

24

[EMIM][CF3SO3] + 2-butanol and [EMIM][EtSO4] + 2-butanol are presented in supplementary

25

information (Table S10). The interaction energy is an important quantity as this show correlation

26

with surface tension [31].

27

Spatial distribution of HOMO and LUMO and corresponding energy values of [EMIM][CF3SO3],

28

[EMIM][EtSO4], [EMIM][CF3SO3] + 2-butanol and [EMIM][EtSO4]+ 2-butanol systems are

29

shown in Figs. 6 and 7, respectively. In Fig. 6 (a), the HOMO is spread mainly over the region of

30

S=O in [CF3SO3] and LUMO is extended over the province of [EMIM]+. Whereas, for

31

[EMIM]+[CF3SO3] + 2-butanol system in Fig. 6 (b), the HOMO is concentrated mainly over the

32

region of 2-butanol and LUMO is spread over the region of [EMIM]+. It is worth mentioning that

-

-

[EMIM][EtSO4] + 2-butanol are presented with numbering scheme and

-

-

-

-

13

1

on addition of 2-buanol in the [EMIM][CF3SO3] and [EMIM][EtSO4], the HOMO is shifted over

2

the 2-butanol molecule which substantiates the higher chemical reactivity of the 2-butanol. In Fig.

3

7 (a), HOMO is extended over the region of S=O in [EtSO4] and LUMO is concentrated over the

4

cation part [EMIM] of the ionic liquid. While for [EMIM]+[EtSO4] + 2-butanol system, Fig. 7

5

(b), the almost similar spatial distribution of HOMO and LUMO are shown in Fig. 7 (a). This

6

implies that the 2-butanol in [EMIM]+[EtSO4]

7

reactivity. The HOMO-LUMO gap is appreciably altered on addition of

8

[EMIM][CF3SO3] and [EMIM][EtSO4]. Various reactivity parameters, such as ionization energy,

9

electron affinity, electronegativity, chemical potential, chemical hardness, chemical softness,

10

electrophilicity index, obtained from HOMO, LUMO energy values [53] are listed in Table S10 of

11

supplementary information.

-

+

-

-

+ 2-butanol system did not show chemical 2-butanol in

12

Molecular electrostatic potential (MEP) plots of ionic liquids and ionic liquid + 2-butanol

13

systems are presented in Figs. 8 and 9, respectively. These plots are obtained by mapping the

14

electrostatic potential onto constant electron density surface of the system. The different color

15

shows the different values of the electrostatic potential at surface. Red, blue, and green colors

16

indicate negative, positive and zero electrostatic potential, respectively. Thus, the red and blue

17

colored surface may be the site for electrophilic and nucleophilic reactions, respectively, while

18

green colored regions represent neutral sites. Thus, the sites for electrophilic and nucleophilic

19

reactions and neutral regions for the studied ionic liquids and ionic liquid + 2-butanol systems are

20

displayed in terms of colors in Figs. 8 and 9.

21

The quantitative description of the interaction between cation and anion within ionic liquids and

22

between solvent and ionic liquid are presented by NBO analysis. This analysis provides intra and

23

intermolecular electron delocalization within the molecular system in terms of the stabilization

24

energy, E(2). Some significant donor-acceptor interactions related E(2) values are given in Table

25

S11 and S12 (supplementary information). Its high value explains the large electron

26

delocalization. Natural atomic charges of the studied molecular systems are presented in Fig. 10.

27

In Fig. 10, the sulphur atom and oxygen atoms are appeared with the large positive and negative

28

charge values, respectively.

29

3.5. Conclusion

30

The values of VE for [EMIM][CF3SO3] + 2-butanol system show negative to positive deviations,

31

and these increase with the rise in concentration (x1), and then the values start decreasing again

14

1

with minima at lower concentration x1 =0.1092. However, for the system [EMIM][EtSO4] + 2-

2

butanol, the excess molar volumes increase over the entire composition range of IL with minima

3

at lower concentration x1 = 0.1032. Moreover, with increase in temperature, the values of VE

4

decrease for both the studied binary systems. The deviation becomes negative with increasing

5

temperature in case of [EMIM][CF3SO3] + 2-butanol system. Furthermore, the excess molar

6

isentropic

7

[EMIM][CF3SO3] + 2-butanol and [EMIM][EtSO4] + 2-butanol across the entire composition

