Handbook of Ionic Liquids E-Book
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- Herausgeber: Wiley-VCH GmbH
- Kategorie: Wissenschaft und neue Technologien
- Sprache: Englisch
Handbook of Ionic Liquids
A one-stop reference for researchers interested in ionic liquids and their applications
Handbook of Ionic Liquids: Fundamentals, Applications, and Sustainability, constitutes an overview of the latest advances in ionic liquid chemistry. It offers a comprehensive summary of the development history of ionic liquids, their design, and the diverse array of applications—including green and sustainable synthesis, catalysis, drug development and medicine, biotechnology, materials science, and electrochemistry.
The authors explain a variety of processes used to develop novel materials with ionic liquids and describe likely future developments using practical examples taken from contemporary research and development in the field. The book includes discussions of biomass conversion, CO2 capture, and more. You’ll also discover:
- A thorough introduction to the theory of ionic liquids, as well as their different types and recycling methods
- Comprehensive explorations of the physico-chemical properties of ionic liquids
- Practical discussions of ionic liquid synthesis and analysis, including green synthesis and heterocyclic chemistry applications
- Summary of the use of ionic liquids in materials science, including polymers, energy conversion, and storage devices
Perfect for organic, catalytic, physical, analytical, and environmental chemists, Handbook of Ionic Liquids: Fundamentals, Applications, and Sustainability will also benefit electrochemists, materials scientists, and biotechnologists with an interest in ionic liquids and their application.
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Seitenzahl: 978
Veröffentlichungsjahr: 2023
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Table of Contents
Cover
Table of Contents
Title Page
Copyright
Preface
1 History and Development of Ionic Liquids
1.1 Introduction
1.2 Constituents of ILs
1.3 The Brief History
1.4 Ionic Liquid‐Like Systems
1.5 The Generation of ILs
1.6 Structural Development of ILs
1.7 Scope of ILs
1.8 Commercialization of ILs
1.9 Conclusions
Acknowledgments
References
2 Growth of Ionic Liquids and their Applications
2.1 Introduction
2.2 Growth of Ionic Liquids
2.3 Applications of Ionic Liquids
2.4 Conclusion and Future Prospects
References
3 Study of Physicochemical Properties of Ionic Liquids
3.1 Introduction
3.2 Physicochemical Properties of Ionic Liquids
3.3 Conclusion and Perspectives
Acknowledgments
References
4 Ionic Liquids as Green Solvents: Are Ionic Liquids Nontoxic and Biodegradable?
4.1 Introduction
4.2 Toxicity and Biodegradability of Ionic Liquids
4.3 Applications of Ionic Liquids as Green Solvents
4.4 IoNanofluids
4.5 Conclusion
References
5 Promising Uses of Ionic Liquids on Carbon—Carbon and Carbon—Nitrogen Bond Formations
5.1 Introduction
5.2 Carbon—Carbon Bond Formation Reactions
5.3 Carbon—Nitrogen Bond Formation Reaction
5.4 Conclusion
References
6 Ionic Liquids in Separation Techniques
6.1 Introduction
6.2 General Characteristics of ILs
6.3 The Use of ILs in Separation Technology
6.4 Conclusions and Future Perspectives
References
7 Polymers and Ionic Liquids
7.1 Introduction
7.2 Properties of ILs
7.3 Synthesis of PILs
7.4 Types and Application of Common PILs
7.5 Conclusion
References
8 Effect of Ionic Liquids on Electrochemical Biosensors and Other Bioelectrochemical Devices
8.1 Introduction
8.2 The Importance of Ionic Liquids in Electrochemistry
8.3 Fabrication of IL‐Based Sensing Layers
8.4 IL‐Based Electrochemical Biosensors
8.5 Application of Ionic Liquids in Bioelectrochemical Devices
8.6 Conclusions and Future Prospects
References
9 Nanopharmaceuticals With Ionic Liquids: A Novel Approach
9.1 Introduction
9.2 Applications of Ionic Liquids in Various Fields
9.3 Nanotechnology and Ionic Liquids
9.4 Use of Ionic Liquids in Nanocarrier Development (Reported Work)
9.5 Ionic Liquid‐Assisted Metal Nanoparticles
9.6 Conclusion
References
10 Anticancer Activity of Ionic Liquids
10.1 Introduction
10.2 Classification of Ionic Liquids
10.3 Toxicity of Ionic Liquids
10.4 Anticancer Potential of Ionic Liquids
10.5 Conclusions and Future Scope
References
11 Importance of Ionic Liquids in Plant Defense: A Novel Approach
11.1 Introduction
11.2 Generation of ILs and Their Application
11.3 Role of ILs in Plant Defense Mechanisms
11.4 IL Products in Future Management of Agri Industries: An Innovative Approach
11.5 Conclusions
References
12 Theoretical Description of Ionic Liquids
12.1 Introduction
12.2 Ionic Liquid Dynamics
12.3 Theoretical Advances in Force Fields and Electronic Structures
12.4 Mixtures in Ionic Liquids
12.5 Applications of Ionic Liquids in Chemical Processes
12.6 Future Developments
12.7 Conclusion
References
13 Theoretical Understanding of Ionic Liquid Advancements in the Field of Medicine
13.1 Introduction
13.2 A Brief History of Ionic Liquids and Deep Eutectic Solvents
13.3 Biomedical Applications
13.4 Summary and Future Aspects
References
14 Recent Developments in Ionic Liquid Research from Environmental Perspectives
14.1 Introduction
14.2 Applications of Ionic Liquids
14.3 Limitations of Ionic Liquids
14.4 Conclusion
References
Note
15 Ionic Liquids for Sustainable Biomass Conversion in Biorefinery
15.1 Introduction
15.2 Biomass as a Source of Organic Compounds and Fuels
15.3 Biomass Conversion Process
15.4 Value‐Added Organic Compounds from Biomass in Ionic Liquids
15.5 Production of Biodiesel with Ionic Liquids
15.6 Toxicity and Ecotoxicity of ILs for Biorefinery
15.7 Conclusions
References
16 Ionic Liquids for Atmospheric CO
2
Capture: A Techno‐Economic Assessment
16.1 Introduction
16.2 Different Processes of CO
2
Capture
16.3 Conclusion
References
17 Recovery of Biobutanol Using Ionic Liquids
17.1 Introduction
17.2 Biobutanol: First‐Generation Biofuels
17.3 Butanol Production
17.4 Butanol Recovery
17.5 Ionic Liquids
17.6 Recovery of Biobutanol Using Ionic Liquids
17.7 World Butanol Demand
17.8 Conclusion
Acknowledgments
References
18 Bio‐Carboxylic Acid Separation by Ionic Liquids
18.1 Introduction
18.2 Ionic Liquids
18.3 Challenges in the Separation of Bio‐Carboxylic Acids
18.4 Methods for Separating Bio‐Carboxylic Acids
18.5 Separation of Bio‐Carboxylic Acids by the Reactive Extraction Process
18.6 Conclusion and Perspectives
References
19 Current Trends in QSAR and Machine Learning Models of Ionic Liquids: Efficient Tools for Designing Environmentally Safe Solvents for the Future
