A new type IV DES: a competent green catalyst and solvent for the synthesis of α,β-unsaturated diketones and dicyano compounds by Knoevenagel condensation reaction

Article abstract of DOI:10.1039/d0nj02852e

DESs are new and greener alternatives to ionic liquids formed by mixing components that are capable of forming hydrogen bonds between them. The strong hydrogen bond interactions between the constituents make a large depression in the melting points compared to pure constituents. They are emerging as green solvents and have loomed as adorable alternatives to conventional organic solvents and ionic liquids with unique properties. In the present article, four new CeCl₃·7H₂O-based DESs were developed and their physical properties were studied. Their activities were checked in the Knoevenagel condensation reaction of dimedone/malononitrile with various aldehydes. The recyclability of the catalyst/solvent was achieved up to five runs without much change in the activity.

Full text of DOI:10.1039/d0nj02852e

View Article Online
View Journal
NJC
New Journal of Chemistry
Accepted Manuscript
A journal for new directions in chemistry
This article can be cited before page numbers have been issued, to do this please use: S. M, H. K, L. V.
Theresa and K. Sreekumar, New J. Chem., 2020, DOI: 10.1039/D0NJ02852E.
Volume 42
This is an Accepted Manuscript, which has been through the
Number
6
21 March 2018
Pages 3963-4776
Royal Society of Chemistry peer review process and has been
accepted for publication.
NJC
New Journal of Chemistry
rsc.li/njc
A journal for new directions in chemistry
Accepted Manuscripts are published online shortly after acceptance,
before technical editing, formatting and proof reading. Using this free
service, authors can make their results available to the community, in
citable form, before we publish the edited article. We will replace this
Accepted Manuscript with the edited and formatted Advance Article as
soon as it is available.
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes to the
text and/or graphics, which may alter content. The journal’s standard
Terms & Conditions and the Ethical guidelines still apply. In no event
shall the Royal Society of Chemistry be held responsible for any errors
or omissions in this Accepted Manuscript or any consequences arising
from the use of any information it contains.
ISSN 1144-2546
PAPER
Chechia Hu, Tzu-Jen Lin et al.
Yellowish and blue luminescent graphene oxide quantum dots
prepared via a microwave-assisted hydrothermal route using
H2O2 and KMnO4 as oxidizing agents
rsc.li/njc

Page 1 of 24
New Journal of Chemistry
1
2
3
4
5
6
7
8
9
View Article Online
DOI: 10.1039/D0NJ02852E
A New Type IV- DES: A competent green catalyst and solvent
for the synthesis of α, β- unsaturated diketones & dicyano
compounds by Knoevenagel condensation reaction
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Shaibuna M, Hiba K, Letcy V Theresa and K. Sreekumar*
Department of Applied Chemistry, Cochin University of Science and Technology, Cochin,
India.
E-mail: K. Sreekumar- kskpolymer.cusat@gmail.com
Abstract
DESs are new and greener alternative to ionic liquids formed by mixing the components,
which are capable of forming hydrogen bonds between them. The strong hydrogen bond
interactions between the constituents make a large depression in the melting points compared
to pure constituents. They are emerging as green solvents and have loomed as adorable
alternatives to conventional organic solvents and ionic liquids with unique properties. In the
present article, four new CeCl3.7H2O based DESs were developed and their physical
properties were studied. Their activity was checked in Knoevenagel condensation reaction of
dimedone/ malononitrile with various aldehydes. The recyclability of the catalyst/ solvent
was achieved up to five runs without much change in the activity.
Keywords
Deep eutectic solvents, Knoevenagel condensation, Green catalyst and solvent, α, β-
unsaturated diketones & dicyano compounds
Introduction
The fifth principle of green chemistry demands the removal of volatile solvents and their
replacement by safer alternatives.1 Eutectic mixtures are one of the recent alternatives to ionic
liquids; they are obtained from the isobaric phase diagram of a solid-liquid binary system and
the eutectic point indicating the equilibrium between a liquid phase and two crystalline
phases (this corresponds to the minimum in the liquidus curve and can be used as a solvent at
the lowest temperature).2 A binary composition of two constituents, which are liquids at
ambient temperature (freezing point, ≤ 25 ℃) are called deep eutectic solvents, with melting
points much lower than the pure constituents.3-5 This depression in freezing point depends
upon the ability to make hydrogen bonds. Due to the interaction of the hydrogen bond donor
with the salt, electrostatic force between the cation and anion is reduced which limits the
crystallisation of the salt.4,6
1

New Journal of Chemistry
Page 2 of 24
1
2
3
4
View Article Online
DOI: 10.1039/D0NJ02852E
They can be considered as a subclass of room temperature ionic liquids. But, they are not
5
6
7
8
single molecules, but a mixture of components and their properties can be tuned by changing
the constituents used.7,8 One component comes up with hydrogen donating ability and the
other shows hydrogen bond accepting ability through anions. No covalent bond is formed, so
that the solvent keeps the identities of the starting compounds.8 This solvents are
characterised by molecular ionic clusters within a complex hydrogen bonding network and
are non volatile, biodegradable, biocompatible, cost effective, can be prepared easily with
100 % atom economy and exhibit a wide liquid range.9
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
The toxicity of deep eutectic solvents were investigated in some previous reports. In 2013, M.
Hayyan et al first studied the toxicity of choline chloride (ChCl) based DESs with four
hydrogen bond donors including glycerine, ethylene glycol, triethylene glycol and urea and
found some toxic profile and was higher than pure constituents.10 Concentration of DESs,
type of individual components and their molar ratio, and interaction with living organism
were the important toxicity dependent factors. 11
The general mode of preparation includes the mixing of two components with moderate
heating and are first reported by Abbott et al.12 The unusual solvation properties are strongly
influenced by the strength of hydrogen bonds. Abbott et al. reported the solvation properties
in 2003 using choline chloride-urea DES. Amino acids, aromatic acids, salts that are
sparingly soluble in water, inorganic salts etc. are found to be soluble in DESs.13 In addition
to the hydrophilic DESs, hydrophobic DESs were also introduced recently, which were used
to purify water from metal ions,14 pesticides15 and active pharmaceutical ingredients (APIs),16
which make serious public health issues. Nanoscale clustering of alcoholic solutes in deep
eutectic solvents was also studied.17 Hydrophilic DESs have been applied in different fields
including electrochemistry,18,19 extraction,20,21 catalysis,22-24 gas separation25 etc. Recently,
Type 5 DESs designed from molecular substances (non- ionic deep eutectic solvents) were
also introduced and applied in polymer synthesis.26 Another important application of DESs is
in the field of organometallic chemistry. In 2014, Vidal et al used DESs for the
27
chemoselective addition of organolithium and Grignard reagents to ketones in Air.
In
addition to this, they accomplished the chemoselective addition of organolithium reagents to
28
non-activated imines and quinolines in DESs.
eutectic solvents now-a-days.
These highlight the relevance of deep
In organic chemistry, lanthanide reagents have experienced an extensive growth and are
ideal promoters for various organic synthesis. Lanthanide based DESs can be designed as a
2

