Supramolecular polymeric aggregation behavior and its impact on catalytic properties of imidazolium based hydrophilic ionic liquids

Article abstract of DOI:10.1016/j.molliq.2019.112372

Ionic Liquids (ILs) self-assemble to form supramolecular polymeric clusters/aggregates. The aggregation behavior of ILs influences its activity in the organic synthesis. However, the precise role of ILs in organic reactions is still unknown. It is, therefore, important to comprehend the supramolecular polymeric aggregation behavior of ILs. We are exploring the supramolecular polymeric aggregation behavior of ILs using Electrospray Ionization Mass Spectrometry (ESI-MS). We have synthesized four hydrophilic ILs (1–4) and investigated their aggregation behavior and its impact on catalytic activity in Carbon-Carbon bond formation (Knoevenagel and Claisen-Schmidt condensation). Here, we show that the aggregation behavior of ILs depends on the type and nature of cation and anion. ESI-MS (?ve) spectra reveals two different type of aggregation i.e. [C_nA_n+1]^? & [A₂ + H⁺]^?. We have found that catalytic activity increases with increased [C_nA_n+1]^? supramolecular aggregation. Consequently, highest yield of products obtained in ILs which show decreased anion-anion aggregation [A₂ + H⁺]^? abundance in ESI-MS. We anticipate our results to be a starting point for the establishment of desired ILs for organic synthesis.

Full text of DOI:10.1016/j.molliq.2019.112372

Journal Pre-proof
Supramolecular polymeric aggregation behavior and its impact
on catalytic properties of imidazolium based hydrophilic ionic
liquids
Shoaib Muhammad, Muhammad Naveed Javed, Firdous Imran
Ali, Ahmed Bari, Imran Ali Hashmi
PII:
S0167-7322(19)35991-4
DOI:
https://doi.org/10.1016/j.molliq.2019.112372
MOLLIQ 112372
Reference:
To appear in:
Journal of Molecular Liquids
Received date:
Revised date:
Accepted date:
31 October 2019
14 December 2019
23 December 2019
Please cite this article as: S. Muhammad, M.N. Javed, F.I. Ali, et al., Supramolecular
polymeric aggregation behavior and its impact on catalytic properties of imidazolium
based hydrophilic ionic liquids, Journal of Molecular Liquids(2019), https://doi.org/
1
0.1016/j.molliq.2019.112372
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©
2019 Published by Elsevier.

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Cover Letter
Imran Ali Hashmi
University of Karachi,
Main University Road,
Karachi 75270,
iahashmi@uok.edu.pk
Dear Editor-in-Chief
Journal of Molecular Liquids
Thank you for giving us the opportunity to submit a revised draft of the manuscript “Supramolecular
polymeric aggregation behavior and its impact on catalytic properties of imidazolium based hydrophilic
ionic liquids” for publication in the Journal of Molecular Liquids. We appreciate the time and effort that
you and the reviewers dedicated to providing feedback on our manuscript and are grateful for the
insightful comments on and valuable improvements to our paper. We have incorporated all the
suggestions made by the reviewers. Those changes are highlighted in green (Reviewer 1) and yellow
(
Reviewer 2) within the manuscript.
We hope that you find our responses satisfactory and that the manuscript is now acceptable for
publication.
Sincerely,
Imran
Imran Ali Hashmi, PhD
Assistant Professor, Department of Chemistry,
University of Karachi.
1

Journal Pre-proof
Response to Reviewers
Imran Ali Hashmi
University of Karachi,
Main University Road,
Karachi 75270,
iahashmi@uok.edu.pk
Editor-in-Chief
Journal of Molecular Liquids
Dec 15, 2019
Dear Editor-in-Chief:
Manuscript reference No. MOLLIQ_2019_5775
Thank you for giving us the opportunity to submit a revised draft of the manuscript “Supramolecular
polymeric aggregation behavior and its impact on catalytic properties of imidazolium based hydrophilic
ionic liquids” for publication in the Journal of Molecular Liquids. We appreciate the time and effort that
you and the reviewers dedicated to providing feedback on our manuscript and are grateful for the
insightful comments on and valuable improvements to our paper. We have incorporated all the
suggestions made by the reviewers. Those changes are highlighted in green (Reviewer 1) and yellow
(
Reviewer 2) within the manuscript.
Suggestion, Question,
or Comment from the
Editor
Author’s Response
Change in the Manuscript
In observance of editor following
changes has been done
1
. Introduce page and line We truly appreciate the Editor’s
numbers in the ms file.
suggestion, and we revise our
2
. Highlight in color the
manuscript according to the

Introduce page and line
numbers in the
changes made according editor suggestions and
to the reviewers
comments.
comments.
manuscript

Highlight in color the
changes made according
to the reviewer’s
In the reply letter to the
reviewers,
comments, green for

Reproduce the
(
Reviewer 1) and yellow
individual reviewers
comments, followed by
your response.
(Reviewer 2)

Indicate page and line
numbers where changes
in the ms were done.
2

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Suggestion, Question,
or Comment from
Reviewer #1
Author’s Response
Change in the Manuscript
On page 5, line 3 – 6 of the
submitted form of the
manuscript, the following
comments was revise and
incorporate to the Highlights
section of the manuscript.
1
. The research highlights
should be shortened
We completely agree with the
comments made by the
Reviewer.
This comment was revise and
incorporate to the Highlights
section of the manuscript.
2
. Some of ESI-MS pictures We completely agree with the
can be moved to suggestions made by the
supporting information. Reviewer.
This suggestion was revise and
ESI-MS positive mode (figure 1a
– 4a) of ILs 1 – 4 moves to
supporting information from
main manuscript. Therefore,
supporting information is also
revise. Figure 1a – 4a reference
use in the manuscript so
incorporate to the manuscript
and Supporting Information as
well.
following changes occurred,
Page 20 line # 23 & 24, page 21
line # 5, page 22 line # 4 and
page 23 line # 4.
3
. What is the comparisons We completely agree with the
This question was address and
of catalytic activity for
ILs catalyst and non-ILs
catalyst?
question made by the Reviewer. incorporate to main manuscript
We compare the catalytic
activity of ILs with some other
and highlighted with green color
at page 30 (line # 4 – 12 & Table
non ILs catalyst for Knoevenagel 4)
and Claisen-Schmidt
condensation
Suggestion, Question,
or Comment from
Reviewer #2
Author’s Response
Change in the Manuscript
On page 24, line # 14 of the
submitted form of the
manuscript, the following
question was addressed and
incorporate to the manuscript.
1
. What the exact role of
We completely agree with the
the ILs in the reactions? question made by the Reviewer.
phase-transfer catalysis
This question was addressed
or organic base
and incorporate to the results
and discussion section of the
manuscript.
(
benzoates)?
On page 11, line # 1 & page 12
line # 5 of the submitted form of
the manuscript, the following
question was addressed and
incorporate to the manuscript.
2
. keep the integers of IR
experiment data;
We completely agree with the
suggestions made by the
Reviewer.
This suggestion was revise and
incorporate to the manuscript.
3

