Magnetically recyclable nano-FDP: A novel, efficient nano-organocatalyst for the one-pot multi-component synthesis of pyran derivatives in water under ultrasound Irradiation

Article abstract of DOI:10.1007/s10562-015-1586-4

Highly stable, super-paramagnetic nanoparticle supported L-proline catalyst (nano-FDP) which shows extra-ordinary catalytic activity was synthesized for the first time from economical and easily available starting materials. Characterization of the synthe

Full text of DOI:10.1007/s10562-015-1586-4

Catal Lett
DOI 10.1007/s10562-015-1586-4
Magnetically Recyclable Nano-FDP: A Novel, Efficient Nano-
Organocatalyst for the One-Pot Multi-Component Synthesis
of Pyran Derivatives in Water Under Ultrasound Irradiation
Binoyargha Dam1 Mithu Saha1 Amarta Kumar Pal1
•
•
Received: 9 April 2015 / Accepted: 9 July 2015
Ó Springer Science+Business Media New York 2015
Abstract Highly stable, super-paramagnetic nanoparticle
supported L-proline catalyst (nano-FDP) which shows
extra-ordinary catalytic activity was synthesized for the
first time from economical and easily available starting
materials. Characterization of the synthesized catalyst was
done by FT-IR, EDX, SEM and TEM analysis. Application
of this for synthesis of pyran derivatives under ultrasoni-
cation at room temperature showed excellent results. Use
of water as a solvent which is nature’s own reaction
medium, shorter reaction time, high yield of the desired
product, recovery of the catalyst by external magnetic field,
and its reusability in further runsare the added advantages
of this methodology.
Keywords Novel synthesis of nano-FDP Á Magnetically
separable nano-organocatalyst Á One-pot multi-component
reaction Á Pyrano-pyrazolone derivatives
1 Introduction
Catalysis has emerged as an essential avenue in modern
chemistry because it signifies an innovative way to meet the
challenges of energy and sustainability. Existence of a cata-
lyst is primarily required in both modern organic syntheses as
well as in chemical industries. Green catalysis is a small
chapter of green chemistry but probably the most imperative
one [1].Oneofthe mostimportantcharacteristicthata catalyst
should possess in order to become green is recyclability.
Homogeneous catalysts despite havingmanyadvantageslike:
high TON (Turn Over Number), extraordinary selectivity etc.
cannot fulfil this criterion because of its difficulty in isolation.
However the use of heterogeneous catalyst or catalysts can
emerge as a tremendous remedy to solve these problems [2,
3].
Graphical Abstract
DOPAMINE
+
Fe3O4 NPs
(Hetrogeneous catalyst)
L-proline
nano-FDP
(Homogeneous catalyst)
R
NC
CN
CHO
O
O
+
O
CN
PhNH2NH2 or
NH2NH2.6H2O
R
+
O
NH2
H2O, ((( , 2-10 min
Nanoparticles as heterogeneous catalysts recently
gained lots of attention as green catalyst [4, 5].However, to
separate particles with diameters less than 100 nm from
reaction mixture is quite tedious, but magnetic nanoparti-
cles due to their paramagnetic nature can be easily sepa-
rated [6, 7] by attaching an external magnet. Among
several magnetic nanoparticles, Fe3O4 nanoparticles are
comprehensively studied because of the low cost of starting
materials, simple synthetic procedure and relatively higher
paramagnetic nature [8].
nano-FDP
Electronic supplementary material The online version of this
article (doi:10.1007/s10562-015-1586-4) contains supplementary
material, which is available to authorized users.
& Amarta Kumar Pal
amartya_pal22@yahoo.com
Since last few decades proline received tremendous
priorities in organic synthesis as homogeneous catalyst,
because of its high efficiency, environmentally benign
behaviour and availability in both enantiomeric forms. But
1
Centre for Advanced Studies in Chemistry, North-Eastern
Hill University, Shillong 793022, Meghalaya, India
123

