Triethylene glycol based deep eutectic solvents and their physical properties

ARTICLE IN PRESSJID: JTICE [m5G;March 14, 2015;12:16]

Journal of the Taiwan Institute of Chemical Engineers 000 (2015) 1–7

Contents lists available at ScienceDirect

Journal of the Taiwan Institute of Chemical Engineers

journal homepage: www.elsevier.com/locate/jtice

Triethylene glycol based deep eutectic solvents and their

physical properties

Maan Hayyan a,b,∗, Tayeb Aissaoui c, Mohd Ali Hashim a,d, Mohammed AbdulHakim AlSaadi a,e,Adeeb Hayyan a,d

a University of Malaya Centre for Ionic Liquids (UMCiL), University of Malaya, Kuala Lumpur 50603, Malaysiab Department of Civil Engineering, University of Malaya, Kuala Lumpur 50603, Malaysiac International Islamic University Malaysia, Kuala Lumpur 50728, Malaysiad Department of Chemical Engineering, University of Malaya, Kuala Lumpur 50603, Malaysiae Nanotechnology and Catalysis Research Centre (NANOCAT), University of Malaya, Kuala Lumpur 50603, Malaysia

a r t i c l e i n f o

Article history:

Received 11 February 2014

Revised 20 August 2014

Accepted 24 August 2014

Available online xxx

Keywords:

Deep eutectic solvent

Ionic liquid

Triethylene glycol

Choline chloride

Phosphonium salt

Hydrogen bond donor

a b s t r a c t

Deep eutectic solvents (DESs) have been recently emerged as new ionic liquids (ILs) analogues. The low

vapor pressure, inflammability, biodegradability and positive effect on the environment make DESs more

favorable as neoteric solvents. In this study, triethylene glycol (TEG) was selected as a hydrogen bond donor

(HBD) to form DESs with five types of phosphonium and ammonium salts, namely methyltriphenylphospho-

nium bromide (MTPB), benzyltriphenylphosphonium chloride (BTPC), allyltriphenylphosphonium bromide

(ATPB), choline chloride (2-hydroxyethyl-trimethylammonium) (ChCl) and N,N-diethylenethanolammonium

chloride (DAC). The physical properties of the synthesized DESs were measured such as freezing point, vis-

cosity, electrical conductivity, Walden rule, density, pH and water content. In addition, the Fourier transform

infrared spectroscopy (FTIR) was employed to study the functional groups. The experiments were conducted

at different temperatures, i.e. 25–80 °C. It was found that DESs have suitable properties to be used in industrial

processes such as separation, extraction, biochemical, petroleum and gas technology.

© 2015 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

1

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. Introduction

In the area of green chemistry, the development of reaction effi-

iency, avoidance of toxic reagents, reduction of waste, and the re-

ponsible utilization of resources have a considerable interest in the

aboratory of green media [1].

DESs are widely known as green alternative solvents to the con-

entional ILs [2,3]. DES is a combination of two or more compounds

hich has a melting point lower than that of its individual compo-

ents. They comprise mixtures of organic halide salts, such as ChCl

ith an organic compound which is a HBD. The HBD can form a hy-

rogen bonding with the halide ion, such as amides, amines, alcohols,

arboxylic acids and many more [4]. They are liquids at temperatures

f 100 °C or below and exhibit similar solvent properties to ILs.

DESs are simple to synthesize compared to the conventional ILs.

he components salt and HBD/complexing agent can be easily mixed

nd converted to a total homogenous mixture without any need for

urther purification. Besides, DESs have low synthesis cost due to the

∗ Corresponding author. Tel./fax.: +60 3 7967 5311.

E-mail addresses: [email protected]

(M. Hayyan), [email protected] (A. Hayyan).

s

ttp://dx.doi.org/10.1016/j.jtice.2015.03.001

876-1070/© 2015 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All righ

Please cite this article as: M. Hayyan et al., Triethylene glycol based deep e

Institute of Chemical Engineers (2015), http://dx.doi.org/10.1016/j.jtice.2

ow cost of raw materials. DES is expected to have good biocompat-

bility when using quaternary ammonium salts such as ChCl that is

eing used as an additive in chicken food [1,5,6].

DESs share many characteristics with conventional ILs, e.g. non-

eactive with water and non-volatile [7]. However, DESs cannot be

onsidered as ILs because of the non-ionic chemical structure of

ome of its species, as it can also be formed from non-ionic species

8]. Abbott and co-workers defined DESs using the general formula

1R2R3R4N+X−Y− [9].

