Silica supported-double metal cyanides (DMCs): A green and highly efficient catalytic protocol for isomerisation of 2′-hydroxychalcones to flavanones

Article abstract of DOI:10.1016/j.molcata.2013.03.009

Four different double metal cyanides (NiHCFe, CrHCFe, MnHCFe and ZnHCFe) were synthesized, followed by adsorbed on silica gel and used as Lewis acid catalyst in the isomerisation of substituted 2′-hydroxychalcones to flavanones under solvent-free (dry) condition. Optimization of the reaction condition, temperature effects, DMC catalysts loading and re-useable catalytic activity were further studied during the reaction. Among these catalysts, NiHCFe at 35 mol% loading gave excellent yield (90%) at 100 C temperature in 1.15 h. Catalyst (NiHCFe) easily recovered and re-used six times without much loss of its catalytic activity which gave 80-85% product yields each time. However, these DMCs were failed to give product in the solution phase even prolonging the reaction time at reflux temperature. Similarly, isomerization of substituted 2′-aminochalcones gave 2-5% yields either in solution phase or under solvent-free condition.

Full text of DOI:10.1016/j.molcata.2013.03.009

Journal of Molecular Catalysis A: Chemical 373 (2013) 135–141
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Silica supported-double metal cyanides (DMCs): A green and highly efficient
catalytic protocol for isomerisation of 2ꢀ-hydroxychalcones to flavanones
Naseem Ahmed∗, Naveen Kumar Konduru, Praveen, Anand Kumar, Kamaluddin
Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee 247 667 (UK), India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 6 June 2012
Received in revised form 26 February 2013
Accepted 3 March 2013
Available online 19 March 2013
Four different double metal cyanides (NiHCFe, CrHCFe, MnHCFe and ZnHCFe) were synthesized, fol-
lowed by adsorbed on silica gel and used as Lewis acid catalyst in the isomerisation of substituted
2ꢀ-hydroxychalcones to flavanones under solvent-free (dry) condition. Optimization of the reaction con-
dition, temperature effects, DMC catalysts loading and re-useable catalytic activity were further studied
during the reaction. Among these catalysts, NiHCFe at 35 mol% loading gave excellent yield (90%) at 100 ◦C
temperature in 1.15 h. Catalyst (NiHCFe) easily recovered and re-used six times without much loss of its
catalytic activity which gave 80–85% product yields each time. However, these DMCs were failed to give
product in the solution phase even prolonging the reaction time at reflux temperature. Similarly, isomer-
ization of substituted 2ꢀ-aminochalcones gave 2–5% yields either in solution phase or under solvent-free
condition.
Keywords:
Silica supported-double metal cyanide
(DMC) catalyst
Isomerisation
2ꢀ-Hydroxychalcones
Flavanones
© 2013 Elsevier B.V. All rights reserved.
1. Introduction
like tetrabutylammonium iodide, tetrabutylphosphonium bro-
mide, hexadecyltrimethylammonium bromide; organocatalysts
Flavanones (2,3-dihydroflavones) are central intermediate in
the biogenesis of flavonoids and are present in plants as the largest
single group conferring oxygen ring compounds [1]. They have no
direct involvement in the growth and development of plants. How-
ever, they play an important role in protecting the plants from
microbes and insects attack [2]. These polyphenolic molecules are
the most fascinating and useful secondary metabolites which con-
stitute an important component of human diet and known for their
antioxidant activities [3,4]. They have further diverse spectrum
of biological activities that include hepatoprotectors, hypoten-
sive, antifungal, antibacterial and antitumor [5–8]. In the synthesis
of pharmaceutical and biological significance molecules, they are
widely used as synthons in the laboratory [9].
like glycine, L-proline, L-alanine, L-leucine and pyridine; ZnO
supported-metal oxide (MgO, BaO, K2O and Na2O) catalysts under
solvent free condition at high temperature [17–20] and MgO- and
ZnO-impregnated with various other supports as HZSM-5, Al2O3
and SiO2 [21–24]. Generally, it was observed that the yield of
flavanone is less in solid-supported catalysts up to 100 ◦C might
be due to less adsorption on the active sites and at high tem-
perature (above 160 ◦C), the yield of flavanone is reduced due to
prevention of adsorption [25]. To obviate such problems, recently
several activators/promoters such as Lewis acids and metal salts,
MW, ultrasound and solid support methods have been introduced
[26–28]. However, some of these procedures have drawbacks such
as long reaction time, decomposition, low yields, use of toxic
reagents and tedious work up procedures [29–31] due to high tem-
perature and deactivated and sterically hindered aromatic rings.
Therefore, we have interest in new catalytic system for the syn-
thesis of flavanones. Indeed, we need to develop an efficient and
green protocol due to the growing awareness about environmen-
tal concerns. Therefore, the organic chemists are under increasing
pressure to alter current working practices for the sustainable
development in academia and industry research and to find envi-
ronmentally benign and greener alternatives.
In the biogenesis, 2ꢀ-hydroxychalcones gave flavanones in
the presence of enzyme chalcone isomerase [10]. Therefore, 2ꢀ-
hydroxychalcones are commonly used in the flavanones synthesis
under different acid and base [11,12] catalysts, thermolysis, elec-
trolysis and photolysis [13] in the laboratories. These reactions gave
variable yields (20–90%) depending upon the substituents on the
aromatic rings. Flavanones have also been prepared using other
methods like condensation of phenylpropiolic acid with phenols
[14,15]; solvent free synthesis using MW-irradiation of phloroglu-
cinol and ␤-ketoesters [16]; using phase transfer catalysts
The solid support chemistry has been used for many synthe-
ses [32]. Among the various advantages that solid-phase synthesis
offers are the ability to use excess quantities of reagents to force
reactions to completion and the easy of product isolation by sim-
ple filtration, thus affording the clean products with no further
∗
Corresponding author. Tel.: +91 1332 285745; fax: +91 1332 285745.
E-mail addresses: nasemfcy@iitr.ernet.in, naseem2008@gmail.com (N. Ahmed).
