Role of the hydrogen bond donor component for a proper development of novel hydrophobic deep eutectic solvents

Article abstract of DOI:10.1016/j.molliq.2019.02.107

The environmental impact of chemical applications can be reduced by using novel solvents with green properties. In this field, Deep Eutectic Solvents (DESs) are promising liquids thanks to their low toxicity, high eco-compatibility and high easiness and “greenness” of preparation. DESs are mixtures of a hydrogen bond donor molecule (HBD) and a hydrogen bond acceptor molecule (HBA) at the proper molar ratio. In this paper, we present the preparation of novel hydrophobic deep eutectic solvents and the studies of their properties: density, eutectic profiles, ranges of water separation, contamination of the separated phases, extraction capabilities of phenol model polluting molecules, capabilities of extraction at acidic and basic conditions. Interesting results emerged about the role of the components of the DESs because of the use of a properly-chosen set of liquids. Their capabilities were dependent on the nature of the HBD molecule, and in particular on its hydrophobicity. Even the DESs with highly water-soluble HBA showed to be easily separable from water and really efficacious as extracting agents when prepared with hydrophobic HBDs. The results of the extractions of pollutants in acid and basic conditions showed the capability of water separation and extraction efficiency of these mixtures even with water at pH = 2 and pH = 9; therefore, the phenols could interact with these liquids without involvement of any acid/base-type of interactions.

Full text of DOI:10.1016/j.molliq.2019.02.107

Accepted Manuscript
Role of the hydrogen bond donor component for a proper
development of novel hydrophobic deep eutectic solvents
Matteo Tiecco, Federico Cappellini, Francesco Nicoletti, Tiziana
Del Giacco, Raimondo Germani, Pietro Di Profio
PII:
S0167-7322(18)36342-6
DOI:
Reference:
https://doi.org/10.1016/j.molliq.2019.02.107
MOLLIQ 10508
To appear in:
Journal of Molecular Liquids
Received date:
Revised date:
Accepted date:
5 December 2018
20 February 2019
22 February 2019
Please cite this article as: M. Tiecco, F. Cappellini, F. Nicoletti, et al., Role of the hydrogen
bond donor component for a proper development of novel hydrophobic deep eutectic
solvents, Journal of Molecular Liquids, https://doi.org/10.1016/j.molliq.2019.02.107
This is a PDF file of an unedited manuscript that has been accepted for publication. As
a service to our customers we are providing this early version of the manuscript. The
manuscript will undergo copyediting, typesetting, and review of the resulting proof before
it is published in its final form. 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.

ACCEPTED MANUSCRIPT
ROLE OF THE HYDROGEN BOND DONOR COMPONENT FOR A
PROPER DEVELOPMENT OF NOVEL HYDROPHOBIC DEEP
EUTECTIC SOLVENTS
Matteo Tiecco a, Federico Cappellini b, Francesco Nicoletti b, Tiziana Del Giacco b, Raimondo
Germani *b, Pietro Di Profio a.
a
Department of Pharmacy, University of Chieti-Pescara “G. D’Annunzio”, via dei Vestini 31,
66100, Chieti, ITALY
b Department of Chemistry, Biology and Biotechnology, University of Perugia, via Elce di Sotto
8, 06123, Perugia, ITALY
* Corresponding Author: Prof. Raimondo Germani: raimondo.germani@unipg.it Department
of Chemistry, Biology and Biotechnology, University of Perugia, Via Elce di Sotto 8 - 06123
Perugia, ITALY. Tel. +39 075 585 5538; Fax +39 075 585 5560.

ACCEPTED MANUSCRIPT
ABSTRACT
The environmental impact of chemical applications can be reduced by using novel solvents
with green properties. In this field, Deep Eutectic Solvents (DESs) are promising liquids
thanks to their low toxicity, high eco-compatibility and high easiness and “greenness” of
preparation. DESs are mixtures of a hydrogen bond donor molecule (HBD) and a hydrogen
bond acceptor molecule (HBA) at the proper molar ratio. In this paper, we present the
preparation of novel hydrophobic deep eutectic solvents and the studies of their properties:
density, eutectic profiles, ranges of water separation, contamination of the separated phases,
extraction capabilities of phenol model polluting molecules, capabilities of extraction at acidic
and basic conditions. Interesting results emerged about the role of the components of the
DESs because of the use of a properly-chosen set of liquids. Their capabilities were dependent
on the nature of the HBD molecule, and in particular on its hydrophobicity. Even the DESs
with highly water-soluble HBA showed to be easily separable from water and really
efficacious as extracting agents when prepared with hydrophobic HBDs. The results of the
extractions of pollutants in acid and basic conditions showed the capability of water
separation and extraction efficiency of these mixtures even with water at pH = 2 and pH = 9;
therefore, the phenols could interact with these liquids without involvement of any acid/base-
type of interactions.
KEYWORDS
2

ACCEPTED MANUSCRIPT
Deep Eutectic Solvents; Hydrogen Bond Donor; Green Liquids; Liquid-Liquid Extractions;
Phenols; Hydrophobic.
1. INTRODUCTION
Novel organic liquids with potentially green advantages are representing an advance in the
green chemistry framework[1,2]. This is thanks to their favourable green properties, such as
low flammability, low or absent vapour pressure, high recycle and reuse capability. In this
field, the most commonly used and known liquids are represented by Ionic Liquids (ILs):
molten salts which are liquid at temperatures below 100°C due to bulky, asymmetric cations
and weakly coordinating anions that destabilize the crystal lattice[3,4]. Even if the
applications of ILs are spread with advantageous properties in many relevant topics (such as
organic synthesis, extraction media, biocatalysys, separation, etc.[5–8]), recent studies are
revealing their disadvantageous characteristics in terms of their toxicity[9]. ILs, in fact, are
active towards all levels of life and many ecosystems are vulnerable to their
contamination[10,11]. Moreover, the synthesis of ILs involves the use of organic solvents[12].
In recent years DESs have been rapidly emerging as a side-class of ILs with the same
advantageous characteristics but with better properties in terms of their “greenness”[13,14].
DESs could be divided into four classes depending on the molecules involved, but they can
simply be defined as mixtures of a hydrogen bond donor molecule (HBD) and a hydrogen
acceptor (HBA) molecule at the proper molar ratio[15,16]. The network of hydrogen bonds
occurring between the molecules leads to a strong decrease in the melting points of the
mixtures, often over 100°C, then to a formation of stable liquids at temperatures generally
lower than 70-80°C, or even at room temperature (RTDESs: Room Temperature Deep Eutectic
Solvents)[17]. The synthesis of DESs is performed by simply heating and mixing the two
components (usually solids) at temperatures between 70°C to 100°C for times spanning from
minutes to hours; a liquid is then obtained with a yield of 100% and with an atom economy of
100%. This represents the first “green” advantage of the DESs over ILs. The second advantage
is represented by their low or absent toxicity, as it has been emerging from recent papers[18–
20]. A peculiar and highly relevant class of DESs is represented by NADESs (Natural Deep
Eutectic Solvents): these are mixtures of molecules of natural source, therefore with high
bioavailability and biocompatibility[21,22]. Besides the green advantages, DESs share many
practical advantages with ILs: in synthetic chemistry, “out of the hood” procedures can be
performed thanks to the absent volatility of these mixtures; this is a strong economic
advantage in industrial applications[23,24]. Moreover, no anhydrification of the media is
required using DESs in commonly anhydrous-condition reactions: Pd-catalysed C-H bond
3