19.1 Ionic Liquids and Their Structural Characteristics
19.2 Properties of ILs
19.3 Application of ILs
19.4 Do ILs Follow Green Chemistry Principles and Are Hazard Free for Environment?
19.5 Regulatory Proposals for Toxicity Assessment of ILs
19.6 Why In Silico Modeling Is Needed for ILs
19.7 Predictive Toxicity Models for ILs
19.8 Databases of Ionic Liquid
19.9 Overview and Future Avenues
Declaration of Competing Interest
Acknowledgments
References
20 Advances in Simulation Research on Ionic Liquid Electrolytes
20.1 Simulation Method of Ionic Liquid Electrolytes
20.2 Advances in Simulation of Ionic Liquid Electrolytes in Batteries
20.3 Advances in Simulation of Ionic Liquid Electrolytes in Capacitors
20.4 Conclusion
References
21 Applications of Ionic Liquids in Heterocyclic Chemistry
21.1 Introduction
21.2 Application of Ionic Liquids in the Syntheses of Various Heterocycles
21.3 Conclusion and Future Prospective
References
22 Application of Ionic Liquids in Drug Development
22.1 Introduction
22.2 Classification of Ionic Liquids
22.3 General Synthetic Methodologies
22.4 An Overview of Applications in Diverse Fields
22.5 Specific Applications in the Field of Pharmaceutical Development
References
23 Application of Ionic Liquids in Biocatalysis and Biotechnology
23.1 Introduction
23.2 Properties of Ionic Liquids
23.3 Whole‐Cell Biotransformations
23.4 Ionic Liquids as Solvents for Enzyme Catalysis
23.5 Enzyme Selectivity in Ionic Liquids
23.6 Ionic Liquid Stability of Enzymes
23.7 Application of Ionic Liquids in Bioethanol Production
23.8 Ionic Liquids Applied in the Synthesis of Biodiesel
23.9 Conclusion
References
Index
End User License Agreement
List of Tables
Chapter 4
Table 4.1 The log
10
EC
50
values of some test systems of ILs and few commonly ...
Chapter 6
Table 6.1 IL‐based separation of some common value‐added compounds and their...
Table 6.2 The most commonly exhibited physical properties of ionic liquids w...
Table 6.3 Application of ionic liquid additives in the chromatography‐based ...
Chapter 7
Table 7.1 Basic properties of ILs.
Table 7.2 Synthesis of PILs with different moieties in their polymer backbon...
Table 7.3 Types, properties, and advantages of PILs.
Table 7.4 Application of ionic liquids.
Chapter 8
Table 8.1 Conductivity, viscosity, and electrochemical values of some mentio...
Chapter 11
Table 11.1 Application of ionic liquids in plant protection from the stresso...
Chapter 14
Table 14.1 Composition of model oils (MOs).
Chapter 15
Table 15.1 Catalytic hydrolysis of lignocellulose into monosugars in ILs.
Table 15.2 Biodiesel production in ILs.
Chapter 17
Table 17.1 Comparison of butanol with other fuels [13–16].
Chapter 18
Table 18.1 Available separation methods for the separation of bio‐carboxylic...
Table 18.2 Separation of bio‐carboxylic acids with ionic liquids through rea...
Chapter 19
Table 19.1 Characteristics and essential properties of ILs, which make them ...
Table 19.2 List of organisms used for toxicological screening of ILs.
Table 19.3 Comprehensive details of different predictive toxicity in silico ...
Table 19.4 Databases of ILs for modeling purposes.
Chapter 23
Table 23.1 Physical properties of typical ionic liquids [5, 14, 22].
Table 23.2 Examples of ionic liquids applied in whole‐cell reactions using i...
Table 23.3 Examples of ionic liquids applied in isolated enzyme catalysis.
Table 23.4 Ionic liquids capable of dissolving cellulose, hemicelluloses, an...
Table 23.5 Pretreatment of biomass for bioethanol production assisted by ion...
Table 23.6 Ionic liquids applied as solvents for enzyme‐catalyzed transester...
Table 23.7 Methanolysis of sunflower oil by
Candida antarctica
at different ...
List of Illustrations
Chapter 1
Figure 1.1 Widely studied cations and anions of ionic liquids.
Figure 1.2 Structure of heptachlorodialuminate salt.
Figure 1.3 The evolution of the scientific focus on ILs from unique physical...
Figure 1.4 Structures of 3‐sulfopropyl triphenyl phosphonium
p
‐toluene sulfo...
Scheme 1.1 Chemisorption of CO
2
by a task‐specific IL.
Scheme 1.2 Synthesis of [BMIM][lactate].
Scheme 1.3 Chiral ILs derived from the “chiral pool.”
Scheme 1.4 Synthesis of (2‐hydroxyethyl)‐ammonium lactate‐based ILs.
Figure 1.5 Recently reported poly‐IL chemical structures.
Figure 1.6 Structures of energetic ILs.
Scheme 1.5 Formation of metal‐containing ILs containing ferrocenium.
Figure 1.7 Structures of Lewis acidic ILs.
Scheme 1.6 Synthesis of Brønsted acidic ILs with acidic...
Figure 1.8 Structures of basic ILs.
Figure 1.9 Common cations in magnetic ILs: (a) [Emim], (b) [Bmim], (c) [P
6,6
...
Figure 1.10 Common anions in magnetic ILs: (a) [FeCl
4
], (b) [MnCl
4
], (c) [Co...
Figure 1.11 The number of publications and patents each year from 2001 to 20...
Figure 1.12 Design of some well‐known applications of ILs.
Chapter 2
Figure 2.1 Overview of some commonly used cations and anions as constituents...
Scheme 2.1 Typical synthesis paths for ionic liquids.
Scheme 2.2 Nucleophilic substitution of a chloride anion with a sulfonium ca...
Scheme 2.3 Dediazoniation of benzenediazonium in [bmim][Br]–[bmim][NTf
2
] to ...
Figure 2.2 (a) Schematic model of a hexagonal ZnO micropyramid synthesized i...
Scheme 2.4 IL‐catalyzed Friedel–Crafts reaction of PCl
3
and benzene.
Scheme 2.5 IL‐catalyzed alkylation of phenol.
Scheme 2.6 IL‐catalyzed esterification of alcohol.
Scheme 2.7 IL‐catalyzed synthesis of 3‐vinyl ketones.
Scheme 2.8 IL‐catalyzed Henry reaction.
Scheme 2.9 IL‐catalyzed Heck reaction.
Scheme 2.10 IL‐catalyzed Michael addition reaction.
Chapter 3
Figure 3.1 Illustration of experimental vs. calculated MP plot for (a) GCM1 ...
Figure 3.2 Graphical representation of Walden plot.
Chapter 4
Figure 4.1 The comprehension of the toxicity assessment of the cations and a...
Figure 4.2 The toxicity effect of ILs with long alkyl chains on (a) rat C
6
g...
Figure 4.3 Applications of ILs in various sectors.
Figure 4.4 (a) The variation of thermal conductivity with the temperature of...
Figure 4.5 (a) The variation of viscosity with the temperature of IL and INF...
Figure 4.6 (a) The variation of viscosity with the temperature of IL and INF...
Chapter 5
Figure 5.1 Some commonly used ILs.
Scheme 5.1 Heck coupling in the presence of TBHP and TBAB.
Scheme 5.2 Heck coupling by PdCl
2
/[NBu
4
]Br.
Scheme 5.3 [bmim][PF
6
]‐mediated Heck coupling.
Scheme 5.4 Heck coupling in the presence of Pd‐NHC and imidazolium‐based IL....
Scheme 5.5. [Bu
4
N][
L
‐PRO]‐mediated Heck coupling with 2,3‐dihydrofuran.
