Fly-ash:H2SO4 catalyzed solvent free efficient synthesis of some aryl chalcones under microwave irradiation

Article abstract of DOI:10.1016/j.saa.2012.01.054

Some 2E aryl chalcones have been synthesized using greener catalyst Fly-ash:H₂SO₄ assisted solvent free environmentally benign Crossed-Aldol reaction. The yields of chalcones are more than 90%. The synthesized chalcones are characterized by their physical constants and spectral data.

Full text of DOI:10.1016/j.saa.2012.01.054

Spectrochimica Acta Part A 91 (2012) 18–22
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Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
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Short communication
Fly-ash:H2SO4 catalyzed solvent free efficient synthesis of some aryl chalcones
under microwave irradiation
G. Thirunarayanan∗, P. Mayavel, K. Thirumurthy
Department of Chemistry, Annamalai University, Annamalainagar 608 002, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Some 2E aryl chalcones have been synthesized using greener catalyst Fly-ash:H2SO4 assisted solvent
free environmentally benign Crossed-Aldol reaction. The yields of chalcones are more than 90%. The
synthesized chalcones are characterized by their physical constants and spectral data.
© 2012 Elsevier B.V. All rights reserved.
Received 1 December 2011
Received in revised form 19 January 2012
Accepted 23 January 2012
Keywords:
Fly-ash:H2SO4
Greener synthesis
Crossed-Aldol reaction
2E aryl chalcones
1. Introduction
spectral data as they are unknown compounds so far. The purities
of the known synthesized chalcones have been checked by their
Heterogeneous catalytic Aldol and Crossed-Aldol condensa-
tion is a powerful tool for formation of carbon–carbon bond in
many kinds of carbonyl compounds [1]. Also microwave assisted
solvent free Aldol and Crossed-Aldol condensation were useful
synthesis of carbonyl compounds [2]. Thermal aldol reaction is
found to be sluggish and took longer time with low yields. How-
ever in the microwave heating conditions, the rate of reaction
is fast as a result the reaction times are shorter and yield are
high with easy isolation of products. Numerous green catalysts
have been used for synthesizing chalcones such as silica-sulphuric
acid [1,3], anhydrous zinc chloride [4], clay [5], ground chem-
istry catalysts-grinding the reactants with sodium hydroxide [6],
aqueous alkali in lower temperature [7], solid sulphonic acid
from aqueous alkali in lower temperature [7], solid sulphonic
acid from bamboo [8], barium hydroxide [9] anhydrous sodium
bicarbonate [10], microwave assisted synthesis [11], Fly-ash:water
[12] and sulphated titania [13]. Chalcones possess various multi-
pronged activities such as antimicrobial [14], antidepressants [15],
antiplasmodial [16], anti-aids [17] and insect antifeedant activ-
ities [18,19]. In the present investigation, the authors wish to
report a new versatile catalyst Fly-ash:H2SO4 for efficient syn-
thesizing chalcones by Crossed-Aldol condensation reaction. The
yields of chalcones are more than 96%. The synthesized chalcones
are characterized by their physical constants, mass, IR and NMR
physical constants and their spectral data earlier published in the
literature.
2. Experimental
2.1. Materials and methods
All chemicals were procured from E-Merck brand. Fly ash was
collected from Thermal Power Plant-II, Neyveli Lignite Corpo-
ration (NLC), Neyveli, Tamil Nadu, India. Melting points of all
chalcones were determined in open glass capillaries on Mettler
FP51 melting point apparatus and are uncorrected. Infrared spec-
tra (KBr, 4000–400 cm−1) were recorded on an Avatar-300 Fourier
transform spectrophotometer. The NMR spectra of unknown com-
pounds were recorded in Bruker AVIII 5000 spectrometer operating
at 500 MHz for 1H NMR spectra and 125.46 MHz for 13C NMR spec-
tra in CDCl3 solvent using TMS as internal standard. Electron impact
(EI, 70 eV) and chemical ionization mode FAB+ mass spectra were
recorded with a Varian 500 spectrometer.
