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Abstract The disclosure of deep eutectic solvents represents a landmark in green
chemistry. These systems were reported only 17 years ago and yet resulted in a
plethora of publications covering various research areas and diverse fields of application. Their economic and straightforward preparation using highly accessible and
natural compounds together with their extremely great tunability were enough to
consider them as alternatives to the conventional organic solvents. Besides, deep
eutectic solvents hold interesting properties suggesting a promising contribution in
multiple domains.
Herein, the classification of deep eutectic solvents and the reported preparation
methods to date are presented. Further, their physicochemical properties, namely,
their phase behavior, density, viscosity, ionic conductivity, surface tension, and
polarity, are summarized. The stated properties are affected by various parameters
such as the choice of the forming compounds, their molar ratio, the temperature,
and the water content. Finally, in the last section, we entirely present the impact of
water on both the physicochemical properties and the characteristic supramolecular
network of deep eutectic solvents.
Keywords Deep eutectic solvents · Eutectic point · Phase behavior · Natural deep
eutectic solvents · Hydrogen bond acceptor · Hydrogen bond donor · Choline
chloride · Physicochemical properties · Water · Supramolecular network
Abbreviations
BA
Butyric acid
CA
Caprylic acid
ChCl
Choline chloride
DEG
Diethylene glycol
DES
Deep eutectic solvents
DSC
Differential scanning calorimetry
EG
Ethylene glycol
G
Glycerol
HBA
Hydrogen bond acceptor
HBD
Hydrogen bond donor
LA
Lactic acid
Lev
Levulinic acid
MA
Malonic acid
MD
Molecular dynamics
NADES
Natural deep eutectic solvents
NMR
Nuclear magnetic resonance
PEG
Polyethylene glycol
RAMEB Randomly methylated β-cyclodextrin
TBABr
Tetrabutylammonium bromide
TBACl
Tetrabutylammonium chloride
T. El Achkar et al.