On-water magnetic NiFe2O4 nanoparticle-catalyzed Michael additions of active methylene compounds, aromatic/aliphatic amines, alcohols and thiols to conjugated alkenes

Article abstract of DOI:10.1039/c6ra21160g

Here, we have demonstrated the Michael addition of active methylene compounds, aromatic/aliphatic amines, thiols and alcohols to conjugated alkenes using magnetic nano-NiFe₂O₄ as reusable catalyst in water. Nano-NiFe₂O₄ efficiently catalyzed the formation of C-C and C-X (X = N, S, O etc.) bond through 1,4-addition reactions.

Full text of DOI:10.1039/c6ra21160g

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On-water magnetic NiFe2O4 nanoparticle-
catalyzed Michael additions of active methylene
compounds, aromatic/aliphatic amines, alcohols
and thiols to conjugated alkenes†
Cite this: RSC Adv., 2016, 6, 95951
*
Soumen Payra, Arijit Saha and Subhash Banerjee
Received 23rd August 2016
Accepted 3rd October 2016
Here, we have demonstrated the Michael addition of active methylene compounds, aromatic/aliphatic
amines, thiols and alcohols to conjugated alkenes using magnetic nano-NiFe2O4 as reusable catalyst in
water. Nano-NiFe2O4 efficiently catalyzed the formation of C–C and C–X (X ¼ N, S, O etc.) bond
through 1,4-addition reactions.
DOI: 10.1039/c6ra21160g
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The designing and vigilant utilization of catalysts can make an synthesis of variety natural products, antibiotics and other
industrialized protocol economic, greener and more sustain- nitrogen, oxygen, sulphur containing bio-molecules.8,9 Various
able by reducing the formation of harmful waste to human catalysts including strong bases, Lewis acids, metal complexes,
health and the environment. The sustainability and applica- and oxides have been used for C–C and C–X Michael addition
bility of the protocol can be enhanced by using water as solvent. reactions10–13 that oen lead to undesirable side reactions,14 and
Among other catalysts, the development of magnetic nano- most of these catalysts were homogeneous in nature. However,
particles (MNP) paved the way on catalysis as well as in drug there is a lack of common method using a robust and reusable
delivery, and remediation.1,2 These MNP are robust, inexpen- catalyst to carry out the C–C and C–X Michael addition reac-
sive, easily accessible and possess high surface to volume ratio. tions. In this paper, we have demonstrated general protocol for
In addition, they added advantage of being separable by means the carbon–carbon and carbon–heteroatom bond formation via
of external magnet aer completion of the reaction. Thus, Michael addition reactions using nano-NiFe2O4 as reusable
introduction of MNPs as catalyst in useful organic trans- catalyst in water (Scheme 1).
formations will be appreciated. However, literature study
To accomplish this research, initially, we have prepared
reveals that among these MNPs, NiFe2O4 nanoparticles (NPs) NiFe2O4 NPs by following our previously reported method6l via
have extensively been used as supporting materials for active sol–gel method (see ESI 1 for detailed procedure†). The powder
catalysts due to the high magnetic nature and robustness.3,4 X-ray diffraction (XRD) pattern (Fig. 1) of the prepared material
Interestingly, only few reports are present on the application of reveals the formation of face centred cubic spinel NiFe2O4
NiFe2O4 NPs in organic transformations.5 As a part of our (ref. 15) where the Bragg reection peaks were indexed to Fd3m
continuous effort in the eld of nano-catalysis6 recently, we space group (JCPDS le no. 10-0325). The broadening of peaks
have demonstrated the catalytic activity of nano-NiFe2O4 in indicates the formation of nano-particulate NiFe2O4 (average
transfer hydrogenation–dehydrogenation6n and in the synthesis size ꢀ 16 nm, calculated from Scherrer formula using XRD
of 2-alkoxyimidazopyridines.6l
plane 440). The formation of spherical NiFe2O4 NPs with
On the other hand, the Michael addition is one of the most average particle sizes of 15 nm was also evident from high
useful tool for the carbon–carbon (C–C; so called classical
Michael addition reaction) bond-forming reactions and has
wide synthetic applications in organic synthesis.7 Alternatively,
carbon–heteroatom (C–X) bond formations via aza-Michael (X ¼
N), thia-Michael (X ¼ S), oxa-Michael (X ¼ O) addition reactions
have attracted more attention due to wide applications in
Department of Chemistry, Guru Ghasidas Vishwavidyalaya (A Central University),
Bilaspur – 495009, Chhattisgarh, India. E-mail: ocsb2006@gmail.com
† Electronic supplementary information (ESI) available: Detailed experimental
procedure and characterization of catalyst and Michael addition; copies of 1H
and 13C NMR of the products listed in Tables 2–5, reusability of NiFe2O4. See
Scheme 1 NiFe2O4 NPs catalyzed Michael addition reactions.