Scheme 5.6. Heck coupling with TAAIL.
Scheme 5.7 Formation of C—C bond using alkyne and alkene substituents.
Scheme 5.8 Suzuki coupling in the presence of [HEMPy][Pro] TSIL.
Scheme 5.9 Suzuki coupling in the presence of polymeric IL, poly[vbim][Tf
2
N]...
Scheme 5.10 Suzuki coupling in the presence of Pd‐NP‐PIL.
Scheme 5.11 Suzuki coupling using IL‐supported Pd‐NP.
Scheme 5.12 Synthesis of 1,3,5‐triphenylbenzene using PIL.
Scheme 5.13 Ultrasound‐assisted Sonogashira coupling using IL.
Scheme 5.14 Choline hydroxide and Pd‐catalyst‐mediated Sonogashira coupling....
Scheme 5.15 Using IL [TBP][4EtOV] to form C—C bond.
Scheme 5.16 Reaction of aryl halides derivatives with phenylacetylenes in th...
Scheme 5.17 Synthesis of MC‐supported cobalt‐NHC catalyst.
Scheme 5.18 Stille reactions catalyzed by tin reagents supported by ionic li...
Scheme 5.19 Recycling of IL‐tin reagent.
Scheme 5.20 TSIL immobilized with organostananes employed in Stille coupling...
Scheme 5.21 {[CN‐bmim]PF
6
} used in synthesis of C—C bond.
Scheme 5.22 Synthesis of γ‐valerolactone.
Scheme 5.23 Hiyama coupling in the presence of IL.
Scheme 5.24 Aldol condensation using [TAIm]OH.
Scheme 5.25 Aldol condensation using chiral RTIL.
Scheme 5.26 Claisen–Schmidt condensation using
n
‐BuTMG ethylene glycol.
Scheme 5.27 Friedel–Crafts alkylation via IL.
Scheme 5.28 Ionic gel [Bmim]OH‐promoted Erlenmeyer–Plochl and Henry reaction...
Scheme 5.29 RCM reaction via IL‐supported Grubb's ruthenium catalyst.
Scheme 5.30 The synthesis of 3,4‐dihydropyrimidin‐2(1
H
)‐ones using acidic IL...
Scheme 5.31 PSBIL‐catalyzed Biginelli reaction.
Scheme 5.32 Synthesis of 4‐oxo‐6‐aryl‐2‐thioxo‐1,2,3,4‐tetrahydropyrimidine‐...
Scheme 5.33 1,3‐Bis(carboxymethyl)imidazolium chloride [BCMIM][Cl]‐mediated ...
Scheme 5.34 Allylic substitution reaction using ILs.
Scheme 5.35 N‐Allylation via bcmim‐Cl IL.
Scheme 5.36 Anion‐dependent ILs are used to form different regioselective al...
Scheme 5.37 TSIL [BHEDIMP][CF
3
CO
2
]‐promoted Mannich reaction.
Scheme 5.38 [BMIm][BF
4
] IL mediated synthesis of formamides, 1,2‐bis(N‐heter...
Scheme 5.39 [Bmim][BF
4
] with
L
‐proline‐catalyzed reaction.
Scheme 5.40 (a) Chemical structure of [Li(G3)]TFSI (1) and [Li(G4)]TFSI (2) ...
Scheme 5.41 Synthesis of pyrazole derivatives by ILs.
Scheme 5.42 Synthesis of N‐substituted 1‐aryltriazenes...
Scheme 5.43 Synthesis of spiro‐1,2,4‐triazolidine‐5‐thiones using TSIL.
Scheme 5.44 Synthesis of pyridine derivatives in the presence of [Et
3
NH][HSO
Scheme 5.45 Synthesis of imidazole derivatives using [DBUH
+
][Im
−
]....
Scheme 5.46 Synthesis of 1
H
‐pyrazolo[1,2‐
b
]phthalazine‐5,10‐dionev via DIPEA...
Scheme 5.47 Synthesis of triazoloquinazolinones, chromeno[4,3‐
d
]benzothiazol...
Scheme 5.48 Synthesis of polytriazoles using Cu‐IL.
Chapter 7
Figure 7.1 Qualitative description for typical volatility and polarity chara...
Figure 7.2 Characteristic chemical structures of PILs.
Figure 7.3 Common route of polymeric ionic liquids.
Chapter 8
Figure 8.1 Applications of ionic liquids in various fields.
Figure 8.2 Properties, advantages, and applications of CNMs‐ILs.
Chapter 9
Figure 9.1 Pharmaceutical applications of ILs.
Figure 9.2 Types of ionic liquids.
Figure 9.3 Commonly used anions and cations in ILs (R represents the alkyl g...
Figure 9.4 Mechanism of the solubility of LASSBio‐294 drug in ILs.
Chapter 10
Figure 10.1 Structures of cations commonly used in ionic liquids.
Figure 10.2 Structures of anions commonly used in ionic liquids.
Figure 10.3 Some third generation ionic liquids having anticancer properties...
Chapter 11
Figure 11.1 Different types of functional activity of ionic liquids in plant...
Figure 11.2 Diagrammatic illustration of plants' resistance against biotic a...
Chapter 12
Figure 12.1 Effect ionic liquids on the reactivity of a chemical reaction.
Chapter 13
Figure 13.1 Common cations and anions used to create ionic liquids [3].
Figure 13.2 Schematic representation of lysozyme (LYZ) stabilization in surf...
Chapter 14
Figure 14.1 Common cations and anions that can be paired for ionic liquids....
Figure 14.2 Ionic liquids in terms of less toxicity and more biodegradabilit...
Figure 14.3 Qualities of a green solvent.
Figure 14.4 Designs of ionic liquids for specific applications.
Figure 14.5 Surface film on reactive metal on treatment with ionic liquids....
Figure 14.6 Correlation diagram of ILC properties with applications [17].
Figure 14.7 Ionic liquids/biopolymers for different biomedical applications....
Chapter 15
Figure 15.1 Ionic liquids consist of cations and anions.
Figure 15.2 The concept of ionic liquid‐based biorefinery.
Figure 15.3 Transesterification of triglycerides to biodiesel in the presenc...
Chapter 16
Figure 16.1 Oxidative degradation mechanism of MEA, as proposed by Rooney et...
Figure 16.2 Reaction between MEA and its acidic degradation product, as prop...
Figure 16.3 Structure of choline‐based ILs and their CO
2
absorption mechanis...
Figure 16.4 CO
2
absorption mechanism of [P
1111
][Gly] by Shaikh et al. [137]....
Figure 16.5 Flow diagram of the Rectisol wash process.
Figure 16.6 Possible mechanism for the cycloaddition of CO
2
with epoxides ca...
Chapter 17
Figure 17.1 Classification of biofuels based on feedstock.
Figure 17.2 Butanol production via biochemical conversion.
Figure 17.3 Butanol production via petrochemical conversion.
Figure 17.4 Pervaporation process. (a) Pervaporation vacuum operation. (b) C...
Figure 17.5 Perstraction.
Figure 17.6 Advantages and disadvantages of biobutanol recovery techniques....
Figure 17.7 Comparison between ionic liquids and traditional salts.
Figure 17.8 Commercial‐scale industries producing ionic liquids.
Figure 17.9 Applications of ionic liquids.
Figure 17.10 World butanol demand (bn gallons).
