Metal free synthesis of tetrahydrobenzo[: A] xanthenes using orange peel as a natural and low cost efficient heterogeneous catalyst

Article abstract of DOI:10.1039/c6ra17607k

In this work, a facile, efficient and metal free catalytic system has been developed for the synthesis of tetrahydrobenzo[a]xanthene derivatives via a one-pot three-component condensation of various aldehydes, 2-naphthol, and dimedone. For the first time,

Full text of DOI:10.1039/c6ra17607k

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Metal free synthesis of tetrahydrobenzo[a]
xanthenes using orange peel as a natural and low
Cite this: RSC Adv., 2016, 6, 87082
cost efficient heterogeneous catalyst
a
a
Faezeh Taghavi, Mostafa Gholizadeh, Amir Sh. Saljooghia
*
and Mohammad Ramezanib
In this work, a facile, efficient and metal free catalytic system has been developed for the synthesis of
tetrahydrobenzo[a]xanthene derivatives via
a one-pot three-component condensation of various
Received 10th July 2016
Accepted 2nd September 2016
aldehydes, 2-naphthol, and dimedone. For the first time, the orange peel as a green, acidic, and low cost
natural catalyst with high porosity and high efficiency was used in tetrahydrobenzo[a]xanthenes synthesis
procedure. This environmental-friendly novel catalytic system led to the desired products in high to
excellent yields under solvent free conditions at 120 ꢀC.
DOI: 10.1039/c6ra17607k
www.rsc.org/advances
Zr(HSO4)4,14 dodecan tungstophosphoric acid (PWA),15 iodine,16
InCl3/P2O5,17 p-toluenesulfonic acid/ionic liquid ([bmim]BF4),18
trichloroacetic acid,19 tetradecyl trimethyl ammonium bromide
1. Introduction
Over the past decade, much attention has been given to the
development of new procedures in organic synthesis for envi-
ronmentally benign processes due to increasing green chem-
istry concerns.1 Also, highly efficient and clean techniques of
synthesis such as solvent-free and multicomponent reactions
(MCRs) are highly regarded. Multi-component reactions (MCRs)
are excellent tools in synthetic organic chemistry and drug
discovery due to their product diversity, high efficiency, simple
procedures, convergence, less energy consumption, decreased
reaction steps and time saving.2 Therefore, the new MCRs which
meet the credentials of green chemistry aspects as well as cost
effectiveness have gained much attention in organic chemistry.3
Xanthene and its derivatives have acquired immense atten-
tion because of their diverse range of biological and pharma-
ceutical properties such as anti-inammatory,4 antibacterial5
and antimalarial agents.6 The importance of xanthene deriva-
tives clearly was realized from their usage as dyes,7 uorescent
materials for visualization of biomolecules,8 sensitizers in
photodynamic therapy for destroying the tumor cells in laser
technologies9 and useful materials for photodynamic therapy.10
The tetrahydrobenzo[a]xanthene, because of their wide range of
pharmacological, industrial and synthetic applications are of
utmost importance11 and many methods for the synthesis of
these xanthenes have been reported in the literature. One of
these methods is the condensation reaction of aldehydes, 2-
naphthol and cyclic 1,3-dicarbonyl compounds, with various
catalysts such as NaHSO4$SiO2,12 strontium triate,13
(TTAB),20 cyanuric chloride,21 silica sulfuric acid (SSA),22 trityl
chloride (TrCl),23 tetra(n-butyl)ammonium uoride (TBAF),24
proline triate,25 perchloric acid,26 and Cr(SO4)2$4H2O.27 These
methods suffer from many drawbacks including the use of
expensive and toxic metals, high-cost reagents, long reaction
times in combination with high reaction temperatures, strong
Lewis acids, low yield, harsh reaction conditions, organic
solvents and tedious work-up processes and difficulty in sepa-
ration and recovery of the catalyst.