Type I DES Y = MClx, M = Zn, Sn, Fe, Al, Ga

Type II DES Y = MClx•yH2O, M = Cr, Co, Cu, Ni, Fe

Type III DES Y = R5Z with Z = −CONH2, −COOH, −OH

Noting that the same group also defined a fourth type of DES which

s composed of metal chlorides (e.g. ZnCl2) mixed with different HBDs

uch as urea, ethylene glycol, acetamide or hexanediol (type IV DES)

8,9].

The conventional solvent TEG causes some industrial problems

uch as [10]:

1. TEG solutions may be contaminated by dirt, scale, and iron oxide.

2. Overheating of TEG solution may lead to decomposed products

and cause some loss of efficiency.

ts reserved.

utectic solvents and their physical properties, Journal of the Taiwan

015.03.001

http://dx.doi.org/10.1016/j.jtice.2015.03.001

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2 M. Hayyan et al. / Journal of the Taiwan Institute of Chemical Engineers 000 (2015) 1–7


Table 1

Composition and abbreviation of DESs analyzed in this research.

Salts Abbreviation HBD Molar

ratio

Symbol Phase

Methyltriphenylphosphonium

bromide

MTPB TEG 1:4 DES4 Liquid

Benzyltriphenylphosphonium

chloride

BTPC TEG 1:8 DES18 Liquid

Allyltriphenylphosphonium

bromide

ATPB TEG 1:10 DES30 Liquid

Choline chloride ChCl TEG 1:3 DES35 Liquid

N,N-Diethylenethanolammonium

chloride

DAC TEG 1:4 DES46 Liquid

Scheme 1. TEG and salts molecular structures.

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3. TEG can be lost due to foaming, degradation, inadequate mist

extraction and many other reasons.

The aforementioned industrial problems encouraged researchers

to develop and improve new or alternative solvents to replace TEG.

As compared to traditional organic solvents, DESs are not considered

as volatile organic solvents and not flammable, making their storage

is convenient. From the viewpoint of green chemistry, these DESs

are even more attractive since some of them have been proven to be

biodegradable and compatible with enzymes. Additionally, synthesis

of DESs is economically more viable compared to ILs, easy to handle

and no purification is required; and thus, their large-scale up use is

feasible [8].

Recently, researchers devote their efforts to implement DESs in

the industrial applications. Rimsza and Corrales (2010) used ChCl-

based DESs as agents for surface contaminant cleaning to selec-

tively remove CuO from a silicon dioxide surface [11]. ChCl-based

DES was also used as functional additives for starch based plastics

[12]. Also, DESs were employed as catalysts for biodiesel production

from industrial low-grade crude palm oil [13,14]. DESs play mul-

tiple roles in the synthesis of polymers and related materials [7].

DESs are viable co-solvents for enzyme-catalyzed epoxide hydroly-

sis [15]. Gore et al. (2011) reported the multicomponent synthesis

of valuable biologically active dihydropyrimidinone (DHPM) in acidic

DESs [16]. DESs have been employed as electrolytes for electrode-

position of metals, for electropolishing and for dye sensitized solar

cells [8].

Owing to their promising applications, many efforts have been

devoted to the physicochemical characterization of DESs such as

freezing point, viscosity, conductivity, and pH [8]. Recently, Hayyan

et al. have reported the physical properties of fructose and glucose-

based DESs synthesized from mixing of ChCl with the monosaccharide

sugar d-glucose anhydrous [6,17]. Previous studies have measured

the physical properties of ChCl, DAC, MTPB and BTPC based DESs with

glycerol (GL) and ethylene glycol (EG) as HBD [18,19]. Densities and

refractive indices of DESs (choline chloride + ethylene glycol or glyc-

erol) and their aqueous mixtures were studied by Leron et al. [18]. It is

observed that the above researchers have arrived to the potentiality

of DESs to be used in the industry with higher performance comaring

to the conventional solvents.

In this study, TEG was used as a HBD to mix with different salts

forming new DESs. TEG was selected as one of the recommended gly-

cols that widely used in the industry. It is the most popularly glycol

used as it provides superior dew point depression. Furthermore, it is

easier to regenerate up to �99%, has a high decomposition temper-

ature with relatively high reliability, low performing cost, and low

vaporization losses [10]. It is also used as heat transfer fluids [20].