DOI: 10.1039/c6ra21160g
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Table 1 Optimization of reaction conditionsa
Entry Catalyst
Solvent
Temperature Time Yieldb (%)
1
2
3
4
5
6
7
8
NiFe2O4 NPs H2O : EtOH 100 ꢁ
Fe3O4 NPs
NiO NPs
C
C
C
C
C
C
C
C
C
C
C
C
C
1 h
1 h
1 h
1 h
1 h
1 h
1 h
1 h
1 h
1 h
1 h
1 h
1 h
93
43
51
30
Nd
Nd
Nd
94c
52d
94
H2O : EtOH 100 ꢁ
H2O : EtOH 100 ꢁ
CuFe2O4 NPs H2O : EtOH 100 ꢁ
ZnFe2O4 NPs H2O : EtOH 100 ꢁ
MgFe2O4 NPs H2O : EtOH 100 ꢁ
CoFe2O4 NPs H2O : EtOH 100 ꢁ
NiFe2O4 NPs H2O : EtOH 100 ꢁ
NiFe2O4 NPs H2O : EtOH 100 ꢁ
Fig. 1 The powder XRD pattern of nano-NiFe2O4.
9
10
11
13
14
NiFe2O4 NPs Toluene
NiFe2O4 NPs DMF
NiFe2O4 NPs DCM
NiFe2O4 NPs DCE
100 ꢁ
100 ꢁ
100 ꢁ
100 ꢁ
43
48
50
resolution transmission electron microscopic (HRTEM) image
(Fig. 2).
Next, we have attempted C–C Michael addition by the reac-
tion of 1,3-diphenyl-prop-2-ene-1-one (1a, 1 mmol) and dieth-
ylmalonate (2a, 1.2 mmol) using nano-NiFe2O4 (10 mg) in
water–ethanol mixture (1 : 1; 2 mL). It was observed good yield
of Michael adduct (3a) isolated aer 1 h (entry 1, Table 1). To
establish the superiority of nano-NiFe2O4 we have carried out
the same reaction with different catalysts. It was observed that
Fe3O4 NPs, NiO NPs and CuFe2O4 could initiate the Michael
addition reaction but the yields were very less (entries 2–4, Table
1) but other ferrites like, ZnFe2O4, MgFe2O4 and CoFe2O4, were
found to be inactive in the reaction (entries 5–7, Table 1).
It was observed that only 10 mg of nano-NiFe2O4 was suffi-
cient to carry out the reaction smoothly and yield remained
same when the catalyst loading was increased to 15 mg (entry 8,
Table 1). However, decreasing the catalyst amount to 5 mg, the
yield of product decreased (entry 9, Table 1). The screening of
solvents for the reaction it was observed that water–ethanol
mixture and toluene (entry 10) gave the better results compared
a
Reactions were carried out with 1,3-diphenyl-prop-2-ene-1-one (1
b
mmol) and diethylmalonate (1 mmol) and 10 mg of NiFe2O4. Yield
of isolated product. c 15 mg of NiFe2O4. d 5 mg of NiFe2O4 was used.
to other solvents tested here (entries 11–14, Table 1). Thus, 10
mg of nano-NiFe2O4 for 1 mmol of substrates in 2 mL of water–
ethanol mixture (1 : 1) at 100 ꢁC was considered as optimum
reaction conditions.
Using optimized reaction conditions and following a simple
experimental procedure16 (detailed procedure provided in ESI
7†) we have explored the scope of the Michael addition reaction.
We have observed that various active methylene compounds
were smoothly reacted with conjugated alkenes such as conju-
gated ketones/carboxylic esters/nitriles under the optimized
reaction conditions producing excellent yields of Michael
adduct within short reaction time (0.5–1.5 h). The results were
presented in Table 2. All the reactions listed in Table 2 are very
clean and high yielding (89–98%). Aer the completion of
reaction the nano-NiFe2O4 catalyst was separated simply by an
external magnet and the product was extracted with ethyl
acetate. The NiFe2O4 NPs were washed with water and ethanol
respectively, dried and reused for subsequent reactions. The
reusability of nano-NiFe2O4 was investigated for the Michael
addition of 1,3-diphenyl-prop-2-ene-1-one (1.0 mmol; 208 mg)
and diethylmalonate (1.2 mmol; 192 mg) as model reaction.
It was observed that nano-NiFe2O4 was very stable under the
reaction conditions and little loss of yields were observed even
aer 10th cycle (Fig. 3).
Next, we have applied nano-NiFe2O4 in aza-Michael reaction
of aromatic/aliphatic amines to conjugated alkenes. The aza-
Michael addition of aliphatic amines is more facile than
aromatic amines due their poor nucleophilicity and strong basic
or fancy/expensive catalysts are required to initiate the reaction.