Nowadays, using metal catalysts are not always eco-friendly
and for this reason, serious environmental pollution oen
occurs.28 Because of the strict environmental, there is an
immense demand for metal-free, green and safe synthetic
methods that reduce the use of toxic waste and stop the
formation of inorganic wastes leading to high yield of the
desired product.29 Therefore, it is extremely important to
explicate a protocol which can construct such complex mole-
cules in a single step using reusable heterogeneous, inexpen-
sive, metal-free and green catalyst in a simple procedure under
solvent free conditions with excellent yields. In this paper, we
report an efficient metal free synthesis of tetrahydrobenzo[a]
xanthenes in the presence of orange peel as green heteroge-
neous catalyst.
2. Experimental
2.1 Materials
All compounds were obtained from Sigma-Aldrich and Merck in
analytical grade and used without further purication. The
melting points of products were determined with an Electro
thermal Type 9100 melting point apparatus. The FT-IR spectra
aDepartment of Chemistry, Ferdowsi University of Mashhad, P. O. Box 91775-1436,
Mashhad, Iran. E-mail: M_Gholizadeh@um.ac.ir; Tel: +98-513880-5527
bPharmaceutical Research Center, School of Pharmacy, Mashhad University of Medical
Sciences, P. O. Box 917775-1365, Mashhad, Iran
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were recorded on an Avatar 370 FT-IR Therma Nicolet spec-
trometer. The NMR spectra were provided on Brucker Avance
400 MHz instruments in chloroform (CDCl3). Mass spectra were
recorded with Agilent Technologies (HP) 5973 Network Mass
Selective Detector and Shimadzu GC-MS-QP5050 instruments at
70 eV. Elemental compositions were determined with a Leo
1450 VP scanning electron microscope spectrometer (SEM).
Inductively coupled plasma (ICP) was carried out on a Varian,
VISTA-PRO, CCD, Australia. All yields refer to isolated products
aer purication by recrystallization.
12-(4-Fluorophenyl)-9,9-dimethyl-8,9,10,12-tetrahydro-11H-
benzo[a]xanthen-11-one (4g). White powder, mp 185–186 ꢀC,
yield 95%. IR (KBr) nmax/cmꢁ1: 3.071, 2.961, 1.639, 1.594, 1.473,
1
1.377, 1.225, 1.181, 1.159, 1.148, 839, 810, 767, 745 cmꢁ1. H-
NMR (400 MHz, CDCl3): d 0.99 (s, 3H, CH3), 1.15 (s, 3H, CH3),
2
2
2.25–2.36 (ABquartet, 2H, JHH ¼ 16.4 Hz, JHH ¼ 16.4 Hz C]C–
CHAHB), 2.60 (s, 2H, CH2), 5.73 (s, 1H, CH), 6.88 (t, J ¼ 8.8 Hz,
2H, arom-H), 7.30–7.50 (m, 5H, arom-H), 7.81 (t, 2H, arom, H),
7.95 (d, J ¼ 8.0 Hz, 1H, arom-H).
9,9-Dimethyl-12-(p-tolyl)-8,9,10,12-tetrahydro-11H-benzo[a]
xanthen-11-one (4i). White powder, mp 175–177 ꢀC, yield 92%.
IR (KBr) nmax/cmꢁ1: 3.073, 2.954, 2.870, 1.650, 1.598, 1.465,
2.2 Catalyst preparation
1
1.372, 1.227, 1.185, 1.148, 1.111, 813, 757 cmꢁ1. H-NMR (400
In order to prepare the catalyst, the orange peel was powdered,
MHz, CDCl3): d 1.01 (s, 3H, CH3), 1.15 (s, 3H, CH3), 2.22 (s, 3H,
ꢀ
washed with distilled water and dried at 80 C for 2 h.