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3
. The integrals of H NMR
spectrum of ILs are not
consistent with the
number of hydrogen
number. Please revised
them
We completely agree with the
question made by the Reviewer. incorporate to main manuscript
This question was addressed
and incorporate to the
Experimental section of the
manuscript.
This question was address and
and highlighted with yellow
color at page 11 line # 4 & 22
and page 12 line # 8 & 27
We hope that you find our responses satisfactory and that the manuscript is now acceptable for
publication.
Sincerely,
Imran
Imran Ali Hashmi, PhD
Assistant Professor, Department of Chemistry,
University of Karachi.
4

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Research Highlights
1
2
3
4
. Imidazolium based hydrophilic ILs containing benzoates as anion
. Aggregation behavior of ILs showing cation-anion & anion-anion aggregations
. Catalytic potential depends upon availability of anion-anion aggregation
. Catalytic activity exhibit inverse relationship with anion-anion aggregation
5

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Referee suggestions
Professor Tom Welton
Department of Chemistry, Imperial College London, South Kensington Campus, London SW7
AZ, United Kingdom
2
t.welton@imperial.ac.uk
Professor Douglas MacFarlane
School of Chemistry and ARC Centre of Excellence for Electromaterials Science, Monash
University, Clayton, Victoria 3800, Australia
Douglas.MacFarlane@monash.edu
Professor Diego A. Alonso
Department of Organic Chemistry and Institute of Organic Synthesis (ISO), Faculty of
Sciences, University of Alicante, PO Box 99, 03080 Alicante, Spain
diego.alonso@ua.es
6

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Supramolecular polymeric aggregation behavior and its impact on catalytic
properties of imidazolium based hydrophilic ionic liquids
a
a
a
b
Shoaib Muhammad , Muhammad Naveed Javed , Firdous Imran Ali , Ahmed Bari , Imran Ali
a *
Hashmi ,
a
Department of Chemistry, University of Karachi, Main University Road, Karachi - 75270,
Sindh, Pakistan.
b
Department of Pharmaceutical Chemistry, College of Pharmacy, King Saud University, P.O.
Box 2457, Riyadh 11451, Saudi Arabia.
*
Corresponding author, e-mail: iahashmi@uok.edu.pk
Abstract:
Ionic Liquids (ILs) self-assemble to form supramolecular polymeric clusters/aggregates. The
aggregation behavior of ILs influences its activity in the organic synthesis. However, the precise
role of ILs in organic reactions is still unknown. It is, therefore, important to comprehend the
supramolecular polymeric aggregation behavior of ILs. We are exploring the supramolecular
polymeric aggregation behavior of ILs using Electrospray Ionization Mass Spectrometry (ESI-
MS). We have synthesized four hydrophilic ILs (1-4) and investigated their aggregation behavior
and its impact on catalytic activity in Carbon-Carbon bond formation (Knoevenagel and Claisen-
Schmidt condensation). Here, we show that the aggregation behavior of ILs depends on the type
and nature of cation and anion. ESI-MS (-ve) spectra reveals two different type of aggregation
-
+ -
i.e. [C A ] & [A + H ] . We have found that catalytic activity increases with increased
n
n+1
2
-
[
C A ] supramolecular aggregation. Consequently, highest yield of products obtained in ILs
n n+1
+
-
which show decreased anion-anion aggregation [A + H ] abundance in ESI-MS. We anticipate
2
our results to be a starting point for the establishment of desired ILs for organic synthesis.
Keywords: Ionic Liquids; Supramolecular aggregation; ESI-MS; Catalysis; Knoevenagel
condensation; Claisen-Schmidt condensation.
7

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1
. Introduction
Ionic Liquids (ILs), as a class of molten salts, are composed entirely of ions and their melting
point is around or below 100 °C [1-4]. ILs exhibit unique physiochemical properties that make
them potential candidates for many applications in industry and academia [5]. ILs can help in
controlling environmental pollution due to their thermally stable and non-flammable character
with negligible vapor pressure [6, 7]. ILs can be used as a solvent in multiphasic catalytic
reactions due to their tunable solvation properties and adjustable miscibility with organic
substrates [8]. ILs can promote re-cyclization and polar/ionic catalyst through immobilization
[
9]. The unique ionic environment of ILs stabilizes reaction intermediates, resulting in improved
catalytic activities as compared to traditional volatile organic solvents [10]. Use of ILs as a
reaction medium in catalytic reaction has been reported in literature, including two-phase
catalysis, transition metal catalysis, nanoparticle catalysis and biocatalysts [1, 9, 11-13].
In recent years, the role of ILs as a catalyst instead of reaction media or catalyst support has been
investigated in many organic reactions, including Hydrogenation [14], Hydroformylation [15],
Pyrano[2,3-d]pyrimidine derivatives [16], 2-amino-4-arylquinoline-3-carbonitrile derivatives
[
17], Knoevenagel condensation [4], Friedel Craft reaction [18], Wittig reaction [19], Stille
reaction [20] and so on. Although, Boon, Levisky, Pflug and Wilkes [21] first time reported
catalytic activity of ILs in 1986. They used dialkylimidazolium chloroaluminate, as a catalyst in
Friedel-Crafts acylation [21]. This was followed by the first generation pioneering ILs like 1-
+
-
butyl-3-methylimidazolium
hexafluorophosphate
([BMIM ][PF ])
and
1-butyl-3-
6
+
-
methylimidazolium tetrafluoroborate [BMIM ][BF ] [22]. These ILs suffer with some
4
-
-
environmental disadvantages. PF and BF anions are susceptible hydrolyze in the presence of
6
4
water to produce toxic HF and/or fluorides [23]. The disposal of these fluorides is expensive and
problematic. Consequently, some groups have used benzoates as alternative anions to avoid toxic
halogenated anions and to customize physical properties [24]. In view of the above-mentioned
facts, further exploration of the role of ILs as catalysts in the organic transformations may
provide advances in greener technologies for a variety of industrial applications.
8

