Recent Advances in Ionic Liquids

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Recent advances in ionic liquids: green unconventionalsolvents of this century: part ISuresh a & Jagir S. Sandhu aa Department of Chemistry , Punjabi University , Patiala, 147002, Punjab, IndiaPublished online: 19 May 2011.

To cite this article: Suresh & Jagir S. Sandhu (2011) Recent advances in ionic liquids: green unconventional solvents of thiscentury: part I, Green Chemistry Letters and Reviews, 4:4, 289-310, DOI: 10.1080/17518253.2011.572294

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RESEARCH REVIEW

Recent advances in ionic liquids: green unconventional solvents of this century: part I

Suresh and Jagir S. Sandhu*

Department of Chemistry, Punjabi University, Patiala 147002, Punjab, India

(Received 23 October 2009; final version received 11 March 2011)

The present overview describes ionic liquids as alternate, attractive solvents of today and tomorrow in organic

synthesis. Since this subject is too wide and developments have been too fast, only a recent account is presentedon indispensable carbon-carbon bond forming named reactions such as Knoevenagel, Michael Aldol, BiginelliReaction, and so on, which has never been done before exclusively.

Keywords: ionic liquids; Aldol reaction; Knoevenagel reaction; Michael reaction; Biginelli reaction; green

chemistry

Introduction

There have been fast developments in all spheres of

our society and these are interwoven with problems

related to environmental pollution. Certainly, access

to advanced materials and their preparation processes

were great contributions to these developments (1).

A good amount of contributions to these problems

come from chemical/material developments. Thus,

overall alarming environmental pollution prompted

the government of the United States (2, 3) to issue an

act (Pollution Prevention Act, 1990). This provided

an impetus to other countries and arose worldwide

concern and in the scientists playing a significant role

in developing pollution-free methodologies/processes

(4, 5). Significant approaches are listed below:

. Supercritical liquids

. Biodegradable materials

. Catalysts selection/developments

. Biological process

. Ionic liquids

. Last but not least avoiding organic solvents

All the above areas contributed significantly to the

development (6�33) of green chemistry. Twelveprinciples of Green Chemistry were laid down by

Paul Anastas and John Warner (34) as follows:

(1) Prevention: It is better to prevent waste than to treat

or clean up waste after it has been created.

(2) Atom economy: Synthetic methods should be de-

signed to maximize the incorporation of all materials

used in the process into the final product.

(3) Less hazardous chemical syntheses: Wherever prac-

ticable, synthetic methods should be designed to use

and generate substances that possess little or no

toxicity to human health and the environment.

(4) Designing safer chemicals: Chemical products should

be designed to effect their desired function while

minimizing their toxicity.

(5) Safer solvents and auxiliaries: The use of auxiliary

substances (e.g. solvents, separation agents, etc.)

should be made unnecessary wherever possible and

innocuous when used.

(6) Design for energy efficiency: Energy requirements of

chemical processes should be recognized for their

environmental and economic impacts and should be

minimized. If possible, synthetic methods should be

conducted at ambient temperature and pressure.

(7) Use of renewable feedstocks: A raw material or

feedstock should be renewable rather than depleting

whenever technically and economically practicable.

(8) Reduce derivatives: Unnecessary derivatization (use

of blocking groups, protection/deprotection, tem-

porary modification of physical/chemical processes)

should be minimized or avoided if possible, because

such steps require additional reagents and can

generate waste.

(9) Catalysis: Catalytic reagents (as selective as possible)

are superior to stoichiometric reagents.

(10) Design for degradation: Chemical products should be

designed so that at the end of their function they

break down into innocuous degradation products

and do not persist in the environment.

(11) Real-time analysis for pollution prevention: Analyti-

cal methodologies need to be further developed to

allow for real-time, in-process monitoring and con-

trol prior to the formation of hazardous substances.

*Corresponding author. Email: [email protected]

Green Chemistry Letters and ReviewsVol. 4, No. 4, December 2011, 289�310

ISSN 1751-8253 print/ISSN 1751-7192 online

# 2011 Taylor & Francis

http://dx.doi.org/10.1080/17518253.2011.572294

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(12) Inherently safer chemistry for accident prevention:

Substances and the form of a substance used in a

chemical process should be chosen to minimize the

potential for chemical accidents including releases,

explosions, and fires.

