Volumetric and compressibility studies of aqueous triethylammonium based protic ionic liquids at T = 298.15 K

Accepted Manuscript Volumetric and compressibility studies of aqueous triethylammonium based protic ionic liquids at T=298.15K

Kunal R. Patil, D.H. Dagade PII: DOI: Reference:

S0167-7322(17)32876-3 doi:10.1016/j.molliq.2017.10.137 MOLLIQ 8100

To appear in:

Journal of Molecular Liquids

Received date: Revised date: Accepted date:

29 June 2017 27 October 2017 29 October 2017

Please cite this article as: Kunal R. Patil, D.H. Dagade , Volumetric and compressibility studies of aqueous triethylammonium based protic ionic liquids at T=298.15K. The address for the corresponding author was captured as affiliation for all authors. Please check if appropriate. Molliq(2017), doi:10.1016/j.molliq.2017.10.137

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ACCEPTED MANUSCRIPT Volumetric

and

Compressibility

Studies

of

Aqueous

Triethylammonium Based Protic Ionic Liquids at T = 298.15 K Kunal R. Patil and D. H. Dagade* Department of Chemistry, Shivaji University, Kolhapur 416004, India

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Abstract: The significant considerations have centred on the utilization of the bio-ionic liquids as green solvents to replace or minimize conventional environment-harming organic

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solvents. Ionic liquids have many remarkable environment-accepting properties such as ease of reuse, low vapour pressure, and thermal stability etc. The present work focuses on

formate

triethylammonium

butanoate

[TEAF], [TEAB],

triethylammonium triethylammonium

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triethylammonium

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thermodynamic understanding of aqueous solutions of protic ionic liquids (PILs) namely propionate glycolate

[TEAP],

[TEAG],

and

triethylammonium pyruvate [TEAPy]. The density and speed of sound measurements for

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aqueous solutions of these PILs are reported at T = 298.15 K and the data were used to obtain the apparent and partial molar volumes, isentropic and apparent molar isentropic compressibilities for aqueous PILs solution. From the data of density and sound speed, we electrostriction,

hydration

D

estimated

numbers

of

PILs,

limiting

volumetric

and

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compressibility properties and finally discussed the results obtained in terms of ion-ion, ionsolvent interaction through hydration behaviour of PILs, kosmotropic effect, hydrophobic interactions, etc.

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Keywords: Protic ionic liquids, Partial molar volume, Isentropic compressibility, Hydration

AC

number, Electrostriction, Kosmotropic effect.

1

ACCEPTED MANUSCRIPT 1.

INTRODUCTION The probability of generating ionic liquids from renewable and non-toxic natural

sources is now pulling in consideration. Especially, Fukumoto et al. [1] and Tao et al. [2] synthesized amino acid ionic liquids (AAILs) from the natural amino acids. AAILs are more attractive amongst the researchers due to the huge natural abundance amino acids, ability to form strong cooperative H-bonds and hydrophobic tuning that is helpful for dissolution of

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biomaterials likes, DNA, cellulose, and different carbohydrates [3,4]. In addition, AAILs have potential use Diels-Alder reactions as catalysts [2]. Recently, Fukaya et al. [5] and Tao

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et al. [6] synthesized the cholinium-based bio ionic liquids in which carboxylic acids and amino acid used as anions. The physicochemical properties of such bio-ionic liquids show

SC

that these ILs have strong H-bonding abilities than the conventional ILs. The scientists from the Joint BioEnergy Institute [7-9] have produced bio-ionic liquids containing tertiary amines

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as cations and dihydrogen phosphate as anion used for the manufacturing of biofuels i.e. bioethanol from plant biomass.

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Recently, researcher reviewed properties of aprotic ionic liquids (APILs) and protic ionic liquids (PILs) as well as their applications in various field [10-13]. In comparison with

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APILs, PILs often have higher fluidity, higher conductivity, lower melting points, etc. [14] and are less expensive and preparation is more easy as their synthesis does not involved the

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formation of byproducts [13]. NMR [15], far-IR [16], X-ray diffraction [17], neutron diffraction [17] and DFT simulation [16,18] studies demonstrates hydrogen bonding in PILs. The most considered case of the capacity of a PIL to frame supramolecular assembly through

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hydrogen bonding is ethylammonium nitrate (EAN) ionic liquid [19]. PILs has been widely used in various biological applications such as protein crystallization, protein separation and

AC

purification [20,21], cellulose dissolution [22,23] as well as in the field of chromatography [24] also in the field of electrochemical devices [25-27]. In a recent communications [4,2831], we reported thermodynamic investigation of ionic interactions and hydration behaviour for APILs in aqueous solutions at molecular level. We showed that the hydration number and ion-water interactions as well as ion-pair formation mainly depends on the size, shape and charge density of ions. As compared to simple imidazolium based halide the amino acid APILs get more hydrated due to the strong cooperative H-bonding of amino acids anions with water revealed from results of concentration dependence of partial molar entropies and enthalpy-entropy compensation effects [4,28-31]. The hydrophobic hydration and cooperative H-bonding of ions is responsible for the formation of more ordered water-structure around 2

ACCEPTED MANUSCRIPT the ions (kosmotropic effect). In continuation to our earlier work focused on understanding of molecular interactions through thermodynamics study of aqueous ionic liquids, we are reporting here thermodynamic properties of some protic ionic liquids in aqueous solutions. To explore potential use of triethylammonium based PILs, it is necessary to understand the nature of interactions such as H-bonding, van der Waal forces, ion-pairing, ionic and hydrophobic hydration in aqueous solutions. In this context, we are reporting

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herewith density and sound speed measurements for the triethylammonium based PILs namely triethylammonium formate [TEAF], triethylammonium propionate [TEAP], butanoate

[TEAB],

triethylammonium

glycolate

[TEAG]

and

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triethylammonium

2.

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triethylammonium pyruvate [TEAPy] in aqueous solutions at T = 298.15 K. Experimental Methods

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2.1 Materials

All chemicals procured from different manufacturers, required for the synthesis of

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triethylammonium based protic ionic liquids, are listed in Table 1 with mass fraction purity and were used without further purification. Table 1

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Chemical Name, CAS No., Molecular mass, Purity and Source of Chemicals Used

121-44-8

Molecular mass (g·mol−1) 101.19

Mass Fraction Purity ≥ 0.99a

Formic acid

64-18-6

46.03

≥ 0.85a

Qualigens

Propanoic acid

79-09-4

74.08

≥ 0.99 a

Merck

107-92-6

88.11

≥ 0.98a

Merck

79-14-1

76.05

≥ 0.99a

Sigma-Aldrich

127-17-3

88.06

≥ 0.98a

Aldrich

141.95

≥ 0.98a

Merck

CAS No.

Triethylamine

AC

Glycolic acid

CE

Butanoic acid

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Chemical name

Pyruvic acid Phosphorus

1314-56-3

pentaoxide TEAF

585-29-5

147.22

≥ 0.98c

TEAPb

51009-80-4

175.27

≥ 0.98c

TEABb

7304-94-4

189.30

≥ 0.99c

b

3

Source Merck

Synthesized in Lab Synthesized in Lab Synthesized in

ACCEPTED MANUSCRIPT Lab TEAG

178461-51-3

177.24

≥ 0.98c

TEAPyb

-

189.25

≥ 0.99c

b

a

Synthesized in Lab Synthesized in Lab

Used as received without purification.

b

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All the PILs used here are synthesized (see section 2.2 below). Triethylammonium formate (TEAF), triethylammonium propionate (TEAP), triethylammonium butanoate (TEAB), triethylammonium glycolate (TEAG), and triethylammonium pyruvate (TEAPy). c

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SC

RI

Dried at 343.15 K for 2 days under vacuum in presence of P2O5. The synthesized PIL was dried by employing high vacuum at 343.15 K. The purity was checked by 1H NMR spectroscopic techniques. No any traces of impurities were detected in 1H NMR spectra. The impurities in the original reactants and water content in the synthesized ionic liquids after drying were taken into consideration while reporting the final purity of the synthesized ionic liquids.