ACCEPTED MANUSCRIPT
activation[25], and Grignard and organo-lithium reactions[26] are recent relevant examples
of this topic.
A further advantage in the use of DESs is their “active” role: they can act as acid catalysts
preventing the use of harmful acids in many chemical reactions; besides the components of
the mixtures could be reactants of a chemical process[27,28]. Recently, gold nanoparticles
were obtained without the use of any reducing agents thanks to the action of the NADESs
(Oxalic acid/Betaine)[29]. Chiral DESs (made with chiral components) revealed to be
structured liquids that can permit to determine an enantiomeric excess in a probe chemical
reaction, with values that are the same observed in literature in the same process[30].
A relevant field in which DESs are finding fruitful applications, is their use as extraction and
separation agents; their high solubilization capabilities permit their use as extracting agents
of relevant substances from biological matrixes[31]. DESs have been currently widely studied
as extraction agents of phenols and phenolic compounds from different matrices; in fact these
molecules revealed a great affinity with them[32]. Therefore, preconcentration/separation
analytical steps can be successfully performed in these novel green and sustainable
mixtures[33,34]. In recent literature, novel hydrophobic Deep Eutectic Solvents have been
emerging as highly promising water-insoluble media, with applications as extracting and
removal agents from aqueous samples of transition metal ions, of polycyclic aromatic
hydrocarbons, of pesticides, of phytocannabinoids and so on.[35–38]
Although the most common used DESs in literature are mixtures of choline chloride with urea,
ethylene glycol and glycerol[39], the differences and the different properties and capabilities
that can be obtained by changing the HBD and/or the HBA components of the mixtures
promote a fine tuning of the DESs for specific applications[40]. This pushes forward for a
better comprehension of the DESs components role and their effect on the liquid properties.
In this work, we present the preparation of novel hydrophobic Deep Eutectic Solvents; the
characterization of their properties (eutectic profiles, density, water separation,
contamination of the separated phases); their extraction capabilities from aqueous media of
polluting nitro-substituted phenols and a dye, even at acid and basic pH. The HBD and the
HBA molecules were properly chosen in order to obtain structure/activity relationships,
revealing that the HBD has a prominent role for an effective separation and for the extraction
efficiency from water. Moreover, some of these mixtures are NADESs, just thanks to the
natural source of the components, increasing the “greenness” of these liquids. The
environmental favourable properties of these DESs and their cost-effective preparation
promote them as a promising tool for water liquid-liquid extraction processes.
4

ACCEPTED MANUSCRIPT
2. EXPERIMENTAL
2.1 Reagents and Materials
Glycolic acid (GLY), phenylacetic acid (PhAA), thymol (THY), trimethylglycine (TMG), 4-
nitrophenol (PNP), 2,4-dinitrophenol (DNP), Phenol Red (PhRed), 2-phenoxypropanoic acid,
methyl 4-hydroxybenzoate, 2-(3-methoxyphenyl)acetic acid, (1S)-(+)-camphorsulfonic acid,
3,4,5-trihydroxybenzoic acid and L-menthol were purchased from Sigma-Aldrich/Merck
(purities >99%). The solids were dried with P2O5 under vacuum overnight before use. N,N-
dimethyl-N,N-didodecylammonium chloride (DDDACl) was synthesised using a procedure
previously published[41]: N,N-dimethyldodecyl amine was synthesised from 1-dodecylamine,
formic acid and formaldehyde via Leuckart-Wallach reaction; DDDACl was obtained by
refluxing N,N-dimethyldodecyl amine with 1-dodecylchloride in acetonitrile. M.p. = 129-
1
131°C. H NMR (400 MHz, MeOD) δ 3.33-3.28 (m, 4H), 3.07 (s, 6H), 1.80–1.74 (m, 4H), 1.41–
1.31 (m, 36H), 0.93-0.89 (t, 6H).ꢀ13C NMR (101 MHz, CDCl3) δ 63.9, 51.7, 32.1, 29.8-26.4, 23.0-
22.9, 14.3. (Spectra reported in Supporting Information section, Figures SI-1 and SI-2).
2.2 DESs preparation
The HBA and the HBD solid components were weighed at proper molar ratios in a flask fitted
with a stopper. The solid mixtures were magnetically stirred and heated at temperatures
spanning from 40° to 100°C until homogeneous liquids were formed.
2.3 Eutectic profiles
In a 10 mL round-bottomed flask equipped with a thermometer, weighed amounts of HBD
and HBA solid components were introduced and gently heated and mixed until homogenous
liquids were formed. The freezing points of the DESs were determined by cooling the
mixtures in an ice bath (or an acetone/liquid nitrogen mixture for the mixtures with very low
melting temperatures) and determining the freezing temperature with the thermometer. The
eutectic profiles were determined by repeating the procedure at different HBA/HBD molar
ratios. All the experiments were repeated in triplicate and the errors were calculated as
standard deviations of the samples.
2.4 Density
5

ACCEPTED MANUSCRIPT
The density of the DESs were determined via weighing 1mL of liquid in a flask at 25.0°C using
an analytical balance: the flasks were held in a thermostated bath for 1 hour then the volume
was adjusted using a Pasteur pipette. The experiments were repeated in triplicate and the
errors were calculated as standard deviations of the samples.
2.5 Water content
The water content of all the DESs was evaluated via Karl-Fischer titration with Metrohm 684
KF Coulometer. The measures were performed when the values of the samples observed were
stable and reproducible (in times spanning from minutes to hours depending on the sample
analysed)[42].
2.6 Water separation
DESs were weighed in centrifuge tubes and specific amounts of bidistilled H2O were added to
the liquids. The mixtures were centrifuged (Beckman Coulter Allegra 64 R, 6500 RPM, 30 min,
25°C) whenever they remained opalescent after stirring and mixing at room temperature,
giving bi-phasic solutions. The samples were then centrifuged after each water addition.
2.7 Phases contamination
After separation of the phases, the water content of the DESs phases were measured via Karl-
Fisher titration. The experiments were repeated in triplicate. The aqueous phases were
1
analysed via H-NMR measurements (Bruker Avance 400, 400 MHz) using D2O for the
separation and an internal standard (Maleic acid, Sigma ≥99%) for the evaluation of the
amounts of DESs components in water: specific amounts of D2O phases were dissolved in
MeOD solutions of the standard (3.30x10-3 M). The spectra were acquired with only one scan
in order to avoid any error due to possible different relaxation times of the different nuclei.
Absolute integral values (TopSpin 3.5 software, Bruker) were used for the quantitative
analysis. The experiments were repeated in triplicate and the errors were calculated as
standard deviations of the samples.
2.8 Extraction efficiency
The DESs were mixed with water solutions of 4-nitrophenol (1x10-2 M), 2,4-dinitrophenol
(1x10-3 M), Phenol Red (1x10-3 M) at 35% w/w (25% w/w for Glycolic acid/ N,N-dimethyl-
N,N-didodecylammonium chloride DES). The solutions were stirred for 1 minute at room
temperature with a vortex, then centrifuged (Beckman Coulter Allegra 64 R, 6500 RPM, 30
6