As DESs are new mixtures, different types of salts and HBDs were

used to form DESs. This work is a further effort to contribute in the

green engineering. In this study, new types of DESs have been syn-

thesized and introduced based on TEG as the HBD with five types of

phosphonium and ammonium salts. It was measured physical proper-

ties including freezing point, viscosity, electrical conductivity, Walden

rule, density, and water content as a function of temperature. In ad-

dition, the functional groups were identified using FTIR.

2. Experimental work

2.1. Chemicals

MTPB, BTPC, ATPB, ChCl and DAC with purity 98% were synthesized

and supplied by Merck, Germany TEG with purity 99% was supplied by

R&M Chemicals Ltd, UK. Table 1 shows the salts, HBD, abbreviations,

molar ratios, symbols and phases of the five selected DESs. Scheme 1

shows the molecular structure of the five salts and HBD. K



.2. Experimental method

Table 1S (Supporting Information) shows the 52 synthesized DESs.

ifferent phases appeared during and after preparing the DESs such

s solid, semi-solid, crystal and liquid. Only five synthesized DESs

ere selected.

All chemicals were dried prior to the preparation stage and kept in

glove box to control the moisture. Each of the five salts (MTPB, BTPC,

TPB, ChCl and DAC) was mixed with the HBD (TEG) in an incubator

haker (Brunswick Scientific Model INNOVA 40R). The mixture of the

alt and HBD was shaken at 350 rpm and 80 °C until the DES became

homogeneous mixture without any precipitation. The synthesized

amples were kept in a glove box to avoid humidity that may affect

he physical properties of the DESs.

Differential scanning calorimetry (DSC) (DES1 STARe System)

ETTLER TOLEDO was used to measure the freezing point for the five

elected DESs. Rotational viscometer (Anton Paar Rheolab QC) was

sed for measuring the viscosity. The variation in the temperature

as controlled by external water circulator (Techne-Tempette TE-

A) with a temperature range 25–80 °C. Tensiometer KRUSS (K100M)

as used to measure the density with a temperature range 25–75 °Controlled by the external water circulator. Conductivity was mea-

ured by Multi-Parameter Analyzer (DZS-708) with a temperature

ange 25–80 °C. Water content of the five DESs was measured by

arl Fisher (Coulometric KF Titrator C30) at room temperature. FT-IR


015.03.001


M. Hayyan et al. / Journal of the Taiwan Institute of Chemical Engineers 000 (2015) 1–7 3


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20 30 40 50 60 70 80 90

1/(m

Pa.

s)

0.0

5.0e-8

1.0e-7

1.5e-7

2.0e-7

2.5e-7

DES4

DES18

DES30

DES35

DES46

1/η

θ/°C

Fig. 1. Dynamic viscosity, η, of five DESs as a function of salt/HBD with temperature

range 25–80 °C.

20 30 40 50 60 70 80 90

K/m

S.c

m-1

0

2

4

6

8

10

γ

θ/°C

DES4DES18DES30DES35DES46

Fig. 2. Conductivities, γ , of DESs as a function of temperature in the range of 25–80 °C.

m

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d

pectrometer (Perkin-Elmer) was used to analyze the functional

roup of the DESs at room temperature.

The estimated uncertainty for the freezing point is ±0.19 °C, for the

iscosity ±1% of full scale range. The uncertainty for the conductivity

s ±0.5% F.S. +1 digit, for the density it is ±0.00001 g/cm. The water

ontent uncertainty is ±0.5%.

. Results and discussion

In this study, 52 DESs were synthesized in different molar ratios

1:1–1:10, salt:HBD). However, precipitates were observed in some

ESs after synthesis, Table 1S (Supporting Information). Therefore,

he selection of the desired molar ratio was the minimum molar ration

hat provided the most stable homogeneous mixture, as illustrated in

able 1.