2.2 Synthesis of PILs

Synthesis of PILs were carried out in different ways using reported methods [32,33].

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The dropwise additions of stoichiometric quantity of carboxylic acids like formic acid, propionic acids, butanoic acid were made in triethylamine in the round bottom flask which was kept in a circulating heated water-bath and fixed with a reflux condenser with constant

formate

[TEAF],

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triethylammonium

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stirring at 60 ºC for 1 hour and then at 70 ºC for 2 hours for completion of reaction to form triethylammonium

propionate

[TEAP],

triethylammonium butanoate [TEAB] as shown in Scheme in 1. For the synthesis of triethylammonium

pyruvate

[TEAPy]

and

triethylammonium

glycolate

[TEAG],

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stoichiometric quantity of pyruvic acid and glycolic acid were added into the triethylamine at room temperature with constant stirring for 24 hour (Scheme 1). All ionic liquids thus

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obtained were kept under vacuum at 70 ºC in presence of phosphorous pentaoxide (P2O5) for 2 days. The structures of the five synthesized PILs were confirmed by using 1H NMR spectra obtained from the 300 MHz Bruker instrument in CDCl3 as a solvent (see Supplementary Data, Fig. S1-S5). Further, pH-metric titration of aqueous PILs showed absence of any unreacted component in the final product. Finally, water contents in the prepared ionic liquids were determined by Karl-Fischer titration (TKF 55) and found to be 0.21 mass % in TEAF, 0.16 mass % in TEAP, 0.27 mass % in TEAB, 0.43 mass % in TEAG and 0.60 mass % in TEAPy, which were taken into consideration during preparation of solution. All the solutions of PILs were prepared on molality basis and whenever necessary converted to molarity scale using density data at T = 298.15 K. Quartz doubly distilled water was used for the entire 4

ACCEPTED MANUSCRIPT work. A Mettler Toledo ML204/A01 balance having readability of 0.1 mg was used for weighing.

60

0C

x Reflu

NH

R-COOH

R= H, C2H5, C3H7

R. T.

Acid

NH R-COO

R= CH3CO, CH2OH PILs

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SC

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Triethylamine

PT

N

R-COO

Scheme 1: Synthesis route of triethylammonium based PILs. 2.3 Density Measurements

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Density of pure PILs and their aqueous binary solutions were measured at T = 298.15 K with an Anton Paar (model: DMA 60/602) vibrating-tube digital densitometer in the

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concentration range ~0.008 to ~1.0 molkg−1. The temperature constancy of the vibrating tube was better than ± 0.02 K for which a Julabo F-25 cryostat was used. After applying humidity 510−3 kgm−3.

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and lab pressure corrections, the uncertainty in the density measurements was found to be ±

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2.4 Speed of Sound Measurements The speed of sound measurements were carried out for aqueous solutions of PILs at T = 298.15 K in the concentration range of 0.05 to 0.5 molkg−1 by using ultrasonic interferometer operating at 2 MHz frequency, (M/S Mittle Enterprises). The constant temperature 298.15 ± 0.05 K was achieved inside the cell of interferometer by circulating water by means of a Julabo F-25 cryostat having an accuracy of ±0.01 K. The reproducibility of measurements were checked by obtaining speed of sound in pure water at T = 298.15 K 1497.6 ms−1 [28,30,31,34]. The standard deviation in speed of sound measurements was found to be ±0.5 ms−1. 5

ACCEPTED MANUSCRIPT 3. Results 3.1 Volumetric Properties The density () data of aqueous solutions of Triethylammonium based PILs in the concentration range of ~0.008 to ~1.0 molkg−1 at T = 298.15 K are reported in Table 2. The apparent molar volume ( V ), the partial molar volume of solvent ( V 1 ) and partial molar

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volume of solute ( V 2 ) of aqueous PILs solutions were calculated from experimental density

m1/ 2 dv 2 d m

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V 2  v 

SC

 M         V   2    0     m0 

MA

M1 m3/ 2 dv V1  V  2 d m 0 1

RI

data using standard equations (1) to (3) [35].

(1)

(2)

(3)



represents the densities in kg.m−3 for water and aqueous PILs

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mol.kg−1 whereas, 0 and

D

In equations (1) to (3), M2 is the molar mass of PILs in kg.mol−1 and m is the molality in

solutions, respectively and V10 is the molar volume of pure water. All data, thus obtained at T = 298.15 K for aqueous solutions of PILs, are included in Table 2. The V data can be fitted

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with concentration (mol.dm−3) using the equation (4)

V  V0  SV c  BV c  DV c 2

(4)

AC

where V0 is the limiting apparent molar volume of studied PILs and SV is the Debye-Hückel limiting slope SV = 1.868105 (m3mol1)3/2 [36] for aqueous solutions of 1:1 electrolyte at 298.15 K. BV and DV are the deviation parameters and were obtained along-with V0 by least square fit of function ( V  SV c ) with concentration c through equation (4) (see Fig. 1). The data for ( V0  V 2 ), BV and DV for studied PILs in aqueous solutions at 298.15 K are 0

given in Table 3.

6

ACCEPTED MANUSCRIPT Table 2

Density (), Apparent Molar Volume ( V ), Partial Molar Volume of PILs ( V2 ) and Partial Molar Volume of Water ( V1 ) for Aqueous Solutions of PILs at T = 298.15 K and 1·105 N·m−2 Atmospheric Pressure (P)a. m