8

range and at all temperatures and at pressure, 0.1MPa and these increase with an increase in

9

temperature. Similarly, ∆η show negative deviations relative to ideal mixing values over the entire

10

composition range at all temperatures and pressure. The negative values of ∆η increase at lower x1

11

and then decrease with concentration for both studied systems. However, the magnitude of

12

negative values decrease with an increase in temperature. The trends of variations of VE,

13

∆η parameters illustrate the effect of temperature on the intermolecular interactions for the studied

14

binary systems. The excess/deviation properties, VE,

15

to Redlich-Kister polynomial equation. The negative deviation of VE suggests, the presence of

16

attractive interactions

17

interstitial position of structural network of another component. It also suggest the occurance of

18

strong packing phenonmenon between IL and solvent molecules. While, the positive deviation

19

suggests, the weaker interaction and less efficient packing. The

20

compressibility of the system and herein, both the systems are less compressible than ideal one

21

attributing, strong interaction between the molecules of IL and solvent. However, the trend of ∆η

22

explains the shape and size of the molecule and their specific molecular interactions. The negative

23

deviation suggest the existence of stronger interaction while, the positive deviation suggest the

24

weaker one between the IL and solvent molecules. Besides, the DFT/B3LYP-D3 calculations

25

have been performed to obtain the information regarding molecular geometry, non-covalent

26

interactions, electrochemical stability, interaction energies, chemical reactivity descriptors and

27

various other molecular parameters of the studied systems. Shifts in structural parameters have

28

been noticed due to interactions present within the studied molecular systems. These interactions

29

have also been quantified using NBO analysis. As per HOMO-LUMO spatial plots, the 2-butanol

30

solvent has shown higher chemical reactivity in [EMIM][CF3SO3] + 2-butanol than that of the

31

[EMIM][EtSO3] + 2-butanol system. The appreciable increment in HOMO-LUMO gap (which

32

implies decrement in reactivity) has also been noticed on the addition of 2-butanol in ionic liquid

33

[EMIM]+ [EtSO4] .

compressibility

-

values

show

negative

magnitude

,

for

both

the

mixtures

,

and

and ∆η for all systems have been fitted

due to the accommodation of molecules of one component into the

,

data explains the

15

1

Acknowledgments

2

The authors are thankful to the Chairman, Department of Chemistry, A.M.U., Aligarh for

3

providing the necessary facility for the compilation of this work. Financial support from the UGC

4

Major Research Project [F. No. 41-240/2012(SR)], UGC-SAP (DRS-II), DST-FIST, and DST-

5

PURSE Programme. are sincerely acknowledged. . The author (Urooj Fatima) sincerely

6

acknowledges financial support from University Grants Commission (UGC), New Delhi, for

7

providing the fellowship.

8

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(303.15 to 343.15) K, J. Chem. Eng. Data 55 (2010) 2310-2315.

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43 A. Rodriguez, J. Canosa, J. Tojo, Physical Properties of Binary Mixtures (Dimethyl

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Carbonate + Alcohols) at Several Temperatures, J. Chem. Eng. Data 46 (2001) 1476-1486.

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Binary Mixtures of 1-Chlorobutane with Butanol Isomers at Several Temperatures, J.

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Chem. Eng. Data 50 (2005) 677-682.

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Mixtures of Butanenitrile with Butanol Isomers at Several Temperatures, J. Chem. Eng.

17

Data 45 (2000) 1182-1188.

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Binary Mixtures of Aliphatic Alcohols (C1−C4) with Nitroethane from 293.15 K to

20

313.15 K, J. Chem. Eng. Data 45 (2000) 450-456.

21

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22

Methyl-1-propanol, and 2-Methyl-2-propanol, J. Chem. Eng. Data 44 (1999) 788-791.

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new working pair: 1-Ethyl-3-methylimidazolium ethylsulfate and water, Chem. Eng. J.,

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2010, 156, 613-617.