.1. Freezing point

The liquid state of DES is resulted through freezing point depres-

ion. Hydrogen bonding and complex interaction between the halide

nion of the salt and HBD is more energetically favored relative to the

attice energies of the pure constituents [4]. Similar to the HBD, the

ature of the salt also affects the DES freezing point [8]. The freez-

ng point depressed in a considerable manner following the general

ehavior of DES combination. The range for the five DESs is −16.59

o −19.83 °C. The highest freezing point was for DES45 and the lower

reezing point was for DES35. The freezing points for DES18, DES30 and

ES35 are −19.49, −19.52 and −19.83 °C, respectively. Thus, DES18,

ES30 and DES35 have potential industrial applications. The freezing

oint of TEG is -7 °C and the salt MTPB is 234 °C. The freezing point

f resulted DES4 was deceased to −18.17 °C. The result of DES4 was

n agreement with previous studies reported DESs MTPB:TEG and

hCl:EG [19,21]. The freezing point for the salt BTPC is 239 °C af-

er forming DES18 the freezing point was −19.49 °C. Similar freezing

oints were found for DES30 and DES35. These results are in agree-

ent with a previous study reported DESs formed by DAC:TEG at

ratio of 1:3 and 1:4 [19]. The freezing point for the salt DAC is

36 °C whereas after preparing DES46 the freezing point decreased to

16.59 °C which is close to the value reported by Abbot et al. (2003) for

hCl:urea [22].

.2. Viscosity

The viscosity of DESs is an important property to be addressed.

ig. 1 shows that the temperature has a significant effect on viscosity.

he viscosity decreased with temperature increment. The viscosity of

ESs followed the order, DES4 > DES18 > DES35 > DES46 > DES30. Ow-

ng to their potential applications as green media, the development

f DESs with low viscosities is desirable [8]. The viscosity behavior in

unction with temperature is shown in Fig. 1. The viscosities of eu-

ectic mixtures are mainly affected by the chemical nature of the DES

omponents (i.e. salts and HBDs) [8].

The lowest viscosities for the studied DESs, DES30, DES46, DES35,

ES18 and DES4 are 49.9, 84.6, 110.4, 116.7 and 136.1 mPa s, respec-

ively at 80 °C. At room temperature DES46 has the lowest viscosity

10 mPa s comparing to other DESs. DES30 (using ATPB as a salt) is a

ovel DES giving the lowest viscosity 49.9 mPa s at 80 °C comparing

o the other synthesized DESs. The viscosity of DES30 at room tem-

erature was compared with D’Agostino et al. (2011) for ChCl:urea

t molar ratio of 1:2 and ChCl:malonic acid at molar ratio of 1:2 [23]

nd Chen et al. (2013) for imidazolium-based ILs [23,24]. It was found

hat the viscosity of the DES30 is lower. The high viscosity of DESs is

ften attributed to the presence of an extensive hydrogen bond net-

ork between components, which results in a lower mobility of free

pecies within the DES [8].



The viscosities of the studied DESs were fitted using the Arrhenius

odel as shown below:

= η0 e

[− Eη

RT

](1)

here:

T: temperature in K,

R: gas constant in J/mol K,

Eη: activation energy in Pa L/mol,

η0: pre-exponential constant in mPa s,

η: viscosity in mPa s.

.3. Conductivity

Owing to their high viscosities, most of DESs display poor ionic

onductivities (lower than 2 mS/cm at room temperature) [8]. In

his study, the five DESs have conductivities in the range 0.212–

.77 mS/cm increasing with temperature increase. The molecular

tructure of the salts and HBDs has an impact on the conductivity.

The tendency of the conductivity for DES18 and DES30 was in-

reasing with approximate values. Fig. 2 shows that the conductivity

ncreases from 0.212 to 2.46 mS/cm for DES18 and from 0.464 to

.08 mS/cm for DES30. On the other hand, DES35 has the highest con-

uctivity at room temperature and at 80 °C; Fig. 2 also shows the

ramatic increase from 1.41 to 8.77 mS/cm for DES35. Consequently,


015.03.001




log[(10-5.Pa.s)/μ]

-8 -6 -4 -2

mc.S/

Kgol2-

e lom

1-]

-8

-6

-4

-2

DES4

DES18

DES30

DES35

DES46

KCl(aq)C-phosphateC-HCl

Fig. 3. Walden plot for KCl(aq), salts and DESs at temperatures 25–80 °C.

20 30 40 50 60 70 80

p/g.

cm-3

1.06

1.08

1.10

1.12

1.14

1.16

1.18

1.20

1.22

1.24

DES4

DES18

DES30

DES35

DES46

θ/°C

Fig. 4. Densities ρ of DESs as a function of temperature of the range of 25–75 °C.

i

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C

a

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it can be employed in electrochemical applications. The conductivity

of DES46 as an ammonium based DESs was compared with Siongco

et al. (2013) for N,N-diethylethanolammonium chloride:Gl and N,N-

diethylethanolammonium chloride:EG at 1:2 molar ratio [25]. It was

found that DES46 has higher conductivity.