1381-1169/$ – see front matter © 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molcata.2013.03.009

136
N. Ahmed et al. / Journal of Molecular Catalysis A: Chemical 373 (2013) 135–141
need for conventional work-up and purification. Therefore, homo-
geneous catalysts have been extensively investigated, but only few
heterogeneous catalysts have been found. Heterogeneous catalysts
in the organic synthesis have special interest from environmental
and economical point of view. They have high turn-over numbers
and easily separated from reaction mixtures. Similarly, it is found
that the cyclization reaction of hydroxy group to a carbon–carbon
unsaturated bond (like 2ꢀ-hydroxychalcones) is thermodynami-
cally feasible but has high activation barriers.
The double metal cyanides (DMCs) are heterogeneous catalysts
which have zeolite-type case structure and contain only Lewis
acid sites [33]. These lowers the activation energy and so used
as industrially applied solid Lewis catalysts for the ring open-
ing and polymerization of epoxides producing polyether–polyols
[34], transesterification of carbonates [35] and multi-component
coupling reactions [36]. They were also reported as catalysts in
hydroamination, copolymerization of CO2 with propylene, cyclo-
hexene and other epoxide ring opening reactions [37–39].
by completely dried by heating under vacuum. DMCs-silica gel
adsorbed catalysts were directly used in the reaction.
2.5. General procedure for the synthesis of flavanones
2ꢀ-Hydroxychalcone (1 mmol) in minimum CHCl3 was added
drop wise on a mixture of silica gel (3 mmol, 180.24 mg) and NiHCFe
catalyst (35 mol%, 12 mg) or 2ꢀ-hydroxychalcone (1 mmol) in min-
imum CHCl3 was added drop wise on DMCs–silica gel adsorbed
catalysts (190–192 mg). Followed by evaporation of solvent, the
reaction mixture was stirred and grinded at 100 ◦C temperature.
Thin layer chromatography (TLC) monitoring, the reaction was
completed in 1–1.15 h. The reaction mixture was cooled, dis-
solved in dichloromethane (CH2Cl2) and filtered DMC catalyst dried
under vacuum for re-use. Dichloromethane solvent was evaporated
in vacuo and recrystallized from methanol to obtain the pure prod-
uct.
We report herein first time the use of NiHCFe, CrHCFe, MnHCFe,
ZnHCFe catalysts for the isomerisation of 2ꢀ-hydroxychalcone to
flavanone using silica gel support under solvent-free condition.
2.6. Characterization data for compounds 1b–20b
2-(4-Methoxyphenyl)-2,3-dihydrochromen-4-one (1b): Yield
80%; light yellow solid; mp: 95–96 ◦C (Lit. [45] 95–97 ◦C); IR ꢀmax
(KBr, cm−1): 2956, 2923, 1680 (C O), 1590, 1320, 1225; 1H NMR
(500 MHz, CDCl3): ı 7.81 (dd, 1 H, J = 8.0 and 2 Hz), 7.52–7.48 (m,
1H), 7.41 (d, 2H, 8.5 Hz), 7.07–7.03 (m, 2H), 6.96 (dd, 2H, J = 8.5 and
1.5 Hz), 5.43 (dd, 1H, J = 13.5 and 2.5 Hz), 3.85 (s, 3H), 3.11 (dd, 1H,
J = 16.5 and 13.5), 2.86 (dd, 1H, J = 17.0 and 3 Hz).
2-(4-Bromophenyl)-2,3-dihydrochromen-4-one (2b): Yield 90%;
light yellow solid; mp: 119 ◦C (Lit. [46] 118–119 ◦C); IR ꢀmax
(KBr, cm−1): 2965, 2930, 1685 (C O), 1566, 1300, 1230; 1H NMR
(500 MHz, CDCl3): ı 7.82 (dd, 1H, J = 8.0 and 2 Hz), 7.48–7.59 (m,
3H), 7.34–7.49 (m, 2H), 7.03–7.10 (m, 2H), 5.47 (dd, 1H, J = 13.0 and
3 Hz), 3.04 (dd, 1H, J = 16 and 13.0 Hz), 2.88 (dd, 1H, J = 16 and 3 Hz).
2-(3,4-Dimethoxyphenyl)-2,3-dihydrochromen-4-one (3b): Yield
78%; light yellow solid; mp: 148–149 ◦C; IR ꢀmax (KBr, cm−1): 2954,
2934, 1676 (C O), 1545, 1322, 1221; 1H NMR (500 MHz, CDCl3): ı
8.20 (dd, 1H, J = 1.5 Hz, J = 7.8 Hz), 7.53 (d, 1H, J = 7.5 Hz), 7.51 (dd,
1H, J = 8 and 2 Hz),7.40 (dd, 1H, J = 8 and 6 Hz), 7.36 (d, 1H, J = 2 Hz),
6.96 (d, 1H, J = 8 Hz), 6.72 (s, 1H), 5.43 (dd, 1H, J = 13.5 and 2.5 Hz),
3.98 (s, 3H), 3.95 (s, 3H), 3.11 (dd, 1H, J = 16.5 and 13.5 Hz), 2.86
(dd, 1H, J = 17.0 and 3 Hz). 13CNMR (125 MHz, CDCl3) 178.3, 163.3,
156.1, 152.1, 149.3, 133.6, 125.6, 124.2, 123.9, 120.0, 118.0, 111.2,
108.8, 106.4, 56.1.
2. Experimental
2.1. Reagents and materials
The reagents (chemicals) were purchased from commercial
sources and used without further purification. All reactions were
monitored by TLC using pre-coated silica gel aluminum plates (con-
tain ∼13% CaSO4 ½ H2O, silica gel/UV254) purchased from Merck.
Visualization of TLC plates was accomplished with UV lamp (short
UV, 254 nm) and charring with 5% methanolic H2SO4 spray reagent.
Metal hexacyanoferrate (MHCFe) was synthesized from potassium
hexacyanoferrate (II), following Alam et al. method [40–42]. Chal-
cone derivatives were synthesized according a reported procedure
[43,44].