ACCEPTED MANUSCRIPT
min, 25°C). 25 µL of aqueous phases were dissolved in 2 ml of water (in 2 ml of NaOH 0.01 M
for Phenol Red samples) and the UV-Vis spectra (Agilent 8453 UV-VIS spectrophotometer,
temperature controlled at 25°C with a Peltier system Agilent 890890A) were registered and
compared with the spectra of the starting aqueous solutions at the same dilution. The
extraction efficiency percentage (E%) was determined as a ratio of the absorbances using the
formula:
where A are the absorbances of analyte before (0) and after (i) the extractions.
The wavelengths considered were: 318 nm for 4-nitrophenol (Molar Extinction Coefficient:
9092.2 M-1cm-1); 359 nm for 2,4-dinitrophenol (11651 M-1cm-1); 559 nm for phenol red at
pH=12 (56325 M-1cm-1).
The acid and basic solutions experiments were carried out in the same manners but using
acidic (0.01 M HCl, pH ≈ 2) or basic (1x10-5 M NaOH, pH ≈ 9) solutions of 2,4-dinitrophenol
mixing them at 35% w/w with the DESs. 25 µL of aqueous phases were dissolved in 2 ml of
neutral water then analysed via UV-VIS with the same procedure described above.
All the experiments were repeated in triplicate and the errors were calculated as standard
deviations of the samples.
3. RESULTS AND DISCUSSION
3.1 DESs PREPARATION
A set of differently structured molecules (carboxylic acids, alcohols, phenols) were at first
analysed as HBD for their capacity of liquid formation when mixed with the HBA N,N-
dimethyl-N,N-didodecylammonium chloride. Phenylacetic acid, 2-phenoxypropanoic acid,
methyl
4-hydroxybenzoate,
2-(3-methoxyphenyl)acetic
acid,
thymol,
(1S)-(+)-
camphorsulfonic acid, 3,4,5-trihydroxybenzoic acid, glycolic acid and L-menthol gave
homogeneous liquids at the temperatures between 25°C and 50°C. The DESs investigated in
this work were prepared by combining three of these HBD compounds and two HBA
molecules: Thymol (THY), Phenylacetic acid (PhAA) and Glycolic acid (GLY) as HBD and
Trimethylglycine (TMG) and N,N-dimethyl-N,N-didodecylammonium chloride (DDDACl) as
HBA. The choice of these molecules was made to evaluate the effect of the hydrophobicity of
7

ACCEPTED MANUSCRIPT
the components of the DESs on the hydrophobicity of the resulting liquids and because the
resulting DESs are liquid at room temperature. These molecules have, in fact, different
solubility in water; THY, PhAA and DDDACl have low water solubility (5.7x10-3 M, 0.13 M and
0.0125 M maximum water solubility respectively at 25.0°C), while TMG and GLY can be
considered as highly soluble (5.22
M and 8.02 M maximum water solubility
respectively)[43,44]. Figure 1 shows the structures of these molecules; the ones scarcely
soluble in water are reported in red, and the hydrophilic ones are reported in blue.
Figure 1: HBD molecules HBA molecules used for hydrophobic DESs preparation: Thymol (THY), Phenylacetic acid (PhAA) and
Glycolic acid (GLY) as HBD and Trimethylglycine (TMG) and N,N-dimethyl-N,N-didodecylammonium chloride (DDDACl) as HBA. The
molecules with water solubility higher than 1 M are coloured in blue, the ones with water solubility lower than 1 M are coloured in
red.
The three HBD and the two HBA molecules were mixed to give six deep eutectic solvents.
PhAA/TMG and GLY/TMG DESs were previously synthesized in our laboratories[20], and
their hydrophobic properties were analysed in this study in order to obtain a homogeneous
set of liquids. The other mixtures (THY/DDDACl, PhAA/DDDACl, GLY/DDDACl and THY/TMG)
are novel DESs prepared and characterized in this work. In Table 1 the eutectic ratios, the
melting points and the densities of these DESs are reported, all the eutectic profiles are
reported in Supporting Information sections (Figure SI-3).
8

ACCEPTED MANUSCRIPT
Table 1: DESs used in this worka.
Eutectic ratio
DES freezing
point, °C
-20 ± 1
-7 ± 1
Density,
HBD
HBA
(HBD:HBA)
g/mL (25°C)
0.884 ± 0.022
0.941 ± 0.024
1.040 ± 0.024
0.959 ± 0.026
1.161 ± 0.030
1.274 ± 0.031
THY
PhAA
GLY
DDDACl
DDDACl
DDDACl
TMG
2:1
2:1
3:1
3:1
2:1
2:1
5 ± 1
THY
PhAA
GLY
-15 ± 1
-7 ± 1
TMG
TMG
-36 ± 2
a PhAA/TMG and GLY/TMG mixtures values were previously measured[20].
All these mixtures are liquid at temperatures lower than 0°C, except for GLY/DDDACl that
showed a freezing point slightly above this value (5°C). Three of these liquids (the ones with
TMG as HBA) are NADESs and this increases the “greenness” of these mixtures.
3.2 WATER SEPARATION
The capabilities of separation from water were evaluated for all the DESs. Specific amounts of
H2O were added to the liquids, and the mixtures were centrifuged whenever they remained
opalescent after stirring and mixing them at room temperature. The amounts of water in the
pure DESs were measured via Karl-Fisher titration and were added to the values of water
added in the mixtures. GLY/DDDACl DES did not show any water separation at any water
concentration. Therefore we prepared another DES with the same components but with a
different molar ratio: we used a 2:1 HBD:HBA molar ratio even if the eutectic point was at 3:1;
in this way the hydrophilic component amount in the DES was decreased. With this molar
ratio, the melting point was still below room temperature (21°C) so it was applied in the
experiments giving a water separation.
In Figure 2 the phase separations of the liquids are reported, as well as the molar ratios of the
DESs; all the measurements were performed at 25°C.
9