2
2
CH3), 2.25–2.36 (ABquartet, 2H, JHH ¼ 16.4 Hz, JHH ¼ 16.4 Hz
C]C–CHAHB), 2.60 (s, 2H, CH2), 5.69 (s, 1H, CH), 7.00 (d, J ¼ 8.0
Hz, 2H, arom-H), 7.25 (d, J ¼ 8.0 Hz, 2H, arom-H), 7.34 (d, J ¼
8.8 Hz, 1H, arom-H), 7.37–7.49 (m, 2H, arom-H), 7.79 (t, J ¼ 8.8
Hz, 2H, arom-H), 8.03 (d, J ¼ 8.4 Hz, 1H, arom-H).
2.3 General procedure for the preparation of 12-substituted-
8,9,10,12-tetrahydro benzoxanthen-11-ones
Powdered orange peel (0.05 g) was added to the mixture of
aromatic aldehyde 1 (1 mmol), 2-naphthol 2 (1 mmol), and
dimedone 3 (1 mmol) under solvent free condition. The mixture
9,9-Dimethyl-12-(3-nitrophenyl)-8,9,10,12-tetrahydro-11H-
ꢀ
benzo[a]xanthen-11-one (4k). White powder, mp 170–172 C,
yield 90%. IR (KBr) nmax/cmꢁ1: 3.072, 2.958, 1.650, 1.596, 1.530,
ꢀ
was stirred at 120 C for the appropriate time which was pre-
1.468, 1.375, 1.349, 1.225, 1.193, 1.177, 1.145, 1.094, 812 cmꢁ1
.
sented in Table 2. The progress of the reaction was monitored
by thin-layer chromatography (TLC) in ethyl acetate : n-hexane,
1 : 4. Aer completion of the reaction (monitored by TLC),
boiling ethanol was added to the reaction mixture. The catalyst
was ltered off and the reaction mixture was cooled to room
temperature. The precipitated crude product was then removed
by ltration and recrystallized from absolute ethanol to give
pure product. The spectral data for selected product are pre-
sented as follows:
1H NMR (400 MHz, CDCl3): d 0.99 (s, 3H, CH3), 1.17 (s, 3H, CH3),
2
2
2.25–2.38 (ABquartet, 2H, JHH ¼ 16.4 Hz, JHH ¼ 16.4 Hz C]C–
CHAHB), 2.64 (s, 2H, CH2), 5.85 (s, 1H, CH), 7.38–7.50 (m, 4H,
arom-H), 7.84–7.98 (m, 5H, arom-H), 8.15 (t, J ¼ 1.6 Hz, 1H,
arom-H).
3. Results and discussion
9,9-Dimethyl-12-phenyl-8,9,10,12-tetrahydro-11H-benzo[a]
xanthen-11-one (4a). White powder, mp 149–150 ꢀC, yield 95%.
IR (KBr) nmax/cmꢁ1: 3054, 2957–2886, 1651. 1H-NMR (400 MHz,
CDCl3) d (ppm): 0.99 (s, 3H, CH3), 1.15 (s, 3H, CH3), 2.25–2.36
The FT-IR spectrum of orange peel and the 5th recovered orange
peel was shown in Fig. 1. As shown in Fig. 1a, broad bands
centred at 3400 cmꢁ1 attributed to stretching vibration of
hydroxyl groups. The absorption bands at 1738 cmꢁ1 are
assigned to C]O carbonyl group. As shown in Fig. 1b, shape,
position and relative intensity of all characteristic peaks are well
preserved. These results indicated that no considerable changes
were observed on the chemical structure of functional groups
and the hydrogen bonding network (Fig. 1).
2
2
(ABquartet, JHH ¼ 16.4 Hz, JHH ¼ 16.4 Hz, 2H, C]C–CHAHB),
2.60 (s, 2H, CH2), 5.74 (s, 1H, CH), 7.08 (tt, J ¼ 7.2, 1.2 Hz, 1H,
arom-H), 7.20 (t, J ¼ 8 Hz, 2H, arom-H), 7.35–7.48 (m, 5H, arom-
H), 7.77–7.83 (m, 2H, arom-H), 8.03 (d, J ¼ 8.4 Hz, 1H, arom-H).