2.2. Equipment
Melting points were recorded on perfit apparatus and are uncor-
rected. Elemental analysis was performed on a Vario EL–HNS
analyzer. FT infrared (FTIR) spectra were recorded on a Nexus
Thermo Nicolet FT-IR spectrometer using KBr pellets. 1H and 13C
NMR spectra were recorded in deuterated chloroform (CDCl3) on
a 500 MHz and 125 MHz (Bruker) respectively. Chemical shifts are
given in parts per million (ppm) referenced to TMS.
2-(3,4,5-Trimethoxyphenyl)-2,3-dihydrochromen-4-one
(4b):
Yield 75%; light yellow solid; mp = 165–166 ◦C; IR ꢀmax (KBr,
cm−1): 2956, 2923, 1680 (C O), 1630, 1600, 1590, 1320, 1300,
1225, 964; 1H NMR (500 MHz, CDCl3): ı 8.06 (d, 2H, J = 8 Hz), 6.95
(d, 2H, J = 8 Hz), 6.66 (d, 1H, J = 2.5 Hz), 6.78 (d, 1H, J = 2.5 Hz), 5.32
(dd, 1H, J = 13.5 and 2 Hz), 3.88 (s, 9H), 2.70 (dd, 1H, J = 13.5 and
2.0 Hz), 2.98 (dd, 1H, J = 16.8 and 13.0 Hz).
2.3. Preparation of metal hexacyanoferrates (II)
A solution of potassium hexacyanoferrate (II) (167 mL, 0.1 M)
was slowly added to an aqueous solution of the respective metal
nitrate (500 mL, 0.1 M) with constant stirring at room temperature.
A slight excess of metal salt was used for complete precipitation. A
reaction mixture was then heated at 60 ◦C on a water bath for 2–3 h
and kept as such for 24 h at ambient temperature. After 24 h, the
precipitate was filtered on a Buckner funnel, washed thoroughly
with Millipore water and dried in an oven at 60 ◦C. The dried prod-
uct was powdered and sieved with 100 mesh size.
2-(3-Nitrophenyl)-2,3-dihydrochromen-4-one (5b): Yield 89%;
light yellow solid; mp = 173–174 ◦C (Lit. [47] 174–176 ◦C); IR ꢀmax
(KBr, cm−1): 2956, 2923, 1698 (C O), 1630, 1527 (CH = CH), 1490
(CNO2), 1320, 1230, 965. 1H NMR (500 MHz, CDCl3); 8.2 (s, 1H), 8.12
(dd, 2H, J = 14 and 3 Hz), 7.6 (d, 1H, 16 Hz), 7.52 (d, 2H, 14 Hz), 6.95
(d, 2H, J = 8 Hz), 5.8 (dd, 1H, J = 13.5 and 2 Hz), 3.11 (dd, 1H, J = 16.5
and 13.5 Hz), 2.86 (dd, 1H, J = 17.0 and 3 Hz).
7-Methoxy-2-(3-nitrophenyl)-2,3-dihydrochromen-4-one (6b):
Yield = 86%. light yellow solid; mp = 89 ◦C; IR ꢀmax (KBr, cm−1):
2985, 1627 (C O), 1630, 1527, 1486 (CNO2), 1320, 1224. 1H NMR
(500 MHz, CDCl3); 8.2 (s, 1H), 8.12 (dd, 1H, J = 13 Hz), 7.6 (d, 1H,
16 Hz), 7.52 (d, 2H, 14 Hz), 6.95 (d, 2H, J = 8 Hz), 5.8 (dd, 1H, J = 13.5
and 2 Hz), 3.73 (s, 3H), 3.11 (dd, 1H, J = 16.5 and 13.5 Hz), 2.86 (dd,
1H, J = 17.0 and 3 Hz). 13C NMR (CDCl3, 125 MHz): ı 196.9, 165.7,
157.9, 148.6, 141.6, 133.3, 130.4, 129.9, 122.4, 120, 112.7, 105.8,
100.4, 78, 55.9, 42.8.
2.4. General procedure for the adsorption of double metal
cyanide on silica
To a mixture of double metal cyanide (DMC, 35 mol%, CrHCFe –
12.5 mg; MnHCFe – 11.6 mg; NiHCFe – 12 mg; ZnHCFe – 13.3 mg)
and silica gel (3 mmol, 180.24 mg) was added minimum amount
of water. The slurry was stirred and grinded for 2 min, followed

N. Ahmed et al. / Journal of Molecular Catalysis A: Chemical 373 (2013) 135–141
137
2-(4-Chlorophenyl)-7-methoxy-2,3-dihydrochromen-4-one (7b):
2-(4-Dimethylaminophenyl) chroman-4-one (16b): Yield 30%;
light yellow solid; mp: 119–120 ◦C (Lit. [46] 116–117 ◦C); 1H NMR
(500 MHz, CDCl3): ı 7.85 (dd, 1H, J = 8.3 and 1.7 Hz), 7.46–7.52 (m,
1H), 7.35 (d, 2H, J = 8.7 Hz), 7.00–7.05 (m, 2H), 6.77 (d, 2H, J = 8 Hz),
5.38 (dd, 1H, J = 13.3 and 2.8 Hz), 3.16 (dd, 1H, J = 17 and 14 Hz), 2.98
(s, 6H), 2.87 (dd, 1H, J = 17 and 3 Hz).
Yield = 85%; light yellow solid; mp = 122 ◦C (Lit. [48] 120–121 ◦C);
IR ꢀmax (KBr, cm−1): 2972, 2910, 1688 (C = O), 1553, 1315, 1223; 1
H
NMR (500 MHz, CDCl3): ı 7.81 (dd, 1H, J = 8.0 and 2 Hz), 7.47–7.57
(m, 3H), 7.34–7.49 (m, 2H), 7.03–7.10 (m, 2H), 5.45 (dd, 1H, J = 13.0
and 2.5 Hz), 3.73 (s, 3H), 3.04 (dd, 1H, J = 16 and 13.0 Hz), 2.86 (dd,
1H, J = 16 and 3 Hz).