Ionic liquids fulfill all conditions of green chemistry

required of green solvents; prominently, they are not

volatile and several of them are recyclable and do not

leave any hazardous wastes on work-up.

Ionic liquids (ILs) background

Keeping in mind the above principles of green

chemistry, ILs have attracted much attention in the

scientific community (chemists, biologists, and other

related workers) during the past two decades or so.

Here, in this mini review we are presenting recent

developments (e.g. 1999 to 2009 also if scanty work is

there deviations are made) in selected carbon-carbon

bond forming reactions such as Knoevenagel,

Michael Aldol, Biginelli Reaction, and so on. Before

we proceed further, we provide some background

information about these new solvents promoted as

future green solvents of the present century. Histori-

cally, ILs are mentioned as molten salts and this dates

back to 1914 or even before (35), when the first ionic

liquid was reported. However, its earliest use was as a

propellant in warfare specifically � ethylammoniumnitrate. Though there are no hard and fast rules layed

down, there are considered to be ionic salts sub-

stances having a melting point up to 1008C. They arecertainly advocated to have the following properties,

which have generated a voluminous body of research

(36�45):

(1) Unlike conventional solvents, they are not volatile

and do not have any vapor pressure;

(2) They are stable over a long temperature range;

(3) They can be called universal solvents, as they can

dissolve a range of organic compounds;

(4) They can dissolve even gases like H2, CO, O2, and

CO2. They can be used even under supercritical CO2;

(5) In ILs, the solubility determining factors are cations

and anions of which these are composed;

(6) They do not participate in co-ordination with metal

complexes, macrocycles like enzymes, etc;

(7) Mainly, the ionic character of ILs accelerates the

rate of reaction even under MW irradiations;

(8) They are stable and can be stored without decom-

position for a long time;

(9) ILs have found extensive use in the control of

stereoselectivity.

(10) The viscosity of ILs derived form imidazoles can be

manipulated by variations in branching.

Because of these attractive properties, ILs are

employed in a broad area of applications listed below

(46�71):

(1) Solvent extraction (46);

(2) Physico-chemical processes (47);

(3) ILs as media for nucleophilic substitution reactions(47);

(4) As mobile phase modifier in HPLC (48);

(5) Electrodeposition of metals and semiconductors inILs (49);

(6) Chemical analysis (50);

(7) Dye-sensitized solar cells (51, 52);

(8) ILs for the nuclear fuel cycle: electrodeposition andextraction (53);

(9) Nuclear-based separations (54);

(10) Oil shale processing (55);

(11) Separation of petrochemical relevance (56);

(12) Synthesis of functional nanoparticles and other

inorganic nanostructures (57);

(13) ILs as solvents for electrochemistry (58);

(14) ILs as solvents for polymerization processes (59);

(15) Chemical and biochemical transformations (60);

(16) materials chemistry (61);

(17) Biocatalysts in ILs (62�71).

There are many types of ILs available commercially

and some of these that are conveniently available

and used in organic synthesis. The following selected

classes are given below as a reference for the readers

and some of these are often used in the reactions

presented in this paper.

Ionic liquids classification

Ionic Liquids-AnionsA) Borate:I. Tetracyanoborate TCB: [B(CN)4]�

II. Tetrafluoroborate TFB: [BF4]�

III. Oxalatoborate BOB: [B(C2O4)2]�

B) Dicyanamide DCN: [N(CN)2]�

C) Halide: Br�, Cl�, F�, I�

I. Bromide: BrII. Chloride: Cl�

III. Fluoride: F�

IV. Iodide: I�

D) Bis(trifluoromethylsulfonyl)imide NTF:

[N(SO2CF3)2]�

E) Nonaflate NON: [C4H9SO3]�

F) PhosphateI. AlkylphosphateII. Fluoroalkylphosphate FAP: [(C2F5)3PF3]

�

III. Hexafluorophosphate HFP: [PF6]�

G) Sulfate HSO4: [HSO4]�, and Alkylsulfate:

[RSO4]�

290 Suresh and J.S. Sandhu

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H) SulfonateI. Methanesulfonate MSO: [CH3SO3]

�

II. Tosylate TOS: [CH3C6H4SO3]�

III. Trifluoromethanesulfonate OTF:[CF3SO3]

�

I) Thiocyanate SCN: [SCN]�

J) Tricyanomethide TCC: [C(CN)3]�

http://www.merck-chemicals.com/1-butyl-3-methylimidazolium-tricyanomethane/MDA_CHEM-490330/p_Klmb.s1OrfMAAAEj0FgLFwSw