Here, nano-NiFe2O4 showed excellent catalytic activity
towards aza-Michael addition of aromatic amines to conjugated
Fig. 2 The TEM image of nano-NiFe2O4.
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Table 2 Classical Michael addition reactiona,b
Table 3 Aza-Michael addition reaction with aromatic aminea,b
a
Reaction conditions: aromatic amine (1.0 mmol), Michael acceptor
(1.5 mmol), 10 mg NiFe2O4 NPs at 100 ꢁC in water and Rf value in
(9 : 1) petroleum ether and ethyl acetate mixture. Yields refer to
b
those of pure isolated products.
to produce Michael adducts (7a–i) at room temperature. The
results were presented in Table 4. All the reactions were very fast
(20–30 min) and high yielding (92–99%). The detailed experi-
mental procedures have been provided in ESI 8 and 9.†
The excellent catalytic activity of nano-NiFe2O4 in classical
Michael and aza-Michael addition reactions prompted us to
explore its performance in the more challenging oxa-Michael
a
Reaction conditions: active methylene compound (1.2 mmol), Michael
acceptor (1.0 mmol), NiFe2O4 NPs (10 mg) in water–EtOH (1 : 1) mixture
2 mL at 100 ꢁC for 1.5 h under air and Rf value in (9 : 1) petroleum ether
b
and ethyl acetate mixture. Yields refer to those of pure isolated
products.
alkenes in water. Thus, when a mixture of aniline (1 mmol; 93
mg), methyl acrylate (1.5 mmol; 129 mg) and nano-NiFe2O4
(10 mg) is reuxed in water (2 mL), methyl 3-phenyl propionate
was obtained in excellent yield (176 mg; 98%). Aromatic amines
with electron donating and electron withdrawing groups
underwent conjugate addition to a,b-unsaturated ester, nitrile
and amide under the optimized reaction conditions providing
excellent yields (89–99%) of products (5a–i, Table 3). In addition
to aromatic amines the nano-NiFe2O4 catalyst also enabled the
aza-Michael addition of aliphatic amines to conjugated alkenes
Table
4 Aza-Michael addition reactions of aliphatic amines to
conjugated alkenesa,b
a
Reaction conditions: aliphatic amine (1.0 mmol), Michael acceptor
(1.5 mmol) in presence of 10 mg NiFe2O4 NPs under air at room
temperature in water and Rf value in (9 : 1) petroleum ether and ethyl
acetate mixture. b Yields of pure isolated products.
Fig. 3 Represents the reusability of nano-NiFe2O4 for the synthesis of
diethyl 2-(3-oxo-1,3-diphenylpropyl)malonate (3a).
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Table 6 Thia-Michael addition reactionsa,b
addition of aliphatic alcohol to conjugated alkenes. The
nucleophilicity of alcohols are very poor due to electronegativity
of oxygen atom. Interestingly, we have observed that nano-
NiFe2O4 activated the alcohol to participate in oxa-Michael
addition to b-nitrostyrene derivatives. Thus, when b-nitro-
styrene (1 mmol; 149 mg) was reuxed with nano-NiFe2O4 (10
mg) in ethanol (2 mL), good yield (172 mg; 88%) of oxa-Michael
adducts, 1-(1-ethoxy-2-nitroethyl)benzene was obtained aer 2
hours (entry 1, Table 5). Here, ethanol act as nucleophile as well
as solvent and no other solvent is required. The detailed
procedure for the oxa-Michael addition has been given in ESI
10.† Various aliphatic primary alcohols such as ethyl alcohol,
propyl alcohol and butyl alcohol were participated smoothly
giving good yields (73–90%) of oxa-Michael adducts (9a–i, Table
5) with different b-nitrostyrenes. Both electron donating and
electron withdrawing group present in the benzene ring of
nitrostyrene were tolerated well in this reaction conditions. All
the reactions are very clean, fast and high yielding (73–90%).
The magnetic nano-NiFe2O4 catalyst was separated simply by
using an external magnet and products were puried by short-
column chromatography over silica gel.
a
Reaction conditions: aromatic thiol (1.0 mmol), Michael acceptor (1.5
mmol) in presence of 10 mg NiFe2O4 NPs under air at 100 ꢁC in water
and Rf value in (9 : 1) petroleum ether and ethyl acetate mixture.
b
Yield of the isolated pure products.