2-(4-Chlorophenyl)-5,7-dimethoxy-2,3-dihydrochromen-4-one
(8b): Yield = 86%; light yellow solid. mp = 101 ◦C; IR ꢀmax (KBr,
cm−1): 1687 (C O); 1H NMR (500 MHz, CDCl3): ı 7.82 (dd, 2H,
J = 8.0 and 2 Hz), 7.13 (dd, 2H, J = 8.0 and 2 Hz), 5.95 (s, 1H), 5.91 (s,
1H), 5.51 (dd, 1H, J = 13.5 and 2.5 Hz), 3.73 (s, 6H), 3.13–3.38 (dd,
1H, J = 17 and 13.5 Hz), 2.86 (dd, 1H, J = 17 and 2.5 Hz). 13C NMR
(CDCl3, 125 MHz): ı 196.9, 166.7, 161.7, 158.9, 138.8, 133.2, 129.1,
128.6, 101, 92.7, 91.9, 79, 55.9, 43.1.
2-(4-Bromophenyl)-2,3-dihydroquinolin-4(1H)-one (17b): Yield
3%; yellow colour solid; mp = 161 ◦C (Lit. [49] 160 ◦C).
2-(4-Methoxyphenyl)-2,3-dihydroquinolin-4(1H)-one
(18b):
Yield 5%; yellow colour solid; mp = 145 ◦C (Lit. [49] 145 ◦C).
7-Bromo-2-(4-nitrophenyl)-2,3-dihydroquinolin-4(1H)-one
(19b): Yield 3%; yellow colour solid; mp: > 250 ◦C (Lit. [29]
>250 ◦C).
2-(3,4-Dimethoxyphenyl)-2,3-dihydroquinolin-4(1H)-one (20b):
Yield 2%; yellow semi solid (Lit. [49] semisolid).
2-p-Tolyl-2,3-dihydrochromen-4-one (9b): Yield = 80%; light yel-
low solid; mp = 70–71 ◦C (Lit. [41] 68–70 ◦C); IR ꢀmax (KBr, cm−1):
2985, 1627 (C O), 1630, 1527, 1320, 1224. 1H NMR (500 MHz,
CDCl3): ı 7.84 (dd, 1H, J = 8 and 2 Hz), 7.53–7.47 (m, 1H), 7.43–7.41
(m, 2H), 7.39–7.31 (m, 2H), 7.02–6.93 (m, 2H), 5.37 (dd, 1H, J = 13.0
and 2.5 Hz), 3.00 (dd, 1H, J = 14.5 and 13.0 Hz), 2.787 (dd, 1H, J = 17
and 3 Hz), 2.30 (s, 3H).
3. Results and discussion
3.1. Characterization of (DMCs)
3.1.1. CHN, TGA/DTA, XRD
The percentage of carbon, hydrogen and nitrogen present in
MHCFe (II) were recorded on an Elementar Vario ELHI CHNS ana-
lyzer. In order to measure the water of crystallization present in
MHCFe, thermo gravimetric analysis (TG) was carried out with
the thermal analyzer (EXSTAR TG/DTA 6300, SII Nano Technol-
ogy Inc., Japan). The heating rate was 10 ◦C/min. All measurements
were carried out in a static air atmosphere using Al2O3 as a refer-
ence. The purity of MHCFe was checked by comparing the X-ray
diffraction (Brucker AXS D8 Advance) data of the complex. The
relative-intensity data and inter planner spacing (d) were in good
agreement with the reported values.
7-Methoxy-2-p-tolyl-2,3-dihydrochromen-4-one
(10b):
Yield = 81%; light yellow solid; mp = 67 ◦C; IR ꢀmax (KBr, cm−1):
2985, 1679 (C O), 1630, 1527, 1320, 1224. 1H NMR (500 MHz,
CDCl3) ı 7.84 (dd, 1H, J = 8 and 2 Hz), 7.53–7.47 (m, 1H), 7.43–7.41
(m, 2H), 7.39–7.31 (m, 2H), 7.02–6.93 (m, 2H), 5.37 (dd, 1H, J = 13.0
and 2.5 Hz), 3.46 (s, 3H), 3.00 (dd, 1H, J = 14.5 and 13.0 Hz), 2.787
(1H, dd, J = 17 and 3 Hz), 2.30 (s, 3H). 13C NMR (CDCl3, 125 MHz) ı
198, 165, 159, 139, 138.3, 132.1, 129.8, 127.4, 112.3, 105.8, 100.4,
79.3, 58.1, 46.2, 24.7.
5,7-Dimethoxy-2-p-tolyl-2,3-dihydrochromen-4-one
(11b):
Yield = 83%; light yellow solid; mp = 72 ◦C; IR ꢀmax (KBr, cm−1):
1694 (C O). 1H NMR (500 MHz, CDCl3): ı 7.90 (d, 2H, J = 8.4 Hz),
6.95 (d, 2H, J = 8.8 Hz), 6.66 (d, 1H, J = 2.5 Hz), 6.78 (d, 1H, J = 2.5 Hz),
5.32 (dd, 1H, J = 13.5 and 2.0 Hz), 3.88 (s, 6H), 2.70 (dd, 1H, J = 13.5
and 2.0 Hz), 2.98 (dd, 1H, J = 16.8, 13.0 Hz), 2.26 (s, 3H). 13C NMR
(CDCl3, 125 MHz): ı 196.9, 166.7, 161.7, 158.9, 137.7, 137.3, 129.3,
127.1, 101, 92.7, 91.9, 79, 55.9, 52.7, 43.1, 24.3.
3.1.2. Surface area measurement
The Brunauer–Emmett–Teller (BET) method has been used to
determine the surface area of MHCFe complexes on a surface area
analyzer (micromeritics ASAP 2010, UK). In this technique, the sur-
face area was determined by physical adsorption of gases at their
boiling temperatures. The determined values of the surface areas
are: 25.91, 2.55, 68.07 and 158.30 m2 g−1 in case of Cr-, Mn-, Ni-,
Zn-HCFe(II), respectively.