ρ

106 V

/mol.kg−1

/kg.m−3

/m3.mol−1

106 V2

106 V1

m

/m3.mol−1 /m3.mol−1 /mol.kg−1

ρ

106 V

/kg.m−3

/m3.mol−1 TEAP

T P

106 V1

169.41 ± 0.62

169.41

18.068

169.34

18.068

997.26

169.33 ± 0.15

169.33

18.068

TEAF 0.0000

997.05

0.0087

997.14

137.09 ± 0.58

137.14

0.0174

997.23

137.14 ± 0.29

0.0342

997.41

0.0522

106 V2

I R

C S U

/m3.mol−1 /m3.mol−1

0.0000

997.05

18.068

0.0081

997.10

137.19

18.068

0.0173

137.07 ± 0.15

137.12

18.068

0.0339

997.59

137.13 ± 0.10

137.16

18.068

0.0505

N A

169.34 ± 0.29

997.37

169.34 ± 0.10

169.33

18.068

0.0695

997.77

137.11 ± 0.07

137.11

18.068

0.0686

997.48

169.30 ± 0.07

169.28

18.068

0.0871

997.95

137.09 ± 0.06

137.07

18.068

0.0858

997.59

169.30 ± 0.06

169.28

18.068

0.1074

998.16

137.07 ± 0.05

137.02

18.068

0.1060

997.72

169.25 ± 0.05

169.22

18.068

0.1224

998.32

137.04 ± 0.04

18.068

0.1239

997.84

169.19 ± 0.04

169.15

18.068

0.1435

998.54

137.01 ± 0.04

136.91

18.068

0.1376

997.93

169.18 ± 0.04

169.12

18.068

0.1605

998.71

137.01 ± 0.03

136.89

18.068

0.1586

998.07

169.11 ± 0.03

169.04

18.068

0.1817

998.92

137.01 ± 0.03

136.88

18.068

0.1815

998.23

169.05 ± 0.03

168.97

18.068

0.2251

999.37

136.95 ± 0.02

136.78

18.068

0.2152

998.45

169.00 ± 0.02

168.89

18.068

0.2687

999.81

136.94 ± 0.02

136.75

18.068

0.2642

998.78

168.89 ± 0.02

168.75

18.068

0.3182

1000.30

136.94 ± 0.02

136.73

18.068

0.3026

999.05

168.81 ± 0.02

168.64

18.068

PT

C A

E C 136.97

D E

M

7

997.16

ACCEPTED MANUSCRIPT 0.3566

1000.67

136.92 ± 0.01

136.72

18.068

0.3501

999.36

168.74 ± 0.02

168.55

18.068

0.4077

1001.18

136.90 ± 0.01

136.71

18.068

0.3911

999.65

168.66 ± 0.01

168.45

18.069

0.4660

1001.74

136.88 ± 0.01

136.73

18.068

0.4270

999.89

168.62 ± 0.01

168.39

18.069

0.5547

1002.55

136.92 ± 0.01

136.86

18.068

0.5288

1000.58

168.46 ± 0.01

168.21

0.6472

1003.39

136.93 ± 0.01

137.01

18.068

0.6324

1001.28

168.34 ± 0.01

168.08

18.070

0.7470

1004.27

136.93 ± 0.01

137.21

18.067

0.7293

1001.92

168.24 ± 0.01

T P

18.069

168.00

18.070

0.8540

1005.19

136.95 ± 0.01

137.49

18.065

0.8302

1002.57

168.16 ± 0.01

167.98

18.070

1.0010

1006.41

136.96 ± 0.01

137.94

18.061

1.0099

1003.68

168.06 ± 0.01

168.03

18.068

TEAB

I R

C S U

TEAG

N A 997.31

150.01 ± 0.52

150.00

18.068

0.0181

997.55

149.66 ± 0.28

149.64

18.068

18.068

0.0360

998.06

149.18 ± 0.14

149.13

18.068

18.068

0.0529

998.55

148.95 ± 0.10

148.88

18.068

186.73

18.068

0.0706

999.06

148.83 ± 0.07

148.73

18.068

186.84 ± 0.06

186.62

18.068

0.0874

999.54

148.71 ± 0.06

148.60

18.068

997.35

186.81 ± 0.05

186.52

18.068

0.1105

1000.19

148.63 ± 0.05

148.50

18.068

0.1193

997.41

186.75 ± 0.04

186.40

18.068

0.1346

1000.89

148.44 ± 0.04

148.31

18.068

0.1374

997.47

186.68 ± 0.04

186.28

18.068

0.1408

1001.07

148.42 ± 0.04

148.28

18.068

0.0000

997.05

0.0000

0.0083

997.07

187.11 ± 0.60

187.14

18.068

0.0168

997.10

186.96 ± 0.30

186.97

18.068

0.0334

997.14

186.93 ± 0.15

186.89

0.0501

997.19

186.92 ± 0.10

186.82

0.0674

997.24

186.90 ± 0.07

0.0837

997.29

0.1031

C C

A

D E

T P E

M

0.0097

8

997.05

ACCEPTED MANUSCRIPT 0.1594

997.54

186.63 ± 0.03

186.17

18.068

0.1591

1001.59

148.37 ± 0.03

148.24

18.068

0.1713

997.59

186.59 ± 0.03

186.09

18.068

0.1792

1002.16

148.32 ± 0.03

148.20

18.068

0.2193

997.76

186.44 ± 0.02

185.84

18.068

0.2226

1003.37

148.28 ± 0.02

148.21

18.068

0.2610

997.92

186.33 ± 0.02

185.66

18.068

0.2608

1004.42

148.24 ± 0.02

0.3088

998.10

186.24 ± 0.02

185.50

18.068

0.3120

1005.80

148.23 ± 0.02

0.3531

998.27

186.15 ± 0.02

185.39

18.068

0.3531

1006.91

148.20 ± 0.01

0.3907

998.42

186.07 ± 0.01

185.30

18.069

0.3929

1007.95

0.4409

998.62

185.99 ± 0.01

185.22

18.069

0.4404

0.5420

999.02

185.84 ± 0.01

185.17

18.069

0.5349

0.6361

999.37

185.75 ± 0.01

185.24

18.069

0.7456

999.77

185.68 ± 0.01

185.45

0.8309

1000.06

185.65 ± 0.01

185.67

1.0571

1000.68

185.73 ± 0.01

T P 148.23

18.068

148.28

18.068

148.31

18.068

148.24 ± 0.01

148.36

18.068

1009.19

148.21 ± 0.01

148.34

18.068

1011.61

148.22 ± 0.01

148.24

18.068

0.6301

1013.99

148.20 ± 0.01

148.00

18.069

18.068

0.7257

1016.29

148.24 ± 0.01

147.83

18.071

18.068

0.8238

1018.68

148.14 ± 0.01

147.71

18.073

186.62

18.061

1.0662

1024.10

148.23 ± 0.01

150.37

18.030

D E

T P E

C C

A

0.0000

997.05

0.0184

997.44

168.27 ± 0.27

168.28

18.068

0.0354

997.80

168.39 ± 0.14

168.40

18.068

0.0519

998.14

168.43 ± 0.10

168.44

18.068

9

SC

U N

A M

TEAPy

I R

ACCEPTED MANUSCRIPT 0.0695

998.51

168.45 ± 0.07

168.46

18.068

0.0875

998.88

168.47 ± 0.06

168.48

18.068

0.1109

999.36

168.48 ± 0.05

168.50

18.068

0.1302

999.75

168.49 ± 0.04

168.50

18.068

0.1446

1000.04

168.50 ± 0.04

168.51

18.068

0.1678

1000.50

168.51 ± 0.03

168.51

18.068

0.1751

1000.65

168.51 ± 0.03

168.51

18.068

0.2243

1001.62

168.51 ± 0.02

168.50

18.068

0.2716

1002.55

168.50 ± 0.02

168.49

18.068

0.3174

1003.43

168.49 ± 0.02

168.46

18.068

0.3642

1004.32

168.48 ± 0.01

168.43

18.068

0.4094

1005.18

168.46 ± 0.01

168.40

18.068

0.4596

1006.12

168.43 ± 0.01

168.35

18.068

0.5644

1008.04

168.36 ± 0.01

168.23

0.6602

1009.76

168.30 ± 0.01

0.7693

1011.67

168.23 ± 0.01

0.8784

1013.53

168.15 ± 0.01

E C

18.069

0.9332

1014.46

168.11 ± 0.01

C A

168.12

D E

T P

I R

C S U

N A

M

PT

18.069

167.99

18.070

167.86

18.072

167.78

18.072

Standard uncertainties u and u(T) = 0.02 K, u(m) = 1.10−4 mol.kg−1. The combined standard uncertainties in uc(ρ) = 5.10−3 kg.m−3.

10

ACCEPTED MANUSCRIPT Table 3 Data for Densities (IL), and Molar Volumes (Vm) of Pure PILs and Limiting Apparent Molar Volumes ( V0 ), Deviation Parameter (Bv and Dv), Excess Molar Volume (VE), Electrostricted Hydration Numbers (𝑛ℎ𝑒𝑙𝑒 ) for PILs in Aqueous Solution at T = 298.15 K and 1·105 N·m−2 Atmospheric Pressure.

IL PILs

/kg m−3

TEAF

1023.83

.

106. V 2  V0 0

106. 𝑉𝑚 /m

mol−1

3.

3.

/m mol

−1

109 .BV /m

mol−2

6.