Arrhenius-like equation was used to predict the conductivity be-

havior of the five DESs.

γ = γ0 e

[− Eγ

RT

](2)

where:

T: temperature in K,

R: gas constant in J/mol K,

Eγ : is the activation energy in Pa L/mol,

γ 0: constant in mS/cm,

γ : conductivity in mS/cm.

3.4. Walden rule

The Walden plot has been used increasingly in the last years

to illustrate the conductivity–viscosity relationship of pure ILs [26].

Walden rule is often obeyed well empirically, especially by solutions

of large and only weakly coordinating ions in solvents with nonspe-

cific ion–solvent interactions [26]. The Walden rule relates the mo-

bility of ions to the fluidity of their surrounding medium according to

following equation [27]:

�η = k (3)

where � is the molar conductivity and η is the viscosity; k is a temper-

ature dependent constant. On a logarithmic plot of �, representing

the ion mobility, versus the fluidity φ (φ = η−1) one can compare the

tendency to form ions of non-aqueous electrolyte solutions, molten

salts and ILs [27].

The question of whether DESs are ILs or not has been raised re-

cently [8]. Therefore, investigating the Walden rule would help to

categorize the family of DESs. An ‘‘ideal’’ reference line, established

by using dilute aqueous KCl solutions, is representative for indepen-

dent ions without any interionic interactions [27]. The proximity of

the plotted values to the KCl reference line is an indicator of the interi-

onic interactions between solvent’s anions and cations [27]. Solvents

with high tendency to form ions are located close to the reference

line while solvents with low tendency to form ions are situated fur-

ther away [27]. Fig. 3 shows that all the studied DESs are not lo-

cated close to the KCl reference line. The far locations of the DESs T



ndicate the non-ionic structure of the DESs and support the argu-

ent that DESs could not be considered as ILs. This work was com-

ared with two salts of carvedilol carvedilol-hydrochloride (C-HCl)

nd carvedilol-dihydrogen phosphate (C-phosphate) [28]. It was no-

iced that these salts were located closer to the KCl(aq) reference line

omparing to the five studied DESs and this is due to their high ionic

obility [28].

.5. Density

Fig. 4 depicts the density of DESs. In general, the density decreases

ith temperature increase. The highest density was for DES4. In con-

rast, the lowest density was for DES46. The results for DES35 are less

han recent densities measured for ChCl-based DESs in different mo-

ar ratio [19]. As for DES4, the results were compared with Hayyan

t al. (2012) for ChCl:d-fructose at a molar ratio 2.5:1, the results

re in agreement [6]. The densities of the two novel DESs, DES18

nd DES30 were compared with Królikowska and Hofman (2012) for

hiocyanate-based ILs [29]. It was found that DES18 and DES30 have

igher densities at room temperature and this is because of the large

olecular size of the salts; BTPC and ATPB.

The behavior of the five DESs was linear and the results were fitted

y a linear relationship as follows:

/g/cm3 = a(θ/◦C)+ b (4)

here:

θ : temperature in °C,

b: constant depends on the type of the DES,

ρ: density in g/cm3.

.6. Water content

Water has a significant impact on the physical properties of DESs.

herefore, it is essentially important to measure the water content of

ESs. The water content range was between 6.958 and 10.340 mg/g.

he highest value was for DES4 10.340 mg/g and the lowest value

as for DES30 6.958 mg/g. DES30 can be considered as less hygro-

copic comparing to other DESs. The water content for DES18, DES35

nd DES46 were 8.128, 7.062 and 9.173 mg/g, respectively. The re-

ults of DES4 and DES35 were compared with a previous study for

hCl:Gl at molar ratio 1:1 and 1:3 [30]. DES35 was in agreement with

previous study [30]. In contrast, the result of DES4 (MTPB as salt)

as in disagreement for MTPB:EG at molar ratio 1:3, 1:4 and 1:5 [30].

his can be implied to the strength of the H-bonding interaction that


015.03.001




Fig. 5. FTIR spectra of DESs at room temperature in the region of (a) 2340–4000 cm−1 and (b) 408–1594 cm−1.

Fig. 6. FTIR spectra of the HBD and five salts at room temperature in the region of (a) 1840–4000 cm−1 and (b) 400–1650 cm−1.

a

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D

ppears to be in direct correlation with the water solubility in the

ESs [31].

