649
5. Synthesis: Green solvents synthesis should have high atom economy. It means
the waste produced during the synthesis should be minimum and the reactant
used should be completely converted into the product.
6. Toxicity: The solvents should exhibit negligible toxicity.
7. Biodegradability: Solvent should be biodegradable and also should not produce toxic products or by-products.
8. Performance: A green solvent should have same or superior performances to
replace conventional solvents.
9. Stability: A green solvent should have high thermal and chemical stability.
10. Flammability: It should be inflammable.
11. Storage: Easy to store and should fulfill all criteria for safe and easy
transportation.
12. Renewability: Raw materials should be renewable for the green solvents production to avoid carbon footprint.
Researchers are therefore focused on the development of environmental-friendly
novel green solvents to replace the conventional solvents. In recent years, active
research has been performed on ionic liquids and deep eutectic solvents.
3 Ionic Liquids
These solvents are mainly composed of cations and anions, and they exist in a liquid
state at room temperature and atmospheric pressure. Ionic liquid is also called the
molten salts, liquid organic salt, or fused salt because of their existence in the liquid
form below the room temperature [36]. The conventional salt remains in a solid
state at normal room temperature and has a high melting point which limits their use
as solvent. In salts, there are large attractive forces between cation and anion which
lock them together. These attractive forces can be weakened by increasing temperature, making them into bulkier group or by enduring asymmetry. In case of ionic
liquids, attractive forces between anions and cation are weak because of their irregular shapes. Paul Walden in 1914 first described about the ionic liquid which was
ethylammonium nitrate which is known as first room temperature ionic liquid [37].
A comparison between the ionic liquids and common salts has been given in Table 1.
The list of different cation and anion combination used to make ILs is shown in
Fig. 3. Their physical as well as chemical properties can be controlled by the appropriate choice of anion and cation. Therefore, these are also known as designer solvent. Ionic liquids have found its application in different fields such as acid gas
removal, catalysis, chemical synthesis, electrochemistry, etc. [38]. Till date, the use
of ionic liquid is limited to laboratory scale only, and efforts are made for its commercialization. ILs are commonly referred as green solvents because of negligible
vapor pressure and low flammability which make them environmental friendly.
However, in recent year, the term “green” for ILs has become dubious since their
synthesis results in by-product and waste generation [39]. In addition, the synthesis
of ILs requires complex purification steps which add cost to the solvent.
Potential Application of Ionic Liquids and Deep Eutectic Solvents in Reduction…
5. Synthesis: Green solvents synthesis should have high atom economy. It means
the waste produced during the synthesis should be minimum and the reactant
used should be completely converted into the product.
6. Toxicity: The solvents should exhibit negligible toxicity.
7. Biodegradability: Solvent should be biodegradable and also should not produce toxic products or by-products.
8. Performance: A green solvent should have same or superior performances to
replace conventional solvents.
9. Stability: A green solvent should have high thermal and chemical stability.
10. Flammability: It should be inflammable.
11. Storage: Easy to store and should fulfill all criteria for safe and easy
transportation.
12. Renewability: Raw materials should be renewable for the green solvents production to avoid carbon footprint.
Researchers are therefore focused on the development of environmental-friendly
novel green solvents to replace the conventional solvents. In recent years, active
research has been performed on ionic liquids and deep eutectic solvents.
3 Ionic Liquids
These solvents are mainly composed of cations and anions, and they exist in a liquid
state at room temperature and atmospheric pressure. Ionic liquid is also called the
molten salts, liquid organic salt, or fused salt because of their existence in the liquid
form below the room temperature [36]. The conventional salt remains in a solid
state at normal room temperature and has a high melting point which limits their use
as solvent. In salts, there are large attractive forces between cation and anion which
lock them together. These attractive forces can be weakened by increasing temperature, making them into bulkier group or by enduring asymmetry. In case of ionic
liquids, attractive forces between anions and cation are weak because of their irregular shapes. Paul Walden in 1914 first described about the ionic liquid which was
ethylammonium nitrate which is known as first room temperature ionic liquid [37].
A comparison between the ionic liquids and common salts has been given in Table 1.
The list of different cation and anion combination used to make ILs is shown in
Fig. 3. Their physical as well as chemical properties can be controlled by the appropriate choice of anion and cation. Therefore, these are also known as designer solvent. Ionic liquids have found its application in different fields such as acid gas
removal, catalysis, chemical synthesis, electrochemistry, etc. [38]. Till date, the use
of ionic liquid is limited to laboratory scale only, and efforts are made for its commercialization. ILs are commonly referred as green solvents because of negligible
vapor pressure and low flammability which make them environmental friendly.
However, in recent year, the term “green” for ILs has become dubious since their
synthesis results in by-product and waste generation [39]. In addition, the synthesis
of ILs requires complex purification steps which add cost to the solvent.
Potential Application of Ionic Liquids and Deep Eutectic Solvents in Reduction…