Chapter 18
Figure 18.1 Applications of bio‐carboxylic acids in various sectors.
Figure 18.2 Types of ionic liquids [29] / with permission of Elsevier.
Figure 18.3 Applications of ionic liquids in various sectors.
Chapter 19
Figure 19.1 Chemical structures of selective IL cations. R, R
1
, R
2
, and R
3
a...
Figure 19.2 Chemical structures of selective IL anions. R, R
1
, R
2
, and R
3
ar...
Figure 19.3 Application of ILs in different fields of research and day‐to‐da...
Figure 19.4 Major in silico approaches used for toxicity and property modeli...
Figure 19.5 Workflow of in silico modeling approaches.
Chapter 20
Figure 20.1 Multiscale simulation method for ionic liquids in electrolytes [...
Figure 20.2 Application of DFT in electrolytes. (a) Charge distribution in L...
Figure 20.3 Application of AIMD in electrolytes. (a–c) Diffusion trajectorie...
Figure 20.4 Application of MD in electrolytes. (a) Snapshots of different li...
Figure 20.5 (a) Diagrammatic drawing of two Li
+
cation solvation structu...
Figure 20.6 (a) Metal cation residence time and (b) displacement of the meta...
Figure 20.7 Simulation of ionic liquid electrolytes in plate‐electrode capac...
Figure 20.8 (a) Influence of electrode curvature on the differential capacit...
Chapter 21
Figure 21.1 Three generations of ionic liquids.
Figure 21.2 Few properties of ionic liquids taht help them in attaining the ...
Scheme 21.1 Synthetic procedure of
IL 1
.
Scheme 21.2 Application of
IL 1
for synthesis of a 5‐substituted‐1
H
‐tetrazol...
Scheme 21.3 Application of
IL 1
for synthesis of Rufinamide.
Scheme 21.4 Synthesis of pyrazolone derivatives using
IL 2
.
Scheme 21.5 Probable mechanism for synthesizing chromeno[2,3‐
c
]pyrazol‐4(1
H
)...
Scheme 21.6 Syntheses of IL 3 and IL 4.
Scheme 21.7 Synthesis of tryptanthrin using
IL 3
and
IL 4
.
Scheme 21.8 Synthesis of pyranopyridine derivatives using
IL5
.
Scheme 21.9 Synthesis of
IL 6
(PEGMA‐g‐TEGBDIM).
Scheme 21.10 PEGMA‐g‐TEGBDIM (
IL 6
)‐mediated synthesis of aryl‐benzo[4,5]imi...
Scheme 21.11 Synthesis of acridinedione derivatives using ionic liquid [Bmim...
Scheme 21.12
IL 7
mediated one‐pot multicomponent reaction between dimethylf...
Scheme 21.13 Ionic liquid [Emim]
+
[EtSO
4
]
−
mediated synthesis of st...
Scheme 21.14 Synthesis of diverse range of benzofuran derivatives using ioni...
Scheme 21.15 Synthesis of substituted and unsubstituted coumarins in ionic l...
Scheme 21.16 Pd‐catalyzed, ionic liquid [C
2
OHmim]
+
[Cl]
−
mediated o...
Scheme 21.17 Ionic liquid [C
2
O
2
mim]
+
[Cl]
−
mediated synthesis of po...
Scheme 21.18 Synthesis of a diverse range of allylisoxazoles and carbonyl is...
Scheme 21.19 Synthesis of quinazolinone derivatives using [BSMIm]
+
[OTs]
−
...
Scheme 21.20 Plausible mechanism for the synthesis of
54
.
Scheme 21.21 Synthesis of 5‐aryl‐2‐thioxopyrrolidine‐3,3‐diester via ring op...
Scheme 21.22 Synthesis of [1,3]benzoxazine‐2‐thione (
58
) and 3‐thioxohexahyd...
Scheme 21.23
IL 21
catalyzed synthesis of naphthopyrans, styrenes, and carbi...
Scheme 21.24 BAIL (
IL 22
)‐catalyzed imidazole synthesis under ultrasound irr...
Scheme 21.25
s
catalyzed synthesis of substituted imidazoles.
Scheme 21.26
IL 24
catalyzed synthesis of 2,4,5‐trisubstituted imidazoles.
Scheme 21.27 Choline acetate (
IL 25
)‐mediated synthesis of 2‐amino‐4
H
‐chrome...
Scheme 21.28 Synthesis of pyran derivatives using
IL 26
.
Scheme 21.29 [H
2
‐DABCO][HSO
4
]
2
‐mediated synthesis of benzimidazoquinazolinon...
Scheme 21.30 Synthesis of pyrimido[4,5‐b]quinolines (
82
) and pyrimido[4,5‐d]...
Scheme 21.31 Triethyl ammonium acetate‐catalyzed synthesis of dihydropyrimid...
Scheme 21.32 Application of
IL 30
for the synthesis of pyrazolodihydropyridi...
Scheme 21.33 Synthesis of cyclic carbonates usingPMO@IL‐NTf
2
(
IL 31
).
Scheme 21.34
g
‐C
3
N
4
‐SO
3
H‐catalyzed synthesis of
bis
(indolyl)methanes and pyr...
Chapter 22
Figure 22.1 Challenges for future applications of ionic liquids in drug deli...
Chapter 23
Figure 23.1 Building blocks for bioactive ionic liquids.
Figure 23.2 Pretreatment of biomass in ionic liquid.
Figure 23.3 Enzymatic biodiesel process in ionic liquids.
Guide
Cover
Table of Contents
Title Page
Copyright
Preface
Begin Reading
Index
End User License Agreement
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Handbook of Ionic Liquids
Fundamentals, Applications, and Sustainability
Edited by Sanchayita Rajkhowa, Pardeep Singh, Anik Sen, and Jyotirmoy Sarma
Editors
Dr. Sanchayita Rajkhowa
Department of Chemistry
Haflong Govt. College
Dima Hasao, Assam
India
Dr. Pardeep Singh
Department of environmental studies
PGDAV College
University of Delhi
New Delhi
India
Dr. Anik Sen
Department of Chemistry
GITAM (Deemed to be University)
Visakhapatnam, Andhra Pradesh
India
Dr. Jyotirmoy Sarma
Department of Chemistry
GITAM (Deemed to be University)
Visakhapatnam, Andhra Pradesh
India
Cover: © qimono/Pixabay
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Preface
Almost every “new” discovery was preceded not only by earlier work upon which you based your research but also by developments you wish you had been aware of before you got started. The roots of ionic liquids (ILs) go back to alchemists' studies on molten nitrates and ammonium salts, although they are in unorganized fashion over a century ago. It was followed by the systematic study, which began with Humphry Davy's pioneering work on the electrolytic decomposition of simple molten salts under the influence of an applied DC electric field, to produce the elements that initially had been chemically combined in the salt form. Davy was the first person to work with high‐melting simple salts for scientific research. Later, it is known that the Nobel Prize–winning physicist Sir William Ramsay worked with ILs at an ambient temperature called “syrupy ionic liquids” that he prepared by combining acids with picoline. Nevertheless, the independent work on molten salts can be rooted back to 1914 when Paul Walden discovered ethylammonium nitrate, [EtNH3][NO3] that has a melting point of 12 °C. Almost 40 years later, Hurley and Weir (1951) made a solution by mixing alkylpyridinium halides with “true inorganic salts” from which the metals could be electroplated. The electrodeposition of metals is still a burning topic in the field of IL research. With the discovery of room temperature ILs (RTILs), it gained a wider attention from researchers with different academic backgrounds by the late twentieth century. Another fact for ILs being so popular and studied lies with its environmentally benign nature, although some groups deny this fact for several ILs. Whatever one's stance in this debate, there is no doubt about the application of ILs to “clean” and/or “green” technologies, particularly the growing green chemistry movement in so much so that at one point the RSC journal Green Chemistry was forced to limit the papers about ILs that it would accept. As this field has grown extensively over the years, it is often noticed that researchers are more focused on one or two applications of ILs along with their physical properties in present times.