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The Carbon-Carbon bond formation is an important class of reactions in organic synthesis [25].
The Knoevenagel and Claisen-Schmidt condensation reactions are the widely used methods for
the preparation of Carbon-Carbon bond formation [26]. The products of these condensations
have significant pharmacological and biological applications including anti-angiogenesis, anti-
inflammatory and anti-cancer activities [27-29]. Hence, biological importance of these
compounds has attained vital attention from different medicinal and pharmaceutical industry.
Therefore, numerous synthetic protocols are described with the aim of finding more effective
approach using different materials. But, limitations of these protocols include difficult work‐up,
poor yields and toxic elements [30]. The advancement of environmentally friendly and efficient
protocols for the synthesis of Knoevenagel condensation and Claisen-Schmidt condensation and
their derivatives is still an important task in synthetic chemistry.
Herein, we report the synthesis and characterization of four hydrophilic imidazolium benzoates
based ILs. Furthermore, this work is in continuation of our previous study to establish
relationship between supramolecular aggregation behavior and its effect on catalytic activity of
ILs in the organic synthesis [4]. Many microscopic and spectroscopic techniques are reported in
literature to probe supramolecular polymeric aggregation but in this study, we have used ESI-MS
for analyzing the aggregation behavior due to non-covalent interactions between ions in ILs.
ESI-MS has advantage over other techniques in terms of high sensitivity, specificity, good mass
accuracy, little amount of sample is required for analysis and preserving solution phase
information in gaseous phase etc. Furthermore, ESI-MS is the ultimate method of choice for
direct analysis of non-volatile and ionic compounds. It is also called softest ionization and this
feature is considered as disadvantage due to little information of fragmentation, but this will be
overcome through ESI-MS-MS analysis.
2
2
. Methods and Materials
.1. General
9

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Dried glassware has been used to carry out all reactions. All chemicals were purchased from
Sigma-Aldrich Company and verified via TLC and FTIR techniques. Thin Layer
Chromatography (TLC) was performed by pre-coated aluminium plates, Kieselgel 60, F254,
0
.25mm, e. Merck, Darmstadt, Germany. Chromatograms were detected by UV 254 nm and
iodine tank. Solvents were evaporated under vacuum on rotary evaporator with a water bath
temperature below 40 °C. FTIR recorded on Fourier Transformed Spectrophotometer by
H
Shimadzu. ESI-MS was performed on AB SCIEX QSTA R XL LCMSMS Q-Tof (P 3.2,
1
13
acetonitrile:water 1:1). H NMR and C NMR were obtained from AVANCE AV-300,
AVANCE AV-500 CRYOPROBE and BRUKER. Melting Point was taken in Stuart Digital
Melting Apparatus SMP 10.
2
.2. Synthesis of 1-Hexyl-3-methylimidazolium bromide
A flask was charged with a solution of 1-methylimidazole (29.4 mmol) in 10 mL
dichloromethane (DCM). The flask was cooled with ice bath and 29.4 mmol of 1-bromohexane
was added dropwise. Ice bath was removed, and the solution was stirred about 15 min at room
temperature. The solvent was then evaporated in vacuo. A colorless liquid was obtained, and the
yield of product is 99.87 %. The spectral data of the product is in accordance with that of
reported in literatures [24].
2
.3. General Method (GM-I) for Ion-exchange metathesis (1-4)
In a two-necked round bottom flask a mixture of 1-hexyl-3-methylimidazolium bromide (19
mmol), sodium bicarbonate (22 mmol), and respective benzoic acid (20 mmol) in 12 mL water.
The solution is stirred for 30 min. Water was then evaporated, followed by addition of cold
ethanol. Ethanol is decanted and evaporated to obtain a pure product leaving behind inorganic
salt.
2
.3.1. Synthesis of 1-hexyl-3-methylimidazolium 2-hydroxybenzoate (1)
1
0

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The IL 1 is obtained by according to GM-I. The pure product is wax-like, light-yellow and
highly hygroscopic in nature. Yield is 95.43 %.
-1
IR max KBr cm : 3437.0 (H O), 3149.1, 3093.4 (aromatic C-H stretching), 2956.3, 2932.4,
2
2
861.5 (aliphatic C-H stretching), 1627.7 (C=O), 1574.4 (C=N), 1458.2 (C=C), 1388.2 (C-O),
166.1 (C-C).
1
1
H-NMR (DMSO-d , 500 MHz)  ppm: 16.17 (s, 1H), 9.21 (s, 1H), 7.79 (s, 1H), 7.72 (s, 1H),
6
7
.68 (s, 1H), 7.13 (s, 1H), 6.61 (s, 2H), 4.16 (s, 2H), 3.86 (s, 3H), 1.77 (s, 2H), 1.26 (s, 6H), 0.86
(s, 3H).
1
3
C-NMR (DMSO, 125 MHz)  ppm: 172.25, 163.23, 137.03, 131.82, 130.43, 124.06, 122.72,
1
20.87, 116.42, 116.22, 49.22, 36.21, 31.00, 29.80, 25.60, 22.32, 14.29.
+
2
+
HR-ESI-MS +ve calcd. for C H N m/z 139.1235, found m/z 139.1266; calcd. for C H N
8
15
10 19
2
-
m/z 167.1548, found m/z 167.1545; HR-ESI-MS -ve calcd. for C HO m/z 92.9976, found m/z
5
2
-
-
9
2
3.0298; calcd. for C H O m/z 137.0238, found m/z 137.0135; calcd. for [C H O +H] m/z
7 5 3 14 10 6
-
75.0555, found m/z 275.0598; calcd. for [C H O +Na] m/z 297.0375, found m/z 297.0318;
14
10
6
-
-
calcd. for C H N O m/z 441.2025, found m/z 441.2008; calcd. for C H N O m/z 745.3812,
2
4
29
2
6
41 53
4
9
found m/z 745.3772.
2
.3.2. Synthesis of 1-hexyl-3-methylimidazolium 2-aminobenzoate (2)
The IL 2 is obtained by according to GM-I. The pure product is wax-like brown and hygroscopic
in nature. Yield is 95.71%.
-1
IR max KBr cm : 3432.2 (H O), 3146.8, 3085.1 (aromatic C-H stretching), 2956.6, 2931.3,
2
2
860.3 (aliphatic C-H stretching), 1612.2 (C=O), 1574.2 (C=N), 1464.2 (C=C), 1376.3 (C-O),
166.4 (C-C).
1
1
H-NMR (DMSO-d , 500 MHz)  ppm: 9.28 (s, 1H), 7.7952 (s, 1H), 7.74 (t, 2H), 6.96 (t, 1H),
6
6
.53 (d, 2H), 6.38 (t, 2H), 4.17 (t, 2H), 3.86 (s, 3H), 1.77 (s, 2H), 1.26 (s, 6H), 0.862 (s, 3H).
1
3
C-NMR (DMSO, 125 MHz)  ppm: 172.87, 150.64, 137.13, 132.17, 130.28, 124.04, 122.71,
1
20.52, 115.60, 114.16, 49.20, 36.19, 31.01, 29.82, 25.61, 22.33, 14.30.
+
HR-ESI-MS +ve calcd. for C H N m/z 167.1548, found m/z 167.1534; HR-ESI-MS -ve
1
0
19
2
-
-
calcd. for C H N m/z 92.0500, found m/z 92.0490; calcd. for C H NO m/z 136.0398, found m/z
6
6
7
6
2
-
1
36.0357; calcd. for [C H N O +H] m/z 273.0875, found m/z 273.0911; calcd. for
14 12 2 4
1
1