B. Dam et al.
major drawbacks of using proline as catalyst are its sepa-
ration and reusability. In order to overcome these problems
we thought of implementing L-proline on Fe3O4 nanopar-
ticles which would make it a merger of homogeneous and
heterogeneous catalyst thereby increasing its greenness and
resolving above mentioned complications.
2 Experimental
2.1 Design and Synthesis of Nano-FDP
Recently, organocatalyst have been extensively used in
organic synthesis, but still there is a lack of using it
under sustainable condition. Though proline is an effi-
cient catalyst for many organic transformations but its
recovery from reaction mixture is very difficult, so we
planed to attach proline with magnetic nanoparticles for
making it easily recyclable. Dopamine a cheap and stable
molecule under ambient condition contains phenolic –OH
and aliphatic amine group. The phenolic –OH group
strongly co-ordinates to ferrite molecule by chelating
effect and the amine functionality binds with the car-
bonyl group of L-proline via amide bond formation
thereby keeping the secondary amine site of L-proline
free for catalysis.
Because of the mounting environmental concern on eco-
logical safety and global warming chemists throughout the
world are developing new methodologies which are efficient
and eco-friendly. So, focus on ‘‘green chemistry’’ using
environmentally benign conditions and reagents are of
utmost importance for the synthesis of widely used organic
compounds. Keeping in mind the principles of ‘‘green
chemistry’’ it is appealing to carry out reactions in nature’s
own reaction medium, i.e. water rather than using organic
solvents which are harmful. Unique structure and physio-
chemical properties of water lead to particular interactions
like H-bonding, hydrophobic interaction, trans-phase inter-
action and polarity which influence the rate of reaction and
shows additive outcomes. In addition to the above evidences
organic reactions using water as a solvent provides certain
other advantageslike insolubility of the desired product, easy
work up procedures which simplifies their isolation [9].
Multi-component reactions (MCRs) [10] have emerged as
convergent chemical processes that involve the well defined
condensation of more than two reactants to form desired
products with very high atom efficiency. This strategy of
MCR offers significant environment friendly features in true
sense like reduction in number of steps, energy consumption
and waste production [11].
Nano-FDP was synthesized by a simple, cost effective
and efficient method as shown in Scheme 1. Elaborate
synthesis paper is described in supporting information.
2.2 Catalyst Characterization
2.2.1 FT-IR
Comparative FT-IR spectra of nano-FDP, Fe3O4-DOPA
and Fe3O4 NPs is shown in Fig. 2. Prominent peak at
around 591–611 cm-1 which appears in all the three
spectra is due to Fe–O vibration. Peaks at 1630 and
1400 cm-1 in the spectrum of Fe3O4-DOPA are due to
primary –NH2 bending, and –C–N stretching of dopa-
mine moiety, indicating the successful attachment of
dopamine molecule on Fe3O4 NPs. These peaks are also
present in the spectrum of nano-FDP in almost the same
region, but peak at 1465 cm-1 has become more
prominent and sharp which indicates the secondary –N–
H stretching of amide linkage. The prominent peak at
1685 cm-1 in the spectrum of nano-FDP is the charac-
teristic peak of carbonyl group which arises due to the
stretching of amide carbonyl bond indicating the suc-
cessful attachment of L-proline with dopamine via amide
bond formation. The peak at around 3430 cm-1 in the
spectrum of Fe3O4 NPs is because of –OH stretching
vibration of Fe3O4 NPs [32] this is also present in the
other two spectra at 3415 and 3465 cm-1. If we observe
carefully, peak at around 3465 cm-1 in the spectrum of
nano-FDP is very sharp indicating the –N–H stretching
of L-proline moiety.
Ultrasonication activates organic reactions due to cavi-
tational collapse. Cavitation produce high temperature and
pressure inside the bubbles, leading to blustery flow of the
liquid and improved mass transfer [12]. Compared with
traditional methods, this method provides higher yield and
selectivity, with milder reaction condition and shorter
reaction time [13].
Pyran is an important class of heterocyclic compound
which is of significant importance in pharmaceutical indus-
try and also in medical world owing to its promising
medicinal and biological activities (Fig. 1) like anti-tumour,
anti-cancer, anti-microbial, anti-oxidant, anti-proliferative,
anti-inflammatory, anti-HIV, anti-tumour, analgesics etc.
[14–30]. On continuing our exploration for synthesis and
application of different nanoparticles in multi-component
reactions [31], we herein report a novel method for synthesis
of nano-Fe3O4-DOPA-L-proline (nano-FDP) which shows
extraordinary catalytic activity in one-pot, multi-component
synthesis of pyran derivatives under ultrasonic irradiation.
123