ACCEPTED MANUSCRIPT
DES
DES position
Water Content, %w/w
30 40 50 60 70
in DES/H2O
separation
HBD
HBA
10
20
80
90
THY
PhAA
GLY
DDDACl
DDDACl
upper phase
upper phase
a
DDDACl upper phase
THY
TMG
TMG
TMG
upper phase
lower phase
n.a.
PhAA
GLY
Mono-Phasic
Bi-Phasic
Precipitation/Gel
Figure 2: Relative position of the DESs phase in water separation: in orange those liquids with densities lower than water and in
pink the ones higher than water; phase separation table of the DESs from water (blue: monophasic; green: bi-phasic; yellow:
precipitation of solid materials or gel formation). T = 25°C. a = DES prepared at HBD:HBA ratio of 2, density = 0.959 g/mL.
All the DESs solubilized water at values lower than 10% w/w. This could be due a “structural”
role of the water that could participate to HBD-HBA interactions with the components[21,45–
47]. THY/DDDACl DES showed a very good separation from water at about 10-15% w/w of
water, and the two phases exist in all the % range until over 90% w/w. The same behaviour
was observed for the DES with the same HBD molecule but with TMG as HBA (THY/TMG
DES), which showed a separation at slightly lower % values (about 10-12% w/w).
PhAA/DDDACl DES showed a range of separation spanning between 18-23% w/w until 50-
53% w/w; after these values the mixture became “gel-like”, possibly due to the organization
of amphiphilic DDDACl with the aromatic portion of the acid[48]. PhAA/TMG DES showed
also a small range of separation from water after centrifugation, and it spans from 30-31%
w/w to 40-42% w/w; at higher amounts of water a precipitate is observed. These data were
really interesting as these PhAA-based DESs could be considered as both hydrophobic and
hydrophilic: they can be efficaciously separated from water in a certain range of
concentrations and they can be water-miscible at other concentrations (from 0% until 20-
30% w/w). This is relevant and promising for the use of these DESs in extraction applications
as they can be separated both from water and from organic apolar solvents. The
PhAA/DDDACl is formed by synthetic HBA molecule (DDDACl), therefore it has a lower
“greenness”; on the contrary, TMG is a natural source molecule as well as PhAA; therefore
10

ACCEPTED MANUSCRIPT
PhAA/TMG DES is a NADES (Natural Deep Eutectic Solvent). Glycolic acid based DESs showed
difficult separations from water: GLY/TMG DES is totally hydrophilic and it was not possible
to separate it from water in all the concentration range. GLY/DDDACl showed a small range of
separations from water, spanning from 20-22% w/w to 31-35% w/w and it must be
considered that this DES was separated from water only when the ratio between HBD and
HBA molecules was decreased in terms of the hydrophilic molecule. This behaviour showed to
impact also on the other properties of this DES as it will be shown in this work.
These data showed the role of the components of these DESs in their water separation: the
HBD molecule, and in particular its hydrophobicity/hydrophilicity, is the driving force that
leads to an efficacious separation from water. Also the DESs formed with highly water-soluble
HBA (such as TMG) revealed to be separable from water in case of hydrophobic HBD
counterpart. The glycolic acid (that is highly water soluble) gave, in fact, water-total soluble
DES (GLY/TMG) or a DES (GLY/DDDACl) that resulted separated once used in a HBD:HBA
ratio with lower amounts of hydrophilic HBD, and in a small range of concentration. The DESs
with PhAA as HBD revealed to be the best in our set in terms of their separation from water,
since the separation can be modulated with small changes of water amount; PhAA/TMG is
even more relevant because it is a NADESs.
The densities of these liquids are lower than the density of water except for PhAA/TMG that
has a density higher than water. GLY/DDDACl DES showed a change in its density by changing
the molar ratio of HBD to HBA, with a value of 0.959 g/mL with 2:1 HBD:HBA molar ratio,
while it was 1.040 g/mL in the case of 3:1 HBD:HBA.
3.3 PHASES CONTAMINATION
The efficacy of the separation of the two DES/water phases was evaluated with two
techniques. The water amount in the DES phase after the centrifugation was evaluated by
Karl-Fisher titration. The contamination/solubilization of HBD and HBA components in water
was evaluated after separation of D2O phases dissolving an amount of them in a MeOD
solution of an internal standard (maleic acid); the absolute integral values of the relative
1
peaks of H-NMR spectra were used for an estimation of the molecules in water. In these
experiments all the DESs/water samples were prepared at 35% w/w of water. This was made
for many reasons: at this value, all the DESs show an effective separation; it is the lower
values of DESs that can be used for a separation; all the measured data can be compared
between the different mixtures. GLY/DDDACl DES was used at 25% w/w of water because it
11

ACCEPTED MANUSCRIPT
has a small range of water separation and it cannot be separated from water at 35% w/w
(Figure 2).
In Table 2 the DESs analyzed, the amount of water percent in the DESs phase (the starting of
the pure DESs and after the separation) and the amount (M) of the HBD and HBA components
in the water phases after the centrifugation are reported; in the same Table the data of the
1
molar ratio of HBD:HBA in water phases are reported. In Figure 3 the H-NMR spectra of the
water phases of PhAA/TMG DES is reported (25 µL of D2O phases in CD3OD solution); all the
other 1H-NMR spectra are reported in Supporting Information (Figures SI-4-5-6-7).
Table 2: Phase contaminations of the DESs/water biphasic systems a.
DES
H2O in DESs phase, %
DES components in H2O, M
After
separation
HBD
HBA
Pure DES
HBD
HBA
HBD:HBA
THY
PhAA
GLY
DDDACl
DDDACl
DDDACl
TMG
2.2 ± 0.2
2.1 ± 0.1
3.2 ± 0.1
0.4 ± 0.1
1.6 ± 0.1
4.2 ± 0.8
7.2 ± 0.2
traces
(6.3 ± 0.3)x10-5
2.8 ± 0.5
traces
traces
n.a.
n.a.
21.4 ± 0.6
28.3 ± 0.8
4.4 ± 0.1
23.9 ± 0.4
n.a.
1.3 ± 0.3
1.8 ± 0.2
2.4 ± 0.4
n.a.
≈ 2:1
≈ 1:90
≈ 1:5.7
n.a.
THY
PhAA
GLY
0.020 ± 0.003
0.42 ± 0.06
n.a.
TMG
TMG
a
Water amount 35% w/w except for GLY/DDDACl DES (25% w/w of water); water percent in the DESs phase (pure DES, after the
separation) evaluated via Karl-Fisher titration; amount (M) of the HBD and HBA components and their ratio in the water phases
1
after the centrifugation measured via H-NMR spectroscopy. All the experiments were repeated in triplicate and the errors were
evaluated as standard deviations of the samples.
Figure 3: 1H-NMR spectra of the D2O phases separated from PhAA/TMG DES in CD3OD. Maleic acid as internal standard.
12