Page 3 of 24
New Journal of Chemistry
1
2
3
4
View Article Online
DOI: 10.1039/D0NJ02852E
greener solvent or CVD precursor, which are applicable in superconductors, lasers,
5
6
7
8
electronics, and magnets etc. Edler et al. introduced a series of lanthanide “Type IV” DESs
based on lanthanide nitrate hydrate with urea mixtures (Ln = Ce, Pr, Nd) with their physical
properties . 29
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
The present study was focused on the preparation of four new Type IV- DESs, study of their
physicochemical properties and application as green catalyst as well as reaction medium for
the synthesis of α, β- unsaturated diketones and α, β-unsaturated dicyano compounds by
Knoevenagel condensation reaction. CeCl3.7H2O was the metal salt hydrate used. Cerium is
the most abundant element in the lanthanide series which is more abundant than the transition
elements cobalt, tin and zinc in lanthanide series, which displayed promising applications in
many fields. The most common source of Ce+3 is CeCl3.7H2O and is the most stable
oxidation state of cerium. In addition to this, water tolerance, inexpensive, higher stability
and purity makes this selection reasonable. Biorenewable and environmentally benign urea,
polyols (ethylene glycol and glycerol) and naturally occurring organic acid (lactic acid)] were
used as hydrogen bond donors. Their physical properties like density, viscosity, acidity,
thermal stability and solubility in common solvents were studied based on the previous
report. 30 To the best of our knowledge, there is no previous report for the selective synthesis
of α, β- unsaturated diketone in deep eutectic solvents. This highlights the importance of
introducing a new green method using DESs.
Applicability of the new DESs in organic synthesis was evaluated by performing
Knoevenagel condensation reaction of dimedone/ malononitrile with various aldehydes.
There are only a limited number of reports for the selective synthesis of α, β- unsaturated
diketone derived from dimedone and many other reports display its formation as an
intermediate during the formation of Arylmethylene bis (3- hydroxy-2-cyclohexene-1-ones)
and Xanthenediones31,32 etc. Knoevenagel condensation reaction is a crucial and widely
accepted method for carbon- carbon bond forming reaction and can be used for the synthesis
of molecules, which are used as fluorescent dyes, perfumes, cosmetics, pharmaceuticals and
calcium antagonists etc.33 Substituted alkenes are also the basic constituents of important
drugs because of their broad biological activities like antibacterial, antimalarial, antitumor,
antioxidant etc.34 The reaction was catalysed by weak bases such as ammonia, urea, pyridine
etc.35 Some other acidic catalysts were also introduced recently. These include Silica-
supported tungstic acid (STA),36 Hf(IV) metal-organic framework (MOF),37 Cross-linked
polystyrene copolymer,38 etc. However, most of them experienced one or more defects like
toxic catalyst, additives, volatile solvents, higher temperature, higher cost, lower yield, non
3

New Journal of Chemistry
Page 4 of 24
1
2
3
4
View Article Online
DOI: 10.1039/D0NJ02852E
recyclable catalyst, long reaction time, limited substrate scope, formation of side products etc.
5
6
7
In that event, it is necessary to introduce an alternate method to overcome all these
difficulties.
8
9
Experimental
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Preparation of DES
Deep eutectic solvents were prepared by mixing the metal chloride hydrate (CeCl3.7H2O) and
hydrogen bond donors (urea, ethylene glycol, glycerol and lactic acid) at different molar
ratios. A clear, colourless, homogeneous liquid was formed by heating the mixture of two
constituents at 40-60°C for 10-15 minutes. The mixture was cooled to room temperature and
used for further studies without any purification process.
General procedure for Knoevenagel condensation reaction in DES
A mixture of aldehyde (1 mmol), dimedone/ malononitrile (1 mmol) and DES (0.5 mmol)
was stirred at room temperature for the time as indicated in Table 7, the progress of the
reaction was monitored using TLC. After completion of the reaction, distilled water was
added to the reaction mixture and the product precipitated was filtered and analysed by TLC,
GCMS, 1H NMR, 13C NMR and melting point measurements.
Recycling of DES
After completion of the reaction, a minimum amount of ethyl acetate was added to the filtrate
containing both DES and excess reactants and mixed well. The deep eutectic solvent (highly
soluble in water and insoluble in ethyl acetate) present in the water layer was separated from
ethyl acetate layer and the water was evaporated from the mixture by gentle heating about 60
°C. The DES was completely dried by using vacuum oven at 60-70°C and used for further
four cycles.
Results and discussion
The present manuscript outlines the preparation of four new Type IV- deep eutectic solvents
formed from a metal chloride hydrate (CeCl3.7H2O) with urea, ethylene glycol, glycerol and
lactic acid (as hydrogen bond donors) respectively. The air/ moisture insensitivity, increased
scope, low cost and wide availability of hydrated metal halides make the selection of metal
chloride hydrate. The interaction between the hydrogen bond donor and the anion of metal
chloride hydrate leads to an increase in the effective size; this results in a decrease in the
4