12-(4-Bromophenyl)-9,9-dimethyl-8,9,10,12-tetrahydro-11H-
benzo[a]xanthen-11-one (4c). White powder, mp 187–189 ꢀC,
yield 95%. IR (KBr) nmax/cmꢁ1: 3.064, 2.962, 1.643, 1.593, 1.515,
The morphology of orange peel was studied with scanning
electron microscopy (SEM). The smooth amorphous morphology
1
1.484, 1.374, 1.222, 1.175, 1.010, 837, 811, 755 cmꢁ1. H-NMR
(400 MHz, CDCl3): d 1.00 (s, 3H, CH3), 1.02 (s, 3H, CH3),
2
2
(ABquartet, 2H, JHH ¼ 16.4 Hz, JHH ¼ 16.4 Hz C]C–CHAHB),
2.60 (s, 2H, CH2), 5.70 (s, 1H, CH), 7.23–7.25 (m, 2H, arom-H),
7.30–7.36 (m, 5H, arom-H), 7.79–7.83 (m, 2H, arom-H), 7.93
(d, J ¼ 8.4 Hz, 1H, arom-H).
12-(4-Chlorophenyl)-9,9-dimethyl-8,9,10,12-tetrahydro-11H-
benzo[a]xanthen-11-one (4f). White powder, mp 191–193 ꢀC,
yield 95%. IR (KBr) nmax/cmꢁ1: 3.071, 2.960, 1.640, 1.594, 1.488,
1
1.376, 1.225, 1.181, 1.146, 1.092, 838, 811, 747 cmꢁ1. H-NMR
(400 MHz, CDCl3): d 0.99 (s, 3H, CH3), 1.15 (s, 3H, CH3), 2.25–
2
2
2.36 (ABquartet, 2H, JHH ¼ 16.4 Hz, JHH ¼ 16.4 Hz C]C–
CHAHB), 2.602 (s, 2H, CH2), 5.71 (s, 1H, CH), 7.15–7.17 (m, 2H,
arom-H), 7.31–7.49 (m, 5H, arom-H), 7.79–7.83 (m, 2H, arom-
H), 7.94 (d, J ¼ 8 Hz, 1H, arom-H).
Fig. 1 FTIR spectra of (a) orange peel, (b) recovered orange peel.
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of orange peel surface was shown in (Fig. 2a). Also, SEM image of
As a model reaction, condensation of benzaldehyde, 2-
powdered orange peel showed high porosity in comparison with naphtol and dimedone was carried out in the presence of
non-powdered orange peel (Fig. 2b). High porosity of powdered orange peel. For optimization of the reaction conditions
orange peel could provide an adequate morphology for organic various parameters such as catalyst amount, solvent and
materials and various solvents adsorption for catalytic purposes. reaction temperature were investigated as shown in Table 1.
The main ingredients of 7 g orange peel contain 5.8 calories, Desired product was produced only with 13% yield when the
water (4.4 g), protein (0.1 g), total fat (0.0 g), total carbohydrate reaction was carried out without catalyst under solvent free
(1.5 g), ber (0.6 g), ash (0.0 g), and minerals. Elemental content condition at 120 ꢀC (Table 1, entry 1), under the same reaction
of the catalyst (0.242 g of orange peel) was characterized by condition, 98% yield was obtained aer 60 min in the presence
inductively coupled plasma analyses (ICP), which resulted in the of 0.05 g of orange peel (Table 1, entry 3). In order to evaluate
following output: Al (90.719 ppm), Cu (9.998 ppm), Se (0.334 the effect of solvent, different solvents including H2O, EtOH,
ppm), Ni (21.075 ppm), Pb (11.040 ppm), Zn (64.341 ppm), Mg CH2Cl2, toluene, CHCl3, THF, and EtOAc were used under
(824.002 ppm), K (185.674 ppm), Na (273.493 ppm), P (290.394 reux in the presence of orange peel (Table 1, entries 6–12).