Ionic Liquids-CationsA) Ammoniums N(R,R1,R2,R3):

N+

R1

R

R3 R2B) Guanidiniums GUA:

C NH2

NH2

NH2

+

C) Imidazoles MIM:I. Disubstituted Imidazoles

N+

NRCH3

II. Trisubstituted Imidazoles

N+

NRCH3

CH3

D) Morpholines MOEMMO:

N+

O

CH3O

CH3

E) Phosphoniums PH3T:

P+

H3C

H3C

CH3

CH3

[ ]4

[ ]4

[ ]4

[ ]12

F) Piperidines MOEMPIP:

N+

CH3O

CH3

G) Pyridiniums PYR:

N+

R R

H) Pyrrolidines MPL:

N+H3CR

I) Sulfones

S+

CH3

CH3CH3

Apart from the areas mentioned in the forgoing

pages there are special reviews and even journals

devoted to developments in organic synthesis (72�85). The authors are presenting the latest develop-

ments using ILs in the following named reactions of

organic chemistry, which has never been done by

previous reviewers exclusively. This paper also in-

cludes the authors’ own work in the area of green

chemistry

. Aldol reaction

. Knoevenagel reaction

. Michael reaction

. Biginellli and Hanstzch reaction (combination ofKnoevenagel and Michael)

. Other related ones like Doebnor modification

Aldol reaction

Among carbon-carbon bond forming reactions in

organic chemistry, the Aldol reaction (Scheme 1) is

the most popular for this process; it was discovered

by Charles-Adolphe Wurtz and A. P. Borodin

R

H

O

+MeMe

O

IL

R Me

OH O

R = Ph, 4-O2NC6H4, 2-O2NC6H4, 4-BrC6H4, 4-MeC6H4, i-Pr, 3-O2NC6H4.

Scheme 1. Simple Aldol reaction using Ils.

Green Chemistry Letters and Reviews 291

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independently in 1872 and thus have a long history(86�88). Aldol, when dehydrates, yields ab-unsatu-rated ketones called chalcones and is known as theClaisen�Schmidt reaction.In both these reactions the present authors, while

looking for greener procedures/processes, have devel-oped the use of Al(III) and Bi(III) (89). However, theuse of ILs in this reaction is of latest interest and isdiscussed below.

Knoevenagel reaction

This reaction represents an efficient way of producingcarbon-carbon double bonds and was discoveredback in 1894 by Knoevenagel (101�103). The con-ventional Knoevenagel reaction (Scheme 2) has beenreported in several reviews and monographs; how-ever, the use of ILs in this reaction is recent. In thepursuit of developing green chemistry we did makeconsiderable efforts for solvent free and also milderLewis acids catalysts developments such as LiBr,CdI2, BiCl3, KI, Alum (104�108), and so on.Evidently, these were milder processes than the earlierreported ones employing strong Lewis acids or strongorganic bases. No doubt that ILs are of currentinterest for use in this reaction and developments aregiven below.

Doebner condensation/modification

Doebner condensation is a modified version ofKnoevenagel reaction and pyridine or piperidinetype catalysts have always been used to produceunsaturated acid from aldehydes and malonic acids(Scheme 3 and 4).Evidently, these catalysts are harmful to humans.

In pursuit of green processes, the present authorsused BiCl3 as a mild catalyst (141). In IL this reaction

was used, though less studied but there are a few cases

such as this reaction, being carried (142) in ionic

liquids [Bmim]BF4 and [Bpyr]BF4 (I & II) to synthe-

size ab-unsaturated carboxylic acid.

Michael reaction

The discovery of this reaction dates back to 1883; it

was generalized by and named after Arthur Michael(143�145). The reaction is very similar to the Knoe-venagel reaction and in conventional chemistry, in

both the reactions, similar solvents and catalysts have

been employed and volumous research work reported

and both seem complementary to each other. Pre-cisely, Knoevenagel is 1-2 and Michael is 1-4 con-

jugate addition (Scheme 5) on to carbonyl and

electron deficient alkenes, respectively. In pursuit of

green chemistry, here also the authors made con-

siderable contributions in developing some environ-mentally benign protocols using non-polluting

catalysts and replacing volatile organic solvents

(VOCs) under solvent-free conditions. Already re-

ported by the authors are catalysts like BiCl3, Cu(II),

alumina, and so on (146�151), efforts to obtainsolvent-free mild catalyst are much reported by theauthors. ILs being solvents of the present, their recent

progress is given here.