Page 5 of 24
New Journal of Chemistry
1
2
3
4
View Article Online
DOI: 10.1039/D0NJ02852E
interaction with cations and a depression in the freezing point. DESs were prepared at
5
6
7
different ratios by changing the molar ratio of hydrogen bond donor for a fixed amount of
CeCl3.7H2O; the observations are given in Table 1.
8
9
The mixture of CeCl3.7H2O with urea at 1:1 and 1:2 ratios didn’t form a clear melt on gentle
heating, prolonged heating made precipitation from this mixture and were concluded as
unsuccessful combinations (Table 1, Entry 1 & 2). CeCl3.7H2O with urea at 1:3 & 1:4
formed a clear melt on heating, but it became a semisolid upon storage (Table 1, Entry 3 &
4). But, both at 1:5 & 1:6 ratios existed as a clear melt at room temperature and are successful
combinations (Table 1, Entry 5 & 6). Similarly, CeCl3.7H2O with ethylene glycol and
glycerol formed clear DES at 1:2 ratio (Table 1, Entry 8 & 11). In the same way, CeCl3.7H2O
with lactic acid formed a successful combination at 1:4 ratio (Table 1, Entry 16) and the
optimal ratio of DES formed depended upon the hydrogen bonding ability of the components.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Table 1 CeCl3.7H2O based deep eutectic solvents at different compositions
Entry
1
DES
Ce:U
Ce: U
Ce: U
Ce:U
Ratio
1:1
1:2
1:3
1:4
1:5
1:6
1:1
1:2
1:3
1:1
1.2
1:3
1:1
1:2
1:3
1:4
State at RT
No clear melt
No clear melt
Semisolid
Semisolid
Liquid
Liquid
Semisolid
Liquid
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Ce: U
Ce: U
Ce: EG
Ce: EG
Ce: EG
Ce: Gly
Ce: Gly
Ce: Gly
Ce: Lac
Ce: Lac
Ce: Lac
Ce: Lac
Liquid
Semisolid
Liquid
Liquid
No clear melt
No clear melt
Semisolid
Liquid
Ce = CeCl3.7H2O, U= Urea, EG= Ethylene glycol, Gly= Glycerol, Lac= Lactic acid)
The four successful DESs abbreviated as DES 4 (CeCl3.7H2O- urea at 1:5 ratio, Table 1,
Entry 5), DES 5 (CeCl3.7H2O- ethylene glycol at 1:2 ratio, Table 1, Entry 8), DES 6
(CeCl3.7H2O- glycerol at 1:2 ratio, Table 1, Entry 11) and DES 7 (CeCl3.7H2O- lactic acid at
1:4 ratio, Table 1, Entry 16) were selected for further physicochemical studies. (The
abbreviation is given as a continuation to previously reported DESs (DES 1, DES 2 & DES
3).30
5

New Journal of Chemistry
Page 6 of 24
1
2
3
4
View Article Online
DOI: 10.1039/D0NJ02852E
DSC analysis
5
6
7
8
In order to determine the thermal behaviour, Differential Scanning Calorimetry (DSC) was
performed. Only glass transition temperature was observed instead of melting point for all the
three DESs. The same phenomenon was previously reported in Choline Chloride- lactic
9
acid,39 Potassium carbonate- glycerol 40 and ZrOCl2.8H2O- ethylene glycol/ glycerol DESs
30
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
and these groups are called Low Transition Temperature Mixture (LTTM).40 The glass
transition temperature of DES 4 (CeCl3.7H2O- urea at 1:5 ratio), DES 5 (CeCl3.7H2O-
ethylene glycol at 1:2 ratio) , DES 6 (CeCl3.7H2O- glycerol at 1:2 ratio) & DES 7
(CeCl3.7H2O- lactic acid at 1:4 ratio) are -64 (Figure 1a), -20 (Figure 1b) -18 °C (Figure 1c)
& -55 °C (Figure 1d) respectively. Corresponding values are given in Table 2.
Figure 1 a) DSC curve of DES 4
6

Page 7 of 24
New Journal of Chemistry
1
2
3
4
View Article Online
DOI: 10.1039/D0NJ02852E
Figure 1 b) DSC curve of DES 5
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 1 c) DSC curve of DES 6
Figure 1 d) DSC curve of DES 7
Density
The densities of most deep eutectic solvents are available and can be readily measured. They
are highly depending upon the hydrogen bonding interaction between the constituents and
were determined using relative density bottle. Density of DES 4 is 1.64 g/ cm3 (CeCl3.7H2O/
7

New Journal of Chemistry
Page 8 of 24
1
2
3
4
5
6
7
8
9
View Article Online
Urea at 1:5 ratio, Table 2, entry 1). DES 5 (CeCl3.7H2O /ethylene glycol at 1:D2OrI:a10ti.1o0)39a/Dn0dNJ02852E
DES 6 (CeCl3.7H2O/ glycerol at 1:2 ratio) had the same density (1.76 g/cm3, Table 2, entry 2
and 3). Among the four deep eutectic solvents, lowest density was noticed for DES 7
(CeCl3.7H2O/ lactic acid at 1:4 ratio). The values are higher than the density of water.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Table 2 Properties of DESs prepared
DES
Mole Abrevation
ratio
Glass transition
temperature, Tg(°C)
Density
Viscosity
(g/cm3) ( )/(mPa.s )
Entry
1
2
3
4
Ce: U
Ce: EG
Ce: Gly
Ce: Lac
1:5
1:2
1:2
1:4
DES 4
DES 5
DES 6
DES 7
-64
-20
-18
-55
1.64
1.76
1.76
1.55
195.39
290.40
868.73
564.64
Ce = CeCl3.7H2O , U= Urea, EG= Ethylene glycol, Gly= Glycerol, Lac= Lactic acid
Viscosity
Viscosity measurement is an important transport property, which controls many applications
of DESs like synthesis, catalysis, other solvent applications etc. Here, viscosity was
determined using Ostwald viscometer, which is based on Poiseuille’s law. The lowest
viscosity was noticed for DES 4 (CeCl3.7H2O/ Urea at 1:5 ratio, viscosity = 195.39 mPa.s,
Table 2, entry 1) compared to others. DES 6 has the highest viscosity value of 868.73 mPa s,
Table 2, entry 3) and 290.40 mPa.s, 564.64 mPa.s for DES 5 & DES 7 respectively. The
viscosity values are highly affected by the hydrogen bond donors. Glycerol has higher
viscosity compared to ethylene glycol and the corresponding DES (DES 6) is highly viscous.
Acidity
Reports for the determination of acidity of deep eutectic solvents are limited. Most papers are
based on pH measurements, which are limited to Brønsted acidic DESs and will not give
sufficient information about DESs containing both Brønsted and Lewis acid sites. The acidity
of DESs was determined by IR spectroscopy using pyridine as probe (Py-IR), which was
reported recently in the case of ZrOCl2.8H2O based DESs.30 This is a general method for the
determination of acidity of clay catalysts and ionic liquids.41, 42 The IR spectrum of pyridine
in the range 1400- 1700 cm-1 was recorded and could be used to differentiate Lewis and
Brønsted sites.43 Two prominent peaks were obtained by the interaction of pyridine with dual
acidic catalysts. A peak at 1450 cm-1 indicated the Lewis acidity (Py-Lewis complex is
formed by the interaction of pyridine with Lewis acid site) and the band at 1540 cm-1 along
with the band at 1640 cm-1 could be used to indicate the Brønsted acidity [pyridinium ion
8