The idea of publishing a book on ILs was conceived a couple of years back as I was going through one of my old pieces of work and looking for its future aspects. During that time, I realized that this field has enormous potential mainly due to its peculiar properties, such as the absence of flammability and good ability to dissolve organic, organometallic, and even some inorganic compounds. ILs offer numerous advantages over conventional organic solvents for carrying out organic reactions, such as easier product recovery, recyclable catalysts, and reusable ILs. In addition, ILs exhibit distinct thermodynamic and kinetic behaviors. Rates of reaction are often enhanced, and selectivity is frequently better. I discussed this topic with Dr. Jyotirmoy Sarma and Dr. Pardeep Singh to have their views on the relevance of the topic with current research trends. Dr. Sarma remarked on the chemical applications of ILs, while Dr. Singh offered some insights on the environmental sustainability and green chemistry aspects of the same. Dr. Anik Sen, with his profound theoretical and experimental knowledge, has suggested including recent theoretical studies on this field in order to provide readers with a substantial understanding of ILs. This is how our journey in framing the Handbook of Ionic Liquids: Fundamentals, Applications and Sustainability began.
This book emphasizes on the basic concepts of ILs, their properties and applications, their recent advancements in various fields, and their theoretical understanding.
Dr. Sanchayita Rajkhowa
1History and Development of Ionic Liquids
Sumana Brahma and Ramesh L. Gardas
Indian Institute of Technology Madras, Department of Chemistry, IIT P.O., Chennai 600036, India
1.1 Introduction
For the past two decades, the term ionic liquid (IL) has been familiar to a very small number of research groups. However, ILs have attracted significant attention as innovative fluids in a wide range of research fields during this period [8, 60]. Generally, ILs are liquids that exist only in ionic form [79]. ILs can be defined as liquids consisting of ions with a melting point ≤100 °C. In another way, ILs, which exist as liquids at or near room temperature, are frequently termed room temperature ionic liquids (RTILs) [54]. In 1914, Paul Walden reported ethylammonium nitrate as the first IL [13]. According to Walden, the liquid, i.e. ethylammonium nitrate, composed of cations and anions and a minimal amount of molecular species, is an IL. Since the nineteenth century, several synonyms and abbreviations have been given to ILs by different research groups. Among the scientific community, the most frequent synonyms of ILs are molten salt, molten organic salt, low‐melting salt, fused organic salt, ambient temperature ILs, neoteric solvent, and many more [40].
ILs are associated with unique features such as high ionic conductivity, high viscosity, low volatility, nonflammability, negligible vapor pressure, tunable solubility, and a wide electrochemical potential window [82]. All the mentioned IL properties can be altered by tuning the combination of the cations and anions of the ILs. Hence, ILs can also be termed “designer solvents” [55]. Due to their unique properties, ILs are used in various research applications. A multidisciplinary research on ILs is developing, including materials science, biotechnology, chemical engineering, chemistry, energy field, and atmospheric chemistry. Due to the low‐volatile, nonflammable nature of ILs, they are highly preferred over any conventional organic volatile solvents or catalysts in various physical and chemical processes [73].
Furthermore, recently, green technology has been the greatest challenge for researchers concerning environmental hazards. The linkage between ILs and green chemistry is associated with the solvent properties of ILs [17]. ILs are also entitled to green solvents as they possess negligible vapor pressure and high thermal stability, resulting in advantages such as product recovery, desulfurization of liquid fuel, ease of containment, and recycling capability [42, 51]. ILs never possess the explorer risk compared with volatile organic solvents. In terms of volatility, molecular solvents could not (except molten polymers) reach even near the ILs.
ILs can exhibit high polarity. Based on the normalized polarity scale, the polarities of tetramethylsilane and water are 0.0 and 1.0, respectively, whereas the polarity of ILs is usually in the range of 0.6–0.7 [85]. Due to their high polarity, ILs are used as catalysts in various chemical and biochemical reactions. ILs easily dissolve in different solvents, including organic, inorganic, polar and nonpolar, and polymeric compounds. From the chemical engineering perspective, the most critical disadvantage, i.e. gas/liquid–solid mass transfer limitations during catalytic reactions, is resolved using efficient IL catalysts, as reported in detail by Tan et al. [75].
In view of the growing field of renewable energy, it is necessary to replace the conventional volatile electrolytes with green electrolytes in energy storage devices such as batteries, supercapacitors, fuel cells, and dye‐sensitized solar cells. [44, 84]. ILs are appropriate in energy storage devices because of their high conductivity, low volatility, nonflammability, and high electrochemical and thermal stability. Imidazole‐ and pyrrolidinium‐based electrolytes have exhibited promising outcomes as electrolytes in lithium‐ion batteries and capacitors [14]. However, the investigation and deep learning of ILs as electrolytes for new devices such as hybrid batteries and Al oxygen/ion batteries and for CO2 reduction are in the early stages [53].
Millions of ILs can be synthesized by tuning the combination of cations and anions with desired properties and applications. Based on their properties and applications, ILs can be classified as task‐specific ILs, energetic ILs, magnetic ILs, polyionic liquids, and supported ILs. [52]. For a specific process, screening for appropriate ILs is a prerequisite. To identify the structure–performance relationships, it is required to determine the nature of the interactions between cations–cations, anions–anions, and cations–anions of IL species [12]. Therefore, experimental, theoretical, and computational methods are needed to summarize the proper nature of ILs. More profound knowledge of IL nature at the microscopic scale will support the interpretation of macroscopic fluid phenomena and therefore endorse the application of ILs in industry. The multiscale features of ILs extending from the molecular level to the industrial level have been described by Dong and his coworkers [38]. Because of a wide range of applications and prospects of the ILs in the industry, ILs were exclusively named as "solvents of the future" in industrial processes [65]. However, the toxicity of ILs is identified as an emerging limitation for practical applications of ILs. ILs containing high alkyl chain lengths or fluorine anions are more toxic [97]. The toxicity can be affected by changing the structure of ILs . Hence, a detailed toxicity analysis is recommended before real‐life applications of ILs. The brief history, development, and future scope are further summarized in the next section.
1.2 Constituents of ILs
ILs are usually made up of organic cations and inorganic anions. Generally, nitrogen‐ (imidazolium, pyrrolidinium, pyridinium, ammonium, choline, etc.) or phosphorus‐containing cation moieties with linear or branched alkyl chains are used to prepare ILs.
Figure 1.1 Widely studied cations and anions of ionic liquids.
The most commonly used anions are halides (Cl−, Br−, I−), nitrate [NO3−], chloroaluminates [AlCl4−, Al2Cl7−], hexafluorophosphates [PF6−], tetrafluoroborate [BF4−], alkyl carboxylate [RCOO−], acetate [CH3COO−], trifluoromethylsulfonate [CF3SO3−], triflate [OTf−], and bistriflamide [NTf2−]. Recently, amino acids are also used as anions. The most studied cations and anions are shown in Figure 1.1.