2-(4-Hydroxy-3-methoxyphenyl)-2,3-dihydrochromen-4-one
(12b): Yield = 60%; light yellow solid; mp = 96 ◦C; IR ꢀmax (KBr,
cm−1): 1672 (C O). 1H NMR (500 MHz, CDCl3): ı 8.0 (s, br, OH,
1H), 7.45 (m, 2H), 7.10 (m, 2H), 6.85 (m, 1H), 6.58 (m, 1H), 6.53 (m,
1H), 5.51 (dd, 1H, J = 13.5 and 2.0 Hz), 3.73 (s, 3H), 3.13–3.38 (dd,
1H, J = 14.5 and 13.0 Hz), 2.78 (dd, 1H, J = 17 and 3 Hz). 13C NMR
(CDCl3, 125 MHz): ı 199.1, 157.1, 153.1, 145.6, 135.2, 131.9, 129.6,
122.1, 121.6, 120.0, 118.9, 115.2, 112.6, 76.1, 55.1, 43.9.
2-(3-Nitrophenyl)-2,3-dihydrochromen-4-one (13b): Yield = 70%;
light yellow colour solid; mp = 70 ◦C; IR ꢀmax (KBr, cm−1): 1683
(C O). 1H NMR (500 MHz, CDCl3): ı 8.15 (s, 1H), 8.13 (d, 1H,
J = 16 Hz), 7.79 (d, 1H, J = 12 Hz), 7.58 (d, 1H, J = 13 Hz), 7.45 (dd, 1H,
J = 13 and 3 Hz), 7.32–7.30 (m, 1H), 6.91–6.88 (m, 2H), 5.51 (dd, 1H),
3.13–3.38 (dd, 1H, J = 17 and 13.5 Hz), 2.86 (dd, 1H, J = 17 and 2.5 Hz).
The MnHCFe surface area (2.55 m2 g−1) is low. It might be due to
higher magnetic behaviour of manganese (agglomeration occurs)
compared to that of other metal present in MnHCFe. It was further
verified by FE-SEM (Field Emission Scanning Electron Microscopy).
FE-SEM images were recorded using a FEI Quanta 200F microscope
operating at 20 kV. The microscope was also used to record the
EDXA (Energy dispersive X-ray analysis) spectra. Elements present
in the MnHCFe were verified by the EDXA spectrum too. SEM
images showed the shape and surface morphology of the MnHCFe
(Fig. 1).
The XRD pattern of CrHCFe, MnHCFe, NiHCFe and ZnHCFe were
analyzed using JCPDS (Joint Committee on Powder Diffraction Stan-
dards) diffraction files. The JCPDS data of MHCFe were carefully
compared. All the diffraction peaks of the experimental pattern
matched with those of the relative intensities of the compounds
MnHCFe (JCPDS file number 48–0910) (Fig. 2), NiHCFe (JCPDS
file number 14–0291) (Fig. 3) and ZnHCFe (JCPDS file number
01–0433) (Fig. 4). Chromium ferrocyanide is a light greenish col-
ored amorphous solid and gave no X-ray line. The MHCFe were
also characterized by TG/DT analysis. The thermogram of CrHCFe,
MnHCFe, NiHCFe and ZnHCFe showed a mass loss corresponding
to nearly 2.28, 0.55, 0.74 and 2.45 water molecules, respectively.
The CHNS analysis data are shown in Table 1. Results of elemen-
tal analysis affirm that experimental values are in good agreement
2-(4-Chlorophenyl)-2,3-dihydrochromen-4-one
(14b):
Yield = 90%; light yellow colour solid; mp = 83 ◦C (Lit. [45]
84–85 ◦C); IR ꢀmax (KBr, cm−1): 2985, 1627 (C O), 1630, 1320,
1224. 1H NMR (500 MHz, CDCl3): ı 7.86 (d, 1H, J = 8 Hz), 7.50–7.55
(m, 1H), 7.40–7.46 (m, 4H), 7.05–7.11 (m, 2H), 5.47 (dd, 1H, J = 13.0
and 3 Hz), 3.07 (dd, 1H, J = 17 and 13.0 Hz), 2.87 (dd, 1H, J = 17 and
3 Hz).
2-Phenyl-2,3-dihydrochromen-4-one (15b): Yield = 80%; light
yellow solid; mp = 76 ◦C (Lit. [45] 78–79 ◦C; IR ꢀmax (KBr, cm−1):
2990, 1664 (C O), 1630, 1320, 1242. 1H NMR (500 MHz, CDCl3):
ı 7.86 (d, 2H, J = 8 Hz), 7.45–7.36 (m, 3H), 7.60 (dd, 1H, J = 8.4 and
3.0 Hz), 7.20–7.0 (m, 2H), 6.91 (m, 1H), 5.3 (dd, 1H, J = 14 and 3 Hz),
2.73 (dd, 1H, J = 14.0 and 3 Hz), 2.97 (dd, 1H, J = 17.0 and 14.0 Hz).

138
N. Ahmed et al. / Journal of Molecular Catalysis A: Chemical 373 (2013) 135–141
Fig. 1. FE-SEM image for MnHCFe.
with theoretical value. From the XRD, CHN analysis, TG/DTA, the
closest molecular formula of the synthesized MHCFe complexes is
as follows.
3.2. Effects of temperature and catalyst loading on product yields
To test DMCs catalytic activity in the isomerisation of
2ꢀ-hydroxychalcones, we have used (E)-3-(4-chlorophenyl)-1-(2-
hydroxyphenyl) prop-2-en-1-one (Scheme 1). Batch experiments
were performed with different DMC catalysts on silica gel at
1. Cr2[Fe(CN)6]·2.28H2O
2. Mn2[Fe(CN)6]·0.55H2O
3. Ni2[Fe(CN)6]·0.74H2O
4. Zn2[Fe(CN)6]·2.59H2O
Table 1
Carbon, Nitrogen, Hydrogen analysis of MHCFe.
DMC
Carbon (%)
Nitrogen (%)
Hydrogen (%)
CrHCFe
MnHCFe
NiHCFe
ZnHCFe
20.17 (19.19)
21.71 (20.87)
21.02 (20.32)
18.50 (17.75)
23.54 (22.31)
25.33 (23.38)
24.52 (24.59)
21.58 (20.78)
0.013 (0.023)
0.003 (0.006)
0.004 (0.005)
0.013 (0.019)
400
2.51
Fig. 3. XRD graph for nickel-ferrocyanide.