Biginelli and Hanztsch reactions

Development of environmental benign protocols can

be briefly characterized as time saving, pollution

free, and reducing reaction steps (novel nomencla-

ture for these is multi-component reactions MCRs);clearly these are prominent steps toward green

chemistry. These two reactions are selected since

they are now three well-developed component reac-

tions and also they are a combination of previously

discussed two reactions, viz., Knoevenagel followedby Michael so both are tandem/cascade reactions

(Scheme 6). The following scheme presenting a

plausible reaction scheme for the Biginelli reaction

is accepted today.Here, urea, acetoacetic ester, and aldehydes are

employed (see Scheme 7) as a three component one

RCHO +EWG1

EWG2RHC

R2

R1

Cat.

-H2O

Scheme 2. Acid catalyzed Knoevenagel reaction.

OH

O

OH

O

H

O

R1

R2

R3R1

R2

R3

+H

OH

O

Cat.

Scheme 3. Base or acid catalyzed Doebner modification.


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pot synthesis. For detailed accounts of both thesereactions see the most recent accounts (161, 162).Though conventional Biginelli involves aldehydes,urea, and active methylene compounds, authorsdemonstrated that even ketones can participate inthis reaction affording unconventional Biginelli com-pounds in excellent yields (163).

As usual, organic reactions are named after their

discoverers. In conventional preparative methods of

Biginelli compounds and Hanstzch pyridines, hun-

dreds of papers have been published employing green,

mild Lewis acids. The authors made considerable

efforts in developing green process/procedures for

these reactions as well. As such, the authors made

significant contribution for finding green reactions/

protocols and demonstrated the efficacy of LiBr, Cu,

Ni, Ga(III), lactic acid, and their salts in solvent-free

conditions too (164�168). Certainly, these weremilder Lewis acids than the ones used conventionally

earlier, as there were no corrosive side products or

waste formed during aqueous work-up so these were

Scheme 4. IL catalyzed Doebner condensation.

X Y

O O

R

+ H2C EWGIL/Catalyst

O

YOC

R

EWGX

Scheme 5. Michael reaction employing a variety ofcatalysts.

I & II

NH

NH

R

O

NH

NH

O

R

H3C

H3C

H3C

H3C

OH

NH

OO

H2N

R

R'O2C

R'O2C

R CH

N+

NH2

O

H

+OR'

O O

-H2O

89

10 2

Scheme 6. A plausible reaction pathway of Biginelli reaction.

CHO

+ NH2H2N

O

CH3O

+ NH

NH

OR

R

Catalysts

Solvents

Scheme 7. Ketone instead of 1,3-dicarbonyl employed Biginelli reaction.


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greener protocols. The use of ILs in combination withmild Lewis acids is a fertile area of research andsystematic developments are given below.

Hantzsch reactions

Historically 1, 4-dihydropyridine 1 preparation isdescribed by Arthur Hantzsch more than a centuryago (190, 191). Exploration of these pyridines initiallywere quite slow, later it picked up very fast because oftheir structural resemblance to reduced nicotinamideadenine dinucleotide (NADH) 2, which is an estab-lished hydrogen transferring agent in biologicalprocesses (192). Clearly, the Hantzsch pyridines area subset of the co-enzyme 2.

NH

R

OR1

OO

R1O

Me Me

NN

N

N

N

NH2

OCH2O

OHOH

P

O

OH

O

OH

O

O

PH2C

O

H

OH

H

OH

CONH2

H H

HH H

H

1 2

These pyridines are commonly called Hantzschpyridines and the reaction is called Hantzsch reac-tion. The original synthesis reported by Hantzsch isthree components coupling reaction in refluxingethanol, which involved acetoacetic ester, benzalde-hyde, and ammonia (Scheme 8).