Page 9 of 24
New Journal of Chemistry
1
2
3
4
([PyH]+) was formed by the interaction of pyridine with the Brønsted acid sites].42-47 At VfiierwsAtr,ticle Online
DOI: 10.1039/D0NJ02852E
5
6
7
the FTIR spectrum of pure DESs was checked in order to confirm that there was no peak at
this prominent area. The spectrum is given in Figure 2.
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 2 FTIR spectrum of DES 4, DES 5, DES 6& DES 7
Figure 3 FIIR spectrum of pyridine- DES mixture
The FTIR spectrum of pyridine & DES mixture is given in Figure 3. A peak at 1450 cm-1 was
observed in the case of DES 4 after the addition of pyridine, indicating the Lewis acidity
9

New Journal of Chemistry
Page 10 of 24
1
2
3
4
which was not present in DES 5, DES 6 and DES 7. Similarly, a peak at 1640 cm-1ViwewaAsrticle Online
DOI: 10.1039/D0NJ02852E
5
6
7
8
present in all the four deep eutectic solvents indicating the Brønsted acidity. From the results
it could be concluded that all the four DESs (DES 4, DES 5, DES 6 & DES 7) were Brønsted
acidic and dual acidity was observed in DES 4 (both Brønsted and Lewis acidic).
The pH measurement was also performed to varify the acidity measurement; the results are
given in Table 3. Among them, higher acidity was observed for DES 7 (Ph= 2.02) and there
was not much difference in the Brønsted acidity of remaining three deep eutectic solvents.
Table 3 Acidity and thermal stability of the prepared DESs.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Peak for Lewis Peak for Bronsted
pH
Complete decomposition
Entry DES
site (cm-1)
site (cm-1)
~1640
takes place at T (°C)
1
2
3
4
DES 4
DES 5
DES 6
DES 7
1450
4.71
4.44
4.27
2.02
275
143
150
127
-
-
-
~1640
~1640
~1640
Thermal stability
Decomposition and thermal stability was studied by thermogravimetry and highest thermal
stability was observed for DES 4 (Table 3, Entry 1), it was stable up to 275 ℃ and
decomposition started after that. For DES 5, decomposition started at 103 ℃, which may be
due to dehydration and it decomposed completely at 143 ℃ (Table 3, Entry 2).
Decomposition took place for DES 6 at 150 ℃ (Table 3, Entry 3) and DES 7 at 127 ℃
(Table 3, Entry 4). Their corresponding TG/ DTG plots are given below (Fig 4a, 4b, 4c &
4d).
Figure 4a) TG curve of DES 4
10

Page 11 of 24
New Journal of Chemistry
1
2
3
4
View Article Online
DOI: 10.1039/D0NJ02852E
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 4b) TG curve of DES 5
Figure 4c) TG curve of DES 6
Figure 4d) TG curve of DES 7
11

New Journal of Chemistry
Page 12 of 24
1
2
3
4
View Article Online
DOI: 10.1039/D0NJ02852E
Solubility in common solvents
5
6
7
8
Studies of miscibility properties of DES are important for biphasic systems and extraction
processes. Solubility of DESs was highly dependent upon the hydrogen bonding ability,
solvents which are able to form strong hydrogen bonds with chloride ion tend to be miscible.
Based on this, DESs are highly soluble in protic solvents like water, methanol, ethanol etc.
and insoluble in aprotic ones like hexane, chloroform, ethyl acetate etc. The results are
consistent with the previous reports.30 The solubility of DES 4 - DES 7 are given in Table 4.
This makes the use of ethyl acetate to remove some organic waste from the mixture after
reaction during recycling process.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Table 4 Solubility of DESs in common solvents for CeCl3.7H2O based DESs
Entry Solvents
Ce
Urea EG Gly Lac DES 4
DES 5
DES 6 DES 7
1
2
Water
Methanol
Ethanol
Acetone
CH3CN
DCM
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
3
S
S
S
S
S
S
S
S
S
4
IS
IS
IS
IS
IS
IS
IS
IS
IS
SS
SS
IS
IS
IS
S
IS
IS
IS
IS
IS
IS
IS
S
IS
IS
IS
IS
IS
IS
IS
IS
IS
IS
IS
IS
IS
IS
IS
IS
IS
IS
IS
IS
IS
IS
IS
IS
IS
IS
IS
IS
5
S
S
6
IS
IS
IS
IS
S
IS
IS
IS
S
7
CHCl3
Hexane
EtOAc
THF
8
9
10
S
(S-Soluble, IS-Insoluble, SS-Sparingly soluble)
Catalytic activity
In order to check the activity of the new catalyst DES 4, DES 5, DES 6 & DES 7 (Table 2,
entry 1-4), reaction between benzaldehyde and dimedone (5, 5- Dimethyl-1, 3-
cyclohexanedione)/ malononitrile was conducted as the model reaction for the synthesis of α,
β-unsaturated diketones and dicyano compounds. At first, the reaction was conducted
between benzaldehyde (1 mmol) and dimedone (1 mmol)/ malononitrile (1 mmol) in the
absence of any catalyst and solvent at RT; only traces of products were observed even after 4
h. Later, the same reaction was repeated by using 0.5 mmol of three different catalysts (DES
4- DES 7) at room temperature. In reaction 1 (reaction between benzaldehyde and dimedone),
12