2.2. Preparation and characterization of catalyst
In a 50 mL Borosil beaker, 1 g of Fly-ash and 0.8 mL (0.5 mol)
of sulphuric acid were taken and mixed thoroughly with glass
rod. This mixture was heated on a hot air oven at 85 ◦C for
1 h, cooled to room temperature, stored in a Borosil bottle and
tightly capped. This was characterized by infrared spectra and SEM
analysis.
∗
Corresponding author. Tel.: +91 4144 220015.
E-mail address: drgtnarayanan@gmail.com (G. Thirunarayanan).
1386-1425/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2012.01.054

G. Thirunarayanan et al. / Spectrochimica Acta Part A 91 (2012) 18–22
19
Fig. 1. SEM images of pure fly ash and Fly-ash:H2SO4: (a) Pure Fly-ash (1 ␮m); (b) pure Fly-ash (50 ␮m); (c) Fly-ash:H2SO4 (1 ␮m) (⇒ – corroded); (d) Fly-ash:H2SO4 (50 ␮m)
(⇒ – corroded).
Infrared spectral data of Fly-ash:H2SO4 is ꢀ (cm−1): 3456 (OH);
3010 (C H); 1495, 1390 (C S); 1336, 1154 (S O); and out of plane
modes: 1136, 1090, 976, 890, 850, 820, 667, 658, 620, 580, 498, 425.
The SEM images of pure Fly-ash and Fly-ash:H2SO4 at two dif-
ferent magnifications are shown in Fig. 1a–d. Fig. 1a and b depicted
that the crystallinity is found to be more in pure fly ash. The spheri-
cal shaped particles are clearly seen at both magnifications in Fig. 1a
and b. Fig. 1a reveals that the globular structure of pure fly ash
(round shaped particle). This also seen from Fig. 1c and d that some
of the particles are slightly corroded by H2SO4 (indicated by arrow
mark) and this may be due to dissolution of Fly-ash by H2SO4. This
will further confirmed by Fig. 1d, the well-shaped particles of pure
Fly-ash. Fig. 1b is aggregated to Fig. 1d due to presence of H2SO4.
product was obtained on evaporation. The solid, on recrystalliza-
tion with benzene–hexane mixture gave glittering pale yellow
solid. The insoluble catalyst was recycled by washing the solid
reagent remained on the filter by ethyl acetate (8 mL) followed by
drying in an oven at 100 ◦C for 1 h and it was made reusable for
further reactions.
3. Results and discussion
Fly ash is a waste air-pollutant and it has many chemical species
[10,12,20] SiO2, Fe2O3, Al2O3, CaO, MgO and insoluble residues. The
waste Fly-ash is converted into useful catalyst Fly-ash:H2SO4 by
mixing Fly-ash and sulphuric acid. The sulphuric acid group and
chemical species present in the Fly-ash have enhanced the cat-
alytic activity. During the course of the reactions these species are
responsible for the promoting effects on condensation between the
aryl ketone and aryl aldehydic groups leading to the formation of
unsaturated ketone. The proposed general reaction mechanism is
shown in (Fig. 2). For this condensation, generally a base is used as a
catalyst. In the case of base catalyzed aldol condensation, the mech-
anism generally involves the formation of anion of ketone. Whilst
in our case Fly-ash:H2SO4 act as a solid acid catalyst, it is protonat-
ing the aldehyde. The protonated aldehyde attached by the enolic
2.3. Synthesis of chalcones
An appropriate equi-molar quantities of aryl methyl ketones
(2 mmol), substituted benzaldehydes (2 mmol) and Fly-ash:H2SO4
(0.75 g) were taken in Borosil tube and tightly capped. The
mixture was subjected to microwave heated for 5–6 min in a
microwave oven (Scheme 1) (LG Grill, Intellowave, Microwave
Oven, 160–800 W) and then cooled to room temperature. The
organic layer was separated with dichloromethane and the solid
O
O
O
Fly-ash:H2SO4
480 Watts
Microwave
Ar
CH3
Ar'
H
Ar
C
H
C
H
Ar'
(1-38)
Scheme 1. Synthesis of chalcones by Fly-ash:H2SO4.