ppm), Cr (18.120 ppm), Mn (4.783 ppm), Mo (6.885 ppm), S The results of these experiments revealed that in the presence
(858.694 ppm), Si (4.409 ppm), Fe (472.723 ppm), Ca (7726.53 of these solvents the yield of the desired product was
ppm). It also contained different vitamins, such as vitamin C decreased in comparison with the solvent-free conditions. To
(ascorbic acid; 14%), vitamin A (1%), vitamin B6 (1%), soluble optimise the catalyst amount, the reaction was carried out
sugars, cellulose, hemicellulose, and pectin as the main under solvent free conditions at 120 ꢀC in the presence of
components. The composition of the orange peel varies with different amount of catalyst (0.03 g, 0.05 g, and 0.07 g). The
geographical, cultural and seasonal harvesting and processing. results indicated no signicant increase in yield with
Because of signicant amounts of ascorbic acid in orange peel, it increasing the catalyst amount (Table 1, entries 2, 3, and 5).
has acidic property with pH 5.1 and hence it would act as acid Based on these results, solvent free condition in the presence
catalyst for these reactions. Therefore, we have used this natural of 0.05 g catalyst at 120 ꢀC was chosen as the optimized
catalyst for synthesis of tetrahydrobenzo[a]xanthenes.30 The conditions.
results of the current study indicated that orange peel as
The catalytic activity of orange peel in the synthesis of
a natural material with multifunctional properties and high various tetrahydrobenzo[a]xanthene derivatives under the
porosity possessed high efficiency in green synthesis of tetrahy- optimized conditions was also studied (Table 2). Versatility of
drobenzo[a]xanthenes. In order to remove the pollutions from the optimized condition was demonstrated by three-component
the surface of orange peel, it was powdered, washed with condensation reaction of a range of aromatic aldehydes, 2-
distilled water and dried at 80 ꢀC for 2 h before use (Scheme 1). naphthol and dimedone under solvent-free condition at 120 ꢀC
in the presence of a catalytic amount of orange peel. All
aromatic aldehydes with electron-withdrawing and electron-
releasing groups were converted to the related products in
high to excellent yields (Table 2). The results showed that the
catalytic system was efficient with various substituents on the
benzaldehyde. The conversion of benzaldehydes with electron
withdrawing groups (Table 2, entries 2–7, 11, 12 and 15) was
faster than the electron donating groups analogue (Table 2,
entries 8–10, 13, and 14).
Table 1 Optimization of model reaction catalysed by heterogeneous
orange peel green catalyst
Catalyst
(g)
Temperature
(ꢀC)
Time
(h)
Isolated
yield%
Fig. 2 SEM image of (a) non-powdered orange peel, (b) powdered
orange peel.
Entry
Solvent
1
2
3
4
5
6
7
8
—
Solvent free
Solvent free
Solvent free
Solvent free
Solvent free
H2O
EtOH
CH2Cl2
Toluene
CHCl3
THF
120
120
120
100
1
1
1
1
1
1
1
1
1
1
1
1
13
80
98
80
98
50
60
30
20
25
35
35
0.03
0.05
0.05
0.07
0.05
0.05
0.05
0.05
0.05
0.05
0.05
120
Reux
Reux
Reux
Reux
Reux
Reux
Reux
9
10
11
12
Scheme 1 Synthesis of tetrahydrobenzo[a]xanthene derivatives in the
presence of orange peel.