.7. FTIR

As a novel green solvent, the combination mechanism and molecu-

ar structures of the DESs are still unknown. The observed FTIR spectra

emonstrate the formation of the proton transfer salts. As shown in

ig. 5(a), for the five DESs, the presence of O−H stretching bands be-

ween 3200 and 3500 cm−1 confirms the water contents of the five

ESs [32–35]. Fig. 5(a) also illustrates the existence of C−H stretching

ands of alkanes, CH3 and CH2 between 3000 and 2800 cm−1 [32–35].

ig. 5(a) shows very similar spectrum for the five DESs, this is due to

he water content in the five DESs in addition to the chemical struc-

ures of the HBD/salts. For the phosphonium based DESs including

ES4, DES18 and DES30, the P−H stretching bands may be overlapped

ith C−H vibrational bands in the region of 3000–2800 cm−1 when



he frequency is lower than 3000 cm−1 [32–35], resembling the case

f the N−H stretching frequencies for the ammonium based DESs [32–

5]. Comparing Fig. 5(a) with Fig. 6(a), it is noticed that the stretching

ibration in the region between 2000 and 3100 cm−1 disappeared

fter the formation of the phosphonium and ammonium DESs. For

he five DESs the region between 4000 and 2340 cm−1 contains only

wo peaks which prove the existence of water and the ammonium

nd phosphonium structures.

For ammonium based DESs; DES30 and DES46, the region of 3200–

400 cm−1 is also a characteristic of ammonium structures [32–

5]. It presents the N−H stretching at 2869 cm−1 [32–35]. Table 2

hows the wave numbers appeared in the five DESs and the func-

ional groups that formed after mixing. Fig. 5(b) shows similar spec-

rums for the phosphonium based DESs, DES4, DES18, DES30. In

ontrast, ammonium-based DESs have similar peaks in the same

egion 600–408 cm−1. The presence of the Cl and Br in the formed

ESs is also shown in Fig. 5(b) in the region of 600–408 cm−1 [33–35].


015.03.001




Table 2

The wavenumbers and functional groups of the DESs.

Wavenumber (cm−1) Assignment DESs Ref.

3360 O−H stretching, P−H stretching DES4, DES18, DES30, DES35, DES46 [32–35]

2869 C−H stretching, CH2 stretching, CH3 stretching DES4, DES18, DES30, DES35, DES46 [33–35]

1439 N═N stretching, aromatic P−C stretching, C═C stretching DES4, DES18, DES30, DES35, DES46 [33–35]

1350 Aromatic C−N stretching DES4, DES18, DES30, DES35, DES46 [33–35]

1245 Aromatic P−O stretching, C−O stretching DES4, DES18, DES30, DES35, DES46 [33–35]

1114 Aliphatic C−N stretching, −O stretching DES4, DES18, DES30, DES35, DES46 [33–35]

1060 Aliphatic C−N stretching, aromatic P−O stretching DES4, DES18, DES30, DES35, DES46 [33–35]

997 P−H wagging, P−OH stretching, aromatic P−O stretching DES4 [33–35]

933 P−H wagging, aromatic P−O stretching DES18, DES30, DES35, DES46 [33–35]

888 Aromatic P−O stretching DES4, DES18, DES30, DES35, DES46 [33–35]

830 NH2 wagging and twisting, nitrate N−O stretching DES4, DES18, DES30, DES35, DES46 [33–35]

790 NH2 wagging and twisting DES4, DES18 [33–35]

751 C−X stretching (X = Cl, Br) DES4, DES18, DES30 [33–35]

720 C−X stretching (X = Cl, Br), methylene rocking DES4, DES18, DES30 [33–35]

690 C−X stretching (X = Cl, Br), =C−H bending DES4, DES18, DES30 [33–35]

591 C−X stretching (X = Cl), P−Cl stretching DES18, DES35 [33–35]

561 C−X stretching (X = Cl), P−Cl stretching DES46 [33–35]

519 C−X stretching (X = Br), P−Br stretching DES30 [33–35]


501 C−X stretching (X = Br), P−Br stretching, DES4 [33–35]


[

[

[

[

[

[

[

[

[

[

[

[

[

[

To the best of our knowledge, the analysis of the functional groups

is not conducted often in previous studies for DESs. Therefore, it was

more illustrative to present the functional groups for the five prepared

DESs and to recommend for future studies of DESs.