Page 13 of 24
New Journal of Chemistry
1
2
3
4
5
6
7
8
9
View Article Online
required product was formed in the presence of DES 4 in good to excellent yield DwOiI:th10o.1u03t9a/Dn0yNJ02852E
side product formation. Some side products (Xanthenediones) were formed in the case of
DES 5, DES 6 and DES 7. The observation was confirmed by using some other aldehyde
derivatives and it was concluded that DES 4 was a better catalyst for the selective synthesis
of α, β- unsaturated diketones.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
But in reaction 2 (reaction between benzaldehyde and malononitrile), pure products were
observed with high yield in all the four DESs (DES 4, DES 5 & DES 7 and low yield in DES
6 (may be due to the higher viscosity of DES 6), the observations are given in Table 5. From
this, DES 4 was selected for further studies, for comparing its activity in both reaction 1 and
reaction 2.
Table 5 Catalytic activity of the three DESs in Knoevenagel condensation reaction.
O
O
NC
NC
O
R
CN
CN
R
O
O
H
Reaction 2
Reaction 1
Entry Abrevation
Product formed
Reaction 2
Knoevenagel product Single product with high yield
Reaction 1
1
2
3
4
DES 4
DES 5
DES 6
DES 7
Mixture of products
Mixture of products
Mixture of products
Single product with high yield
Low yield
Single product with high yield
Reaction conditions: aldehydes (1 mmol), dimedone/ malononitrile (1 mmol) and DES (0.5 mmol), RT
Mixture of products- mixture of α, β- unsaturated diketones and Xanthenediones
Based on this observation, DES 4 was selected for further optimisation studies of the catalyst.
The reaction was performed between benzaldehyde and dimedone using different amounts of
the catalyst and the reaction was monitored using TLC. A higher yield (96 %) was obtained
within 10 min using 0.5 mmol of DES 4 for benzaldehyde & dimedone reaction mixture
(Table 6, Entry 8). This optimum catalyst amount was used for benzaldehyde & malononitrile
reaction mixture, in which the reaction was completed within 5 min with an yield of 97 %
(Table 6, Entry 11).
13

New Journal of Chemistry
Page 14 of 24
1
2
3
4
View Article Online
DOI: 10.1039/D0NJ02852E
Table 6 Activity of DES 4 for Knoevenagel condensation reaction
5
6
7
8
Entry
Active methylene
compound
Dimedone
DES 4
Time
(min)
2 h
30
Yield
(%)
(g)
(mmol)
-
9
1
2
-
Trace
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Dimedone
0.014
0.219
0.292
0.366
0.439
0.366
0.366
0.366
0.366
0.366
0.2
0.3
0.4
0.5
0.6
0.5
0.5
0.5
0.5
0.5
65
3
Dimedone
30
76
4
Dimedone
30
85
5
Dimedone
30
96
6
Dimedone
30
97
7
Dimedone
15
96
8
Dimedone
10
96
Incomplete
98
9
Dimedone
5
10
11
Malononitrile
Malononitrile
10
5
97
Reaction conditions: aldehydes (1 mmol), dimedone/ malononitrile (1 mmol) and DES 4, RT
The wide substrate scope was scrutinized by repeating the experiment using diverse
aldehydes like substituted benzaldehydes with electron-donating/ withdrawing substituents,
unsaturated aldehyde, hetero aromatic aldehydes, polycyclic aryl aldehyde etc. (Table 7,
Entry 1-10) under the optimum catalytic conditions and reaction was monitored using TLC,
the results with corresponding yield are given in Table 7. Aromatic aldehydes with electron-
donating/ electron-withdrawing substituents gave the corresponding Knoevenagel products in
high yields except 4- Nitro Benzaldehyde, which gave the Xanthenedione derivative instead
of the expected α, β- unsaturated diketones in the reaction 1, but furnished excellent yield in
reaction 2 (Table 7, Entry 1-6).
To explore the scope and utility of DES, the reaction was repeated between heteroaromatic
aldehydes (Furfural & Thiophenaldehyde) and dimedone/ malononitrile, higher yields were
obtained in both reactions 1 & 2 (Table 7, Entry 7 & 8). In the same way, excellent yield was
obtained by the reaction between dimedone/ malononitrile with unsaturated aldehyde
(cinnamaldehyde) in both reaction 1 & 2 (Table 7, Entry 9). When the substituent was
changed to sterically hindered naphthaldehyde (polycyclic aryl aldehyde), good to excellent
yields were obtained in reaction 1 and only traces of products were observed by in reaction 2
with less purity Table 7, Entry 10). Mild reaction condition, organic solvent free, very short
14

Page 15 of 24
New Journal of Chemistry
1
2
3
4
View Article Online
DOI: 10.1039/D0NJ02852E
reaction time, in expensive catalyst etc. indicate the benefits of DESs for Knoevenagel
5
6
condensation reaction.
7
8
9
Table 7 Knoevenagel condensation reaction between aldehydes using dimedone/
malononitrile
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
O
O
NC
NC
O
R
CN
CN
R
O
O
H
Reaction 2
Reaction 1
Reaction 1
Time (min) Yield (%)
Reaction 2
Entry
R
H
Time (min)
Yield (%)
1
2
3
4
5
6
7
15
10
10
15
30
4 h
15
96
92
93
96
80
-
5
5
97
94
93
95
92
90
93
4-Cl
4-Br
5
4-OMe
5
3,4-di-OMe
10
15
5
4-NO2
O
93
O
S
8
9
5
90
88
85
5
95
88
O
O
20
20
10
30
O
10
Trace
Reaction conditions: aldehydes (1 mmol), dimedone/ malononitrile (1 mmol) and DES 4 (0.5 mmol), RT
Reusability
Reusability is an important factor in organic transformations, which makes them useful for
commercial applications. An important advantage of DES is its recyclability; it was checked
for both the reaction 1 and reaction 2 using benzaldehyde as a model substrate. After each
cycle, the product was washed with water and analysed, catalyst was recovered for the next
round and reused up to 5 cycles for both the reactions with excellent activity.
15