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-
-
[
C H N O +Na] m/z 295.0694, found m/z 295.0712; calcd. for C H N O m/z 439.2345,
14 12 2 4 24 31 4 4
-
found m/z 439.2368; calcd. for C H N O m/z 742.4292, found m/z 742.3151.
4
1
56
7
6
2
.3.3. Synthesis of 1-hexyl-3-methylimidazolium 4-hydroxybenzoate (3)
The IL 3 is obtained by according to GM-I. The pure product is waxy yellow and hygroscopic in
nature. Yield is 95.69%.
-1
IR max KBr cm : 3433.8 (H O), 3145.1, 3083.2 (aromatic C-H stretching), 2956.1, 2930.8,
2
2
861.1 (aliphatic C-H stretching), 1528.4 (C=O), 1569.7 (C=N), 1422.2 (C=C), 1378.0 (C-O),
167.4 (C-C).
1
1
H-NMR (DMSO-d , 500 MHz)  ppm: 9.31 (s, 1H), 7.7 (m, 4H), 6.69 (d, 2H), 4.15 (d, 2H),
6
3
.85 (s, 3H), 3.64 (s, 1H), 1.75 (m, 2H), 1.24 (s, 6H), 0.84 (s, 3H).
1
3
C-NMR (DMSO-d , 125 MHz)  ppm: 171.31, 159.55, 137.13, 131.17, 130.60, 124.02,
6
1
22.69, 114.36, 49.20, 36.18, 31.00, 29.82, 25.60, 22.32, 14.29.
+
2
+
HR-ESI-MS +ve calcd. for C H N m/z 139.1235, found m/z 139.1243; calcd. for C H N
2
8
15
10 19
-
m/z 167.1548, found m/z 167.1515; HR-ESI-MS -ve calcd. for C H O m/z 137.0238, found m/z
7
5
3
-
-
1
37.0173; calcd. for [C H O +H] m/z 275.0555, found m/z 275.0549; calcd. for C H NaO
14 10 6 14 10 6
-
m/z 297.0375, found m/z 297.0561; calcd. for [C H NaO +H] m/z 435.0692, found m/z
21
15
9
-
-
4
35.0700; calcd. for C H Na O m/z 457.0511, found m/z 457.0523; calcd. for C H N NaO
21 15 2 9 31 34 2 9
-
m/z 601.2162, found m/z 601.2168; calcd. for [C H N NaO +H] m/z 739.2478, found m/z
39
39
2
12
-
-
7
39.2452; calcd. C H N Na O m/z 761.2298, found m/z 761.2301; calcd. for C H N NaO
38 39 2 2 12 48 58 4 12
m/z 905.3948, found m/z 905.3909.
2
.3.4. Synthesis of 1-hexyl-3-methylimidazolium 4-aminobenzoate (4)
The IL 4 is obtained by according to GM-I. The Pure product is a waxy light-yellow,
hygroscopic material in nature. Yields are 95.19%.
-1
IR max KBr cm : 3411.1 (H O), 3150.3, 3092.0 (aromatic C-H stretching), 2956.9, 2932.1,
2
2
861.8 (aliphatic C-H stretching), 1601.8 (C=O), 1574.2 (C=N), 1465.4 (C=C), 1378.0 (C-O),
170.1 (C-C).
1
1
H-NMR (DMSO-d , 500 MHz)  ppm: 9.37 (s, 1H), 7.7 (m, 4H), 6.45 (d, 2H), 5.25 (s, 2H),
6
4
.16 (t, 2H), 3.85 (s, 3H), 1.73 (m, 2H), 1.24 (m, 6H), 0.85 (t, 2H).
1
2

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1
3
C-NMR (DMSO-d , 125 MHz) ppm: 171.57, 150.32, 138.34, 137.13, 131.02, 128.72,
6
1
27.10, 123.99, 122.67, 120.97, 112.71, 49.20, 36.17, 33.24, 31.00, 29.83, 25.59, 22.32, 14.29.
+
+
2
HR-ESI-MS +ve calcd. for C H N m/z 138.1282, found m/z 138.0418; calcd. For C H N
9
16
10 19
-
m/z 167.1548, found m/z 167.1307; HR-ESI-MS -ve calcd. for C H N m/z 92.0500, found m/z
6
6
-
-
9
2.0488; calcd. for C H NO m/z 136.0398, found m/z 136.0351; calcd. for [C H N O +H]
7 6 2 14 12 2 4
-
m/z 273.0875, found m/z 273.0899; calcd. for [C H N O +Na] m/z 295.0694, found m/z
14
12
2
4
2
95.0693.
2
.4. General Method (GM-II) for Knoevenagel Condensation (5-19)
To a mixture of malononitrile (9.83 mmol) and aldehyde (9.83 mmol) was added a suitable
amount of water in the presence of catalytic amount of IL 1 (4% mol) under ultrasound
irradiation (Table 2). The solid products were obtained within a minute and separated by
filtration and then washed with water. The crude product was recrystallized in 95% ethanol to
give pure product. All compounds were previously reported and were characterized through
comparison of spectral data with that of reported literature.
2
.4.1. Synthesis of 2-benzylidenemalononitrile (5)
The product 5 was obtained by according to GM-II. Yield 98.86 %, m.p. 84 °C. The product was
characterized through comparison of spectral data with that of reported literature [31]
2
.4.2. Synthesis of 2-(2-hydroxybenzylidene)malononitrile (6)
The product 6 was obtained by according to GM-II. Yield 99.01 %, m.p. 160 °C. The product
was characterized through comparison of spectral data with that of reported literature [31]
2
.4.3. Synthesis of 2-(3-hydroxybenzylidene)malononitrile (7)
The product 7 was obtained by according to GM-II. Yield 96.76 %, m.p. 152 °C. The product
was characterized through comparison of spectral data with that of reported literature [32]
1
3