ACCEPTED MANUSCRIPT
Almost all the pure DESs have low initial water amounts, under 3.3% w/w; GLY/TMG DES
showed the highest value in the set (4.2% w/w), due to its hydrophilicity. After the separation
with water by centrifugation, the differently structured DESs absorbed different amounts of
water. Even in this case the properties showed a correlation with the hydrophobicity of the
HBD portion. THY-based liquids showed an amount of 7.2% and 4.4% w/w of water with the
HBA counterparts (DDDACl and TMG respectively). PhAA HBD ones showed higher values
(spanning from 21.4% to 23.9% w/w), while the GLY/DDDACl liquid showed the highest
value in the set (28.3% w/w); GLY/TMG did not show any water separation; therefore the
water amount value after separation could not be measured.
The contamination of the water phases with HBD and HBA molecules showed that the DES
with both hydrophobic portions (THY/DDDACl) released only traces of the DES molecules in
water (<1x10-7 M); in the water contamination, this DES showed the best properties in the set.
The same HBD with TMG as HBA showed amounts of HBD in water about 0.02 M and 1.8 M of
TMG. The increase of hydrophilicity of the DES led to higher amounts of HBD and HBA
molecules in water: PhAA/DDDACl mixture did not show the presence of the HBA in the water
phases and very low amounts (about 6x10-5 M) of the HBD; PhAA/TMG DES showed amounts
of HBD about 0.42 M and 2.4 M of the HBA. GLY/DDDACl DES showed the higher amounts of
HBD and HBA molecules in the water phase: 2.8 M of HBD and 1.3 M of HBA. These values are
interesting if we consider the solubilities in water of the single HBD and HBA components
(THY = 5.7x10-3 M; PhAA = 0.13 M; DDDACl = 0.0125 M; TMG = 5.22 M; GLY = 8.02 M).
PhAA/TMG DES released an amount of PhAA in water that is higher than its solubility in
water, with a HBD:HBA ratio of about 1:5.7; this could mean that the HBD/HBA components
could be present in the water phases also as DES-structured. Even in the case of THY/TMG
DES the amount of HBD in water was higher than its maximum solubility, with a HBD:HBA
ratio in water of about 1:90; this could be due to the same effect. The most peculiar case in the
set is represented by GLY/DDDACl DES that showed an amount of HBA in water phase higher
than its solubility and in a molar ratio that is the same of the DES itself, so suggesting the
solubilization of the molecules as DES-structured. These data, while suggesting the need of
further investigations with more specific techniques for a better elucidation, hint these HBD
and HBA molecules as being differently structured in the DES; moreover, these interactions
lead to DESs with properties (such as the water solubility) that are different from the starting
materials, as expected.
13

ACCEPTED MANUSCRIPT
3.4 EXTRACTION EFFICIENCY
The extraction efficiency from aqueous media of phenols and a dye were evaluated for all the
novel hydrophobic deep eutectic solvents. These model liquid-liquid extraction experiments
were carried out to determine the efficacy of extraction from water of pollutants of the
differently structured DESs, with a simple and fast liquid-liquid extraction procedure. Three
model-compounds were chosen as analytes: 4-nitrophenol (PNP), 2,4-dinitrophenol (DNP)
and Phenol Red (PhRed). The chosen phenols are reported in the list of priority pollutants of
water[49,50]; the -NO2 substituted ones were chosen in this set because their UV-Vis spectra
do not overlap the ones of the DESs components present in water after the separation. Phenol
Red is widely used as pH indicator and dye but it has a high impact on the environment
because it is found as pollutant in wastewaters, because of its difficult degradation[51]. Figure
4 shows their chemical structures.
Figure 4: Chemical structures of 4-nitrophenol, 2,4-dinitrophenol and Phenol Red used in this work.
The experiments were carried out with a simple and fast procedure: first the water solutions
of the pollutants were mixed for 1 minute with the hydrophobic DESs at room temperature;
then the samples were centrifuged for 30 minutes at 6500 RPM at 25°C giving separated
phases; finally, the water phases were analyzed via UV-Vis spectra analysis comparing their
spectra with the ones before extraction. The mixing time was determined via an experiment
(see Supporting Information) that showed that the extraction efficacy did not change
significantly by mixing the phases in times spanning from 1 minute to 3 hours. All the
experiments were carried out at 35% w/w of water solutions in the DESs: this value was
chosen as the minimum amount of DESs that could be separated from water for all the liquids,
14

ACCEPTED MANUSCRIPT
and to compare the results in the same conditions for all the mixtures. GLY/DDDACl DES was
used at 25% w/w of water solutions because at 35% it is not separable from water.
In Table 3 the results of the extractions of the two phenols and of the Phenol Red are reported
for all the DESs; in Figure 5 the same results are reported as histograms; all the UV-Vis spectra
are reported in Supporting Information (Figures SI-8-21).
Table 3: Extraction efficiency (%) of hydrophobic Deep Eutectic Solventsa.
DES
E%
HBD
HBA
PNP
DNP
PhRed
THY
PhAA
GLY
DDDACl
DDDACl
DDDACl
98.9 ± 0.5 %
98.9 ± 0.3 %
73.9 ± 3.2 %
97.3 ± 1.1 %
98.2 ± 1.5 %
75.6 ± 24.2 %
99.8 ± 0.2 %
99.9 ± 0.1 %
n.a.
THY
PhAA
GLY
TMG
TMG
TMG
98.1 ± 0.9 %
93.9 ± 3.1 %
n.a.
89.9 ± 1.1 %
96.7 ± 1.3 %
n.a.
98.1 ± 1.9 %
89.7 ± 1.2 %
n.a.
a
4-nitrophenol (PNP, starting solution 1x10-2 M), 2,4-dinitrophenol (DNP, starting solution 1x10-3 M) and Phenol Red (PhRed,
starting solution 1x10-2 M). Times of mixing = 1minute; centrifugation at 6500 RPM for 30 minutes at 25°C; 25 µL of aqueous phases
were dissolved in 2 ml of water (in 2 ml of NaOH 0.01 M for Phenol Red samples) and the UV-Vis spectra were compared with the
spectra of the starting solutions at the same dilution. All experiments were repeated in triplicate and the errors were evaluated as
standard deviations of the samples.
15

ACCEPTED MANUSCRIPT
100
90
80
70
60
50
40
30
20
10
0
THY
DDDACl
PhAA
DDDACl
GLY
DDDACl
THY
TMG
PhAA
TMG
PNP
DNP
PhRed
Figure 5: Histogram of extraction efficiencies (%) of hydrophobic Deep Eutectic Solvents of 4-nitrophenol (blue, PNP, starting
solution 1x10-2 M), 2,4-dinitrophenol (yellow, DNP, starting solution 1x10-3 M) and Phenol Red (red, PhRed, starting solution 1x10-2
M). All the experiments were repeated in triplicate and the errors were evaluated as standard deviations of the samples.
The DESs showed almost complete extraction of all the phenols from the water phases, with
values spanning from 90% to 99% for all the samples for all the phenolic compounds. The
only DES that showed lower efficacy (and lower reproducibility) was GLY/DDDACl. This DES
did not show any extracting capability of PhRed (because of the high samples contamination)
and about 75% for the other two (PNP, DNP). This result is similar to that observed in its
capacity of separation from water in terms of the contamination of the two phases. More
efficacious separation led to more efficacious extraction. Again, the HBD compound, and in
particular its hydrophilicity, was responsible for the extraction efficiency. For all the other
DESs, it seemed that there was not a correlation between the nature of the components and
their extraction efficacy as they act all about the same E%. GLY/TMG DES was not analyzed as
it cannot be separated from water.
These results showed again the great affinity of phenolic compounds with Deep Eutectic
Solvents, as it is shown also in literature[32,52,53]. For a deeper understanding of the
mechanism of interaction between the DESs and the phenolic compounds, and therefore of
the extraction efficiency of this class of molecules, we performed an experiment changing the
pH of the water phases. In these manners information about the capability of water
16