1012 .DV /m

mol−3

9.

143.79

136.86 ± 0.02 -3.82 ± 0.16

2.33 ± 0.19

106. 𝑉𝑚𝐸 /m

mol−1

3.

𝑛ℎ𝑒𝑙𝑒

I R

-6.93

1.9

-9.52

2.6

C S U

(1028.0)a TEAP

980.75

178.71

169.19 ± 0.01 -5.45 ± 0.10

2.53 ± 0.12

TEAB

957.56

197.69

186.85 ± 0.02 -6.67 ± 0.11

3.91 ± 0.14

-10.84

2.9

TEAG

1153.33

153.68

149.00 ± 0.15 -7.61 ± 0.10

5.68 ± 1.13

-4.68

1.3

TEAPy

1085.80

174.30

168.09 ± 0.01 -2.06 ± 0.01

-

-6.21

1.7

D E

.aData from Ref. [33]

N A

M

T P E

C C

A

11

T P

ACCEPTED MANUSCRIPT 170 168 166 164 152 150

PT

148

RI

144

188

SC

186 184 182 170

NU

ϕv-SV*c1/2 /m3·mol−1

146

MA

168 166

D

164 138

136 135 0.0

0.2

0.4 0.6 0.8 10−3·c /mol·m−3

CE

134

PT E

137

1.0

AC

Fig. 1. The variation of the parameter ( V  SV * c ) as function of concentration (c) of PILs in aqueous solution at T = 298.15K. TEAF, □; TEAP, ●; TEAB, ■; TEAG, × ; TEAPy, Δ.

12

ACCEPTED MANUSCRIPT 18.08

170

a

b

18.07

168

18.06 18.05

166

18.08 150

18.06

148

18.06 18.04 18.02

NU

184

18.08

SC

) /m3·mol˗1

186

106· (

) /m3·mol˗1

188

RI

18.02

146

106· (

PT

18.04

172

18.08

MA

170

18.06

168

18.04 18.08

D

140

136 134 0.0

0.2

0.4

PT E

138

0.6

0.8

18.06 18.04 18.02 0.0

1.0

0.2

0.4

0.6

10˗3·c

/mol·m˗3

0.8

1.0

CE

10˗3·c /mol·m˗3

Fig. 2. The variation of the parameter a) V 2 and b) V 1 as a function of the concentration (c)

TEAPy, Δ.

AC

of PILs in aqueous solution at T = 298.15K. TEAF,□; TEAP,●; TEAB,■; TEAG,× ;

3.2 Acoustic Properties The speed of sound data of aqueous solutions of PILs in the concentration range 0.05 to 0.5 molkg−1 at T = 298.15 K are given in Table 4. The measured speed of sound (u) value for pure water is 1497.6 ± 0.5 ms−1 at T = 298.15 K and is in close agreement with literature value of 1497.69 ms−1[28,30,31,34]. The variation of the speed of sound parameter (u = usolution-usolvent) as a function of molality of studied PILs in aqueous solutions are shown in Fig. 3. The isentropic compressibility (s) of water and aqueous PIL solutions were obtained 13

ACCEPTED MANUSCRIPT using Laplace equation s = 1/(u2ρ) and are also included in Table 4. The estimated value of (s) for pure water is found to be in good agreement with literature (44.7780·10−11 m2·N−1) [37]. By using the method of propagation of errors and standard deviations obtained for the experimental parameters including concentration and density of pure solvent, the uncertainty in s(δs) is reported in Table 4. The variation of s with molality of the studied PILs at T = 298.15 K is shown in Fig. 4. The apparent molar isentropic compressibility ( KS ) of aqueous

s





0    s 0   s       m0   

(5)

RI

M  K   2 s  

PT

solutions of PILs were calculated using equation (5)

SC

where, 𝛽𝑠0 isentropic compressibility for pure water. The uncertainties in KS values were reported in the Table 4. The concentration dependence of apparent molar isentropic

NU

compressibility ( KS ) for aqueous solutions of studied PILs at T = 298.15 K are shown in Fig.

MA

5. Limiting apparent molar compressibility ( K0 ) for each PIL in aqueous solution were obtained by linear least square fitting of compressibility data using the following equation

D

k  K0  S K m

PT E

where SK is the experimental limiting slope. The resultant data of

(6)

K0 and SK for aqueous

solutions of PILs are given in Table 5.

CE

The hydration numbers (nh) for studied PILs in aqueous solution were estimated using

AC

Passynski method [38] through equation (7) applicable for aqueous electrolyte solutions

where

nh 

n1   s  1   n2   s0 

(7)

n1 is the number of moles of water, n2 is the number of moles of PILs, s is the

isentropic compressibility of solution and s0 is the isentropic compressibility of pure water. The concentration dependent hydration numbers for the studied PILs in aqueous solutions are given in Table 4 at T = 298.15 K (shown in Fig. 6).

14

ACCEPTED MANUSCRIPT Table 4 Speed of Sound (u), isentropic compressibility (βs), apparent molar isentropic compressibility ( KS ) and hydration number (nh) data for aqueous solution of triethylammonium based protic ionic liquids at t = 298.15 k and 1·105 nm−2 atmospheric pressure (p)a.