Table 1
Analytical and mass spectral data of chalcones synthesized by Fly-ash:H2SO4 catalyzed aryl methyl ketones and substituted benzaldehydes reaction of the type Ar CO CH3 + Arꢀ CHO → Ar CO CH CH Arꢀ under microwave
irradiation.
ꢀ
◦
Entry
Ar
Ar
Product
COCH CHC
M.W.
Yield (%)
M.p. ( C)
Mass (m/z)
1
2
3
4
5
6
7
8
9
C
H
C
C
C
C
H
C
H
H
5
208
294
273
262
291
291
213
223
294
93
94
95
92
94
94
92
92
92
55–56 (55–58) [20]
87–88 (87–88) [20]
104–105 (104–105) [21]
140–141 (140) [23]
122–123 (122) [22]
164–165 (164) [21]
120–121 (119–120) [22]
98–99 (98–99) [20]
90–91
–
–
–
–
–
–
–
–
6
5
6
5
6
5
6
4-N(CH
)
C
H
H
4-N(CH
)
C
H
COCH CHC
H
5
3
2
6
4
6
5
3
2
6
4
6
C
C
C
C
H
H
H
H
H
(1-Naph)
N(3-Indole)
C
C
C
C
C
H
H
H
H
H
COCH CHC
COCH CHC
COCH CHC
COCH CHC
COCH CHC
H
6
6
6
6
5
5
5
5
10
7
6
6
6
6
6
5
5
5
5
5
10
8
7
H
H
H
H
H
N
OH
OCH
8
6
6
4
4
3
4-OHC
4-OCH
H
6
4
6
6
4
C
H
3
6
4
3
4-NH
4-NH
4-NH
C
C
C
H
H
H
C
C
H
H
(3-Furyl)
2
2
2
6
6
6
5
4
4
4
3
4-NH
4-NH
C
C
H
H
COCH CHC
COCH CHC
H
H
6
5
2
2
6
6
4
4
6
6
5
4
4-N(C
H
)
C
H
N(CH
)
294[M+], 256, 222,
2
5
2
6
4
3
2
165, 146, 144, 133,
124, 111, 92, 35, 16
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
4-NH
4-NH
4-F-C
2,4-Cl
3,4-Cl
4-(OH)C
C
C
H
H
H
2,6-Cl
C
H
4-NH
4-NH
C
C
H
H
COCH CHC
COCH CHC
H
Cl
7
291
273
226
276
276
226
258
396
292
310
284
258
310
284
296
284
198
210
204
308
292
90
93
90
94
94
90
94
95
94
93
94
94
95
94
90
95
95
94
95
92
96
98–99
124–125
291[M+]
273[M+]
–
–
–
–
–
–
–
–
–
–
–
–
–
–
2
6
6
4
4
2
6
3
2
2
6
6
4
6
3
2
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
H
(1-Naph)
H
2
10
7
4
10
H
4-FC
H
COCH CHC
H
49–50 (49–50) [20]
80–82 (80–81) [24]
100–101 (100–101) [16]
63–64 (63–64) [20]
100–102 (100–102) [23]
103–104 (103–104) [20]
122–123 (122–123) [20]
113–114 (113–114) [20]
98–99 (98) [20]
104–105 (104–105) [20]
67–68 (67–68) [20]
123–124 (123–124) [20]
150–151 (150–151) [20]
153–154 (153–154) [20]
80–81 (80–81) [20]
137–138 (137–138) [20]
6
4
6
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
6
4
6
5
C
H
H
2,4-Cl
3,4-Cl
2,5-(OH)C
C
C
H
H
COCH CHC
H
5
H
2
6
3
3
4
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
2
2
6
3
6
6
C
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
COCH CHC
2
6
6
3
5
H
H
COCH CHC
H
6
6
3
6
5
C
H
(1-Naph)
C
H
COCH:CHC
H
10
7
10
7
6
5
4-BrC
4-ClC
4-OCH
H
(1-Naph)
4-BrC
4-ClC
4-OCH
H
COCH CHC
H
5
10
10
6
10
10
6
6
H
(1-Naph)
H
COCH CHC