Evidently, the first step isKnoevenagel followed byMichael, and later on cyclization incorporating in thering system (Scheme 9). For a detailed account andmechanism see (193). Since these molecules had greatsignificance to biologists, they are taken to be privi-leged molecule of chemistry (possessing more than oneactivity) and their use in clinical practice attractedmuch attention of chemists to develop greener produc-tion process. Present authors also made effectivecontribution in this direction (194, 195). Some selectedexamples of these molecules in clinical use are pre-sented below. As such there are more than two dozendrug molecules in clinical use from this family. Need-less to say, a similar number is under developmentstage as anti-hypertensive agents (196, 197). For aselection see below:Lercanidipine(Lerdip, Recordati, Italy, 1997)Aranidipine

(Bec/Sapresta, Maruko Seiyaku, Japan, 1996)

Cilnidipine

(Cinalong or Siscard, Fujirebio, Japan, 1995)

Efonidipine Hydrochloride Ethanol

(Landel, Nissan chemical, Japan, 1994)

NH

CH3 CH3

H3CO2C

NO2

O

OCH3CH3

N

CH3

. ClH

NH

CO2CH3

CH3CH3

O

OCH3

O

NO2

NH

CH3CH3

O

OO

OMeO

NO2


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Nilvadipine

(Nivadil, Fujisawa, Japan, 1989)

Isradipine

(Prescal, Sandoz, Switzerland, 1989)

Felodipine

(Plendil, Astra, Sweden, 1988)

Nifedipine

(1977)

Naturally, because of commercial significance ofHantzsch 1,4-dihydropyridine (DHP), ILs are used

NH

Ar

OC2H5

OO

CH3H3C H3C

H5C2O H5C2O

O

O

OC2H5

CH3

O

O

+

Ar

CHO

NH4OH

1

Scheme 8. Synthesis of Hantzsch pyridine.

ArCH

O

OOO

4

Ar OO

OO

3

NH3

H2N

OO Ar

OH O

NH2

Ar OO

ONH

OC2H5

OC2H5OC2H5

OC2H5

OO

H5C2O

H5C2O

H3C

H3C

H3C

CH3

CH3

CH3

OC2H5

OC2H5

H5C2O

H5C2O

H3C

H3C

CH3

CH3

Ar

- H2O

- H2O

7

81

Scheme 9. A plausible reaction pathway of Hantzsch 1,4-dihydropyridine.

NH

O

O

CH3

CH3CH3

O

OCH3

CH3

N

O

N

NH

O

O

CH3

CH3CH3

O

OCH3

Cl

Cl

NH

NO2

CH3 CN

O

O

CH3

O

OCH3

CH3

NH

P

CH3 CH3

O

O

N

O

O

CH3

CH3

O

NO2

HCl EtOH..

NH

NO2

COOCH3H3COOC

CH3 CH3


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in this important reaction and these developments are given in Table 1:

Table 1. ILs used in DHP as catalysts or/and solvents.

Catalyst used Reaction conditions References

Without catalyst 1,1,3,3-N,N,N?,N?-tetramethylguanidiniumtrifluoroacetate, ultrasound irradiation, r.t., 1.45�2.30 h

N H2

N

NCH3

CH3

CH3

CH3+

CF3COO-

(198)

3,4,5-Trifluorobenzeneboronicacid/ InCl3

1-butyl-3-methylimidazolium chloride, r.t.

N+

NCH3 C4H10

Cl-

(199)

Without catalyst 1-n-butyl-3-methylimidazolium hexafluorophosphate or1-n-butyl-3-methylimidazolium tetrafluoroborate, r.t.,4.5�12 h

N+

NCH3 C4H10

PF6-

or

N+

NCH3 C4H10

BF4-

(200)

Without catalyst 1-methylimidazolium trifluoroacetate, r.t.

N+

NHCH3

CF3COO-

(201)

1-Butyl-3-methylimidazoliumhydroxide

N+

NCH3 C4H10

OH-

solvent-free, r.t., 0.5�1.5 h (202)

1-Butyl-3-methylimidazoliumhydroxide

N+

NCH3 C4H10

OH-

solvent-free, r.t., 0.5�4.0 h (203)

Without catalyst 1-n-butyl-3-methylimidazolium tetrafluoroborate

N+

NCH3 C4H10

BF4-

(204)


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Catalyst used

Without catalyst

Reaction conditions

1-n-butyl-3-methylimidazoliumsaccharinate

N N+

CH3 C4H9

N -

S

OO

O

References

(205)

Table 2. ILs used in Aldol reaction act as catalyst or solvent or both catalyst and solvent.