4. Conclusion

In this study, the physical properties of five selected DESs were

investigated which are freezing point, viscosity, electrical conductiv-

ity, Walden rule, density, pH and water content. In addition, FTIR was

used to identify the functional groups of the DESs. It was deduced

that the mixing of either ammonium or phosphonium as salts with

TEG as the HBD had a considerable influence on the physical proper-

ties of the DESs. The temperature is also one of the main factors that

affect the physical properties such as viscosity, density and pH. The

physical properties of these DESs showed a potential applicability for

some industries which can replace the conventional solvents.

Acknowledgements

The authors would like to express their thanks to University of

Malaya HIR-MOHE (D000003-16001) and University of Malaya Centre

for Ionic Liquids (UMCiL) for their support to this research. We would

also like to thank Hanee Farzana Hizaddin for her assistance in using

Turbomole and COSMOthermX.

Supplementary Materials

Supplementary material associated with this article can be found,

in the online version, at doi:10.1016/j.jtice.2015.03.001.

References

[1] Hayyan M, Hashim MA, Hayyan A, Al-Saadi MA, AlNashef IM, Mirghani MES, et al.Are deep eutectic solvents benign or toxic? Chemosphere 2013;90:2193–5.

[2] Leron RB, Li M-H. Solubility of carbon dioxide in a choline chloride–ethylene glycolbased deep eutectic solvent. Thermochim Acta 2013;551:14–19.

[3] Kareem MA, Mjalli FS, Hashim MA, Hadj-Kali MKO, Bagh FSG, Alnashef IM. Phaseequilibria of toluene/heptane with tetrabutylphosphonium bromide based deep

eutectic solvents for the potential use in the separation of aromatics from naphtha.Fluid Phase Equilib 2012;333:47–54.

[4] Hayyan M, Mjalli FS, Hashim MA, AlNashef IM. A novel technique for separating

glycerine from palm oil-based biodiesel using ionic liquids. Fuel Process Technol2010;91:116–20.

[5] Jhong H-R, Wong DS-H, Wan C-C, Wang Y-Y, Wei T-C. A novel deep eutecticsolvent-based ionic liquid used as electrolyte for dye-sensitized solar cells. Elec-

trochem Commun 2009;11:209–11.



[6] Hayyan A, Mjalli FS, AlNashef IM, Al-Wahaibi T, Al-Wahaibi YM, Hashim MA. Fruitsugar-based deep eutectic solvents and their physical properties. Thermochim

Acta 2012;541:70–5.[7] Carriazo D, Serrano M, Gutie´rrez M, Ferrer M, del Monte F. Deep-eutectic solvents

playing multiple roles in the synthesis of polymers and related materials. Chem

Soc Rev 2012;41:4996–5014.[8] Zhang Q, De Oliveira Vigier K, Royer S, Jerome F. Deep eutectic solvents: syntheses,

properties and applications. Chem Soc Rev 2012;41:7108–46.[9] Abbott AP, Barron JC, Ryder KS, Wilson D. Eutectic-based ionic liquids with metal-

containing anions and cations. Chemistry 2007;22:6495–501.[10] Xiuli Wang X, Michael E. Advanced natural gas engineering. Houston , T X: Gulf

Publishing Company; 2009.

11] Rimsza JM, Corrales LR. Adsorption complexes of copper and copper oxidein the deep eutectic solvent 2:1 urea–choline chloride. J Mol Struct 2012;987:57–

61.12] Leroy E, Decaen P, Jacquet P, Coativy G, Pontoire B, Reguerre A-L, et al. Deep

eutectic solvents as functional additives for starch based plastics. Green Chem2012;14:3063–6.

13] Hayyan A, Hashim MA, Hayyan M, Mjalli FS, AlNAshef IM. A novel ammonium

based eutectic solvent for the treatment of free fatty acid and synthesis of biodieselfuel. Ind Crops Prod 2013;46:392–8.

14] Hayyan A, Hashim MA, Mjalli FS, Hayyan M, AlNashef IM. A novel phosphonium-based deep eutectic catalyst for biodiesel production from industrial low grade

crude palm oil. Chem Eng Sci 2013;92:81–8.15] Lindberg D, de la Fuente Revenga M, Widersten M. Deep eutectic solvents (DESs)

are viable cosolvents for enzyme-catalyzed epoxide hydrolysis. J Biotechnol

2010;147:169–71.16] Gore S, Baskaran S, Koenig B. Efficient synthesis of 3,4-dihydropyrimidin-2-ones

in low melting tartaric acid-urea mixtures. Green Chem 2011;13:1009–13.17] Hayyan A, Mjalli FS, AlNashef IM, Al-Wahaibi YM, Al-Wahaibi T, Hashim MA.