In addition to the above mentioned Michael addition reac-
tions, we have also applied nano-NiFe2O4 in Michael addition of
aromatic thiol to conjugated ketones/carboxylic esters/nitriles
and as expected the nano-catalyst provided excellent yields
(86–99%) of thia-Michael adducts (11a–f, Table 6) within very
short time period (10–15 minutes) in water at room tempera-
ture. The general experimental procedure has been provided in
ESI 11.†
Finally, leaching study was performed to check the hetero-
geneity stability of the catalyst by hot ltration test for the
Table 5 Oxa-Michael addition of alcohols to conjugated alkenesa,b
Fig. 4 Results of leaching study by hot filtration test performed with:
(a) filtrate removed after 30 min (black line) and (b) complete run (red
line) for the synthesis of diethyl 2-(3-oxo-1,3-diphenylpropyl)
malonate.
synthesis of diethyl 2-(3-oxo-1,3-diphenylpropyl)malonate (3a).
The catalyst, nano-NiFe2O4 was separated from reaction mixture
(aer 30 minutes associated with 30% conversion) by an external
magnet under hot conditions and remaining mixture was
continued to stir under standard reaction conditions for addi-
tional 2.0 h. However, no such signicance improvement of yield
of diethyl 2-(3-oxo-1,3-diphenylpropyl)malonate product was
observed aer separation of catalyst from the reaction mixture.
The results were presented in Fig. 4. These results shows that the
nano-NiFe2O4 catalyst was stable at the reaction conditions and
apparently there was no leaching of metal content from NPs.
a
Reaction conditions: b-nitrovinyl benzene (1.0 mmol), aliphatic
Conclusions
primary alcohols (2.0 mL), NiFe2O4 NPs (10 mg), at reux for 2 h in
open air and Rf value in (9 : 1) petroleum ether and ethyl acetate
mixture. b Yield of the isolated pure products.
In conclusion, we have demonstrated a simple, efficient, green
and clean protocol for the carbon–carbon Michael addition and
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carbon–heteroatom namely, aza-, oxa-, thia-Michael addition
reactions using magnetic nano-NiFe2O4 as a reusable catalyst.
The protocol is general, very clean, mild and the products were
obtained in quantitative yields which were puried by column
chromatography short silica gel with ease. All the reactions were
performed either in neat or water and thus the use of volatile
and hazardous solvent have been avoided. The catalyst, NiFe2O4
NPs were easily separated from the reaction mixture by an
external magnet and reused which made the protocol economic
and sustainable. Thus, the present protocol fulls the criteria of
green chemistry and we believe that this upshot will nd many
applications in the eld of green synthesis.
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Acknowledgements
We are pleased to acknowledge Department of Science and
Technology, New Delhi, Govt. of India (No. SB/FT/CS-023/2012)
for the nancial support. Special thanks to Prof. B. C. Ranu and
his group for their help in NMR studies.
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diphenyl-prop-2-ene-1-one with diethyl malonate.
A
mixture of 1,3-diphenyl-prop-2-ene-1-one (1 mmol, 208
mg), diethyl malonate (1.2 mmol, 192 mg) and NiFe2O4 (10
mg) is heated at 100 ꢁC in water–ethanol mixture 2 mL
(1 : 1) under open atmosphere for 1 h (TLC-monitored).
Then, the reaction mixture was cooled to room
temperature and the catalyst was recovered by using an
external strong magnetic eld. The remaining reaction
mixture was evaporated in vacuum to reduce the volume
and extracted with ethyl acetate (20 mL), washed with
water (5 mL; 3 times) followed by brine solution. Then the
extracted solution was dried over anhydrous Na2SO4. The
crude product was obtained by evaporation of solvent in
vacuum which was puried by short column
chromatography over silica gel (60–120 mesh) using
mixture of petroleum ether and ethyl acetate (90 : 10) as an
eluting solvent to afford the pure diethyl 2-(3-oxo-1,3-
diphenylpropyl)malonate (Table 2, entry 1; 93%, 342.5 mg)
as white solid. Rf value (Rf ¼ 0.37) was determined using
petroleum ether and ethyl acetate mixture (9 : 1) as an
eluting agent. The formation of the product was conrmed
by 1H NMR studies. 1H NMR (500 MHz, CDCl3): d 7.90 (d,
J ¼ 7.0 Hz, 2H), 7.52 (t, J ¼ 6.5 Hz, 1H), 7.43 (t, J ¼ 6.5 Hz,
2H), 7.25 (t, J ¼ 8 Hz, 4H), 7.15 (t, J ¼ 6.5 Hz, 1H), 4.19 (d,
J ¼ 6.5 Hz, 3H), 3.96 (d, J ¼ 6.5 Hz, 2H), 3.83 (d, J ¼ 9.5
Hz, 1H), 3.48 (m, 2H), 1.25 (t, J ¼ 6.5 Hz, 3H), 1.00 (t, J ¼
6.5 Hz, 3H). The same protocol was followed for all the
reaction listed in Table 2.
€
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95956 | RSC Adv., 2016, 6, 95951–95956
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