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mixtures:

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8

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10 11 12

13

Table 1 Name of the compound, molar mass, purification method, mass fraction purity, and water content. Compounds CAS number M /g·mol-1 Source Purification Mass Water Method fraction content purity [EMIM][CF3SO3] 145022-44-2 260.23 SigmaWithout ≥98% 140 ppm (Karl Aldrich further Fischer purification method) [EMIM][EtSO4] 342573-75-5 236.29 SigmaWithout ≥95% 192 ppm (Karl Aldrich further Fischer purification method) 2-butanol 74.12 Merck Without ≥99.0 further purification a the Purity as stated by supplier

14 15

Table 2: Coefficients of the Equation 7 for Excess Molar Volumes, VE(m3·mol-1), Excess

16

Molar Isentropic Compressibilities >A?,@ (m3·mol-1·Pa-1), Viscosity Deviations, ∆ƞ (mPa·s)

17

and the Standard Deviations, (σ) at Temperature, T = (298.15 to 323.15) K and Mole

18

Fraction, x1 for the [EMIM][CF3SO3] + 2-butanol and [EMIM][EtSO4] + 2-butanol Systems

19

at Pressure P = 0.1 MPa. T/K

a0

a1

a2

a3

σ

5.8939

-0.9735

0.9461

0.0320

VE [EMIM][CF3SO3] + 2-butanol 298.15

3.1969

21

303.15

3.0552

5.9172

-1.2883

0.9346

0.0310

308.15

2.9402

5.8996

-1.5898

0.9191

0.0284

313.15

2.7776

5.8661

-1.9073

0.7297

0.0331

318.15

2.5326

6.0610

-2.1872

0.1177

0.0380

323.15

2.3498

5.9810

-2.6203

0.3011

0.0497

[EMIM][EtSO4] + 2-butanol 298.15

1.3910

1.1736

1.6818

1.8607

0.0126

303.15

1.3127

1.1194

1.6563

1.8736

0.0121

308.15

1.2454

1.1322

1.6737

1.8433

0.0148

313.15

1.1753

1.1475

1.5874

1.7032

0.0146

318.15

1.0996

1.1916

1.6212

1.5809

0.0113

323.15

1.0597

1.2896

1.4905

1.2598

0.0125

,

[EMIM][CF3SO3] + 2-butanol 298.15

-192.1598

61.1823

-20.6159

6.6485

0.0176

303.15

-176.5122

54.2881

-17.5999

5.4764

0.0140

308.15

-163.0901

48.4483

-15.1145

4.5377

0.1112

313.15

-151.2950

43.4512

-13.0614

3.7875

0.0090

318.15

-141.0342

39.1223

-11.3226

3.1684

0.0073

323.15

-135.1882

36.2192

-10.0943

2.7259

0.0060

[EMIM][EtSO4] + 2-butanol 298.15

-266.1332

96.3987

-37.6494

14.1024

0.0436

303.15

-249.7130

87.9436

-33.2455

12.0854

0.0362

308.15

-236.3613

80.8372

-29.5469

10.4119

0.0303

313.15

-223.7808

74.4531

-26.3716

9.0260

0.0255

318.15

-212.9810

68.8909

-23.6362

7.8530

0.0215

323.15

-208.0183

65.4816

-21.7913

7.0362

0.0187

∆η [EMIM][CF3SO3] + 2-butanol 298.15

-52.3833

-8.6224

41.1715

22.0639

0.4274

303.15

-42.4930

-6.0390

33.5547

17.1863

0.3484

308.15

-34.4491

-3.4993

28.0034

12.6097

0.2946

22

313.15

-28.4983

-2.0285

22.0685

7.6494

0.2682

318.15

-23.7526

-1.1766

19.6246

7.6337

0.2135

323.15

-19.9413

-0.1613

16.7797

5.5439

0.1865

[EMIM][EtSO4] + 2-butanol 298.15

-115.6017

-42.4003

0.0976

0.9423

0.0287

303.15

-84.4011

-31.7359

0.5904

-0.5058

0.1356

308.15

-65.5785

-14.5789

4.9271

-7.0551

0.2696

313.15

-48.5923

-10.6183

-0.5059

-0.1229

0.0425

318.15

-37.9466

-6.4588

-0.3999

0.3340

0.0285

323.15

-28.8155

-1.5513

-1.3426

1.6897

0.0222

1

1.2 (a)

0.4

E

3

V /cm mol

-1

0.8

0.0

-0.4 0.0

2 3

0.2

0.4 0.6 x1 of [EMIM][CF3SO3]

0.8

1.0

23

(b)

3

V /cm mol

-1

0.4

E

0.2

0.0 0.0

0.2

0.4

0.6

0.8

1.0

x1 of [EMIM][EtSO4]

1 2 3

Fig. 1. Excess molar volumes (VE/cm3mol-1) of (a) [EMIM][CF3SO3] + 2-butanol, (b)

4

[EMIM][EtSO4] + 2-butanol as a function of mole fraction at different temperatures ■, 298.15 K;

5

●, 303.15 K; ▲, 308.15 K; ▼, 313.15 K; ♦, 318.15 K and ◄, 323.15 K. The symbols represent

6

experimental values and the solid curves represent calculated values with the Redlich-Kister

7

equation.