H
6
6
6
5
C
H
(1-Naph)
(1-Naph)
C
H
COCH CHC
H
5
3
10
H
6
3
10
H
6
6
5
4-CH
C
4-CH
C
COCH CHC
H
3
10
6
3
10
6
6
C
H
(2-Naph)
C
H
COCH:CHC
H
5
10
7
10
7
6
6-OCH
C
H
(2-Naph)
(2-Naph)
6-OCH
C
H
COCH CHC
H
5
3
10
H
6
3
10
H
6
6
5
6-CH
C
6-CH
C
COCH CHC
H
3
10
6
3
10
6
6
C
C
C
H
(2-Fluorene)
(Biphenyl)
C
C
C
H
COCH CHC
COCH CHC
OCOCH CHC
H
H
13
12
9
13
12
9
6
6
5
H
H
9
9
5
H
O(2-Furyl)
N(2-Pyrrole)
H
H
–
–
–
–
4
3
4
3
6
5
5-CH
C
H
5-CH
C
H
NCOCH CHC
H
3
4
2
3
4
2
6
5
[20]
C
C
H
S(2-thienyl)
(Anthracene)
C
H
SCOCH CHC
H
112–113 (112–113)
124–125 (124–125)
107–110
4
3
4
3
6
5
[20]
H
C
H COCH CHC
H
14 10
14
9
6
5
5-BrC
H
S(2-thienyl)
5-BrC
H
SCOCH CHC
H
H
292[M+], 294[M+2],
214, 201, 160, 131,
90, 82, 78
4
4
2
2
4
4
2
2
6
6
5
4
31
5-BrC
H
S(2-thienyl)
4-BrC
H
5-BrC
H
SCOCH CHC
Br
371
94
173–174
371[M+], 373[M+2],
375[M+4], 290, 214,
188, 180, 160, 82, 78
326[M+], 328[M+2],
290, 165, 160, 82, 78
326[M+], 328[M+2],
290, 214, 188, 180,
160, 82, 78, 77
335[M+], 337[M+2],
319, 304, 290, 214,
174, 160, 120, 82, 78
30, 15
6
4
32
33
5-BrC
5-BrC
H
H
S(2-thienyl)
S(2-thienyl)
2-ClC
4-ClC
H
H
5-BrC
5-BrC
H
H
SCOCH CHC
SCOCH CHC
H
H
Cl
Cl
326
326
94
95
143–145
155–157
4
2
6
4
4
2
6
4
4
2
6
4
4
2
6
4
34
5-BrC
H
S(2-thienyl)
4-N(CH
)
C
H
5-BrC
H
SCOCH CHC
H
N(CH
)
335
92
142–143
4
2
3
2
6
4
4
2
6
4
3
2
35
36
5-BrC
5-BrC
H
H
S(2-thienyl)
S(2-thienyl)
4-FC
H
5-BrC
5-BrC
H
H
SCOCH CHC
SCOCH CHC
H
H
F
I
309
416
90
91
164–165
184–185
309[M+], 311[M+2],
290, 231, 214, 160,
149, 95, 82, 78, 18
416[M+], 418[M+2],
420[M+4], 338, 290,
256, 228, 214, 203,
188, 160, 126, 82, 78
322[M+], 324[M+2],
306, 290, 243, 214,
161, 160, 107, 91, 82,
78, 55, 31, 15
306[M+], 308[M+2],
290, 214, 160, 145, 91,
82, 78, 15
4
2
6
4
4
2
6
4
4-IC
H
4
4
2
6
4
2
6
4
37
38
5-BrC
5-BrC
H
S(2-thienyl)
S(2-thienyl)
4-OCH
C
H
5-BrC
H
SCOCH CHC
H
OCH
3
322
306
93
92
148–149
151–152
4
2
2
3
6
5
4
4
2
2
6
6
4
4
H
4-CH
C
H
C
H
5-BrC
H
SCOCH CHC
H
CH
3
4
3
6
5
6
5

G. Thirunarayanan et al. / Spectrochimica Acta Part A 91 (2012) 18–22
21
OH
Acidic site of
Fly-ashHSO4
C
H
CHO
Fly-ash:H2SO4
OH
C
OH
OH
C
H
C
OH
C
H
H2C
C
Br
Br
Br
S
S
S
H
H
H
OH
O
C
OH
C
H
C
OH
C
C
C
Br
Br
S
S
H
H
H
H
H
H
OH
O
C
OH2
O
C
C
C
C
H
C
Br
Br
S
H
H
H
H
H
OH2
O
C
O
C
H2O
C
H
C
H
Br
C
H
C
S
S
Fig. 2. Proposed mechanism for crossed-aldol reaction of benzaldehydes and 5-bromo-2-thienyl ketone in presence of Fly-ash:H2SO4 catalyst.