New Journal of Chemistry
Page 16 of 24
1
2
3
4
View Article Online
DOI: 10.1039/D0NJ02852E
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 5 Recyclability of DES 4
Comparison with previous reports
A few DESs as catalysts have been reported for Knoevenagel condensation reaction of
aldehydes with malononitrile/ barbiturates/ thiobarbiturates; but there was no report using
dimedone as active methylene compound in DES. Many previous reports indicated that deep
eutectic solvents could be used as a benign catalyst for Knoevenagel condensation reaction.
In 2010 Y.A. Sonawane et al. have used DESs as catalysts/reaction media for the synthesis of
48
diphenylamine-based fluorescent styryl colorants by Knoevenagel condensation reaction.
But it required prolonged reaction time and temperature (50.5-90 ℃, 1-15 h). Similarly, in
2013, B. N. Borse et al. introduced deep eutectic solvents for the synthesis of
pyrimidinedione and pyrimidinetriones-based compounds using barbiturates/ thiobarbiturates
and aldehydes. This also required more time. 49
Most of the previous reports used organic solvents and the reaction was performed in high
temperature to achieve satisfactory results. Here a comparative study was performed with
some recently reported catalysts for both reaction 1 and reaction 2. Only limited publications
are available for the Knoevenagel condensation reaction using 1,3-diketones, because of their
inherent ability to form stable cyclic enols, that make them less reactive compared to other
active methylene compounds.50 Among these, a comparative study was performed using 4-
Chlorobenzaldehyde and dimedone as model substrates and the results are summarised in
Table 8.
16

Page 17 of 24
New Journal of Chemistry
1
2
3
4
View Article Online
DOI: 10.1039/D0NJ02852E
Table 8 Comparison of activity of DES 4 with previous reports (reaction 1)
5
6
7
Entry
Catalyst
Reaction
condition
Yield Reusability
(%)
Ref.
8
9
1
[PEG(mim)2][OH]2
(phase transfer catalyst)
3 h / RT
H2O
88
5 Runs
51
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
2
1 h/ 25 ℃
81
4 Runs
52
Ni-nanoparticles
Ethanol
3
4
IL (2-hydroxyethylammonium 30 min/ RT
63
92
5 Runs
5 Runs
53
54
formate, [H3N+–CH2–CH2–
OH][HCOO−])
20 min/ 50
℃, Ethanol–
water (1:1)
Fe3O4–cysteamine
hydrochloride
5
DES 4
10 min/ RT
97
5 Runs
Present
work
Reactants used: 4- Chlorobenzaldehyde and dimedone
In 2018, F. Poyafar et al. reported a phase transfer catalyst {[PEG(mim)2][OH]2} for
Knoevenagel condensation reaction, but it required prolonged reaction time (3 h)( Table 8,
entry 1). In addition to this, tedious work up was required for the preparation of this catalyst
(Three steps are there, at first, synthesis of [PEG]Br2; second, synthesis of [PEG(mim)2]Br2
and finally, synthesis of [PEG(mim)2][OH]2, required long reaction time and difficult work
up process. Similarly, nickel nanoparticles catalysed Knoevenagel condensation reaction was
reported by A. Kumar et al. (Table 8, entry 2), difficult synthesis method and reaction
conditions (1 h/ 25 ℃, 1 atm, Ethanol) made to think about an alternate method. An ionic
liquid (2-hydroxyethylammonium formate, [H3N+–CH2–CH2–OH][HCOO−]) was also used
as catalyst by H.R. Shaterian et al. (Table 8, entry 3); the reaction was completed within 30
min at RT, but low conversion of reactants was observed (63 % yield). Magnetic nanoparticle
based on Fe3O4–cysteamine hydrochloride was introduced by Maleki et al. in 2017. This
method also suffered some drawbacks related to difficult synthesis of the catalyst, use of
organic solvent, presence of high temperature etc. Overall comparison leads to the conclusion
that the DESs presented here show superior performance under mild reaction conditions and
17

New Journal of Chemistry
Page 18 of 24
1
2
3
4
View Article Online
DOI: 10.1039/D0NJ02852E
can be easily recycled and reused. Similarly, the activity of DES 4 was compared with some
5
6
7
recent reports for reaction 2 (reaction between benzaldehyde and malononitrile) and the
results are summarised in Table 9.
8
9
Table 9 Comparison of activity of DES 4 with previous reports (reaction 2)
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Entry
Catalyst
Reaction
condition
Yield Reusability
(%)
Ref.
1
[PEG(mim)2][OH]2
(phase transfer catalyst)
30 min / RT
H2O
92
5 Runs
51
2
3
55
56
Imine-linked covalent
organic frameworks
12 h/ 100℃,
97
94
-
Toluene
10 min/ 80℃,
microwave
irradiation
Copper-amidocarboxylate
based
metal organic framework
4 Runs
(15 W), MeOH
4
Zn/Cd-metal–organic
6 h/ 60℃
99
99
97
92
-
57
58
59
frameworks
Calix[4]arene-based
polyoxometalate
1 h/ 60℃
2 h/ RT
-
5
6
Molybdenum Carbide
(Mo2C)
5 Runs
5 Runs
7
DES 4
10 min/ RT
Present
work
Reactants used: benzaldehyde and malononitrile
Prolonged reaction time and harsh preparation method of some catalysts like phase transfer
catalyst, Imine-linked covalent organic frameworks, Copper-amidocarboxylate or Zn/Cd-
metal based metal organic framework, Calix[4]arene-based polyoxometalate etc. highlight
the importance of introducing deep eutectic solvents for this reaction.
The present catalyst was found to be very efficient in terms of yield, time, organic solvent
free condition, recyclability etc. and a special attention goes to easy method of preparation of
DESs compared to other catalysts.
18