A Novel, Efficient Nano-Organocatalyst for the One-Pot Multi-Component Synthesis of Pyran…
Scheme 1 Synthesis of nano-
FDP
Fe3O4
NPs
O
FT-IR, SEM,
EDX,TEM
N
H
OH
1
4
(((, r.t, water, 2h
HO
HO
1.NaHCO3,
ice bath,1
5 mins.
2. (BOC)2O, THF,
r.t, 19 hrs.
=
O
NH2
2
H2N
NH2
NH2
NH2
O
Fe3O4
NPs
H2N
H2N
FT-IR,
N
OH
BOC
3
5
1. DIPEA, HBTU
Dry DMF, r.t.,
60 mins.
2. 24 hrs., r.t
HN
O
Fe3O4
NPs
N
BOC
O
6
O
2. Washed with
Saturated sol.
of NaHCO3
1. DCM, TFA
60 mins., r.t
O
Fe3O4
NPs
FT-IR, SEM,
EDX,TEM
HN
N
O
H
O
Fe3O4-DOPA-L-proline (Nano-FDP)
7
O
O
EtOOC COOEt
CN
Ar
O
O
O
OH
CN
Br
O
NH2
O
NH2
HO
OH
Anti-rheumatic
Antiinflamatory
O
Anticancer and Bcl-2 inhibitor
Antitumour
OCH3
H2N
CN
HN
O
N
N
OCH3
Br
O
CN
NH2
O2N
HN
NO2
O
O
O
O
O
N
H
O
CN
NH2
Anticancer
Anticancer
Anticancer and antibacterial
Anti-HIV
Fig. 1 Structures of some biologically and medicinally active pyran derivatives
2.2.2 EDX and SEM
the sizeofthe nanoparticlesare intherange of5–20 nmwhich
is same as that of typical diameter of Fe3O4 NPs. From TEM
images, it is also evident that, black spots are consistently
scattered throughout the sample and this can be attributed to
the presence of Fe3O4 nanoparticles. The corresponding
SAED (Selected Area Electron Diffraction) pattern showed
spotty diffraction proving the crystalline behaviour of the
sample. The width of the L-proline attached dopamine coating
is around 4 nm which is clearly visible in the TEM image of
freshly prepared nano-FDP. Width of the coating and even the
crystalline property of the catalyst is retained after five time of
consecutive uses, which is clearly evident from the ‘after use
TEM images’ and SAED patterns of nano-FDP.
In order to determine elemental composition of nano-FDP,
EDX analysis was performed. The analysis confirmed the
presence of carbon, nitrogen, iron and oxygen (shown in
Fig. 3). SEM images of Fe3O4 NPs, and nano-FDP are shown
in Fig. 4. According to SEM images nano-FDP possess
spherical shape.
2.2.3 TEM
Particle size of nano-FDP was examined by TEM analysis.
The typical TEM images of nano-FDP (Fig. 5) revealed that,
123