ACCEPTED MANUSCRIPT
separation at different pH of the DESs and, above all, eventual acid-base interactions
occurring between the phenols and the DESs HBA/HBD components could be achieved. Two
sets of experiments were performed using DNP as analyte dissolving it in acid and basic
solutions (pH 2 and 9). The pH values were chosen considering the pKa of the components of
the DESs and of DNP (THY = 10.62; PhAA = 4.31; GLY = 3.83; TMG = 1.84; DNP = 4.09)[54–57]
so that at these values all the components result fully protonated/deprotonated.
In Table 4 the E% of DNP of the DESs at pH = 2 and pH = 9 are reported. The experiments were
carried out at 35% w/w of acidic/basic water (25% for GLY/DDDACl). In Figure 6 the same
data are reported as histograms; the experiment at pH = 7 is also reported as comparison. All
the spectra are reported in Supporting Information section (Figures SI-22-31).
Table 4: Extraction efficiency (%) of 2,4-dinitrophenol of the hydrophobic DESs in basic and in acid water phasesa.
DES
DNP E%, %
HBD
HBA
pH = 9
pH = 2
THY
PhAA
GLY
DDDACl
DDDACl
DDDACl
92.7 ± 1.6 %
92.6 ± 0.2 %
54.6 ± 8.4 %
96.2 ± 0.6 %
90.3 ± 3.8 %
40.4 ± 15.9 %
THY
PhAA
GLY
TMG
TMG
TMG
91.0 ± 3.7 %
97.1 ± 1.1 %
n.a.
94.9 ± 2.6 %
91.2 ± 5.5 %
n.a.
a
(DNP, 1x10-3 M); experiments carried out at 35% w/w of acidic/basic water, 25% w/w for GLY/DDDACl mixture. Basic
conditions: pH=9, NaOH 1x10-5 M; acid conditions: (pH=2, HCl 0.01 M). All the experiments were repeated in triplicate and
the errors were evaluated as standard deviations of the samples.
17

ACCEPTED MANUSCRIPT
Figure 6: Extraction Efficiency E% (%) of DNP of DESs at pH = 2 (red), at pH = 7 (yellow) and at pH = 9 (green). All the experiments
were repeated in triplicate and the errors were evaluated as standard deviations of the samples.
The phase separations occurred both in acidic and basic conditions and the extractions are
excellent and spanning from about 90% to 97% E%. These values are slightly below the ones
observed in neutral conditions. Even in this case GLY/DDDACl DES showed a lower efficiency
(from 40% to 54% E%); also in this case, the stability of the phases could impact on the E%.
These experiments revealed two relevant information: the DESs are water phase-separated
and efficacious for the phenols extractions even at acid and basic pH; the phenols could
interact with these liquids with interactions that did not involve any acid/base-type of
interactions. This was demonstrated also by the UV-Vis analysis of the CH3CN diluted DES
phases of THY/DDDACl mixture (see Supporting Information, Figure SI-32): in this case, the
spectra of the analyte extracted both as phenol- and as phenate- were observed.
4. CONCLUSIONS
The Hydrophobic Deep Eutectic Solvents proposed in this work revealed to be excellent tools
for the extraction/removal of polluting phenolic compounds from water. In this study, the
role of the components of the liquids has been revealed. The HBD compound properties, in
18

ACCEPTED MANUSCRIPT
particular its hydrophobicity/hydrophilicity, showed to be fundamental for an efficacious
separation from water and for an effective removal/extraction of organic phenol polluting
molecules from it. The phase separation and the extraction efficiency of these liquids was not
dependent on the pH of the water phases; this revealed these liquids to be effectively
separated under these conditions and still active in their extraction capabilities. Some of these
mixtures, the ones with betaine as HBA, are NADESs (Natural Deep Eutectic Solvents) because
of the natural source of their components, promoting the bio-availability of these mixtures.
Phenylacetic acid/betaine (PhAA/TMG) mixture revealed to be a promising tool in the
extraction topic also thanks to its miscibility with water that can be considered modular.
These liquids are promising tools as hydrophobic extraction agents from different matrices
and as hydrophobic green reaction media.
DECLARATIONS OF INTEREST
None
FUNDING
This research did not receive any specific grant from funding agencies in the public,
commercial, or not-for-profit sectors.
REFERENCES
[1] J.M. DeSimone, Practical approaches to green solvents, Science (80-. ). 297 (2002) 799–
803.
[2] R.A. Sheldon, Green solvents for sustainable organic synthesis: state of the art, Green
Chem. 7 (2005) 267–278.
[3] T. Welton, Room-temperature ionic liquids. Solvents for synthesis and catalysis, Chem.
Rev. 99 (1999) 2071–2084.
[4] P. Wasserscheid, T. Welton, Ionic liquids in synthesis, John Wiley & Sons, 2008.
[5] F. Cardellini, L. Brinchi, R. Germani, M. Tiecco, Convenient Esterification of Carboxylic
Acids by SN2 Reaction Promoted by a Protic Ionic Liquid System Formed in Situ, in
Solvent-Free Conditions, Synth. Commun. 44 (2014) 3248–3256.
19