Page 19 of 24
New Journal of Chemistry
1
2
3
4
View Article Online
DOI: 10.1039/D0NJ02852E
Mechanism of the reaction
5
6
7
8
Based on the observations, a probable mechanism was proposed, which is given below in
Scheme 1 for both reactions 1 & 2. At first, DES interacts with the oxygen atom of carbonyl
carbon to form an activated complex. Nucleophilic attack of active methylene compound on
this activated complex followed by the water elimination forms α, β- unsaturated diketones in
reaction 1 and α, β-unsaturated dicyano compounds in reaction 2.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
H
H
H
H
H
DES
_
DES
H
H
_
N
N
N
N
OH+
H
H
H
H
O
O
O
H
O
OH+
DES
_
H
H
OH+
H
Reaction 1
Reaction 2
O
H
H
H
H
DES
H
O
OH
OH
N
N
H
O
H
O
N
H2O
N
H2O
O
Scheme 1 Probable mechanism for DES catalysed Knoevenagel condensation reaction
19

New Journal of Chemistry
Page 20 of 24
1
2
3
4
View Article Online
DOI: 10.1039/D0NJ02852E
Conclusion
5
6
7
8
Four new deep eutectic solvents based on CeCl3.7H2O with urea, ethylene glycol, glycerol
and lactic acid were successfully introduced with the study of their acidity, density, viscosity,
thermal stability and solubility in common organic solvents and for the first time, α, β-
unsaturated diketones were synthesised in DESs. Also, the benefits of DES for the synthesis
of benzylidenes at room temperature for a wide range of substrates have also been
exemplified and the catalyst was recycled up to five runs without much loss in its activity. A
comparative study was also performed to explain the efficiency of the new deep eutectic
solvents with previous reports and the present catalyst was found to be very efficient in terms
of yield, reaction time, recyclability etc. When correlated with other methods, the easy
preparation of the catalyst is the main highlight of the present method; it took only few
minutes to get DESs from their constituents. Because of their more sustainable, efficient and
economic nature, deep eutectic solvents are excellent alternatives to conventional catalysts.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Acknowledgements
The authors gratefully acknowledge SAIF STIC, CUSAT, CIPET Kochi, CLIF Kerala
University for various analysis and University Grants Commission (UGC), New Delhi, India
for financial support.
Supporting Information
Structure of synthesised products, GC MS and NMR spectra of the compounds are given.
References
1. F. Pena-Pereira, A. Kloskowski and J. Namieśnik, Green Chem., 2015, 17, 3687.
2. X. Meng, K. Ballerat-Busserolles, P. Husson and J. M Andanson, New J.
Chem., 2016, 40, 4492.
3. C. Vidal, L. Merz and J. Garcia-Alvarez, Green Chem., 2015, 17, 3870.
4. Y. Marcus, Deep Eutectic Solvents. Springer, 2019.
5. J. Parnica and M. Antalik, J. Mol. Liq., 2014, 197, 23.
6. A. K. Schweiger, N. Ríos-Lombardía, C. K. Winkler, S. Schmidt, F. Morís, W.
Kroutil, J. Gonzá lez-Sabín and R. Kourist, ACS Sustainable Chem. Eng., 2019, 7,
16364.
7. C. Ruß, and B. König, Green Chem., 2012, 14, 2969.
20

Page 21 of 24
New Journal of Chemistry
1
2
3
4
5
View Article Online
DOI: 10.1039/D0NJ02852E
8. R. J. Isaifan and A. Amhamed, Adv. Chem., 2018, 1.
6
7
8
9
9. A. P. Abbott, K. El Ttaib, G. Frisch, K. J. McKenzie and K. S. Ryder,
Phys. Chem. Chem. Phys., 2009, 11, 4269.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
10. M. Hayyan, M. A. Hashim, A. Hayyan, M.A. Al-Saadi, I. M. AlNashef , M. E.S.
Mirghani and O. K. Saheed, Chemosphere, 2013, 90, 2193.
11. I. Juneidi, M. Hayyan and M.A. Hashim, RSC Adv., 2015, 5, 83636.
12. P. H. Tran and A. T. Hang, RSC Adv., 2018, 8, 11127.
13. A. P. Abbott, G. Capper, D. L. Davies, R. K. Rasheed, and V. Tambyrajah, Chem.
Commun., 2003, 1, 70.
14. D. J. van Osch, D. Parmentier, C. H. Dietz, A. van den Bruinhorst, R. Tuinier and M.
C. Kroon, Chem. Commun., 2016, 52, 11987.
15. J. Matong, A. Mpupa and P. N. Nomngongo, Eurasian J Anal Chem., 2018, 13, 5.
16. C. Florindo, F. Lima, L. C. Branco and I. M. Marrucho, ACS Sustainable Chem. Eng.,
2019, 7, 14739.
17. . kkinen, O. Alshammari, V. Timmermann, C. D’Agostino and A. Abbott, ACS
Sustainable Chem. Eng., 2019, 7, 15086.
18. C. A. Nkuku, and R. J. LeSuer, J. Phys. Chem. B, 2007, 111, 13271.
19. A. P. Abbott, G. Capper, K. J. McKenzie, and K. S. Ryder, J. Electroanal. Chem.,
2007, 599, 288.
20. J. Huang, X. Guo, T. Xu, L. Fan, X. Zhou, and S. Wu, J. Chromatogr. A, 2019, 1598,
1.
21. A. Söldner, J. Zach and B. König, Green Chem., 2019, 21, 321.
22. F. Liu, Z. Xue, X. Zhao, H. Mou, J. He and T. Mu, Chem. Commun., 2018, 54, 6140.
23. M. Wu, H. Ma, Z. Ma, Y. Jin, C. Chen, X. Guo, and Y. Wang, ACS Sustainable
Chem. Eng., 2018, 6, 9434.
24. A. F. Quivelli, P. Vitale, F. M. Perna and V. Capriati, Front. Chem., 2019, 7, 723.
25. G. Garcia, S. Aparicio, R. Ullah and M. Atilhan, Energy Fuel., 2015, 29, 2616.
26. N. Ndizeye, S. Suriyanarayanan and I. A. Nicholls, Polym. Chem., 2019, 10, 5289.
27. C. Vidal, J. Garcia-Alvarez, A. Hernan-Gomez, A. R. Kennedy, and E. Hevia, Angew.
Chem. Int. Ed., 2014, 53, 5969.
21