3.55
3.03
5.03
Cl
Cl
200
1.59
1.76
B
OH
O
silica supported -DMC
1-3 h, 50 -150 °C
O
C
A
20
40
60
80
O
2θ
Scheme 1. Isomerisation of 2ꢀ-hydroxychalcones to flavanone using silica sup-
Fig. 2. XRD graph for manganese-ferrocyanide.
ported DMC.

N. Ahmed et al. / Journal of Molecular Catalysis A: Chemical 373 (2013) 135–141
139
Reaction time
2500
2000
1500
1000
500
100
4.08
5.38
NiHCFe
CrHCFe
1.15 h
3 h
90
MnHCFe
ZnHCFe
80
70
60
50
40
30
20
10
0
4.48
2 h
3.62
3.10
2.73
2 h
2.51
2.19
20
40
60
80
100
2
Fig. 4. XRD graph for zinc-ferrocyanide.
100
NiHCFe
CrHCFe
MnHCFe
ZnHCFe
0
5
10
15
20
25
30
35
40
45
Mol % of DMC
80
60
40
20
0
Fig. 6. Effects of mol% of DMCs on yields at 100 ◦C for Zn-, Ni-, Mn-HCFe and 150 ◦
for CrHCFe.
C
In the presence of either silica gel or DMC alone, isomerization
reaction failed to occur while DMC in solution in the absence of
silica gel gave the products in low yields (5–10%) even after pro-
longed reaction times and temperature. It has been reported that
silica gel or other solid supports such as neutral alumina, HZSM-5
alone catalyse these reactions in relative low yields [21–24]. This
confirms that DMC plays an important Lewis acid role in our silica
gel supported cyclization reaction. We also tried NiHCFe catalyst for
2ꢀ-aminochalcones using dichloromethane solvent at reflux tem-
perature but failed to get the product and further reactant got
decomposed might be due to poor host-guest chemistry. Some
reactions occur more efficiently in the solid-state than in solu-
tion phase because of more tight and regular arrangement of the
substrate molecules in the solid-state reaction [50]. Therefore, we
tried isomerization of 2ꢀ-aminochalcones under solvent free reac-
tion conditions (Table 2, entries 17–20), however got poor yields in
this case might be due to poor nucleophilicity of nitrogen. Hence,
silica supported DMC is less efficient for the isomerization of 2ꢀ-
aminochalcones as compared to 2ꢀ-hydroxychalcones.
40
60
80
100
120
140
160
Temperature (0C)
Fig. 5. Effects of temperature on product yields.
different temperature (50–150 ◦C) and different mol% (5–40 mol%)
of catalysts and amount of catalysts and time required.
Temperature effects were studied upto 150 ◦C by keeping mol%
of catalyst constant (10 mol%). We have found that NiHCFe, ZnHCFe,
MnHCFe at 100 ◦C given high yields, but CrHCFe at 150 ◦C given high
yields (Fig. 5). After that keeping temperature as constant at 100 ◦C
for NiHCFe, ZnHCFe, MnHCFe and for CrHCFe 150 ◦C, we studied the
quantity of mol% of catalyst and time required for consuming reac-
tant. We found that NiHCFe at 35 mol% gave 90% yields in 1.15 h;
CrHCFe at 35 mol% gave 80% yields in 3 h; MnHCFe at 25 mol% gave
70% yields in 2 h; ZnHCFe at 30 mol% gave 60% yields in 2 h (Fig. 6).
Further increasing mol% of catalyst and reaction time has no change
in yields. Therefore, among used DMCs, NiHCFe was found highly
efficient catalyst in the isomerisation of 2ꢀ-hydroxychalcones to
flavanones at 100 ◦C and 35 mol% catalyst loading in 1.15 h.
All the reactions are performed under optimal reaction condi-
tion and results are summarized in Table 2. We observed that the
substituents on the aromatic rings influenced the product yields.
For example, electron releasing substituents such as methyl or
methoxy or trimethoxy or N,Nꢀ-dimethyl on ring B decreases the
product yields (30–80%) (Table 2, entries 1, 3, 4, 9, 12 and 16),
but the same electron releasing groups on ring A increases the
yields (85–86%) (Table 2, entries 7 and 8). Similarly, the presence
of electron-withdrawing substituents such as chlorine or bromine
on ring B increases the yields (90%) (Table 2, entries 2 and 14), but
these groups on ring A decreases the yields (70%) (Table 2, entry
13). Therefore, electron releasing substituents on ring A and elec-
tron withdrawing substituents on ring B facilitates the reaction for
higher yields.
3.3. Proposed reaction mechanism
DMCs might be played an important role in isomerisation of
2ꢀ-hydroxychalcones. These catalysts are hydrophobic (no H2O
adsorption at reaction temperatures) and sites are basic in nature
(no CO adsorption). Similarly, BrØnsted acid sites are absent
(absence of 1546 and 1639 cm−1 bands no absorption of pyridine)
and so the terminal M2+ ion function as Lewis acid sites. Fe in
these structures acts as a metal-dispersing agent and a stabilizer of
the cyano-bridged complex. Mixed-metal complex of ferrocyanide
moiety of Ni2+, Cr2+, Mn2+, Zn2+ ions were attached via bridging
cyanide ligands (Fig. 7). Cyanide ions act not only as ␴-donors (by
donating electrons to Fe), but also as ␲-donors (by chelating to
other metal). Electron donation raises the (CN), because electrons
are removed from the 5␴ orbital which is weakly antibonding in
nature. Consequently, the (C N) band shifts to higher frequencies,
␲-back bonding tends to decrease the ␯ (CN) because of the elec-
trons enter into the anti-bonding 2p␲ orbital. In general, CN−1 is a
good ␴-donor and a poor ␲-acceptor. Thus (CN) for the complexes
is generally higher than the values for free CN−1. IR spectra also
suggest that the cyanide ligands are oriented linearly between the
divalent Metal and Fe with the C atom coordinated to Fe and N atom
coordinated to Ni, Mn, Cr, Zn. Ni-, Cr-, Zn-, Mn-HCFe showed FT-IR
band at 2093, 2073, 2083, 2066 cm−1 respectively due to v (C N),

140
N. Ahmed et al. / Journal of Molecular Catalysis A: Chemical 373 (2013) 135–141
Table 2
Silica gel supported NiHCFe catalyst mediated oxidative cyclization of 2ꢀ-hydroxychalcones and 2ꢀ-aminochalcones.