1-methyl-3-{2-[(2S)-pyrrolidine-2-carbonyloxy]-ethyl}-1H-imidazol-3-ium trifluoroacetate

N+

N

CH3

O

Pro-HCF3COO-

Solvent-free, r.t. 25 h (90)

1(R),2(R)-bis((S)-prolinamido)cyclohexane or(Rax)-2,2?-bis((S)-prolinamido)-1,1?-binaphtyl

NHNHOO

NHNH

or

1

NH

NH

O

O

NH

NH2

(1-butyl-3-methylimidazolium) tetrafluoroborate-water(1:1 v/v), 08C or 268C; 4�10 h or 20�25 h

N+

NCH3 C4H10

BF4-

. H2O

(91)

Imidazolium bis(trifluoromethylsulfonyl)imide-substituted proline and butyldimethylammoniumbis(trifluoromethylsulfonyl) imide-substituted

praline

1-butyl-3-methylimidazoliumBis(trifluoromethylsulfonyl) imide, r.t. 24 h

N+

NCH3 C4H10

N(SO2CF3)2-

(92)

Piperidine

NH

1-butyl-2,3-dimethylimidazolium tetrafluroborate, r.t.

N+

NC4H10

CH3

H3C

BF4-

(93)

Choline hydroxide Solvent-free, r.t.

(94)

Table 1. (Continued)


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Table 2 (Continued)


N-methyl-3-aminopropylated silica (NHMe�SiO2) 1-butyl-3-methylimidazolium hexafluorophosphate, r.t.

N+

NCH3 C4H10

PF6-

(95)

1-butyl-3-methylimidazolium tetrafluoroborate

N+

NCH3 C4H10

BF4-

Solvent-free, r.t. (96)

L-proline

NH

O

OHH


N+

NCH3 C4H10

BF4-

(97)

Morpholine

O

NH

1-butyl-3-methylimidazolium tetrafluoroborate,808C, 8�20 h

N+

NCH3 C4H10

BF4-

(98)

NaOH1-butyl-3-methylimidazolium hexafluorophosphate,

408C

N+

NCH3 C4H10

PF6-

(99)

Hydrotalcites 1-butyl-3-methylimidazolium hexafluorophosphate

and 1-butyl-3-methylimidazolium tetrafluoroborate,608C

N+

NCH3 C4H10

PF6-

orN

+N

CH3 C4H10

BF4-

(100)

Table 2 (Continued)

Table 3. ILs used in Knoevenagel reaction act as catalyst or solvent or both catalyst and solvent.


Hydroxyapatite-encapsulated g-Fe2O3 nanoparticlesN-(3-propyltrimethoxysilane)imidazole

Water, 308C, 1h (109)

glycine

NH2

OHO

1,3-dimethylimidazolium methyl sulfate, r.t., 100 min

N+

N

[CH3SO4]-

(110)

[H3N��CH2�CH2�OH][CH3COO_] Solvent-free, r.t. 1 h (111)


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Table 3 (Continued)


1-butyl-3-methylimidazolium imidazolide

N N+

NN

_

Water, r.t. 20 min (112)

Tri-(2-hydroxyethyl)ammonium acetate

N+

O-

O

OH

OH

OH

Tri-(2-hydroxyethyl) ammonium acetate, 808C, ½ h (113)

1-butyl-3-methylimidazolium hexafluorophosphatewith alkali metal hydroxide

N+

NCH3 C4H10

PF6-

. KOH or NaOH

Ethanol, r.t. 6 h (114)

Methoxyl propylamine acetate Solvent-free, 508C, 3�8 h (115)1-butyl-3-methyl imidazolium hydroxide

N+

NCH3 C4H10

HO-

Water, r.t. (116)

Metal carbonate 1-butyl-3-methylimidazolium hexafluorophosphate or1-butyl-3-methylimidazolium bromide- benzene

N+

NCH3 C4H10

PF6-

or

N+

NCH3 C4H10

Br-

.C6H6

(117)

Hexadecyltrimethyl ammonium chloride andethylmethyl imidazolium chloride

N+

C10H25

CH3

CH3

CH3

Cl- N+

NCH3

CH3

Cl-

Tetrahydrofuran, 808C, 12 h (118)

Hydrotalcites or without this catalyst

1-butyl-3-methylimidazolium hexafluorophosphate and1-butyl-3-methylimidazolium tetrafluoroborate, r.t.