1015 KS

m /mol·kg−1

u /ms−1

1011βs /m2∙N−1

0.0000

1497.8

TEAF 44.707 ± 0.021

0.0503

1503.6

44.340 ± 0.021

-12.50 ± 5.9

9.07 ± 0.04

0.1040

1509.3

43.981 ± 0.021

-9.75 ± 2.9

8.67 ± 0.03

0.1496

1513.6

43.711 ± 0.020

-6.93 ± 2.0

8.27 ± 0.03

0.2047

1518.8

43.387 ± 0.020

-5.24 ± 1.4

0.2481

1522.2

43.175 ± 0.020

-2.82 ± 1.2

0.3075

1527.4

42.856 ± 0.020

-1.69 ± 1.0

0.3475

1530.6

42.660 ± 0.202

0.4095

1535.6

0.4463 0.5366

nh

m /molkg−1

/m5N−1mol−1

T P

1011βs /m2∙N−1

u /ms−1

I R

1015 KS

nh

/m5N−1mol−1

1497.6

TEAP 44.719 ± 0.021

1504.8

44.278 ± 0.021

-14.17 ± 6.0

11.04 ± 0.04

1512.6

43.806 ± 0.020

-10.07 ± 2.7

10.42 ± 0.03

0.1498

1517.6

43.506 ± 0.020

-7.62 ± 2.0

10.05 ± 0.02

8.01 ± 0.03

0.2089

1524.6

43.090 ± 0.020

-5.37 ± 1.4

9.68 ± 0.02

7.67 ± 0.02

0.2550

1530.0

42.773 ± 0.020

-4.27 ± 1.1

9.47 ± 0.02

7.47 ± 0.02

0.2986

1535.0

42.483 ± 0.020

-3.41 ± 1.0

9.30 ± 0.01

-0.68 ± 0.8

7.31 ± 0.01

0.3484

1540.2

42.182 ± 0.019

-1.86 ± 0.8

9.04 ± 0.01

42.357 ± 0.020

0.43 ± 0.7

7.13 ± 0.01

0.3945

1545.4

41.885 ± 0.019

-1.39 ± 0.7

8.92 ± 0.01

1537.8

42.221 ± 0.019

1.93 ± 0.6

6.92 ± 0.01

0.4447

1550.8

41.580 ± 0.019

-0.70 ± 0.6

8.76 ± 0.01

1544.4

41.826 ± 0.019

3.41 ± 0.5

6.67 ± 0.01

0.5104

1557.4

41.210 ± 0.019

0.47 ± 0.6

8.54 ± 0.01

D E

T P E

C C

A

C S U

0.0000 0.0496

N A 0.1088

M

TEAB

TEAG

15

ACCEPTED MANUSCRIPT 0.0000

1497.6

44.719 ± 0.021

0.0000

1497.6

44.719 ± 0.021

0.0498

1505.7

44.233 ± 0.021

-15.22 ± 6.0

12.115 ± 0.04

0.0509

1503.2

44.322 ± 0.021

-12.45 ± 5.9

9.70 ± 0.07

0.1068

1513.9

43.747 ± 0.020

-9.59 ± 2.8

11.297 ± 0.02

0.1026

1508.6

43.940 ± 0.021

-10.88 ± 2.9

9.43 ± 0.05

0.1524

1520.4

43.367 ± 0.020

-8.07 ± 1.9

11.015 ± 0.02

0.1508

1513.6

43.591 ± 0.020

-10.31 ± 2.0

9.29 ± 0.05

0.2025

1526.9

42.991 ± 0.020

-5.42 ± 1.4

10.593 ± 0.02

0.2043

1518.9

43.223 ± 0.020

-9.34 ± 1.5

9.09 ± 0.04

0.2503

1532.8

42.653 ± 0.020

-3.27 ± 1.2

10.243 ± 0.02

0.2496

1523.4

42.914 ± 0.020

-8.89 ± 1.2

8.98 ± 0.04

0.3030

1539.7

42.263 ± 0.019

-2.56 ± 1.0

10.060 ± 0.01

0.3044

1529.0

42.537 ± 0.020

-8.84 ± 1.0

8.90 ± 0.03

0.3489

1545.2

41.956 ± 0.019

-1.32 ± 0.8

9.831 ± 0.01

0.3524

1533.5

42.233 ± 0.019

-8.16 ± 0.8

8.76 ± 0.02

0.4019

1551.2

41.623 ± 0.019

0.18 ± 0.7

9.563 ± 0.01

0.4024

1538.3

41.915 ± 0.019

-7.77 ± 0.7

8.65 ± 0.02

0.4523

1556.8

41.316 ± 0.019

1.38 ± 0.6

9.339 ± 0.01

1542.8

41.621 ± 0.019

-7.58 ± 0.7

8.57 ± 0.02

0.5059

1562.8

40.991 ± 0.019

2.28 ± 0.6

D E

0.4486

9.149 ± 0.01

0.5234

1550.0

41.158 ± 0.019

-7.23 ± 0.6

8.45 ± 0.02

T P E

TEAPy

C C

0.0000

1497.4

44.731 ± 0.021

0.0510

1504.5

44.262 ± 0.021

0.1055

1511.4

0.1524 0.2046

-17.60 ± 5.8

11.40 ± 0.04

43.810 ± 0.020

-13.78 ± 2.8

10.84 ± 0.03

1516.8

43.457 ± 0.020

-10.63 ± 1.9

10.38 ± 0.03

1523.0

43.059 ± 0.020

-9.39 ± 1.4

10.14 ± 0.02

A

16

I R

SC

U N

A M

T P

ACCEPTED MANUSCRIPT

a

0.2503

1528.0

42.739 ± 0.020

-7.80 ± 1.2

9.88 ± 0.02

0.3031

1533.7

42.379 ± 0.020

-6.42 ± 1.0

9.63 ± 0.02

0.3539

1539.3

42.030 ± 0.019

-5.73 ± 0.8

9.47 ± 0.01

0.4037

1545.1

41.676 ± 0.019

-5.68 ± 0.7

9.39 ± 0.01

0.4470

1549.6

41.401 ± 0.019

-4.97 ± 0.6

9.24 ± 0.01

0.5152

1556.9

40.963 ± 0.019

-4.38 ± 0.6

9.08 ± 0.01

T P

I R

C S U

Standard uncertainties are u(T) = 0.05K, u(m) = 110−4 molkg−1, The combined standard uncertainties (uc) in uc(c) = 0.5 ms−1.

N A

D E

M

T P E

C C

A

17

ACCEPTED MANUSCRIPT Table 5 Limiting compressibility properties for aqueous solutions of PILs at t = 298.15 k and 1·105 n·m−2 atmospheric pressure (p). 1015  K0 S

S KS

/m5·N−1·mol−1

/m5N−1mol−3/2kg−1/2

TEAF

-21.27 ± 1.20

40.00 ± 5.30

9.44 ± 0.06

TEAP

-25.18 ± 0.70

55.65 ± 3.11

11.41 ± 0.08

TEAB

-26.80 ± 1.37

58.98 ± 6.08

12.51 ± 0.11

TEAG

-16.15 ± 0.51

18.83 ± 2.29

9.86 ± 0.03

TEAPy

-30.58 ± 0.99

66.49 ± 4.36

11.81 ± 0.08

nh0

(hydration number at infinite dilution).

NU

70

MA

60 50

D

40 30

PT E

u / ms1

PT

SC

a

nh a

RI

PILs

20

CE

10

0 0.0 0.1 0.2 0.3 0.4 0.5 0.6

AC

m /molkg1

Fig. 3. The variation of u as function of molality in water for PILs: TEAF, TEAB, ■; TEAG, × ; TEAPy, Δ.

18

□; TEAP, ●;

ACCEPTED MANUSCRIPT

45.0 44.5 43.5 43.0 42.5

PT

1011 βs /m2·N−1

44.0

42.0

RI

41.5 41.0

SC

40.5 0.0 0.1 0.2 0.3 0.4 0.5 0.6

NU

m /mol∙kg−1

Fig. 4. The variation of isentropic compressibility (s) as a function of molality of PILs (m) at

MA

CE

PT E

D

4 2 0 -2 -4 -6 -8 -10 -12 -14 -16 -18

AC

1015  k s /(m5N1  mol1)

T = 298.15 K. TEAF, □; TEAP, ●; TEAB, ■; TEAG, × ; TEAPy, Δ.

0.2 0.3 0.4 0.5 0.6 0.7 0.8 (m /molkg1)1/2

Fig. 5. The dependence of apparent molar isentropic compressibility ( KS ) as a function of square root molality of PILs at T = 298.15 K. TEAF, □; TEAP, ●; TEAB, ■; TEAG, × ; TEAPy, Δ. 19

ACCEPTED MANUSCRIPT 12.5 12.0 11.5 11.0 10.5

nh

10.0 9.5 9.0

PT

8.5 8.0

RI

7.5 7.0

0.0

0.1

0.2

0.4

0.5

0.6

/mol∙kg−1

NU

m

0.3

SC

6.5

Fig. 6. The variation of Hydration number (nh) as a function of molality (m) of PILs at T =

MA

298.15 K. TEAF, □; TEAP, ●; TEAB, ■; TEAG, × ; TEAPy, Δ.

PT E

4.1 Volumetric Properties

D

4. Discussions

From Table 2 and Fig. 1 it is observed that the apparent molar volume ( V ) decreases initially with concentration and becomes more or less constant at higher concentrations for

CE

the studied PILs in aqueous solutions at T = 298.15 K. The initial decrease is due to the ionic hydration at low concentrations and ion-ion association becoming apparent above 0.5

AC

mol.dm−3 except for aqueous TEAF wherein hydration effects are prominent even at higher studied concentrations. The limiting apparent molar volume ( V0 ) reflects information regarding the ion-solvent interactions [39] and found that V0 increases with increase in alkyl chain-length/hydrophobicity ions for a given homologous series [40,41]. Generally, negative sign and magnitude of deviation parameter BV implies that the solute co-sphere overlap effect and existence of hydrophobic interaction, i.e. the increase of ion-ion interaction along with water structure making effect i.e. kosmotropic effect [4,28,31,40]. Many reports show negative BV values for tetraalkylammonium salts [40-43]. Blanco et al. [40] in their study on the symmetric and asymmetric tetraalkylammonium salts, 20