1.3 The Brief History
There are numerous inceptions to the story of ILs in which they were recognized independently. The reporter's opinion will essentially influence the history of ILs [88]. The background of the ILs started with the finding of molten liquid salt. In the early 1990s, Paul Walden was searching for liquid molten salt at a particular temperature at which he could have accomplished his experiment. In 1914, Walden discovered ethyl ammonium nitrate [EtNH3][NO3] with a melting point of 12 °C and termed it the first protic ionic liquid (PIL) [47]. Further, Walden and his coworkers formulated the “Walden rule”, which correlates the equivalent conductivity (λ) as well as viscosity (η) of the liquid (aqueous solution).
Later on, the Walden rule could not interpret the properties of low‐melting silver salt. Further, the Walden rule was modified to the fractional Walden rule by a group of molten salt chemists from a German school [5]. The fractional Walden rule is as follows:
where γ is a constant 0 < γ < 1. But after that, there was no potential progress for molten salt studies for a prolonged time. According to the partial Walden rule, the Arrhenius activation energy for conductivity was lower than that for viscosity in the case of a low‐melting silver iodide salt. Therefore, the silver iodide salt is a good conductor even in its crystalline state near its melting point temperature. The Walden rule was unable to predict the “superionic” behavior of molten salt, which made Walden rule very useful for the classification of ILs.
Furthermore, in the mid‐nineteenth century, chemists observed the so‐called “red oil” during Friedel–Crafts reactions. The “red oil” was the first documented observation of ILs [88]. Using nuclear magnetic resonance (NMR) technique, chemists were able to identify the structure of “red oil,” which was the stable intermediate in Friedel–Crafts reactions termed sigma complex, which was basically heptachlorodialuminate salt (Figure 1.2). Prof. Jerry Atwood from the University of Missouri termed the structure early IL. Afterwards, ILs started to be used as either catalysts or solvent systems for organic reactions. Their effects on the reaction rates and their antimicrobial activity and toxicity were further premediated.
Figure 1.2 Structure of heptachlorodialuminate salt.
Numerous literature surveys suggested that chloroaluminate molten salts attracted significant attention in the mid‐nineteenth century. The research based on chloroaluminate molten salts was mainly conducted by the US Air Force Academy in Colorado Springs. Since the early 1960s, the Air Force Academy has endorsed their research in molten salts/IL systems. The chloroaluminate molten salts were used in various research fields, especially electrochemistry. Hurley and Weir were the first to study the potential benefits of molten salts [40]. They mixed aryl and N‐substituted alkyl pyridinium halides with several metal halides and nitrates to achieve low liquids for electrochemical extractions. At room temperature, they discovered the formation of liquid 1‐ethylpyridinium bromide‐aluminum chloride ([C2py]BrAlCl3). First, they presented a phase diagram for the system, including two eutectics at 1 : 2 at 45 °C and 2 : 1 at −40 °C molar ratios. Bromochloroaluminate was developed at the 1 : 1 M ratio (88 °C). In 1975, Bob Osteryoung and his group further studied [C2py]BrAlCl3 (2 : 1 M ratio mixture) species for the electrochemical study of ferrocene, ferrous(II) diimine complexes, and hexamethyl benzene [98]. The first paper based on the [C2py]BrAlCl3 system was published by the Osteryoung group, and the patent was granted by the Air Force Academy. In 1979, Robinson and Osteryoung used 1‐butylpyridinium chloride‐aluminum chloride ([C4py]‐AlCl3) for electrochemistry and Raman spectroscopy [64]. George Parshall and his group synthesized [Et4N][GeCl3] (melting point of 68 °C) and [Et4N][SnCl3] (melting point of 78 °C) and used them as solvents for hydrogenation reactions [21]. Further, he also worked on [Et3NH][CuCl2] to explore different ammonium and phosphonium chlorocuprate systems. Warren Ford worked on alkyl ammonium alkyl borides and found that triethylhexylammonium triethylhexylboride IL is less viscous among all. In 1983, Chuck Hussey and his groups published a review article on “Room Temperature Molten Salt Systems”. This review includes the development, properties, and application of chloroaluminate systems [16].
Moreover, in the 1980s, research on ILs was carried out by new researchers like Ken Seddon and Tom Welton. In 1981, Evans et al. [26] started the study on [EtNH3][NO3]. They investigated the thermodynamic properties of its solutions of krypton, ethane, methane, and n‐butane. They mainly studied the “hydrophobic bonding” present in the system [11]. They illustrated that [EtNH3][NO3] as a nonaqueous solvent could be used in biochemical systems. Colin Poole and his coworkers used [EtNH3][NO3] as a stationary phase in gas–liquid chromatography [61].
Early in the 1980s, John Wilkes and his coworkers discovered the 1‐alkyl‐3‐methylimidazolium chloride‐aluminum chloride ([CnC1im]Cl‐AlCl3) IL system and examined the transport properties of the systems. Later on, the introduction of 1‐alkyl‐3‐methylimidazolium cations promoted an argument on the role of hydrogen bonding in the structure of ILs. However, all the controversies were fixed by identifying the imidazolium ring protons, which can act as hydrogen bond donors in the presence of hydrogen bond acceptors. Afterwards, researchers focused on removing chloroaluminate species from IL‐chloroaluminate systems. Abdul‐Sada and his group worked on that [3].
In the 1990s, extensive research was performed on ILs by many groups worldwide. In 1992, Wilkes et al. first synthesized water‐ and air‐stable 1‐ethyl‐3‐methylimidazolium‐based ILs [89]. Over the period, several moisture‐stable ILs have been synthesized. In 1996, Bonhote et al. synthesized a new class of ILs by introducing [NTf2]− anions [9]. This class of ILs is significantly less viscous and highly conductive. Fraser and MacFarlane's group also introduced a new subclass of ILs based on phosphonium cation [27]. In 1998, ILs became very popular in the scientific community when the journalist Michael Freemantle wrote the first report in Chemical & Engineering News [91]. Based on the application in different research areas, millions of ILs were synthesized by tuning the combination of cations and anions. Therefore, ILs are termed as “designer solvent.” Ken Seddon had carried forward the extensive research on ILs in the Queen's University Ionic Liquids Laboratory (QUILL). Later, he initiated the collaboration between the academy and industry to explore the industrial applications of ILs.
Further, ILs are used as a green solvent in green technologies. In 2000, Robin Rogers led a NATO Advanced Research Workshop on “Green Industrial Applications of Ionic Liquids” in Heraklion [81]. During this time, Jim Davis termed ILs as task‐specific ILs. In 1999, Joan Brennecke discovered the first biphasic system combining ILs with supercritical CO2. Numerous studies were published on CO2 and other gas solubilities in different ILs. Due to negligible vapor pressure and the nonvolatile nature of ILs, researchers have focused on using ILs as lubricants. In 2001, Ye et al. reported the promising performance of ILs as a lubricant for the first time [92]. In 2004, Phillips and Zabinski used ILs as additives for conventional lubricants [59].