R2
R2
R1
R3
R1
R3
R4
X
silica supported–NiHCFe
100 oC, 1.15 h
R4
XH
O
R5
O
R5
.
Product
XH
R1
R2
R3
R4
R5
Yield (%)a
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
OH
OH
OH
OH
OH
OH
OH
OH
OH
OH
OH
OH
OH
OH
OH
OH
NH2
NH2
NH2
NH2
OCH3
Br
OCH3
OCH3
H
OCH3
Cl
Cl
CH3
CH3
CH3
OH
H
Cl
H
H
H
OCH3
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
OCH3
OCH3
H
OCH3
OCH3
H
H
H
H
H
H
H
H
H
H
H
H
OCH3
H
H
OCH3
H
NO2
H
H
H
H
H
Br
H
80(1b)
90(2b)
78(3b)
75(4b)
89(5b)
86(6b)
85(7b)
86(8b)
80(9b)
81(10b)
83(11b)
60(12b)
70(13b)
90(14b)
80(15b)
30(16b)
3(17b)
5(18b)
3(19b)
2(20b)
OCH3
OCH3
NO2
NO2
H
H
H
H
H
OCH3
H
H
H
H
H
H
H
OCH3
H
N(CH3)2
Br
OCH3
NO2
OCH3
H
H
H
H
H
H
H
a
Obtained yield.
while K4[Fe(C N)6] showed this band at 2039 cm−1 due to v (C N).
IR bands at 1609 and 1450 cm−1 indicated the presence of strong
Lewis acid sites, while BrØnsted acid sites (IR bands at 1639 and
1545 cm−1) were absent, proving that the DMCs are purely Lewis
acid catalysts.
conformation for Lewis acid activation and lower the activation
energy of reaction [45]. The solid surface alone is not sufficient, but
the acidic sites in DMC catalyst have got a real over the isomerisa-
tion of 2ꢀ-hydroxychalcones. M2+ ion in DMC catalyst are the active
sites that activate the carbonyl group of chalcones which is then
attacked by OH group of 2ꢀ-hydroxychalcones.
Presumably, the mechanism of the 2ꢀ-hydroxychalcones
involves the heat-facilitated intramolecular Michael addition of
the hydroxy group to the ␣,␤-unsaturated ketone, whereby the
essential configuration of both the DMC catalyst and the sub-
strate is secured by their attachment to the silica gel matrix. We
have proposed a reaction mechanism for the isomerisation of 2ꢀ-
hydroxychalcones to flavanones using silica gel supported DMC
catalysts (Scheme 2). The importance of silica gel might be related
to the silica gel structure which has a complex surface with cav-
ities of different shapes and sizes. The reaction is takes place
inside the silica cavities which hold the metal in the appropriate
3.4. Effects of catalyst re-use on product yields
Reuse of catalysts have many benefits such as economical and
eco-friendly reaction, prevention of disposal problems and energy
saving. In four different DMCs, NiHCFe catalyst was found excel-
lent for isomerization of 2ꢀ-hydroxychalcone to flavanone. At 100 ◦C
and 35 mol% NiHCFe loading reaction gave 90% yields in 1.15 h.
F
C
N
M
M
C
N
Si
O
C
N
N
Cl
N
O
N
C
C
OH
C
M
N
Si
C
Fe
N
Si
N
C
Fe
O
O
M
C
N
M
O
C
C
M= Ni, Cr, Fe, Mn
N
M= Ni, Cr, Fe, Mn
Fe
C
N
Scheme 2. Proposed mechanism for isomerisation of 2ꢀ-hydroxychalcones using
Fig. 7. Structure of metal hexacyanoferrate.
silica supported DMCs catalysts.

N. Ahmed et al. / Journal of Molecular Catalysis A: Chemical 373 (2013) 135–141
141
100
95
90
85
80
75
70
65
60
References
[1] T.A. Geissman (Ed.), The Chemistry of Flavonoid Compounds, Pergamon Press,
Oxford, 1962.
[2] J.B. Harborne, The Flavonoids – Advances in Research since 1986, Chapman &
Hall, London, 1994.
[3] D. Treutter, Environ. Chem. Lett. 4 (2006) 147.
[4] D.A. Whiting, Nat. Prod. Rep. 18 (2001) 583.
[5] J.A. Ross, C.M. Kasum, Annu. Rev. Nutr. 22 (2002) 19.
[6] S.B. Lotito, B.J. Frei, Biol. Chem. 281 (2006) 37102.
[7] H. Chang, M. Mi, W. Ling, J. Zhu, Q. Zhang, N. Wei, Y. Zhou, Y. Tang, X. Yu, T.
Zhang, J. Wang, J. Yuan, J. Food Biochem. 34 (2010) 1.
[8] J.A. Beutler, J.H. Cardellina II, C.M. Lin, E. Hamel, G.M. Cragg, M.R. Boyd, Bioorg.
Med. Chem. Lett. 3 (1993) 581.
[9] K. Barkova, M. Kinne, R. Ullrich, L. Hennig, A. Fuchsb, M. Hofrichter, Tetrahedron
67 (2011) 4874.
[10] J.M. Jez, J.P.J. Noel, Biol. Chem. 277 (2002) 1361.
[11] A. Kumar, S. Sharma, V.D. Tripathi, S. Srivastava, Tetrahedron 66 (2010) 9445.
[12] C.M. Brennan, I. Hunt, T.C. Jarvis, C.D. Johnson, P.D. Mcdonnel, Can. J. Chem. 68
(1990) 1780.
[13] S. Saravanamurugan, M. Palanichamy, B. Arabindoo, V. Murugesan, J. Mol. Catal.
A: Chem. 128 (2004) 101.
[14] A. Bianco, C. Cavarischia, A. Farina, M. Guiso, C. Marra, Tetrahedron Lett. 44
(2003) 9107.