ACCEPTED MANUSCRIPT showed that tetrabutylammonium bromide has more negative BV value than the tetramethylammonium bromide and were ascertained to more co-sphere overlapping of ionic hydration spheres in tetrabutylammonium ions. In case of tetraalkylammonium hydroxide salts, reported by Klofutar et al. [43] BV becomes more negative as the alkyl chain length increases due to increased hydrophobicity of quaternary ions. The large negative BV values for tetrabutylammonium bromide -11.85 m6.mol−2, tetrabutylammonium butanoate (TBABu)

PT

-18.4 m6.mol−2 and tetrabutylammonium octanoate (TBAOc) -25.0 m6.mol−2 are due to the strong hydrophobic structure making effect [41] Recently, molar volume and heat capacities study of sodium salts of carboxylic acids by Bochmann et al. [44] revealed that the deviation

RI

parameters like BV, and DV changes due to the carboxylate anions and not due to sodium

SC

cation and furthermore comparatively large negative BV value is observed for sodium butanoate -0.373 m6.mol−2 than other small alkyl-chain analogues. All these findings outline

NU

the fact that negative value of BV is an indication of hydrophobicity and its magnitude depends on the hydrophobicity of ions involved. Thus, if both the cations and anions forming a salt are hydrophobic in nature then BV becomes more negative. Recently, we also observed

MA

similar findings for aqueous solutions 1-alky-3-methylimidazolium based halide and amino acid ionic liquids. Seen in this light, all the studied PILs are hydrophobic in nature as all have

D

negative BV values (see Table 3). As the alkyl chain length on anion increases on going from formate to butanoate PILs, BV becomes more negative revealing that hydration effects are

PT E

more prominent in aqueous TEAF whereas hydrophobic ion pairing is apparent in aqueous TEAB solutions. This gets more clearly reflected in the concentration dependent partial molar

CE

volume of solute ( V 2 ) and solvent ( V 1 ) data as shown in Fig. 2 wherein minimum and maximum, respectively, is observed at high concentration end for more hydrophobic PILs such as TEAP and TEAB due to hydrophobic ion association. However, in low concentration

AC

region all PILs shows strong hydration effects similar to those observed for 1-alkyl-3methylimidazolium based amino acid ionic liquids [4,28]. To understand this, we estimated electrostriction and electrostricted hydration numbers (water molecules that bounds firmly to ions and are difficult to remove) using the method presented earlier [28]. The excess molar volume (𝑉𝑚𝐸 ) is nothing but the electrostricted volume of ionic liquid in aqueous solution and can be is calculated using data of molar volume of pure liquid and limiting partial molar volume of PILs in aqueous solutions with the help of equation (8) 𝑉𝑚𝐸 = 𝑉̅20 − 𝑉𝑚 (𝐼𝐿)

21

(8)

ACCEPTED MANUSCRIPT The molar volumes of studied PILs were obtained from density data of pure PILs at T = 298.15 K (see Table 3) and were used to get excess molar volume of PILs using equation (8). The negative values for electrostricted or excess molar volume of PILs at T = 298.15 K indicates that the less volume occupied by solute molecule in aqueous solution than the in its pure state. Data from Table 3 reveals that the negative magnitude of 𝑉𝑚𝐸 values for PILs in water at T = 298.15 K shows the following trend:

PT

TEAG < TEAPy < TEAF < TEAP < TEAB

RI

From this order, we observe that 𝑉𝑚𝐸 becomes more negative with increase of alkyl chain-length of anions on going from formate to butanoate. In case of glycolate and pyruvate

SC

anions, the 𝑉𝑚𝐸 of pyruvate anion is more negative due to keto group and is less hydrophilic as compared to glycolate having hydroxyl group. However, both these PILs are more

NU

hydrophilic as compared to its parent analogue TEAP and hence show less electrostriction effect compared to TEAP. Using electrostriction data for pure water (-3.68·106 m3.mol−1 at T

MA

= 298.15 K) [28], hydration number due to electrostriction effect for PILs can be estimated from following equation.

𝐸 𝑉𝑚

𝑒𝑙𝑒 (𝐻2 𝑂)

(9)

PT E

D

𝑛ℎ𝑒𝑙𝑒 = 𝑉

The estimated values of hydration numbers, included in Table 3, seem to be very small and increases with increases the alkyl chain length of carboxylate anions. It has been

CE

observed that the electrostricted hydration numbers are always small as compared to hydration number estimated from other methods such as compressibility, activity and NIR

AC

spectroscopy etc. [4,28,30,31,45] and are due to the reasons stated earlier. 4.2 Acoustic Properties The examination of Fig. 3 and 4 shows that speed of sound and isentropic compressibility increases and decreases respectively as function of concentration. The order observed for increase in speed of sound is TEAB > TEAP ≈ TEAPy > TEAG > TEAF and reverse trend observed in isentropic compressibility is TEAF > TEAG > TEAP ≈ TEAPy > TEAB. Such a behaviour has also been noted in case of aqueous solutions of amines and polyethylene-glycol in various solvents [46,47]. Patil et al. [31,46-48] reported that the increase in speed of sound and decreases in isentropic compressibility depends upon the 22

ACCEPTED MANUSCRIPT molecular weight of non-electrolytes in aqueous solutions as well as in aqueous solutions of ionic liquids. Recently, we reported that values of apparent molar isentropic compressibility of aprotic ionic liquids in aqueous solution are negative and increase with the concentration like simple alkali halides. It is also observed that, the KS values of amino acid ionic liquids is more negative when the side alkyl chain length increase on the amino acid anions and same trend is observed in imidazolium based halides ILs, due to the increase in hydrophobicity of

PT

imidazolium cation [28,30,31]. The limiting apparent molar isentropic compressibility  K0 S are negative for electrolyte solutions is due to the loss of compressibility due to

RI

electrostriction (see Fig. 5) [28,35,48]. Mathieson [49] and Desnoyers [50] studied that the,

SC

tetraalkylammonium salts have small and negative values of  K0 S due to the hydrophobic ion R4N+ and decrease in compressibility is observed with increase in ionic volume and alkyl chain length of cation. We observe herewith the similar results for studied PILs (see Table 5) analysis. The large negative  K0 S

NU

and can be explained in the similar way supporting the discussion based on volumetric values for studied PILs as compared to the

MA

tetraalkylammonium salts or simple inorganic ions indicate that the anions of studied PILs are more compressible due to large electrostriction resulted due to the strong cooperative Hbonding and hydrophobic hydration effects. Furthermore, we observe that TEAPy and TEAB

PT E

D

show more negative  K0 S values indicating the enhanced water structure making effect due to additional cooperative H-bonding through keto or hydroxyl group along-with carboxylate functionalities.

CE

The hydration numbers estimated from the Passynki’s equation for studied PILs is observed to be higher than the corresponding carboxylic acids [51,52] in aqueous medium

AC

which specifies that the electrostatic ionic hydration and hydrophobic hydration leads to cooperative hydrogen bonding of ionic liquids in aqueous solutions results in high hydration numbers (Table 4). The examination of Fig. 6 it is observed that the hydration number of PILs decreases as function of concentration and increases with the alkyl chain-length of anions, which indicates the ion-ion association at high concentration. High hydration number for the TEAB reveals that more water is organized around a nonpolar part of the anion and hydrophobic effect with kosmotropic behaviour. Overall the higher values of hydration numbers for studied PILs based on compressibility data supports the involvement of cooperative H-bonding between water and ion along-with electrostricted effects and hydrophobic hydration. This observation is in concordance with the recent hydration numbers 23

ACCEPTED MANUSCRIPT estimated from osmotic coefficient and compressibility data for AAILs [4,28] which have been explained in terms of cooperative H-bonding of amino acids anions with water structure making effect and hydrophobic hydration probed by concentration dependence of partial molar entropies and enthalpy-entropy compensation effects. 5. Conclusion

PT

The volumetric and acoustic properties of aqueous solution of triethylammonium based protic ionic liquids at T = 298.15 K shows water structure making effect i.e.