New Journal of Chemistry
Page 22 of 24
1
2
3
4
5
28. C. Vidal, J. Garcia-Alvarez, A. Hernan-Gomez, A. R. Kennedy, and E. Hevia, AnVgieewwAr.ticle Online
DOI: 10.1039/D0NJ02852E
Chem. Int. Ed., 2016, 55, 16145.
6
7
8
29. O. S. Hammond, D.T. Bowron, and K. J. Edler, ACS Sustainable Chem. Eng., 2019,
7, 4932.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
30. M. Shaibuna, L. V Theresa, and K. Sreekumar, Catal. Lett., 2018, 148, 2359.
31. A. Ilangovan, S. Muralidharan, P. Sakthivel, S. Malayappasamy, S. Karuppusamy,
and M. P. Kaushik, Tetrahedron Lett., 2013, 54, 491.
32. D. H. Jung, Y. R. Lee, S. H. Kim and W. S. Lyoo, Bull. Korean Chem. Soc, 2009, 30,
1989.
33. T. Li, W. Zhang, W. Chen, H. N. Miras, and Y. F. Song, Dalton Trans., 2018, 47,
3059.
34. K. Jain, S. Chaudhuri, K. Pal and K. Das, New J. Chem., 2019, 43, 1299.
35. N. D. Shcherban, P. Mäki-Arvela, A. Aho, S. A. Sergiienko, P. S. Yaremov, K.
Eränen and D. Y. Murzin, Catal. Sci. Technol., 2018, 8, 2928.
36. A. M. Jadhav, S. G. Balwe and Y. T. Jeong, Phosphorus, Sulfur, Silicon Relat. Elem.,
2019, 195.
37. A. Das, N. Anbu, A. Dhakshinamoorthy and S. Biswas, Microporous
Mesoporous Mater., 2019, 284, 459.
38. A. Rahmatpour and N. Goodarzi, Catal. Commun., 2019, 124, 24.
39. M. Francisco, A. Bruinhorst, L. F. Zubeir, C. J. Peters and M. C. Kroon, Fluid Phase
Equilib., 2013, 340, 77.
40. J. Naser, F. Mjalli, B. Jibril, S. Al-Hatmi and Z. Gano, Int J Chem Eng Appl., 2013,
4, 114.
41. J. Billingham, C. Breen and J. Yarwood, Clay Miner.,1996, 31, 513.
42. Y. L. Yang and Y. Kou, Chem. Commun., 2004, 2, 226.
43. E. P. Parry, J. Catal., 1963, 2, 371.
44. L. Dai, Q. Zhao, M. Fang, R. Liu, M. Dong and T. Jiang, RSC Adv., 2017, 7, 32427.
45. L. Shiwei, X. Congxia, Y. Shitao, X. Mo and L. Fusheng Chin J Catal., 2009, 30,
401.
46. Shiwei, X. Congxia, Y. Shitao and L. Fusheng Catal. Commun., 2008, 9, 2030.
22

Page 23 of 24
New Journal of Chemistry
1
2
3
4
5
View Article Online
47. T. Barzetti, E. Selli, D. Moscotti and L. Forni, J. Chem. Soc. Faraday TDraOnI: 1s0..,101399/9D60N,J02852E
92, 1401.
6
7
8
48. Y.A. Sonawane, S.B. Phadtare, B. N. Borse, A. R. Jagtap and G.S. Shankarling, Org.
Lett., 2010, 12, 1456.
9
49. B. N. Borse , S. R. Shukla , Y. A. Sonawane and G.S. Shankerling,eSynth. Commun.,
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
2013, 43, 865.via
50. P. Goswami and B. Das, Tetrahedron Lett., 2009, 50, 897.
51. F. Poyafar, M. Fallah-Mehrjardi and S. H. Banitaba, Asian J. Green Chem., 2018, 2,
96.
52. A. Kumar, M. Dewan, A. Saxena, A. De and S. Mozumdar, Catal. Commun.,
2010, 11, 679.
53. H. R. Shaterian, M. Arman and F. Rigi, J. Mol. Liq., 2011, 158, 145.
54. R. Maleki, E. Kolvari, M. Salehi and N. Koukabi, Appl. Organomet. Chem., 2017,
31, e3795.
55. X. Wu, B. Wang, Z. Yang, and L. Chen, J. Mater. Chem., 2019, 7, 5650.
56. A. Karmakar, M.M. Soliman, E. C. B. do Amaral Alegria, G. M Rúbio, M. F. C. G.
da Silva and A. J. Pombeiro,. New J. Chem., 2019, 43, 9843.
57. Z. W. Zhai, S. H. Yang, Y. R. Lv, C. X. Du, X., L. K. Li and S. Q. Zang, Dalton
Trans., 2019, 48, 4007.
58. L. J. Yue, Y. Y. Liu, G. H. Xu and J. F Ma, New J Chem., 2019, 43, 15871.
59. M. Tavakolian and M. M. Najafpour, New J. Chem., 2019, 43, 16437.
.
23

New Journal of Chemistry
Page 24 of 24
1
2
3
4
View Article Online
DOI: 10.1039/D0NJ02852E
5
6
Table of contents entry
7
8
9
Preparation, characterisation and application of novel Type IV- DES from CeCl3.7H2O and
HBDs (urea, ethylene glycol, glycerol & lactic acid)
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60