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2
.4.4. Synthesis of 2-(4-hydroxybenzylidene)malononitrile (8)
The product 8 was obtained by according to GM-II. Yield 96.93 %, m.p. 196 °C. The product
was characterized through comparison of spectral data with that of reported literature [33]
2
.4.5. Synthesis of 2-(3,4-dihydroxybenzylidene)malononitrile (9)
The product 9 was obtained by according to GM-II. Yield 98.05 %, m.p. 225 °C. The product
was characterized through comparison of spectral data with that of reported literature [34]
2
.4.6. Synthesis of 2-(3-methoxybenzylidene)malononitrile (10)
The product 10 was obtained by according to GM-II. Yield 97.48 %, m.p. 106 °C. The product
was characterized through comparison of spectral data with that of reported literature [32]
2
.4.7. Synthesis of 2-(3-hydroxy-4-methoxybenzylidene)malononitrile (11)
The product 11 was obtained by according to GM-II. Yield 97.51 %, m.p. 250 °C. The product
was characterized through comparison of spectral data with that of reported literature [34]
2
.4.8. Synthesis of 2-(4-hydroxy-3-methoxybenzylidene)malononitrile (12)
The product 12 was obtained by according to GM-II. Yield 98.44 %, m.p. 135 °C. The product
was characterized through comparison of spectral data with that of reported literature [31]
2
.4.9. Synthesis of 2-(4-chlorobenzylidene)malononitrile (13)
The product 13 was obtained by according to GM-II. Yield 98.30 %, m.p. 163 °C. The product
was characterized through comparison of spectral data with that of reported literature [31]
2
.4.10. Synthesis of 2-(4-bromobenzylidene)malononitrile (14)
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4

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The product 14 was obtained by according to GM-II. Yield 95.86 %, m.p. 163 °C. The product
was characterized through comparison of spectral data with that of reported literature [31]
2
.4.11. Synthesis of 2-(4-fluorobenzylidene)malononitrile (15)
The product 15 was obtained by according to GM-II. Yield 95.52 %, m.p. 126 °C. The product
was characterized through comparison of spectral data with that of reported literature [31]
2
.4.12. Synthesis of 2-(3-chlorobenzylidene)malononitrile (16)
The product 16 was obtained by according to GM-II. Yield 99.17 %, m.p. 117 °C. The product
was characterized through comparison of spectral data with that of reported literature [33]
2
.4.13. Synthesis of 2-(3-bromobenzylidene)malononitrile (17)
The product 17 was obtained by according to GM-II. Yield 96.92 %, m.p. 110 °C. The product
was characterized through comparison of spectral data with that of reported literature [35]
2
.4.14. Synthesis of 2-(2-chloro-6-fluorobenzylidene)malononitrile (18)
The product 18 was obtained by according to GM-II. Yield 98.16 %, m.p. 90 °C. The product
was characterized through comparison of spectral data with that of reported literature [36]
2
.4.15. Synthesis of 2-(4-(dimethylamino)benzylidene)malononitrile (19)
The product 20 was obtained by according to GM-II. Yield 96.02 %, m.p. 180 °C. The product
was characterized through comparison of spectral data with that of reported literature [37]
2
.5. General Method (GM-III) for Claisen–Schmidt Condensation (20-34)
To a mixture of acetone (4.91 mmol) and aldehyde (9.83 mmol) was added a suitable amount of
water in the presence of catalytic amount of IL 1 (6% mol) under ultrasound irradiation. Solid
products were obtained in appropriate time (Table 2). The products were separated by filtration
1
5

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and washed with water, recrystallized in 95% ethanol to give pure product. All compounds were
previously reported and were characterized through the comparison of spectral data with that of
reported literature.
2
.5.1. Synthesis of (1E,4E)-1,5-diphenylpenta-1,4-dien-3-one (20)
The product 20 was obtained by according to GM-III. Yield 94.75 %, m.p. 113 °C. The product
was characterized through comparison of spectral data with that of reported literature [38]
2
.5.2. Synthesis of (1E,4E)-1,5-bis(2-hydroxyphenyl)penta-1,4-dien-3-one (21)
The product 21 was obtained by according to GM-III. Yield 95.16 %, m.p. 156 °C. The product
was characterized through comparison of spectral data with that of reported literature [38]
2
.5.3. Synthesis of (1E,4E)-1,5-bis(3-hydroxyphenyl)penta-1,4-dien-3-one (22)
The product 22 was obtained by according to GM-III. Yield 92.55 %, m.p. 197 °C. The product
was characterized through comparison of spectral data with that of reported literature [38]
2
.5.4. Synthesis of (1E,4E)-1,5-bis(4-hydroxyphenyl)penta-1,4-dien-3-one (23)
The product 23 was obtained by according to GM-III. Yield 93.09 %, m.p. 237 °C. The product
was characterized through comparison of spectral data with that of reported literature [38]
2
.5.5. Synthesis of (1E,4E)-1,5-bis(3,4-dihydroxyphenyl)penta-1,4-dien-3-one (24)
The product 24 was obtained by according to GM-III. Yield 93.64 %, m.p. 152 °C. The product
was characterized through comparison of spectral data with that of reported literature
2
.5.6. Synthesis of (1E,4E)-1,5-bis(3-methoxyphenyl)penta-1,4-dien-3-one (25)
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6