RI

kosmotropic effect similar to that of tetraalkylammonium salts. The increase in water structure making effect as function of alkyl chain length on anion specifies the importance of

SC

hydrophobic interaction. Large negative values for limiting compressibilities are due to the more electrostriction and hydrophobic hydration effect at infinite dilution whereas the

NU

extremum in the partial molar volume data at higher concentrations is due to ion-association or ion pairing. Higher values hydration numbers for PILs are due to cooperative nature of H-

MA

bonding between ions and water besides the electrostriction and hydrophobic hydration effects.

D

■ AUTHOR INFORMATION

PT E

Corresponding Author

*E-mail: [email protected]

CE

Notes

The author declares no competing financial interest.

AC

■ ACKNOWLEDGMENTS We greatly acknowledge the financial support (research project no. SR/FT/ CS-21/2011 with wide sanction number SERB/F/0694/2012-13) from Science and Engineering Research Board (SERB), New Delhi.

24

ACCEPTED MANUSCRIPT References [1]

K. Fukumoto, M. Yoshizawa, H. Ohno, Room Temperature Ionic Liquids from 20 natural Amino Acids, J. Am. Chem. Soc. 127 (2005) 2398-2399.

[2]

G.H. Tao, L. He, W.-S. Liu, L. Xu, W. Xiong, T. Wang, Y. Kou, Preparation, Characterization and Application of Amino Acid-Based Green Ionic Liquids, Green Chem. 8, (2006) 639–646. A. Mohajeri, A. Ashrafi, Structure and Electronic Properties of Amino Acid Ionic

PT

[3]

Liquids. J. Phys. Chem. A 115 (2011) 6589−6593.

D.H. Dagade, K.R. Madkar, S.P. Shinde, S.S. Barge, Thermodynamic Studies of Ionic

RI

[4]

Hydration and Interactions for Amino Acid Ionic Liquids in Aqueous Solutions at

[5]

SC

298.15 K, J. Phys. Chem. B 117 (2013) 1031−1043.

Y. Fukaya, Y. Iizuka, K. Sekikawa, H. Ohno, Bio Ionic Liquids: Room Temperature

[6]

NU

Ionic Liquids Composed Wholly of Biomaterials, Green Chem. 9 (2007) 1155–1157. D.-J. Tao, Z. Cheng, F.-F. Chen, Z.-M. Li, N. Hu, X.-S. Chen, Synthesis and

MA

Thermophysical Properties of Biocompatible Cholinium-Based Amino Acid Ionic Liquids, J. Chem. Eng. Data, 58 (2013) 1542−1548. [7]

M.J. Liszka, A. Kang, N.V.S.N.M. Konda, K. Tran, J.M. Gladden, S. Singh, J.D.

D

Keasling, C.D. Scown, T.S. Lee, B.A. Simmons, K.L. Sale, Switchable Ionic Liquids

PT E

based on Di-Carboxylic Acids for One-Pot Conversion of Biomass to an Advanced Biofuel, Green Chem. 18 (2016) 4012–4021. [8]

R. Parthasarathi, J. Sun, T. Dutta, N. Sun, S. Pattathil, N.V.S.N.M. Konda, A.G.

CE

Peralta, B.A. Simmons, S. Singh, Activation of Lignocellulosic Biomass for Higher Sugar Yields Using Aqueous Ionic Liquid at Low Severity Process Conditions,

[9]

AC

Biotechnol Biofuels 9 (2016) 160-173. J. Hulsbosch, D.E.D. Vos, K. Binnemans, R. Ameloot, Biobased Ionic Liquids: Solvents for a Green Processing Industry? ACS Sustainable Chem. Eng. 4 (2016) 2917−2931.

[10] R. Ratti, Ionic Liquids: Synthesis and Applications in Catalysis, Adv. Chem. (2014) 1– 16. [11] K. Ghandi, A Review of Ionic Liquids, their Limits and Applications, Green Sustainable Chem. 4 (2014) 44–53. [12] A. Jordan, N. Gathergood, Biodegradation of Ionic Liquids – A Critical Review, Chem. Soc. Rev. 44 (2015) 8200—8237. 25

ACCEPTED MANUSCRIPT [13] T.L. Greaves, C.J. Drummond, Protic Ionic Liquids: Evolving Structure−Property Relationships and Expanding Applications, Chem. Rev. 115 (2015) 11379−11448. [14] H. Markusson, J.-P. Beliѐres, P. Johansson, C.A. Angell, P. Jacobsson, Prediction of Macroscopic Properties of Protic Ionic Liquids by Ab Initio Calculations, J. Phys. Chem. A 111 (2007) 8717-8723. [15] M.S. Miran, H. Kinoshita, T. Yasuda, M.A.B.H. Susan, M. Watanab, Hydrogen Bonds

PT

in Protic Ionic Liquids and their Correlation with Physicochemical Properties Chem. Commun. 47 (2011) 12676–12678.

[16] K. Fumino, A. Wulf, R. Ludwig, Hydrogen Bonding in Protic Ionic Liquids:

RI

Reminiscent of Water, Angew. Chem. Int. Ed. 48 (2009) 3184 –3186.

SC

[17] D. Wakeham, A. Nelson, G.G. Warr, R. Atkin, Probing the Protic Ionic Liquid Surface Using X-Ray Reflectivity, Phys. Chem. Chem. Phys. 13 (2011) 20828–20835.

NU

[18] T. Zentel, O. Kühn, Hydrogen Bonding in the Protic Ionic Liquid Triethylammonium Nitrate Explored by Density Functional Tight Binding Simulations, J. Chem. Phys. 145 (2016) 234504-234512.

Bonding

in

Promoting

MA

[19] A.H. Beesley, D.F. Evans, R.G. Laughlin, Evidence for the Essential Role of Hydrogen Amphiphilic

Self-Assembly:

Measurements

in

3-

D

Methylsydnone, J. Phys. Chem. 92 (1988) 791-793. [20] S.H. Mood, A.H. Golfeshan, M. Tabatabaei, G.S. Jouzani, G.H. Najafi, M. Gholami,

PT E

M. Ardjmand, Lignocellulosic Biomass to Bioethanol, a Comprehensive Review with a Focus on Pretreatment, Renewable Sustainable Energy Rev. 27 (2013) 77−93. [21] D.F. Kennedy, C.J. Drummond, T.S. Peat, J. Newman, Evaluating Protic Ionic Liquids

CE

as Protein Crystallization Additives, Cryst. Growth Des. 11 (2011) 1777−1785. [22] A. Brandt, J. Gräsvik, J.P. Hallett, T. Welton, Deconstruction of Lignocellulosic

AC

Biomass with Ionic Liquids, Green Chem. 15 (2013) 550–583. [23] V. Singh, P.K. Chhotaray, R.L. Gardas, Solvation behaviour and partial molar properties of monosaccharides in aqueous protic ionic liquid solutions, J. Chem. Thermodyn. 71 (2014) 37–49. [24] M.P. Collins, L. Zhou, S.E. Camp, N.D. Danielson, Isopropylammonium Formate as a Mobile Phase Modifier for Liquid Chromatography, J. Chromatogr. Sci. 50 (2012) 869−876. [25] L. Demarconnay, E.G. Calvo, L. Timperman, M. Anouti, D. Lemordant, E. RaymundoPinero, A. Arenillas, J.A. Menendez, F. Beguin, Optimizing the Performance of

26

ACCEPTED MANUSCRIPT Supercapacitors Based on Carbon Electrodes and Protic Ionic Liquids as Electrolytes, Electro-chim. Acta 108 (2013) 361−368. [26] T. Yasuda, M. Watanabe, Protic Ionic Liquids: Fuel Cell Applications, MRS Bull. 38 (2013) 560−566. [27] S. Menne, T. Vogl, A. Balducci, Lithium Coordination in Protic Ionic Liquids, Phys. Chem. Chem. Phys. 16 (2014) 5485−5489.