97
96.5
96
form of the ketone. This catalyst also initializes the dehydration of
the aldol condensed product to form chalcones. A similar mech-
anism has been proposed for this condensation with the catalyst
[13]. In these experiments the products were isolated and the cata-
lyst was washed with ethyl acetate, heated to 100 ◦C then reusable
for further five run reactions. There was no appreciable change in
the percentage of yield of chalcones. In this protocol the reaction
gave better yields of the chalcones during the condensation without
any environmental discharge. The analytical and mass spectral data
are presented in Table 1. The IR and NMR spectral data of unknown
chalcones are presented in supplementary data (Tables S1–S3).
We have investigated the catalytic effect of Fly-ash:H2SO4
on the synthesis of substituted styryl-5-bromo-2-thienyl ketone
(Entry 30) by varying the catalyst quantity from 0.5 g to 1.5 g. As the
catalyst quantity is increased from 0.5 g to 0.75 g, the percentage of
yield of product is increased from 95 to 96%. Further increase the
catalyst amount there is no significant increasing of the percentage
of product. This catalytic effect is shown in (Fig. 3). The optimum
quantity of catalyst loading was found to be 0.75 g. We have carried
out this reaction with various substituted ketones and benzaldehy-
des. The results, analytical and mass spectral data are summarized
in Table 1. There is no significant effect of substituents on the con-
densation reaction. This reaction mechanism was proposed based
on Krishnakumar et al. and Climent et al. [13]. The reusability of this
catalyst was studied the reaction of 5-bromo-2-thienyl ketone and
benzaldehyde. The reusability of catalyst on crossed-aldol reaction
of 5-bromo-2-thienyl ketone and benzaldehydes is given in Table 2.
From Table 2, first two runs gave 96% product. The third, fourth and
fifth runs of reactions gave the yields 95.8%, 95.7% and 95.5% of chal-
cones. There was no appreciable loss in its effect of catalytic activity
was observed up to fifth run.
95.5
95
94.5
0.25
0.5
0.75
1
1.25
1.5
Quanꢀty of catalyst (g)
Fig. 3. Effects of catalyst loading.
4. Conclusion
We have developed an efficient catalytic method for synthe-
sis of chalcones by Crossed-Aldol reaction using a solvent free
environmentally greener catalyst Fly-ash:H2SO4 under microwave
irradiation between aryl ketones and aldehydes. This reaction
protocol offers a simple, economical, environmentally friendly,
non-hazards, easier work-up procedure and good yields.
Table 2
Supplementary data
Reusability of catalyst on condensation of 5-bromo-2-thienyl ketone (2 mmol) and
benzaldehydes (2 mmol) under microwave irradiation.
The IR and NMR spectral data of unknown chalcones are pre-
sented in supplementary data (Tables S1–S3, see supplementary
data).
Run
Yield
1
96
2
96
3
95.8
4
95.7
5
95.5

22
G. Thirunarayanan et al. / Spectrochimica Acta Part A 91 (2012) 18–22
Acknowledgement
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The authors thank to RSIC, IIT Chennai – 600 036 for recording
NMR spectra of chalcones (30–38).
Appendix A. Supplementary data
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