B. Dam et al.
49.5
48
1404
1628
599
2851
2924
46
44
42
40
38
36
34
32
30
28
26
24
22
20
18
16
14
12
10
8
1109
3430
3465
2851
2922
849
1402
1685
1465
1190 1124
1033
804 725
611
%T
583
1630
1400
3415
626
6
4
3.2
3845.5 3600
3200
2800
2400
2000
1800
1600
cm-1
1400
1200
1000
800
600
453.2
Fig. 2 Comparative FT-IR of Fe3O4 NPs (top), nano-FDP (middle) and Fe3O4-DOPA (bottom)
Fig. 3 EDX of nano-FDP
123

A Novel, Efficient Nano-Organocatalyst for the One-Pot Multi-Component Synthesis of Pyran…
Fig. 4 SEM images of a Fe3O4
NPs at 500 nm and b nano-FDP
at 200 nm
Fig. 5 a TEM of Fe3O4 NPs, b TEM of nano-FDP before use at
50 nm, c TEM of nano-FDP before use at 10 nm showing uniform
coating, d SAED of a fraction of nano-FDP before use, e TEM image
of nano-FDP after use at 50 nm, f TEM image of nano-FDP after use
at 5 nm showing the uniform coating, g SAED of nano-FDP after use
123

B. Dam et al.
Cl
H
O
O
O
NC
CN
nan -
o
FDP
CN
9
7
N
o vent
S l
,
(((
N
NH2
Cl
O
11
.
O
12
NH2NH2 H2O
H
a
8
10
a
Scheme 2 Synthesis of pyran derivatives
60
40
20
0
-20
-40
-60
-15000 -10000
-5000
0
5000
10000
15000
Applied field (Oe)
Fig. 7 VSM of nano-FDP
Fig. 6 a Powder XRD of Fe3O4 NPs. b Powder XRD of nano-FDP
3 Results and Discussions
In order to scrutinize the catalytic activity of nano-FDP, we
employed it in four component reaction of ethylacetoacete
(11), hydrazine hydrate (10), aldehyde (8) and malononi-
trile (9) for synthesizing pyran derivatives (12a). Primarily,
ethylacetoacetate (1 mmol) and hydrazine hydrate
(1.5 mmol) were mixed together, which immediately leads
to the formation of white precipitate of 3-methyl-1Hpyra-
zol-5(4H)-one (15a) to which 4-cholorobenzaldehyde
(1 mmol), and malononitrile (1 mmol) along with nano-
FDP were added and ultrasonicated in presence of various
solvents. Scheme 2 (SI-pg-3).Water was chosen as desired
solvent because it was giving excellent yield, its cheap,
easily available and it is nature’s medium for reaction.
After selection of the solvent, we did comparison of
catalytic activity of nano-FDP with other catalysts. The
model reaction was then refluxed, as well as ultrsonicated
in water (10 ml) in presence of various homogeneous and
heterogeneous catalysts like Et3N, morpholine, FeCl2,
FeCl3 glutathione, L-proline, Ni NPs, Pd NPs, Fe3O4 NPs,
Fe3O4 @DOPA NPs, SiO2 NPs, and Fe3O4-DOPA-L-pro-
line (nano- FDP) nanoparticles (Table 1). From Table 1, it
2.2.4 Powder XRD
Figure 6 represents the XRD-diffraction patterns of the
prepared Fe3O4 MNPs and nano-FDP. In both the spectra
prominent peaks at almost same region were observed,
which indicates that crystalline spinal ferrite core structure
is preserved in the final catalyst. The XRD patterns shows
six characteristic peaks at 2h = 30.29°, 35.59°, 43.25°,
53.84°, 57.16°, 62.79° which corresponds to the indices (2
2 0), (3 1 1), (4 0 0), (3 3 1), (4 2 2), (3 3 3), (5 1 1) and (4 4
0) respectively [33].
2.2.5 VSM
Magnetic behaviour of synthesized nano-FDP was studied
by Vibrating Sample Magnetometer (VSM), Fig. 7 shows
the magnetization curve for nano-FDP. The saturation
magnetization value of nano-FDP was found to be
59.89 emu/g, which is slightly lower than that of bare
Fe3O4NPs (67.22 emu/g) [34] because of coating.
123