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The product 25 was obtained by according to GM-III. Yield 93.37 %, m.p. 130 °C. The product
was characterized through comparison of spectral data with that of reported literature [39]
2
.5.7. Synthesis of (1E,4E)-1,5-bis(3-hydroxy-4-methoxyphenyl)penta-1,4-dien-3-one (26)
The product 26 was obtained by according to GM-III. Yield 93.92 %, m.p. 196 °C. The product
was characterized through comparison of spectral data with that of reported literature [39]
2
.5.8. Synthesis of (1E,4E)-1,5-bis(4-hydroxy-3-methoxyphenyl)penta-1,4-dien-3-one (27)
The product 27 was obtained by according to GM-III. Yield 94.30 %, m.p. 90 °C. The product
was characterized through comparison of spectral data with that of reported literature [38]
2
.5.9. Synthesis of (1E,4E)-1,5-bis(4-chlorophenyl)penta-1,4-dien-3-one (28)
The product 28 was obtained by according to GM-III. Yield 94.93 %, m.p. 193 °C. The product
was characterized through comparison of spectral data with that of reported literature [40]
2
.5.10. Synthesis of (1E,4E)-1,5-bis(4-bromophenyl)penta-1,4-dien-3-one (29)
The product 29 was obtained by according to GM-III. Yield 91.56 %, m.p. 212 °C. The product
was characterized through comparison of spectral data with that of reported literature [39]
2
.5.11. Synthesis of (1E,4E)-1,5-bis(4-fluorophenyl)penta-1,4-dien-3-one (30)
The product 30 was obtained by according to GM-III. Yield 91.38 %, m.p. 151 °C. The product
was characterized through comparison of spectral data with that of reported literature [41]
2
.5.12. Synthesis of (1E,4E)-1,5-bis(3-chlorophenyl)penta-1,4-dien-3-one (31)
The product 31 was obtained by according to GM-III. Yield 95.31 %, m.p. 125 °C. The product
was characterized through comparison of spectral data with that of reported literature [38]
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2
.5.13. Synthesis of (1E,4E)-1,5-bis(3-bromophenyl)penta-1,4-dien-3-one (32)
The product 32 was obtained by according to GM-III. Yield 92.89 %, m.p. 117 °C. The product
was characterized through comparison of spectral data with that of reported literature [42]
2
.5.14. Synthesis of (1E,4E)-1,5-bis(2-chloro-6-fluorophenyl)penta-1,4-dien-3-one (33)
The product 33 was obtained by according to GM-III. Yield 93.87 %, m.p. 144 °C. The product
was characterized through comparison of spectral data with that of reported literature [43]
2
.5.15. Synthesis of (1E,4E)-1,5-bis(4-(dimethylamino)phenyl)penta-1,4-dien-3-one (34)
The product 34 was obtained by according to GM-III. Yield 91.86 %, m.p. 191 °C. The product
was characterized through comparison of spectral data with that of reported literature [44]
3
3
. Results & Discussion
.1. Synthesis and characterization of ILs
Beside unique physical and chemical properties, the most notable characteristic of ILs is the
ability of tuning any feature through rational alteration of cation or anion and therefore, design
1
8
and tailoring of ILs according to requirement is an easy task. Theoretically, 10 ILs are possible
to be synthesized [45, 46]. Combinations of suitable cations and anions can help to adjust
viscosity, water miscibility and many other properties of ILs [47, 48].
Methyl imidazole was treated with alkyl halide in dichloromethane at room temperature
Scheme-1. 1-Hexyl-3-methylimidazolium bromide is obtained as a colorless liquid. We observed
that the exchange of bromide with hydroxyl and amino substituted benzoates makes them waxy
yellow/brown hydrophilic ILs at room temperature. Completion of the reaction was monitored
through TLC.
Scheme 1: Synthesis of 1-hexyl-3-methylimidazolium bromide
1
8

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To obtain ILs with desired anion, metathesis of ions is the most crucial step. We converted
carboxylic acid into sodium salt by treating with sodium bicarbonate solution. Four different
ortho or para substituted aromatic acids are selected including salicylic acid, anthranilic acid, p-
hydroxy-benzoic acid and p-amino-benzoic acid. The aqueous solutions of sodium salts of
carboxylic acids are then treated with imidazolium halide as shown in Scheme 2. Metathesis
occurs in the specific time (vide experimental). Water evaporation from solution is followed by
treatment with cold ethanol to separate sodium halide and obtain 1-hexyl-3-methylimidazolium
2
-hydroxybenzoate (1), 1-hexyl-3-methylimidazolium 2-aminobenzoate (2), 1-hexyl-3-
methylimidazolium 4-hydroxybenzoate (3) and 1-hexyl-3-methylimidazolium 4-aminobenzoate
4) respectively.
(
Scheme 2: Metathesis of ions
R = methyl, R = n-hexyl, R = OH, R = H
IL 1
IL 2
IL 3
IL 4
1
2
3
4
R = methyl, R = n-hexyl, R = NH ,
R = H
4
1
2
3
2
R = methyl, R = n-hexyl, R = H,
R = OH
4
1
2
3
R = methyl, R = n-hexyl, R = H,
R = NH2
4
1
2
3
1
For characterization of ILs (1-4), we have used spectroscopic techniques including H-NMR,
1
3
1
C-NMR, IR and ESI-MS. The H-NMR spectrum of 1-hexyl-3-methylimidazolium bromide
shows one proton signal at 9.2 that corresponds to H-2 methine sandwiched between two
nitrogen atoms, thus confirming the formation imidazolium. Additionally, the formation of ILs
1
3
was also supported by the C-NMR spectrum showing C-2 signal around  137.
1
The H-NMR spectrum of IL 1 – 4 further displays signals in the aromatic region. A downfield
1
3
singlet at  16.17 indicates intermolecular/intramolecular H-bonding. C-NMR spectra of all ILs
1-4) display resonances for imidazolium ring for quaternary carbon at  137 (N-C=N), and two
(
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9