The most significant breakthrough in the application of ILs was the utilization of ILs in energy storage devices. ILs can exhibit a wide electrochemical potential window and high conductivity. Therefore, to maximize the energy density of the devices such as lithium‐ion batteries, supercapacitors, fuel cells, and dye‐sensitized solar cells, ILs are used as electrolytes. Furthermore, ILs are used in separations in analytical chemistry and nuclear chemistry. The first application of ILs at the commercial level was BASF's BASIL (biphasic acid scavenging utilizing ionic liquids) process. ILs are also a promising candidate for pharmaceutical applications. In 1998, Davis discovered the first IL derivative from the pharmaceutical constituent (API).
1.4 Ionic Liquid‐Like Systems
During the last century, there was a massive argument on the properties and the characteristic features of molten salt vs. ILs. There was a bit of confusion over which materials should be counted in the IL family and which should be left out. The term IL solely defines a liquid comprised of ions. The restriction is that ILs should be liquid below 100 °C temperature. Tom Welton said, “Room‐temperature ionic liquid, non‐aqueous ionic liquid, molten salt, liquid organic salt, and fused salt have all been used to describe salts in the liquid phase. With the increase in electronic databases, the use of keywords as search tools is becoming ever more important. While authors are free to choose any name that they wish for their systems, I would suggest that they at least include the term ionic liquid in keyword lists” [86]. However, the system consisting of molecular constituents can also often be termed an IL system. For example, the deep eutectic solvents (DESs) are IL‐like systems. The first DESs were discovered by Abbott et al., where choline chloride was mixed with urea (1 : 2 M ratio). Here the formation of ions occurs due to the strong H‐ bond between the donor molecules and the chloride ion. Therefore, the cation–anion interactions are suppressed, resulting in a low melting point and the system performing like the IL system.
Later, based on deep learning, it was found that different types of H‐bonds were present in the system. The urea was responsible for creating a H‐bonded complexed cation [urea(choline)]+ additional to [Cl(urea)2]− ion. In the first paper of Andy Abbott, he termed the system as the DES but not the IL system. Later, another group of materials was included in the IL family, i.e. lithium‐glyme‐solvated IL system [2]. Here, glyme was added to Li salt to make complex cations [Li(glyme)]+. Due to the large size of the complex cations, the interactions between the cations and anions are lowered, causing the low melting point of the system. Watanabe et al. first discovered the system and used it in the application of lithium‐ion batteries. When 5 M lithium perchlorate‐diethyl ether was utilized for organic reaction, it was designated as “fused salt” comprising both [Li(ether)]+ and [Li(ether)2]+ ions.
1.5 The Generation of ILs
To achieve green technology, it is necessary to replace volatile organic solvents. Hence, instead of volatile organic solvents, researchers have focused on the production of IL media for various applications, especially in biocatalytic processes. ILs can resolve the disadvantages of organic solvents, such as high volatility, high flammability, and low thermal and chemical stability. Therefore, ILs have recently been used as solvents in various applications, from biology to electrochemistry. But still, ILs are associated with certain drawbacks in terms of their toxicity and biodegradability [77]. Several recent reports stated that the ILs, including alkylmethylimidazolium cations, primarily used in biocatalysis, are ecotoxic, and the ecotoxicity escalates with the alkyl chain length of the cations. Hence, those ILs cannot be termed “green solvents.” Concerning environmental hazards and health and safety issues, it is essential to synthesize less toxic, biodegradable ILs. Presently, three different generations of ILs can be classified, as illustrated below and represented in Figure 1.3. ILs can be categorized into three distinct generations based on their toxicity [99].
1.5.1 First‐Generation ILs
As stated before, the first known IL was ethylammonium nitrate, as reported by Walden. Afterwards, several ILs were synthesized with different combinations of cations and anions. In the 1980s, Wilkes et al. started the vast research on first‐generation ILs [100]. These ILs are associated with cations such as alkylpyridinium, alkylimidazolium, and dialkylimidazolium. In the case of anions, chloroaluminate and metal halides are mainly used. But those anions are highly reactive with water and air. Those ILs are not appropriate for biotransformations. Due to their high hygroscopic nature, the first‐generation ILs are always carefully handled under an inert atmosphere. Due to this drawback, the application of the first‐generation ILs is very inadequate. Therefore, researchers have further focused on the synthesis of moisture‐insensitive ILs.
1.5.2 Second‐Generation ILs
The second‐generation ILs appeared after a decade. In this category, the chloroaluminate anions are replaced by the anions that are less reactive with air and water, such as Cl−, Br−, I, PF6−, BF4−, and C6H5COO−. In the case of the selection of cations, ammonium‐ and phosphonium‐based cations are included along with alkylpyridinium, alkylimidazolium, and dialkylimidazolium. The second‐generation ILs possess certain properties such as a low melting point, low viscosity, and high solubility. Hence, they hugely succeeded in attracting research interest in several applications in the early 1990s [77]. The maximum number of literature published is in biocatalysis applications. In the early 2000s, the first literature on biocatalysis with ILs media was published. However, second‐generation ILs are also toxic, similar to first‐generation ILs.
Further, the second‐generation ILs are very costly. Gorke et al. stated that the high costs were associated with starting materials and final product purification [32]. Therefore, researchers have further focused on synthesizing less toxic, low‐cost ILs.
Figure 1.3 The evolution of the scientific focus on ILs from unique physical through unique chemical and now biological property sets.
Source: Hough et al. [99]/Royal Society of Chemistry.
1.5.3 Third‐Generation ILs
The third‐generation ILs is mainly associated with cations such as choline. Generally, amino acids, alkylphosphates, alkylsulfates, bis(trifluoromethanesulfonyl)amide (TFSI) [(CF3SO2)2N−], and sugars are used as hydrophobic anions [99]. The choice of cations and anions is based on their being less biodegradable, less toxic, and low cost. The third‐generation ILs is also termed as advanced ILs. These ILs are mainly characterized by their biological activity, such as being bacteriostatic, fungicidal, and herbicidal. Their biological activity is generally related to the anion, where the cations are premeditated to enhance their potentiality in various applications.
This generation also includes a new class of solvent systems, termed “deep eutectic solvents” [80]. DES are highly water‐soluble and more hydrophilic than the second‐generation ILs. DESs are not liquids at room temperature. They are basically mixtures of salts such as choline chloride, alcohols, amides, amines, urea, and carboxylic acids. As this generation is new to the research field, very few reports have been published. But due to their low toxicity and low cost, the third‐generation ILs will reach the commercial level soon [39].
1.6 Structural Development of ILs
Based on the applications, altering the properties of ILs is a prerequisite. The properties of the ILs can be changed by tuning their structures with different combinations of cations and anions. On the basis of cation and anion combinations and their properties, ILs are classified into several categories.
1.6.1 Task‐Specific ILs (TSILs)
Theoretically, millions of ILs can be synthesized by switching the combinations of different cations and anions. Davis et al. first established the perception of designing IL, which can interact with a solute in a specific fashion [19]. For the benzoin condensation reaction, Davis et al. showed that thiazolium‐based IL could perform as both solvent and catalyst. Further, he introduced the term “task‐specific ionic liquids” (TSILs) and described the concept of TSIL in a brief review [18]. He explained how the properties and reactivity of the ILs could be changed by incorporating functional groups into the IL moieties. The TSILs can be defined as ILs with functional groups incorporated covalently into the cations or anions of the ILs. TSILs are also coined as functionalized ILs. Over the last few decades, TSILs have received remarkable consideration owing to their precise properties that can be altered according to the user's needs by tuning the combination of cations and anions [15]. In the last 15 years, several types of TSILs have been intended to perform specific tasks such as organic synthesis (Michael addition, Heck reaction, Knoevenagel condensation, etc.), nanoparticle synthesis, simulation of chirality, CO2 adsorption, and electrochemical applications. [30, 67]. The first synthesized TSIL is 3‐sulfopropyl triphenyl phosphonium p‐toluene sulfonate, as shown in Figure 1.4.