ACCEPTED MANUSCRIPT
[6] A.J. Carmichael, K.R. Seddon, Polarity study of some 1‐alkyl‐3‐methylimidazolium
ambient‐temperature ionic liquids with the solvatochromic dye, Nile Red, J. Phys. Org.
Chem. 13 (2000) 591–595.
[7] S.T. Handy, X. Zhang, Organic synthesis in ionic liquids: the Stille coupling, Org. Lett. 3
(2001) 233–236.
[8] J.G. Huddleston, H.D. Willauer, R.P. Swatloski, A.E. Visser, R.D. Rogers, Room
temperature ionic liquids as novel media for ‘clean’liquid–liquid extraction, Chem.
Commun. (1998) 1765–1766.
[9] T.P.T. Pham, C.-W. Cho, Y.-S. Yun, Environmental fate and toxicity of ionic liquids: a
review, Water Res. 44 (2010) 352–372.
[10] R.J. Bernot, M.A. Brueseke, M.A. Evans‐White, G.A. Lamberti, Acute and chronic toxicity
of imidazolium‐based ionic liquids on Daphnia magna, Environ. Toxicol. Chem. 24
(2005) 87–92.
[11] M.C. Bubalo, K. Radošević, I.R. Redovniković, J. Halambek, V.G. Srček, A brief overview of
the potential environmental hazards of ionic liquids, Ecotoxicol. Environ. Saf. 99 (2014)
1–12.
[12] C.J. Bradaric, A. Downard, C. Kennedy, A.J. Robertson, Y. Zhou, Industrial preparation of
phosphonium ionic liquids, Green Chem. 5 (2003) 143–152.
[13] A.P. Abbott, D. Boothby, G. Capper, D.L. Davies, R.K. Rasheed, Deep eutectic solvents
formed between choline chloride and carboxylic acids: versatile alternatives to ionic
liquids, J. Am. Chem. Soc. 126 (2004) 9142–9147.
[14] E.L. Smith, A.P. Abbott, K.S. Ryder, Deep eutectic solvents (DESs) and their applications,
Chem. Rev. 114 (2014) 11060–11082.
[15] R. Stefanovic, M. Ludwig, G.B. Webber, R. Atkin, A.J. Page, Nanostructure, hydrogen
bonding and rheology in choline chloride deep eutectic solvents as a function of the
hydrogen bond donor, Phys. Chem. Chem. Phys. 19 (2017) 3297–3306.
[16] R. Germani, M. Orlandini, M. Tiecco, T. Del Giacco, Novel low viscous, green and
amphiphilic N-oxides/phenylacetic acid based Deep Eutectic Solvents, J. Mol. Liq. 240
(2017). doi:10.1016/j.molliq.2017.05.084.
[17] F. Cardellini, R. Germani, G. Cardinali, L. Corte, L. Roscini, N. Spreti, M. Tiecco, Room
temperature deep eutectic solvents of (1S)-(+)-10-camphorsulfonic acid and
sulfobetaines: Hydrogen bond-based mixtures with low ionicity and structure-
dependent toxicity, RSC Adv. 5 (2015) 31772–31786.
[18] J. Chen, Q. Wang, M. Liu, L. Zhang, The effect of deep eutectic solvent on the
20

ACCEPTED MANUSCRIPT
pharmacokinetics of salvianolic acid B in rats and its acute toxicity test, J. Chromatogr.
B. 1063 (2017) 60–66.
[19] K. Radošević, M.C. Bubalo, V.G. Srček, D. Grgas, T.L. Dragičević, I.R. Redovniković,
Evaluation of toxicity and biodegradability of choline chloride based deep eutectic
solvents, Ecotoxicol. Environ. Saf. 112 (2015) 46–53.
[20] F. Cardellini, M. Tiecco, R. Germani, G. Cardinali, L. Corte, L. Roscini, N. Spreti, Novel
zwitterionic deep eutectic solvents from trimethylglycine and carboxylic acids:
Characterization of their properties and their toxicity, RSC Adv. 4 (2014) 55990–56002.
[21] Y. Dai, J. van Spronsen, G.-J. Witkamp, R. Verpoorte, Y.H. Choi, Natural deep eutectic
solvents as new potential media for green technology, Anal. Chim. Acta. 766 (2013) 61–
68.
[22] A. Paiva, R. Craveiro, I. Aroso, M. Martins, R.L. Reis, A.R.C. Duarte, Natural deep eutectic
solvents–solvents for the 21st century, ACS Sustain. Chem. Eng. 2 (2014) 1063–1071.
[23] N. Azizi, S. Dezfooli, M. Khajeh, M.M. Hashemi, Efficient deep eutectic solvents catalyzed
synthesis of pyran and benzopyran derivatives, J. Mol. Liq. 186 (2013) 76–80.
[24] S.B. Phadtare, G.S. Shankarling, Halogenation reactions in biodegradable solvent:
Efficient bromination of substituted 1-aminoanthra-9, 10-quinone in deep eutectic
solvent (choline chloride: urea), Green Chem. 12 (2010) 458–462.
[25] A. Punzi, D.I. Coppi, S. Matera, M.A.M. Capozzi, A. Operamolla, R. Ragni, F. Babudri, G.M.
Farinola, Pd-Catalyzed Thiophene–Aryl Coupling Reaction via C–H Bond Activation in
Deep Eutectic Solvents, Org. Lett. 19 (2017) 4754–4757.
[26] C. Vidal, J. García‐Álvarez, A. Hernán‐Gómez, A.R. Kennedy, E. Hevia, Introducing deep
eutectic solvents to polar organometallic chemistry: chemoselective addition of
organolithium and grignard reagents to ketones in air, Angew. Chemie. 126 (2014)
6079–6083.
[27] D.A. Alonso, A. Baeza, R. Chinchilla, G. Guillena, I.M. Pastor, D.J. Ramón, Deep eutectic
solvents: The organic reaction medium of the century, European J. Org. Chem. 2016
(2016) 612–632.
[28] M. Tiecco, R. Germani, F. Cardellini, Carbon-carbon bond formation in acid deep eutectic
solvent: Chalcones synthesis: Via Claisen-Schmidt reaction, RSC Adv. 6 (2016) 43740–
43747.
[29] A. Di Crescenzo, M. Tiecco, R. Zappacosta, S. Boncompagni, P. Di Profio, V. Ettorre, A.
Fontana, R. Germani, G. Siani, Novel zwitterionic Natural Deep Eutectic Solvents as
environmentally friendly media for spontaneous self-assembly of gold nanoparticles, J.
21