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methine at 122 and 120 (C-4 and C-5). The alkyl groups attached to imidazolium shows four
upfield methylene at  31, 29, 25, 22 and a downfield methylene at 49 (N-CH ) and two methyl
2
groups at 36 (N-methyl) and 14.0 (Terminal methyl). In addition, signals for anion in
aromatic region with two downfield signals are visible (Vide Experimental).
-1
The IR spectrum of IL 1 shows a medium intense band at 1627.7 cm (C=O) and a strong band
-1
at 1337.3 cm , which is characteristic of salicylate ion. Furthermore, IR spectra of ILs (1-4)
-1
show absorptions at 1458 and 1574 cm , which can be attributed to the ring skeleton of
-1
imidazolium ion (C=C, C=N), and peaks at 2800 - 3200 cm due to the C-H stretching of methyl
and methylene present as side chain of cation. Due to the hydrophilic nature of ILs, IR spectra
-1
show the presence of water at a broad peak at around 3450 cm .
3
.2. Supramolecular aggregation behavior of ILs in ESI-MS
+
-
It is known that ILs can form cationic [C A ] and anionic [C A ] supramolecular
n+1
n
n
n+1
aggregates/clusters [49]. To study these aggregates ESI-MS is one of the powerful techniques
used to probe this behavior [50]. We have recorded ESI spectra in both positive and negative
mode to study polymeric aggregates. Previously, we have observed that ILs containing
phenoxides (phenolates) as anions do not exhibit supramolecular polymeric aggregation due to
highly delocalized negative ion of oxygen on aromatic ring [4]. The present studies with
aromatic carboxylates as anion reveal strong interaction of cation and anion resulting into
supramolecular polymeric aggregates. However, simple molecular ion peaks of ILs 1-4 are
observed while operating in positive ion mode. The negative ion mode of ESI-MS demonstrates
aggregation behavior of ILs 1-4. Most abundant ions in the spectra of ILs 1-4 are respective
-
cations and anions. Formation of dimer [A + H] is evident in spectra of all ILs studied while
2
operating in negative ion mode.
ESI-MS is soft ionization technique comparing to EI-MS (70 eV), but internal energies in the
range of 1.2 - 2.2 eV allow rearrangements and fragmentations [51]. Figure 1a of supporting
information (SI) and Figure 1b showed that product 1 exhibits peak at m/z 167.1545, which
+
+
corresponds to C (C H N ). However, it does not display any aggregates in positive mode
1
0
19
2
while negative mode displayed series of aggregates which decreasing intensity in which the
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0

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-
-
distinguished peak at m/z 137.0135 agreeing to A (C H O ). Furthermore, negative mode also
7
5
3
displays anion-anion aggregation and anion-anion aggregation with sodium at m/z 275.0598
-
-
which corresponds to [A + H] and at m/z 297.0318 which corresponds to [A + Na] ,
2
2
respectively.
Figure 1b: ESI-MS negative mode of product 1 displayed series of singly negatively charged aggregates.
Figure 2a of SI showed that the positive mode ESI-MS of product 2 exhibits peak at m/z
+
+
1
67.1534 which corresponds to C (C H N ). Moreover, figure 2b showed that negative mode
10 19 2
displayed a series of aggregates with decreasing intensity in which h the most prominent peak
-
-
at m/z 136.0357 corresponds to A (C H NO ). Furthermore, negative mode also displays anion-
7
6
2
anion aggregation and anion-anion aggregation with sodium at m/z 273.0911 that corresponds to
-
-
[
A + H] and at m/z 295.0712 that corresponds to [A + Na] respectively.
2 2
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Figure 2b: ESI-MS negative mode of product 2 displayed series of singly negatively charged aggregates
Figure 3a of SI showed that the positive mode ESI-MS of product 3 exhibits peak at m/z
+
+
1
67.1515 that corresponds to C (C H N ). Moreover, Figure 3b showed that unlike product 1
10 19 2
-
-
and 2, aggregates CA and C A do not appear in negative mode. The ESI-MS negative mode of
2
2
3
-
product 3 suggesting strong anion-anion coordination as [A + H] emerges at m/z 275.0549. In
2
-
addition, the negative mode exhibits at m/z 905.3909 [A C Na] disclosing presence of sodium
4
2
-
-
ion. The prominent peaks in negative mode are at m/z 905.3909 [A C Na] , 761.2301 [A CNa ] ,
4
2
4
2
-
-
-
-
7
2
39.2452 [A CNa + H] , 601.2168 [A CNa] , 457.0523 [A Na ] , 435.0700 [A Na + H] ,
4 3 3 2 3
-
-
-
97.0361 [A +Na] , 275.0549 [A + H] and 137.0173 [A] .
2
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Figure 3b: ESI-MS negative mode of product 3 displayed series of singly negatively charged aggregates
Figure 4a of SI showed that the positive mode ESI-MS of product 4 exhibits a peak at m/z
+
+
1
67.1307 that corresponds to C (C H N ). Moreover, Figure 4b showed that negative mode
10 19 2
does not show anion-cation clusters except anion-anion aggregation and anion-anion aggregation
-
with sodium at m/z 273.0899 correspond to [A + H] and at m/z 295.0693 correspond to [A +
2
2
-
Na] respectively. The nonexistence of cluster formation is attributed to strong anion-anion
interaction.
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Figure 4b: ESI-MS negative mode of product 4 displayed series of singly negatively charged aggregates.
1
The H-NMR spectrum supports this occurrence of sodium ion showing cation-anion ratio as 1:2.
Therefore, further purification was done (vide experimental) and pure products are obtained
1
which are checked by H-NMR. After removal of impurities, these ILs are used as catalysts in
Knoevenagel and Claisen-Schmidt condensation reactions and we analyze the impact of
supramolecular aggregation behavior of ILs on catalytic activity.
3
.3. Catalytic activity of ILs in Knoevenagel and Claisen-Schmidt condensation
reactions
The Carbon-Carbon bond formation reactions is most significant and crucial part of synthetic
organic chemistry [52]. The use of ILs (1-4) as effective catalyst in Knoevenagel and Claisen-
Schmidt Condensation was carried out under ultrasound irradiation. The results revealed that
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these ILs can be used as both organic base and phase transfer catalyst in both reactions with high
yields under mild conditions and short period with high selectivity.
Scheme 3: Synthetic pathway of Knoevenagel and Claisen–Schmidt condensation reactions.
The reaction between benzaldehyde and malononitrile or acetone is used as the model reaction
under ultrasound irradiation to evaluate the catalytic property of ILs as shown in scheme 3.
Among all ILs 1-hexyl-3-methylimidazolium 2-hydroxybenzoate (1) is the most effective and
gives high yield around 98 % (Table 1).
Table 1: Catalyst evaluations for the Knoevenagel and Claisen–Schmidt condensations of
a
aldehydes with malononitrile or acetone
Sr No. Catalyst (mol %) Knoevenagel Condensation Claisen-Schmidt Condensation
b,c
b,c
Time (min)
Yield (%)
0
Time (min)
Yield (%)
0
1
2
3
4
5
6
7
8
9
None
5
1
1
1
1
1
1
1
1
15
15
15
15
15
15
15
15
15
IL – 1 (2 %)
IL – 2 (2 %)
IL – 3 (2 %)
IL – 4 (2 %)
IL – 1 (4 %)
IL – 1 (6 %)
IL – 1 (8 %)
IL – 1 (10 %)
96.32
93.55
90.12
89.69
98.86
98.93
98.95
99.40
92.46
91.61
88.47
85.62
92.80
94.75
94.87
95.10
a
Reaction Conditions: Benzaldehyde (9.83 mmol), Malononitrile (9.83 mmol) or acetone (4.91
mmol), IL (%), H O. Isolated yield. All the reaction was carried under ultrasound irradiation.
b
c
2
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5