A Novel, Efficient Nano-Organocatalyst for the One-Pot Multi-Component Synthesis of Pyran…
Table 1 Catalyst
standardization
Sl. no.
Catalysta
Conventional heating (100 °C)
Ultrasonication (r.t)
Time (min)b
Yield (%)c
Time (min)b
Yield (%)c
1
No catalyst
Et3N
180
30
30
30
30
30
30
30
30
30
30
30
30
15
30
60
55
62
88
68
72
70
78
75
80
91
30
10
10
10
10
10
10
10
10
10
10
10
10
20
36
69
60
68
90
72
85
81
85
79
91
98
2
3
Morpholine
Fecl2
4
5
Fecl3
5
L-Proline
Glutathione
Ni NPs
6
7
8
Pd NPs
9
Fe3O4 NPs
SiO2 NPs
Fe3O4@DOPA NPs
Nano-FDP
10
11
11
Reaction condition: Ethylacetoacetate (1 mmol), hydrazine hydradate (1.5 mmol), 4-Cl C6H5 (1 mmol),
malononitrile (1 mmol), 5 ml water
a
Amount taken for all the solid catalyst was 0.006 g and Et3N taken 0.01 ml
b
Time is in minutes
c
Yield is in %
is evident that all the catalysts successfully promoted the
reaction leading to the formation of the desired product.
But, the synthesized nano-FDP was showing the best result
(highlighted in bold in table 1). In absence of catalyst after
3 h very less amount of product was formed. Though the
reaction was going smoothly in both the conditions i.e.
under refluxed and ultrasonication, but we have chosen
ultrasonication as our reaction medium because it was
found that the desired product formed within very short
time interval under ultrasonication with no side products
and most importantly without supply of any external
thermal energy, i.e. the reaction was carried out at room
temperature (Figs. SI-1, SI-2). On discovering this fact we
carried a detailed observation of the model reaction in
various time scale, and it was found that the complete
conversion of the reactants into desired product took place
after 10 min of irradiation (Fig. SI-2).Amount of catalyst
used also showed significant effect on reaction. 0.006 g of
Nano-FDP under ultrasonication at room temperature is the
best catalyst loading for getting the optimum yield. Further
increase in the catalyst concentration did not affect product
yield (Fig. SI-3). After standardizing all the important
reaction parameters, nano-FDP was used for synthesizing a
series of pyrano-pyrazoles. Various aromatic aldehydes,
active methylene compounds, hydrazine or phenyl hydra-
zine were used and reacted them under optimum condition
(Scheme 3). The position of the phenyl rings didnot have
any effect on the overall product yield as shown in Table 2.
Aldehydes with both the electron-withdrawing and
electron-donating substituents in the phenyl ring gave
excellent yields at room temperature under utrasonication
(Table 2). All the products were characterized on the
basis of their analytical as well as spectroscopic data.
A plausible mechanism for the synthesis of pyrano-
pyrazolones by using nano-FDPis shown in Scheme 4.
According to proposed mechanism, firstly ethyl acetoac-
etate (11) reacts instantly with hydrazine hydrate (10) or
phenyl hydrazine (14) leading to the formation of pyra-
zolone derivatives (15a,b). Then, in the second step nano-
FDP binds with aldehyde forming iminium intermediate
(16) which reacts with malononitrile (9) in Knoevengel
fashion to give cyano-olefin compound (18). Finally nano-
FDP catalyzes the formation of intermediate (19) which
undergoes intermolecular cyclization to afford desired
product (12 or 13).
R
O
R
H
O
O
nano-FDP
CN
(((, 2-12 min
+
+ NH NH
+
NC
CN
2
H2O, r.t
N
Z
O
N
NH2
12 or 13
O
Z
Since our main object is to inspect the recovery and
reusability of the nano-FDP, we applied external magnetic
field for separation. It was our delight that the catalyst get
easily separated without any significant loss of its amount.
Then, after washing and drying we applied it for another
10
11
9
8
R= -H,-CH3, -Cl, -Br, -F, -NO2, -CN,
12; Z=H. 13; Z=Ph
Scheme 3 One-pot for component synthesis of pyran derivatives
using nano-FDP
123