ACCEPTED MANUSCRIPT
Mol. Liq. 268 (2018) 371–375.
[30] T. Palomba, G. Ciancaleoni, T. Del Giacco, R. Germani, F. Ianni, M. Tiecco, Deep Eutectic
Solvents formed by chiral components as chiral reaction media and studies of their
structural properties, J. Mol. Liq. 262 (2018) 285–294.
doi:10.1016/j.molliq.2018.04.096.
[31] L. Duan, L.-L. Dou, L. Guo, P. Li, E.-H. Liu, Comprehensive evaluation of deep eutectic
solvents in extraction of bioactive natural products, ACS Sustain. Chem. Eng. 4 (2016)
2405–2411.
[32] V. Ferrone, S. Genovese, M. Carlucci, M. Tiecco, R. Germani, F. Preziuso, F. Epifano, G.
Carlucci, V.A. Taddeo, A green deep eutectic solvent dispersive liquid-liquid micro-
extraction (DES-DLLME) for the UHPLC-PDA determination of oxyprenylated
phenylpropanoids in olive, soy, peanuts, corn, and sunflower oil, Food Chem. 245
(2018). doi:10.1016/j.foodchem.2017.10.135.
[33] A. Diuzheva, S. Carradori, V. Andruch, M. Locatelli, E.D. Luca, M. Tiecco, R. Germani, L.
Menghini, A. Nocentini, P. Gratteri, C. Campestre, Use of Innovative (Micro)Extraction
Techniques to Characterise Harpagophytum procumbens Root and its Commercial Food
Supplements, Phytochem. Anal. (2017). doi:10.1002/pca.2737.
[34] Y. Dai, G.-J. Witkamp, R. Verpoorte, Y.H. Choi, Natural deep eutectic solvents as a new
extraction media for phenolic metabolites in Carthamus tinctorius L., Anal. Chem. 85
(2013) 6272–6278.
[35] D.J.G.P. van Osch, D. Parmentier, C.H.J.T. Dietz, A. van den Bruinhorst, R. Tuinier, M.C.
Kroon, Removal of alkali and transition metal ions from water with hydrophobic deep
eutectic solvents, Chem. Commun. 52 (2016) 11987–11990. doi:10.1039/C6CC06105B.
[36] P. Makoś, A. Przyjazny, G. Boczkaj, Hydrophobic deep eutectic solvents as “green”
extraction media for polycyclic aromatic hydrocarbons in aqueous samples, J.
Chromatogr. A. (2018). doi:10.1016/j.chroma.2018.07.070.
[37] C. Florindo, L.C. Branco, I.M. Marrucho, Development of hydrophobic deep eutectic
solvents for extraction of pesticides from aqueous environments, Fluid Phase Equilib.
448 (2017) 135–142. doi:10.1016/j.fluid.2017.04.002.
[38] T. Křížek, M. Bursová, R. Horsley, M. Kuchař, P. Tůma, R. Čabala, T. Hložek, Menthol-
based hydrophobic deep eutectic solvents: Towards greener and efficient extraction of
phytocannabinoids, J. Clean. Prod. 193 (2018) 391–396.
doi:10.1016/j.jclepro.2018.05.080.
[39] B. Tang, K.H. Row, Recent developments in deep eutectic solvents in chemical sciences,
22

ACCEPTED MANUSCRIPT
Monatshefte Für Chemie-Chemical Mon. 144 (2013) 1427–1454.
[40] C.R. Wright, L. VandenElzen, T.A. Hopkins, Deep Eutectic Solvents for Induced Circularly
Polarized Luminescence, J. Phys. Chem. B. 122 (2018) 8730–8737.
doi:10.1021/acs.jpcb.8b06148.
[41] A. Cipiciani, R. Germani, G. Savelli, C.A. Bunton, M. Mhala, J.R. Moffatt, The effects of
single-and twin-tailed ionic surfactants upon aromatic nucleophilic substitution, J.
Chem. Soc. Perkin Trans. 2. (1987) 541–546.
[42] M. Margreth, R. Schlink, A. Steinbach, Water determination by Karl Fischer titration,
Pharm. Sci. Encycl. Drug Discov. Dev. Manuf. (2010) 1–34.
[43] N.D. Gillitt, G. Savelli, C.A. Bunton, Premicellization of dimethyl di-n-dodecylammonium
chloride, Langmuir. 22 (2006) 5570–5571.
[44] S.H. Yalkowsky, Y. He, P. Jain, Handbook of aqueous solubility data, CRC press, 2016.
[45] C. Ma, A. Laaksonen, C. Liu, X. Lu, X. Ji, The peculiar effect of water on ionic liquids and
deep eutectic solvents, Chem. Soc. Rev. (2018).
[46] O.S. Hammond, D.T. Bowron, K.J. Edler, The effect of water upon deep eutectic solvent
nanostructure: An unusual transition from ionic mixture to aqueous solution, Angew.
Chemie Int. Ed. 56 (2017) 9782–9785.
[47] L. Weng, M. Toner, Janus-faced role of water in defining nanostructure of choline
chloride/glycerol deep eutectic solvent, Phys. Chem. Chem. Phys. (2018).
doi:10.1039/C8CP03882A.
[48] P. Baglioni, E. Braccalenti, E. Carretti, R. Germani, L. Goracci, G. Savelli, M. Tiecco,
Surfactant-based photorheological fluids: Effect of the surfactant structure, Langmuir.
25 (2009). doi:10.1021/la900465h.
[49] A.T. Lebedev, O. V Polyakova, D.M. Mazur, V.B. Artaev, I. Canet, A. Lallement, M.
Vaïtilingom, L. Deguillaume, A.-M. Delort, Detection of semi-volatile compounds in cloud
waters by GC× GC-TOF-MS. Evidence of phenols and phthalates as priority pollutants,
Environ. Pollut. 241 (2018) 616–625.
[50] N.G. Buckman, J.O. Hill, R.J. Magee, M.J. McCormick, Separation of substituted phenols,
including eleven priority pollutants using high-performance liquid chromatography, J.
Chromatogr. A. 284 (1984) 441–446.
[51] A. Mittal, D. Kaur, A. Malviya, J. Mittal, V.K. Gupta, Adsorption studies on the removal of
coloring agent phenol red from wastewater using waste materials as adsorbents, J.
Colloid Interface Sci. 337 (2009) 345–354.
[52] Z. Wei, X. Qi, T. Li, M. Luo, W. Wang, Y. Zu, Y. Fu, Application of natural deep eutectic
23

ACCEPTED MANUSCRIPT
solvents for extraction and determination of phenolics in Cajanus cajan leaves by ultra
performance liquid chromatography, Sep. Purif. Technol. 149 (2015) 237–244.
[53] T. Gu, M. Zhang, T. Tan, J. Chen, Z. Li, Q. Zhang, H. Qiu, Deep eutectic solvents as novel
extraction media for phenolic compounds from model oil, Chem. Commun. 50 (2014)
11749–11752.
[54] D.C. Elliott, R.M.C. Dawson, W.H. Elliott, K.M. Jones, Data for biochemical research,
Clarendon Press. Oxford. (1959) 221.
[55] W.M. Haynes, CRC handbook of chemistry and physics, CRC press, 2014.
[56] P.J. Pearce, R.J.J. Simkins, Acid strengths of some substituted picric acids, Can. J. Chem.
46 (1968) 241–248.
[57] E.P. Serjeant, B. Dempsey, Ionisation constants of organic acids in aqueous solution,
Pergamon, 1979.
24

ACCEPTED MANUSCRIPT
GRAPHICAL ABSTRACT
25

ACCEPTED MANUSCRIPT
ROLE OF THE HYDROGEN BOND DONOR COMPONENT FOR A
PROPER DEVELOPMENT OF NOVEL HYDROPHOBIC DEEP
EUTECTIC SOLVENTS
Matteo Tiecco, Federico Cappellini, Francesco Nicoletti, Tiziana Del Giacco, Raimondo
Germani*, Pietro Di Profio.
HIGHLIGHTS
- Novel hydrophobic Deep Eutectic Solvents (DESs) are presented.
- Studies on the role of the components showed that the hydrophobicity of the hydrogen bond
donor to be fundamental.
- The hydrophobicity of hydrogen bond donor has an important role in determining water
separation and contamination.
- The DESs with hydrophilic hydrogen bond acceptor can be separated from water, and the
separation could be considered modular.
- The DESs can efficaciously extract phenols and a dye from water with a simple and fast
procedure, even at acid or basic pH.
26