PT

[28] D.H. Dagade, S.P. Shinde, K.R. Madkar, S.S. Barge, Density and Sound Speed Study of Hydration of 1-Butyl-3-methylimidazolium based Amino Acid Ionic Liquids in Aqueous Solutions, J. Chem. Thermodyn. 79 (2014) 192–204.

RI

[29] S.P. Shinde, D,H, Dagade, Osmotic and Activity Coefficients for Binary Aqueous

SC

Solutions of 1-Butyl-3-methylimidazolium Based Amino Acid Ionic Liquids at 298.15 K and at 0.1 MPa, J. Chem. Eng. Data 60 (2015) 635-642.

NU

[30] R.L. Gardas, D.H. Dagade, J.A.P. Coutinho, K.J. Patil, Thermodynamic Studies of Ionic Interactions in Aqueous Solutions of Imidazolium-Based Ionic Liquids [Emim][Br] and [Bmim][Cl], J. Phys. Chem. B 112 (2008) 3380-3389. Dagade, J.A.P. Coutinho, K.J. Patil, Acoustic and Volumetric

MA

[31] R.L Gardas, D.H.

Properties of Aqueous Solutions of Imidazolium based Ionic Liquids at 298.15 K, J.

D

Chem. Thermodyn. 40 (2008) 695–701.

[32] T.L. Greaves, A. Weerawardena, C. Fong, I. Krodkiewska, C.J. Drummond, Protic

PT E

Ionic Liquids: Solvents with Tunable Phase Behavior and Physicochemical Properties, J. Phys. Chem. B 110 (2006) 22479-22487. [33] T.L. Greaves, A. Weerawardena, C. Fong, I. Krodkiewska, C.J. Drummond, Protic

CE

Ionic Liquids: Physicochemical Properties and Behavior as Amphiphile Self-Assembly Solvents, J. Phys. Chem. B 112 (2008) 896-905.

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[34] M. Greenspan, C.E. Tschiegg, Speed of Sound in Water by Direct Method, J. Res. Natl. Bur. Std. 59 (1957) 249–258 [35] H.S. Harned, B.B. Owen, The Physical Chemistry of Electrolyte Solutions, 3rd Ed, American Chemical Society Monograph Series: Reinhold Publishing Corp, New York., (1958). [36] F.J. Millero, The Molal Volumes of Electrolytes, Chem. Rev. 71 (1971) 147-176. [37] F.J. Millero, T. Kublnski, Speed of Sound in Seawater as a Function of Temperature and Salinity at One Atmosphere, J. Acoust. Soc. Am. 57 (1975) 312–319. [38] Passynski, A. Compressibility and Solvation of Solution of Electrolyte. Acta Phys.Chim.USSR 1938, 8, 385–418. 27

ACCEPTED MANUSCRIPT [39] Frank, F. in: F. Franks (Ed.), Water – A Comprehensive Treaties, Vol. IV, plenum Publication, New York, 1973. [40] L.H. Blanco, E.F. Vargas, Apparent Molar Volumes of Symmetric and Asymmetric Tetraalkylammonium Salts in Dilute Aqueous Solutions, J. Solution Chem. 35 (2006) 21-28. [41] P.-A. Leduc, J.E. Desnoyers, Apparent Molal Heat Capacities and Volumes of

PT

Tetrabutylammonium Carboxylates and Related Solutes in Water at 25 ºC, Can. J. Chem. 51 (1973) 2993–2998.

[42] F.J. Millero, W. Drost-Hansen, Apparent Molal Volumes of Ammonium Chloride and

RI

Some Symmetrical Tetraalkylammonium Chlorides at Various Temperatures, J. Phys.

SC

Chem. 72 (1968) 1758-1763.

[43] C. Klofutar, D. Rudan-Tasič, V. Mančič-Klofutar, Partial Molar Volumes of

NU

Tetraalkylammonium Hydroxides in Aqueous Solution at 25°C, J. Solution Chem. 26 (1997) 1037-1047.

[44] S. Bochmann, P.M. May, G. Hefter, Molar Volumes and Heat Capacities of Aqueous

MA

Solutions of Short-Chain Aliphatic Sodium Carboxylates at 25 °C, J. Chem. Eng. Data, 56 (2011) 5081–5087.

D

[45] S.S. Barge, K.R. Patil, D.H. Dagade, NIR Spectral Studies of Hydration Behavior of 1n-Alkyl-3-Metylimidazolium based Bromide and Amino Acid Ionic Liquids at 298.15

PT E

K, (communicated)

[46] M.V. Kaulgud, K.J. Patil, Volumetric and Isentropic Compressibility Behavior of Aqueous Amine Solutions. I, J. Phys. Chem. 78 (1974) 714-717.

CE

[47] S.K. Kushare, S.S. Terdale, D.H. Dagade, K.J. Patil, Compressibility and volumetric studies of polyethylene-glycols in aqueous, methanolic, and benzene solutions at T=

AC

298.15 K, J. Chem. Thermodyn. 39 (2007) 1125–1131. [48] R.R. Kolhapurkar, D.H. Dagade, R.B. Pawar, K.J. Patil, Compressibility studies of aqueous and CCl4 solutions of 18-crown-6 at T= 298.15 K, J. Chem. Thermodyn. 38 (2006) 105–112. [49] J.G. Mathieson, B.E. Conway, partial Molar Compressibilities of salts in Aqueous Solution and Assignments of Ionic Contributions, J. Sol. Chem. 3 (1974) 455-477. [50] J.E. Desnoyers, P R. Philip, Isothermal Compressibilities of Aqueous Solutions of Tetraalkylammonium Bromides, Can. J. Chem. 50 (1972) 1094-1096. [51] A. Burakowski, J. Gliǹski, Hydration Numbers of Nonelectrolytes from Acoustic Methods, Chem. Rev. 112 (2012) 2059–2081. 28

ACCEPTED MANUSCRIPT [52] A. Burakowski, J. Gliǹski, Hydration of ions containing aliphatic chains, Chem. Phy. Lett. 468 (2009) 184–187.

Graphical Abstract 12

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42

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0.6

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0.4

m /mol∙kg−1

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m /mol∙kg−1

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6

41 0.0

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nh

43

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1011 βs / ((N∙m−2)−1)

45

0.5

0.6

ACCEPTED MANUSCRIPT Highlights 1. Density and sound speed measurements for aqueous triethylammonium based ionic liquids at T = 298.15 K are reported. 2. Apparent molar volumes and isentropic compressibility data are given.

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3. Electrostricted volume and electrostriction effect is investigated and discussed. 4. Compressibility based hydration numbers have been estimated and reported.

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5. Hydrophobic hydration and interactions are discussed in terms of water structural

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D

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changes and cooperative H-bonding

30