B. Dam et al.
Table 2 Synthesis of various
pyrano-pyrazolone derivatives
Entry
Aldehydes
Products
Time (Min.)
Yield (%)a
Melting point (°C)
Found
Reported
1
4-Cl C6H5
4-NO2 C6H5
4-Me C6H5
C6H5
12a
12b
12c
13a
13b
13c
13d
13e
13f
10
8
98
96
90
95
89
96
95
97
98
97
96
95
232–234
254–256
207–210
168–170
175–178
171–173
188–190
183–186
174–176
195–198
187–190
192–194
234–236 [35]
251–253 [27]
206–208 [27]
167–169 [36]
176–178 [36]
170–172 [36]
190–192 [36]
181–183 [36]
175–177 [36]
195–197 [36]
189–191 [36]
190–192 [36]
2
3
12
4
4
5
4-Me C6H5
4-F C6H5
6
6
3
7
4-NO2 C6H5
4-Br C6H5
4-Cl C6H5
4-CN C6H5
3-NO2 C6H5
2-Cl C6H5
4
8
2
9
2
10
11
12
13 g
13 h
13i
3
5
6
Reaction condition: Ethylacetoacetate (1 mmol), hydrazine hydradate (1.5 mmol), 4-Cl C6H5 (1 mmol),
malononitrile (1 mmol), 0.006 g nano-FDP, 5 ml water and ultrasonication
a
isolated yield
Scheme 4 Plausible
mechanism
Step 1:
NH2NH2.H2O
10
O
O
or
O
N
R
15
N
Ph.NHNH2
O
14
11
nano-FD
NH
nano-FD
Step 2:
Step 3:
N
O
nano-FDP
nano-FDP
H
CN
CN
NH
N
NC CN
7
N
9
7
H
O
Ar
H
Ar
-H2O
16
CN
17
18
O
N
8
Ar
Ar
CN
H
H
H
CN
CN
nano-FD
NH
nano-FDP
-H2O
N
N
nano-FD
NH
O
N
N
Ar
N
R
N
18
R
R
O
15
O
20
19
H
NH2
Ar
Ar
CN
CN
CN
H
nano-FDP
+ H2O
O
O
N
N
N
N
R
R
21
12 or 13
R= H, Ph
O
Fe3O4
NPs
HN
nano-FDP=
N
H
O
7
O
99
98
95
93
91
set of reaction. It was observed that, catalyst can easily be
reused for another four runs without considerable loss of
catalytic activity (Fig. 8).
88
83
87
100
80
60
40
20
0
83
77
4 Conclusion
1
2
3
4
5
In conclusion, we have developed an efficient, super-param-
agnetic and highly reusable nano-FDP organocatalyst which
was synthesized for the first time using dopamine bridge.
Weight % of recovered catalyst Isolated yield of desired product
Fig. 8 Catalyst recycling
123

A Novel, Efficient Nano-Organocatalyst for the One-Pot Multi-Component Synthesis of Pyran…
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synthesis of pyrano-pyrazolones in water under ultrasonic
irradiation at room temperature. Recovery and reusability of
nano-FDP for five consecutive runs made this procedure more
economically viable and environment friendly.
Acknowledgments We would like to thank DST, India for financial
support (sanctioned no: SERC/F/0293/2012-13), DST-Purse. UGC,
for supporting thiswork under Special Assistance Programme (SAP).
Department of Chemistry-NEHU, SAIF-NEHU, IASST Guwahati,
IIT-Guwahati for helping us in collecting important analytical data.
We would also like to thank NEHU-Non-NET fellowship for financial
assistance.
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