0

(a)

-1

10 Κs,m /m mol Pa

-1

-12

15

E

3

-24

-36

-48 0.0

0.2

0.4

0.6

x1 of [EMIM][CF3SO3]

8

0.8

1.0

24

0

(b)

-1

10 Κs,m /m mol Pa

-1

-15

E

3

-30

15

-45

-60

-75 0.0

0.2

0.4

0.6

0.8

1.0

x1 of [EMIM][EtSO4]

1 2

Fig. 2. Excess molar isentropic compressibilities (1015

3

2-butanol, (b) [EMIM][EtSO4] + 2-butanol as a function of mole fraction at different temperatures

4

■, 298.15 K; ●, 303.15 K; ▲, 308.15 K; ▼, 313.15 K; ♦, 318.15 K and ◄, 323.15 K. The

5

symbols represent experimental values and the solid curves represent calculated values with the

6

Redlich-Kister equation.

0

,

/m3mol-1Pa-1) of (a) [EMIM][CF3SO3] +

(a)

∆η/mPa·s

-4

-8

-12

0.0

0.2

0.4

0.6

x1 of [EMIM][CF3SO3]

7

0.8

1.0

25

0

(b)

∆η/mPa·s

-8

-16

-24

-32 0.0

0.2

0.4

0.6

0.8

1.0

x1 of [EMIM][EtSO4]

1 2

Fig. 3. Viscosity deviations (∆η/mPa·s) of (a) [EMIM][CF3SO3] + 2-butanol, (b) [EMIM][EtSO4]

3

+ 2-butanol as a function of mole fraction at different temperatures ■, 298.15 K; ●, 303.15 K; ▲,

4

308.15 K; ▼, 313.15 K; ♦, 318.15 K and ◄, 323.15 K. The symbols represent experimental

5

values and the solid curves represent calculated values with the Redlich-Kister equation.

6

7 8 9

-

-

Fig. 4. Optimized geometry of (a) [EMIM]+[CF3SO3] ion pair and (b) [EMIM]+[CF3SO3] + 2butanol system

26

1

2 3 4 5

-

-

Fig. 5. Optimized geometry of (a) [EMIM]+[EtSO4] ion pair and (b) [EMIM]+[EtSO4] + 2butanol system.

27

1 2 3 4

+

-

+

-

Fig. 6. Spatial plot of HOMO and LUMO of (a) [EMIM ][CF3SO3 ] and (b) [EMIM ][CF3SO3 ] + 2-butanol system.

28

1 2 3 4 5 6

+

-

+

-

Fig. 7. Spatial plot of HOMO and LUMO of (a) [EMIM ][EtSO4 ] and (b) [EMIM ][EtSO4 ] + 2-butanol system.

29

+

-

+

-

Fig. 8. Molecular electrostatic potential (MEP) plot of (a) [EMIM ][CF3SO3 ] and (b) [EMIM ][CF3SO3 ] + 2-butanol system.

30

+

-

+

-

Fig. 9. Molecular electrostatic potential (MEP) plot of (a) [EMIM ][EtSO4 ] and (b) [EMIM ][EtSO4 ] + 2-butanol system.

31

Fig. 10. Natural atomic charges in ionic liquids and ionic liquid-solvent systems.

32

Experimental thermophysical properties and DFT calculations of imidazolium ionic liquids and 2-butanol mixtures Urooj Fatimaa, Riyazuddeena*, Mohammad Jane Alamb, Shabbir Ahmadb a

Department of Chemistry and bDepartment of Physics, Aligarh Muslim University, Aligarh

202002, U.P., India. *Corresponding author E-mail: [email protected]

Declaration of interest: Declarations of interest: none