Glucose-based deep eutectic solvents: physical properties. J Mol Liq2013;178:137–41.

18] Leron RB, Soriano AN, Li M-H. Densities and refractive indices of the deep eutectic

solvents (choline chloride; ethylene glycol or glycerol) and their aqueous mixturesat the temperature ranging from 298.15 to 333.15 K. J Taiwan Inst Chem Eng

2012;43:551–7.19] Shahbaz K, Baroutian S, Mjalli FS, Hashim MA, AlNashef IM. Densities of ammo-

nium and phosphonium based deep eutectic solvents: prediction using artificialintelligence and group contribution techniques. Thermochim Acta 2012;527:59–

66.

[20] Nuntaphan A, Tiansuwan J, Kiatsiriroat T. Enhancement of heat transport in ther-mosyphon air preheater at high temperature with binary working fluid: a case

study of TEG–water. Appl Therm Eng 2002;22:251–66.21] Shahbaz K, Mjalli FS, Hashim MA, AlNashef IM. Using deep eutectic solvents based

on methyl triphenyl phosphunium bromide for the removal of glycerol from palm-oil-based biodiesel. Energy Fuels 2011;25:2671–8.

22] Abbott AP, Capper G, Davies DL, Rasheed RK, Tambyrajah V. Novel solvent prop-erties of choline chloride/urea mixtures. Chem Commun 2003;0:70–1.

23] D’Agostino C, Harris RC, Abbott AP, Gladden LF, Mantle MD. Molecular motion and

ion diffusion in choline chloride based deep eutectic solvents studied by 1H pulsedfield gradient NMR spectroscopy. Phys Chem Chem Phys 2011;13:21383–91.

24] Chen B-K, Liang M-J, Wu T-Y, Wang HP. A high correlate and simplified QSPR forviscosity of imidazolium-based ionic liquids. Fluid Phase Equilib 2013;350:37–42.

25] Siongco KR, Leron RB, Caparanga AR, Li M-H. Molar heat capacities and electricalconductivities of two ammonium-based deep eutectic solvents and their aqueous

solutions. Thermochim Acta 2013;566:50–6.


015.03.001


http://refhub.elsevier.com/S1876-1070(15)00092-9/bib0001









































































































































[

[

[

[

[

[

[

[

[

[

26] Schreiner C, Zugmann S, Hartl R, Gores HJ. Fractional Walden rule forionic liquids: examples from recent measurements and a critique of the

so-called ideal KCl line for the Walden plot†. J Chem Eng Data 2009;55:1784–8.

27] Pinkert A, Ang KL, Marsh KN, Pang S. Density, viscosity and electrical conductivityof protic alkanolammonium ionic liquids. Phys Chem Chem Phys 2011;13:5136–

43.28] Wojnarowska Z, Wang Y, Pionteck J, Grzybowska K, Sokolov AP, Paluch M. High

Pressure as a key factor to identify the conductivity mechanism in protic ionic

liquids. Phys Rev Lett 2013;111:225–703.29] Królikowska M, Hofman T. Densities, isobaric expansivities and isothermal

compressibilities of the thiocyanate-based ionic liquids. Thermochim Acta2012;530:1–6.



30] Shahbaz K, Mjalli FS, Hashim MA, AlNashef IM. Eutectic solvents for the removalof residual palm oil-based biodiesel catalyst. Sep Purif Technol 2011;81:216–22.

31] Jessica LA, Jennifer LA, Joan FB, Edward JM. Gas solubility in ionic liquids. In:Peter W, Tom W, editors. Ionic liquids in synthesis. Germany: Wiley-VCH Verlag

GmbH, Co. KGaA; 2008. p. 81–93.32] Luo J, Conrad O, Vankelecom IFJ. Physicochemical properties of phosphonium-

based and ammonium-based protic ionic liquids. J Mater Chem 2012;22:20574–9.33] Stuar BH. Infrared spectroscopy: fundamentals and applications. England: John

Wiley and Sons, Ltd; 2004.

34] Roeges NPG. A guide to the complete interpretation of infrared spectra of organicstructures. Chichester , England: John Wiley and Sons Ltd; 1994.

35] Smith B. Infrared spectral interpretation: a systematic approach. USA: CRC P ressLLC; 1999.


015.03.001










































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Triethylene glycol based deep eutectic solvents and their physical properties

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