1
2
3
4
5
6
No. of reuses
[15] M.V. Lebedev, V.G. Nensjdenko, E.S. Balenkov, Synthesis (1998) 89.
[16] J.A. Seijas, M.P.V. Tato, M.M. Martlnez, J.R. Parga, Green Chem. 4 (2002) 390.
[17] S. Saravanamurugan, M. Palanichamy, B. Arabindoo, V. Murugesan, Catal. Com-
mun. 6 (2005) 399.
Fig. 8. Effects on yields of catalyst NiHCFe re-use.
[18] G.W.V. Cave, C.L. Raston, J.L. Scott, Chem. Commun. (2001) 2159.
[19] K. Tanaka, F. Toda, Chem. Rev. 100 (2000) 1025.
[20] T. Welton, Chem. Rev. 99 (1999) 2071.
[21] N. Ahmed, H. Ali, J.E. van Lier, Tetrahedron Lett. 46 (2005) 253.
[22] H.W. Chu, H.T. Wu, Y.J. Lee, Tetrahedron 60 (2004) 2647.
[23] T.W. Bastock, J.H. Clark, K. Martin, B.W. Trenbirth, Green Chem. 4 (2002) 615.
[24] A. Mitsutani, Catal. Today 73 (2002) 57.
[25] J.L. Scott, C.L. Raston, Green Chem. 2 (2000) 245.
[26] N. Ahmed, J.E. van Lier, Tetrahedron Lett. 47 (2006) 2725.
[27] J.K. Makrandi, S. Bala, Synth. Commun. 30 (2000) 3555.
[28] K.H. Kumar, P.T. Perumal, Can. J. Chem. 84 (2006) 1079.
[29] S. Kumar, J.K. Makrandi, Asian J. Chem. 17 (2005) 1293.
[30] J.Y. Park, P.R. Ullapu, H. Choo, J.K. Lee, S.J. Min, A.N. Pae, Y. Kim, D.J. Baek, Y.S.
Cho, Eur. J. Org. Chem. (2008) 5461.
Therefore, NiHCFe was examined for the reusability. After reac-
tion completion, the catalyst was filtered, washed with DCM, dried
under vacuum and reused many times for the next reaction (Fig. 8).
Followed by above reaction condition, it was observed that in first
two re-use gave 85% yields, for 3rd and 4th reuse gave 82.5% yields
and for 5th and 6th reuse gave 80% yields (Fig. 8). These variations
in yields might be due to the loss in work-up.
4. Conclusions
[31] R.C. Kamboj, S. Berar, U. Berar, S.C. Gupta, J. Indian Chem. Soc. 88 (2011) 879.
[32] S.V. Ley, I.R. Baxendale, G. Brusotti, M. Caldarelli, A. Massi, M. Nesi, Farmaco 57
(2002) 321.
[33] P.P. Gravereau, E. Garnier, ActaCrystallogr. C 40 (1984) 1306.
[34] T. Ostrowski, K. Harre, G. H. Grosch, WO2001062825, (2004).
[35] F. Yan, Z. Yuan, P. Lu, W. Luo, L. Yang, L. Deng, Renew. Energy 36 (2011) 2026.
[36] A. Ravindran, R. Srivastava, Chinese J. Catal. 32 (2011) 1597.
[37] I. Kim, M.J. Yi, S.H. Pyun, D.W. Park, C.S. Ha, Stud. Surf. Sci. Catal. 153 (2004)
239.
[38] L. Saikia, J.K. Satyarthi, R. Gonnade, D. Srinivas, P. Ratnasamy, Catal. Lett. 123
(2008) 24.
[39] A. Peeters, P. Valvekens, F. Vermoortele, R. Ameloot, C. Kirschhock, D.D. Vos,
Chem. Commun. 47 (2011) 4114.
In summary, we reported for the first time Ni-, Mn-, Cr- and
Zn-HCFe as a double metal cyanide catalyst in the isomerisation
of 2ꢀ-hydroxychalcone to flavanone. Among four used catalysts,
Lewis-acid, Ni2+ ions in double metal cyanide (NiHCFe) exhibited
good catalytic activity for the flavanone synthesis in excellent yields
under solvent-free condition. The intrinsic catalytic activity of the
heterogeneous catalyst is higher than the most of the known cata-
lysts for this reaction. This method has advantages as economical,
green, reusable and high yields catalyst.
[40] T. Alam, Kamaluddin, Bull. Chem. Soc. Jpn. 72 (1999) 1697.
[41] T. Alam, Kamaluddin, Colloids Surf. A 162 (2000) 89.
[42] T. Alam, H. Tarannum, N. Kumar, Kamaluddin, J. Colloid Interface Sci. 224 (2000)
133.
[43] N. Ahmed, W.H. Ansari, J. Chem. Res. (2003) 572.
[44] N. Ahmed, J.E. van Lier, Tetrahedron Lett. 48 (2007) 13.
[45] U.K. Mallik, M.M. Saha, A.K. Mallik, Indian J. Chem. 28 (1989) 970.
[46] Mondal, A.D. Gupta, A.K. Mallik, Tetrahedron Lett. 52 (2011) 5020.
[47] B.S. Vatkar, A.S. Pratapwar, A.R. Tapas, S.R. Butle, B. Tiwari, Int. J. Chem. Tech
Res. 2 (2010) 504.
Acknowledgements
We are grateful for the financial support through DST-project,
NKK and Praveen thanks for fellowship from CSIR, UGC New Delhi,
respectively.
Appendix A. Supplementary data
[48] J.I. Lee, M.G. Jung, H.J. Jung, Bull. Korean Chem. Soc. 28 (2007) 859.
[49] S. Chandrasekhar, S.N. Pushpavalli, S. Chatla, D. Mukhopadhyay, B. Ganganna,
K. Vijeender, P. Srihari, C.R. Reddy, M.J. Ramaiah, U. Bhadra, Bioorg. Med. Chem.
Lett. 22 (2012) 645.
Supplementary data associated with this article can be
found, in the online version, at http://dx.doi.org/10.1016/j.molcata.
2013.03.009.
[50] F. Toda, K. Tanaka, Chem. Rev. 100 (2000) 1025.