EtOAC
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Table 2 Three-component condensation reaction of various substrates enhanced by orange peel catalysta
Mp (ꢀC)
Entry
Ar
Product
Time (min)
Yield (%)
Found
Reported
Reference
1
2
3
4
5
6
7
8
C6H5
4a
4b
4c
4d
4e
4f
4g
4h
4i
4j
4k
4l
4m
4n
4o
4p
4q
4r
40
30
30
40
40
30
30
55
40
60
40
20
50
50
35
90
75
90
95
90
95
95
90
95
95
85
92
85
90
98
83
90
95
82
85
80
149–150
170–171
187–189
175–176
173–174
191–193
185–186
173–175
175–177
201–203
170–172
176–178
132–133
216–217
201–203
191–193
235–237
201–202
151–153
161–164
186–188
173–174
175–177
187–188
191–193
176–177
173–175
204–205
168–172
174–175
135–137
213–214
196–199
184–188
231–233
200–202
31
32
33
34
35
36
37
38
34
31
39
36
40
41
42
43
41
44
3-Br-C6H4
4-Br-C6H4
2-Cl-C6H4
3-Cl-C6H4
4-Cl-C6H4
4-F-C6H4
3-Me-C6H4
4-Me-C6H4
4-OMe-C6H4
3-NO2-C6H4
4-NO2-C6H4
2-OH-C6H4
4-OH-C6H4
4-CN-C6H4
1-Naphthyl
2-Naphthyl
4-N(Me)2-C6H4
9
10
11
12
13
14
15
16
17
18
a
Reaction conditions: aromatic aldehyde (1 mmol), 2-naphtol (1 mmol), dimedone (1 mmol).
The efficiency of the presented protocol was compared with dimedone could be carried out but the product was obtained
different heterogeneous catalysts reported previously in the with a very poor yield aer a prolonged time (Table 1, entry 1).
literature. The results are shown in Table 3. Based on these
According to chemistry knowledge, orange peel, as an acid,
results, all previously reported methods suffer from long reac- activates the carbonyl group of substrates. As shown in
tion times to achieve appropriate yields as well as use of strong Scheme 2, prior activation of the carbonyl group of aldehyde by
Lewis acids, expensiveness and toxic metals with tedious work- orange peel followed by a nucleophilic attack from C1 of b-
up procedure. Also, orange peel gives better yield in shorter naphthol, provides intermediate A, which serves as an electro-
reaction time than other heterogeneous catalysts.
A plausible mechanism for the reaction methodology under of intermediate C and dehydration affords the desired product.
current development is shown in Scheme 2. In the absence of Furthermore, the recyclability of our proposed catalyst was
phile, ready to be attacked by dimedone. Then, cyclodehydration
the catalyst, the reaction of benzaldehyde and 2-naphthol with studied in the model reaction. Aer completion of the
Table 3 Comparison of catalytic activity between orange peel and other reported catalysts
Entry
Catalyst
Solvent
Temperature (ꢀC)
Other
Time (min)
Yield (%)
Reference
1
2
3
4
5
6
7
8
PEG-400
CAN
I2
—
120
26
80
80
300–420
120
Reux
120
—
330–450
120–144
150–180
120–210
390
115–136
280–420
60
79–90
82–87
70–89
83–95
70–88
79–84
69–89
98
45
46
47
48
49
50
51
CH2Cl2/ETOH
ACOH
[bmim]BF4
ClCH2CH2Cl
—
Ultrasound
—
—
—
—
—
—
P-TSA
Sr(OTF)2
Sulfamic acid
NaHSO4–SiO2
Orange peel
ClCH2CH2Cl
—
This work
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Scheme 2 Plausible reaction pathway catalysed by orange peel.
cost and reusable catalyst plays a crucial role in “electrophilic
activation”. Excellent yields of product, short reaction time,
mild reaction conditions, avoiding the use of organic solvent,
a simple workup procedure, and reusability of the catalyst are
the important and valuable features of this metal free meth-
odology. The resulting tetrahydrobenzo[a]xanthene derivatives
are of importance for organic and medicinal research.
Acknowledgements
The authors gratefully acknowledge the partial support of this
study by Ferdowsi University of Mashhad Research Council.
References
Fig. 3 Recyclability of orange peel catalyst in the synthesis of tetra-
hydrobenzo[a]xanthenes.
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In summary, we have described a convenient and highly effi-
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orange peel as a green and effective catalyst by three-component
one-pot condensation of various aldehydes with 2-naphthol and
dimedone under solvent free condition. This new type of low
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