N+

NCH3 C4H10

PF6-

or N+

NCH3 C4H10

BF4-

(119)

Glycine

NH2

OHO

see IL, 45�558C, 22 h (120)


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Table 3 (Continued)


1-butyl-3-methyl imidazolium hydroxide

N+

NCH3 C4H10

HO-

CH3CN, r.t. 10�15 h (121)

1-butyl-3-methyl imidazolium hydroxide

N+

NCH3 C4H10

HO-

Solvent-free r.t. (122)

Hunig’s base tethered ammonium ionic liquids

N+

CH3

CH3

CH3

O

N

CH3

CH3

CH3

CH3

n

Solvent-free, 30 min. r.t. (123)

Potassium carbonate KCO3 1-n-butyl-3-methylimidazolium bromide, MWI

N+

NCH3 C4H10

Br-

(124)

1-methyl-3-(3-triethoxysilylpropyl imidazoliumchloride

Solvent-free, r.t. h; 1208C (125)

1-butyl-3-methylimidazolium hydroxide

N+

NCH3 C4H10

HO-

Solvent-free, r.t. 10�30 min (126)

L-proline

NH

O

OHH

1-n-butyl-3-methylimidazolium tetrafluoroborate,

12�48 h, 508C(127)

1-n-butyl-3-methylimidazolium tetrafluoroborate

N+

NCH3 C4H10

BF4-

Solvent-free, MWI/grinding, r.t. (128)

1-aminoethyl-3-methylimidazolium hexafluoropho-sphate

N+

NCH3 NH2

PF6-

Water, r.t. (129)

Table 3 (Continued)


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Table 3 (Continued)


Piperidine

NH

1-ethyl-3-methylimidazolium tetrafluoroborate,CH3COOH, r.t.

N+

NCH3

BF4-

(130)

Without catalyst 1-methylimidazolium trifluoroacetate, r.t. 4�30 min

N+

NHCH3

CF3COO-

(131)

Without catalyst Ethylammonium nitrate, r.t. (132)

Piperidine

NH

1-butyl-3-methylimidazolium tetrafluoroborate, r.t.

N+

NCH3 C4H10

BF4-

(133)

1-hexyl-3-methylimidazolium tetrafluoroacetate

N+

NCH3 C6H15

CF3COO-

Solvent-free (134)

2-hydroxyethylammonium acetate

N+

H

H

H

OH

CH3COO-


Without catalyst Ethylammonium nitrate, r.t. (136)

Without catalyst EAN, 1-butyl-3-methylimidazolium hexafluoropho-sphate and 1-butyl-3-methylimidazolium tetrafluorobo-

rate, r.t.

N+

NCH3 C4H10

PF6-

& N+

NCH3 C4H10

BF4-

(137)

1,1,3,3-tetramethylguanidium lactate

N H2

N

NCH3

CH3

CH3

CH3+

Lac-

Solvent-free (138)

Table 3 (Continued)


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Table 3 (Continued)


NaOMe 1-butyl-3-methylimidazolium hexafluorophosphate,3�4.5 h 958C

N+

NCH3 C4H10

PF6-

(139)

GaCl3 Triethylammonium acetate (TEAA), 658C, 30�45 min (140)

Table 4. ILs used in Michael reaction act as catalyst, solvent, or both.


(S)-pyrrolidine sulfonamide

NH

NHS

N+

N

O

O

CH3

CH3

BF4-

Isopropyl alcohol, r.t. (152)

Copper nanoparticles 1-H-tetrazole-5-acetic acid, r.t., 5�15 min

N

N

N+

N

NC

CH3

OH

O

Br -

(153)

Triethylammonium acetate (TEAA) Solvent-free, 258C, 1�20 min (154)

Piperidine

NH

Ionic liquid, r.t. 2 h

N+

NCH3 C2H5

ETSO4-

(155)

N-methylimidazole

N

N

CH3

Imidazolium-based ILs, r.t. (156)

Table 3 (Continued)


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Table 4 (Continued)


Pyrrolidine-based functionalized chiral ionic liquids

N N+

SNH

CH3

O

O

NH

NTf2 -

Methanol, r.t. 3 days (157)

Pyrrolidine-based chiral pyridinium ionic liquids

NH

N+

X-

X = BF4, PF6, NTf2

Solvent-free, 16�48 h, 48C (158)

1-methyl-3-butylimidazolium hydroxide

N+

NCH3 C4H10

HO-

Solvent-free (159)

Metal carbonate 1-butyl-3-methylimidazolium hexafluorophosphate and1-butyl-3-methylimidazolium bromide � benzene

N+

NCH3 C4H10

PF6-

&

N+

NCH3 C4H10

Br-

.C6H6

(160)

Table 4 (Continued)

Table 5. ILs used in Biginelli reaction act as catalyst, solvent, or both.