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Knoevenagel Condensation
Claisen-Schmidth Condensation
100
98
96
94
92
90
88
86
84
IL-1 (2%) IL-2 (2%) IL-3 (2%) IL-4 (2%) IL-1 (4%) IL-1 (6%) IL-1 (8%) IL-1 (10%)
Ionic Liquids (mol %)
Figure 5: Catalytic activity of ILs in Knoevenagel and Claisen–Schmidt condensation reactions
Figure 5 showed the catalytic activity of ILs in Knoevenagel and Claisen–Schmidt condensation
reactions. The IL 1 (4 % mol for Knoevenagel condensation and 6 % mol for Claisen–Schmidt
condensation) provides the moderate to high yield in all cases as shown in Table 2.
Scheme 4: Synthetic pathway of Knoevenagel and Claisen–Schmidt condensation reactions using IL 1.
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a
Table 2: Knoevenagel and Claisen–Schmidt condensation reactions using IL 1 .
Groups Knoevenagel condensation
Claisen-Schmidt Condensation
Time
Yield
Mp
C
Rep mp
Time
(min)
Yield
Mp
C
Rep mp
R1
R2
R3
R4
Entry
b,c
Entry
b,c
°
°
°
°
(
min)
1
(%)
C
(%)
C
H
OH
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
F
5
98.86
99.01
96.76
96.93
98.05
97.48
97.51
98.44
98.30
95.86
95.52
99.17
96.92
98.16
96.02
84
160
152
196
225
106
250
135
163
163
126
117
110
90
82-83 [31]
159-160 [31]
148-150 [32]
193-194 [33]
225 [34]
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
15
10
25
25
15
10
25
15
15
25
25
10
20
15
25
94.75
95.16
92.55
93.09
93.64
93.37
93.92
94.30
94.93
91.56
91.38
95.31
92.89
93.87
91.86
113
156
197
237
152
130
196
90
110-112 [38]
156-157 [38]
199-201 [38]
235-237 [38]
150-154 [53]
130-132 [39]
195-197 [39]
84-86 [38]
6
1
OH
H
H
7
1
H
OH
OH
H
8
1
H
OH
OCH3
OH
OCH3
H
9
1
H
10
11
12
13
14
15
16
17
18
19
1
102-104 [32]
250 [34]
H
OCH3
OH
Cl
1
H
1
134-135 [31]
161-163 [31]
159-161 [31]
125-126 [31]
121-122 [33]
110.0-110.8 [35]
90 [36]
H
1
193
212
151
125
117
144
191
191-193 [40]
211-213 [39]
150-152 [41]
123-125 [38]
118-120 [42]
143.5-144.3 [43]
187-188 [44]
H
H
Br
1
H
H
F
1
H
Cl
H
1
H
Br
H
1
Cl
H
H
H
1
H
N(CH3)2
H
1
179-180
178-179 [37]
a
Reaction Conditions: Benzaldehyde (9.83 mmol), Malononitrile (9.83 mmol) or acetone (4.91 mmol), IL 1 (4 % for Knoevenagel
condensation and 6 % for Claisen–Schmidt condensation), H O. Isolated yield. All the reaction was carried out under ultrasound
b
c
2
irradiation.
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The catalytic activity of IL 1 is observed in Knoevenagel and Claisen–Schmidt condensation
reactions with different aldehydes. The IL 1 provides moderate to high yield in all cases as
shown in figure 6.
Claisen-Schmidt Condensation
Knoevenagel Condensation
100
99
98
97
96
95
94
93
92
91
90
20
21 22 23 24 25 26 27 28 29 30 31 32 33 34
5
6
7
8
9
10 11 12 13 14 15 16 17 18 19
Reaction Number (Entry)
Figure 6: Catalytic activity of IL-1 in Knoevenagel and Claisen–Schmidt condensation reactions
3
.4. Recyclability of the catalyst
The recyclability is an important factor in catalysis field. Therefore, the possibility of reusing of
IL-1 catalyst is evaluated in the model reaction of Knoevenagel and Claisen–Schmidt
condensation under optimum conditions. After each running, the IL-1 is recovered from the
aqueous phase (filtrate), dried and washed with water and reused for subsequent reactions. The
recycled catalyst could be reused four times without losing its activity and efficiency as shown in
Figure 7.
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Knoevenagel Condensation
Claisen-Schmidth Condensation
100
98.86
97.21
94.75
95.13
90
80
70
60
50
40
30
20
10
0
92.36
92.40
91.30 91.43
1
2
3
4
Number of runs
Figure 7: The recycling of IL-1 catalyst in the model reaction of Knoevenagel and Claisen–Schmidt
condensation under optimum conditions.
3
.5. The effect of anions of ILs on catalysis
The effect of substitution on the aromatic ring showed that ILs containing ortho substitution give
the best result in catalysis. On the other hand, para substituted anions give moderate yield in
Knoevenagel and Claisen–Schmidt condensation. We also found the significant relationship
between catalytic activity and aggregation behavior of different ILs. The results revealed that,
catalytic activity increases with increased supramolecular aggregation. This is attributed to
decreases abundance of anion-anion aggregation in ESI-MS. Hence, we can conclude that the
catalytic activity of ILs depends on an availability of anion as shown in Table 3.
2
9