Lee and his coworkers have reviewed the developments in functionalized imidazolium TSILs [46]. Further, Giernoth et al. have shown the potential of TSILs as a gas reservoir, new magnetic materials in chromatography, and other industrial applications. For example, the imidazolium‐cation‐based IL, including amine functionality, can form carbamate upon the addition of CO2 [30]. In this chemisorption approach, the maximum uptake of CO2 is 0.5 mol per mole of IL (Scheme 1.1). However, the synthesis of TSILs is a bit difficult and time‐consuming process. The active functional groups present in TSILs are highly reactive toward the wide range of reactants.
Figure 1.4 Structures of 3‐sulfopropyl triphenyl phosphonium p‐toluene sulfonate.
Scheme 1.1 Chemisorption of CO2 by a task‐specific IL.
1.6.2 Chiral ILs
So far, the RTILs have been used as an alternative to conventional organic solvents for several organic reactions due to their low volatility. The enormous majority of studies associated with RTILs include achiral syntheses [22]. However, there is a rapid growth in literature indicating that chiral ILs have wide applications in the areas of synthesis of chiral compounds, liquid chiral chromatography, liquid crystals, stereoselective polymerization, and NMR chiral discrimination. [71]. In 1996, Herrmann et al. described the synthesis of N‐heterocyclic carbenes of the corresponding imidazole moieties and validated their utilization in an asymmetric homogeneous catalysis reaction [7]. However, there was no consequent attention in the case of the solid precursor (the chiral imidazolium chloride salt).
In 1997, Howard and his coworkers synthesized homochiral dialkylimidazolium bromide salt as a Lewis acid catalyst for the Diels–Alder reaction. In 1997, Seddon and his coworkers studied 1‐butyl‐3‐methylimidazolium ([BMIM]) lactate as the first chiral IL [25]. This chiral IL was synthesized from [BMIM][Cl] and sodium (S)‐2‐hydroxypropionate via anion exchange (Scheme 1.2) [7].
Scheme 1.2 Synthesis of [BMIM][lactate].
The chiral ILs are associated with a chiral center either at the cations or the anions or both within the ILs. These ILs are promoted as catalysts or solvents for the asymmetric synthesis of chiral compounds. The additional benefit of this synthetic approach is the high yield. The synthesis of chiral ILs is challenging because of their chiral nature. In 2002, Wasserscheid and group described the development of numerous new chiral ILs synthesized directly from the “chiralpool” [83]. For example, chiral hydroxyl ammonium salts were prepared by Scheme 1.3.
Scheme 1.3 Chiral ILs derived from the “chiral pool.”
In 2002, Saigo et al. reported the synthesis method and structure of a novel imidazolium‐based IL with planar chirality [43]. In 2003, Bao et al. defined the synthesis of chiral imidazolium ILs from chiral amines (D‐a‐phenylethylamine) and amino acids (L‐alanine, L‐valine, and L‐leucine) with 30–33% yields [6]. In 2004, Vo Thanh et al. premeditated an effectual procedure for preparing chiral ephedrinium ILs using solvent‐free conditions and microwave irradiation [78]. The chiral ILs are used in many organic reactions, such as asymmetric Michael addition, enantioselective hydrogenation reactions, enantioselective photodimerization, Heck reaction, and asymmetric dihydroxylation.
1.6.3 Switchable Polarity Solvent ILs
Switchable ILs are generally derived from alcohols and organic bases [62]. However, their precise solvent structure is still under investigation. They are used in various applications such as gas capture, separations, and nanomaterial synthesis. Predominantly, switchable ILs are green, nonaqueous absorbents for CO2 capture [50]. The improvement of viscosity and regeneration efficiency of switchable ILs is still required. An activator is applied during the synthesis of switchable ILs, which promotes them to equilibrate between very low polarities and high polarities for both anions and cations. Secondary amines are typically used to get switchable ILs by applying CO2 as an activating agent to form the carbamate salt reaction in Eq. (1.1) [57].
The switchable ILs with high polarity were obtained with 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU) and alcohol which switched from lower to higher polarity while activated with CO2.
1.6.4 Bio‐ILs
Imidazolium‐ and benzimidazolium‐based ILs with long alkyl chain lengths are generally toxic, less biodegradable, and also related to other disadvantages. Researchers have started to discover a new class of ILs derived from sustainable bioprecursors to overcome those limitations. Bio‐ILs are comparatively less toxic, biodegradable, and biocompatible [31]. As choline is a precursor of the phospholipids that include biological cell membranes, choline is used as a cation to synthesize ILs. The choline‐containing ILs are more promising and biocompatible than the other bio‐ILs. Apart from choline, 2‐hydroxyalkyl‐ammonium cation is also used to synthesize bio‐ILs (Scheme 1.4). Usually, amino acids and acetic acid are used as counteranions. Scheme 1.4 represents the synthesis.
Scheme 1.4 Synthesis of (2‐hydroxyethyl)‐ammonium lactate‐based ILs.
The European Standards methods are used to scrutinize the toxicity and biodegradability of ILs. For example, according to the European Standards, (2‐hydroxyethyl)‐ammonium lactate was noted to have the highest biodegradable (95%) levels. Choline‐based bio‐ILs are used for drug delivery, solvents for biopolymers, sensors, and actuators [69].
1.6.5 Poly‐ILs
When ILs are incorporated into the polymer chains, they introduce a new class of polymeric materials. Polymerized ILs, termed poly‐ILs, are formed by repeating units of each monomer and associated through a polymeric backbone to develop a macromolecular structure [63]. Poly‐ILs can be dimers, trimers, or oligomers. Based on the application of poly‐ILs, several numbers of poly‐ILs can be synthesized by tuning the monomeric unit of ILs with some unique properties [94]. Poly‐ILs are usually synthesized by the direct radical polymerization of IL monomers. In the 1970s, Salamone et al. first synthesized poly‐ILs with vinyl imidazolium‐based ILs [66]. However, the synthesized poly‐ILs were not able to attract significant attention at the time. In the late 1990s, Ohno et al. discovered several poly‐ILs for the application of solid ion conductor materials [56]. Recently, numerous task‐specific poly‐ILs have been developed based on their applications. The foremost design efforts toward synthesizing novel poly‐ILs are based on vinylimidazolium. Further, poly‐ILs with phosphorous‐containing cations (PILs) have attracted attention in catalysis and gene delivery applications. Döbbelin and his group discovered new poly(diallyldimethylammonium TFSI) poly‐ILs with high ionic conductivities [23]. Apart from the linear poly‐ILs, researchers have focused on nonlinear or branched poly‐ILs due to their high thermal stability. Poly‐ILs are also used as photoresists, corrosion inhibitors, dispersants, and stabilizers. These branched or hyperbranched poly‐ILs are used in phase transfer systems. Tang et al. have reported several new imidazolium‐ and tetraalkylammonium‐based poly‐ILs with unique dielectric properties, mainly used as microwave‐absorbing materials [76].
Figure 1.5 Recently reported poly‐IL chemical structures.
Source: Yuan et al. [95] / Elsevier.