1-butyl-3-methylimidazolium FeCl4

N+

NCH3 C4H10

FeCl4-

Solvent-free, 908C,2�3 h

(169)

L-prolinium sulfate

N+ O

OHH

HHSO3-

Tetrahydrofuran, r.t.21�30 h

(170)


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Table 5 (Continued)


1-hexyl-3-methylimidazolium HSO4

N

N

CH3

Solvent-free, r.t.15�55 min

(171)

Task-specific ionic liquids

N+

R

R

R

SO3H

A-

Solvent-free, 908C,10�15 min

(172)

1-butyl-3-methyl-imidazolium hydrogen sulfate

N+

NCH3 C4H10

HSO4-

Solvent-free, MWI,1408C, 4.4�8 min

(173)

1-butyl-3-methylimidazolium tetrafluoroborate immobilized Cu(acac)2

N+

NCH3 C4H10

BF4-

. Cu(acac)2

Solvent-free, 508C (174)

1-n-butyl-3-methylimidazolium saccharinate

N N+

CH3 C4H9

N -

S

OO

O


Alkylammonium and alkylimidazolium perhaloborates, phosphates,and aluminates

N+

NCH3 Bu

A-

I

N+

N

CH3

CH3 Bu

II

NET3

+A-

A-

III

Et3NH+ A-

Bu4N+ PF6 -

IV

V

A = BF4 -, PF6 -, AlCl4, Al2Cl7

Solvent-free, 1208C,1 h

(176)


N+

NCH3 C4H10

BF4-

Solvent-free (177)

1-methylimidazolium hydrogen sulfate, 1-methylimidazolium trifluoroacetate

N+

NH CH3

HSO4-

, N+

NH CH3

CF3COO-

Solvent-free, 40�90 min,508C

(178)


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Table 5 (Continued)


1-butyl-3-methyl-imidazolium hydrogen sulfate

N+

NCH3 C4H10

HSO4-


Polymer-supported IL

N+

NCH3

.

.n

X-

X = BF4 -, PF6 -

Acid Acetic, 2�4 h 1008C (180)

1-butyl-3-methylimidazolium hexafluorophosphate and


N+

NCH3 C4H10

PF6-

,N

+N

CH3 C4H10

BF4-


1-butyl-3-methylimidazolium chloride 2AlCl3

N+

NCH3 C4H10

Cl-

.2AlCl3


1-n-butylimidazolium tetrafluoroborate

N+

NH C4H10

BF4-

Ultrasound, 40�90 min,308C

(183)

1-butyl-3-methylimidazolium hexafluorophosphate and


N+

NCH3 C4H10

PF6-

,N

+N

CH3 C4H10

BF4-

Solvent-free (184)


N N+

CH3 C4H9

N -

S

OO

O



N N+

CH3 C4H9

N -

S

OO

O

Solvent-free (186)

Table 5 (Continued)


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Conclusions

Ionic liquids are well-known alternative solvents

replacing VOCs, but still some questions remain to

be satisfactorily answered by readers and actual

practioners. Are these really non-toxic recyclable

and economically viable alternatives to VOCs used

specifically in industrial processes? The future of

these solvents seems to be very bright in view of

human health and climate change. Certainly, much

more is needed to be done to see them as really viable

alternatives, in spite of a large number of research

studies being published. ILs hold a very bright future

in various fields of sciences. In this presentation, the

authors have made every effort to be precise and if in

this attempt, unknowingly, any author’s fruitful work

is left out, this is sincerely regretted.

Acknowledgements

Authors wish to thank the Council of Scientific and

Industrial Research (CSIR), New Delhi, India and Indian

National Science Academy (INSA), New Delhi, India for

financial support for this research project.

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