Green and cost effective protocol for the synthesis of 1,8-dioxo-octahydroxanthenes and 1,8-dioxo-decahydroacridines by using sawdust sulphonic acid

Article abstract of DOI:10.1007/s11164-017-3059-4

Abstract: A heterogeneous solid acid catalyst has been prepared by covalent grafting of chlorosulphonic acid on the surface of sawdust (SD-OSO₃H). The structure of the prepared catalyst was assessed by FT-IR, solid state CP/MAS ¹³C-N

Full text of DOI:10.1007/s11164-017-3059-4

Res Chem Intermed
DOI 10.1007/s11164-017-3059-4
Green and cost effective protocol for the synthesis
of 1,8-dioxo-octahydroxanthenes and 1,8-dioxo-
decahydroacridines by using sawdust sulphonic acid
Shrikrishna Karhale1,2
Gajanan Rashinkar3
Monika Patil1
Vasant Helavi1
•
•
•
Received: 7 February 2017 / Accepted: 6 July 2017
Ó Springer Science+Business Media B.V. 2017
Abstract A heterogeneous solid acid catalyst has been prepared by covalent grafting of
chlorosulphonic acid on the surface of sawdust (SD-OSO3H). The structure of the
prepared catalyst was assessed by FT-IR, solid state CP/MAS 13C-NMR spectroscopy,
field emission scanning electron microscopy and energy dispersive X-ray. The catalytic
performance of the solid acid catalyst has been evaluated in the synthesis of 1,8-dioxo-
octahydroxanthenes and 1,8-dioxo-decahydroacridines. High conversion, shorter reac-
tion time, cleaner reaction profile, environmentally benign solvent, simple experimental
and work-up procedure, and reusability of catalyst are the striking features of our syn-
thetic route.
Electronic supplementary material The online version of this article (doi:10.1007/s11164-017-3059-4)
contains supplementary material, which is available to authorized users.
&
Vasant Helavi
vbhelavi@gmail.com
1
2
3
Department of Chemistry, Rajaram College, Kolhapur, Maharashtra 416004, India
Abasaheb Marathe Arts and New Commerce, Science College, Rajapur, Ratnagiri, India
Department of Chemistry, Shivaji University, Kolhapur, Maharashtra 416004, India
123

S. Karhale et al.
Graphical Abstract
Keywords Biomass Á Renewable bioresources Á Sawdust sulphonic
acid Á Green protocol
Introduction
The heterogeneous solid acid catalysts have received captivating attention from both
environmental and economical points of view [1, 2]. The unique attributes of
heterogeneous solid acid catalysts such as a non-toxic nature, exceptional air
stability, low cost, easy availability, immiscibility with common organic solvents,
exceptional catalytic performance and facile recyclability makes the process simple
and eco-friendly [3–6]. The recent quest towards the sustainable development has
spurred considerable interest in employing renewable bioresources as a support
material in heterogeneous catalytic technology [7]. In this regard, biomass
represents the most promising renewable bioresource that has been already
employed as a precursor to synthesize fuels, value added chemicals and useful
materials [8]. Further, the functional structure of biomass provides the opportunities
to generate different functionalities [9]. Cellulose, a linear polysaccharide made up
of b-D-glucose units linked by 1,4 glycosidic bonds, is the most abundant organic
biopolymer on the earth which is derived from biomass [10, 11]. Owing to its easy
availability and a wide range of beneficial physical and chemical properties,
cellulose has become the most common sustainable feedstock to produce materials
for catalytic applications [12–14]. In the recent years, sporadic strides have been
made to employ various natural sources of cellulose instead of refined cellulose
[15]. Sawdust is a natural, renewable, biodegradable and easily available natural
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Green and cost effective protocol for the synthesis of…
source of cellulose obtained from wood as a waste by-product. Owing to hydrophilic
nature, it is widely used as a promising adsorbent for removing heavy metals, acidic
and basic dyes, and other unwanted materials from waste water [16, 17]. The unique
accredit of sawdust is that it contains cellulose, hemicelluloses and lignin which
include a wide variety of hydroxyl groups that can be used as active sites for the
preparation of heterogeneous catalysts. Recently, functionalized sawdust in the form
of sulphonated sawdust (SD-OSO3H) has been employed as an excellent hetero-
geneous Bronsted acid catalyst for mediating significant organic transformations
[18–20]. However, despite impressive catalytic potential, its utility in synthetic
chemistry is not fully exploited. This spurred us to investigate the compatibility of
sawdust sulphonic acid as a catalyst in the synthesis of biological relevant
heterocyclic scaffolds.
Xanthene derivatives are privileged heterocyclic motifs possessing a highly
reactive inbuilt pyran ring. They are key intermediates in number of natural
products as well as important synthons in synthetic organic chemistry [21]. They
have garnered increasing attention because of their potential applications in
biological and pharmacological regions [22–24]. Furthermore, this structural motif
is also used as a corrosion inhibitor [25], in photodynamic therapy [26], laser
technologies [27], fluorescent materials for the visualization of biomolecules [28] as
well as selective positive allosteric modulators of metabotropic glutamate receptors
[29]. Owing to their unique biological profile, numerous methodologies have been
developed for the synthesis of 1,8-dioxo-octahydroxanthenes [30–44]. The most
popular method involves the reaction between dimedone and aryl aldehydes. A wide
array of catalysts has been reported to catalyze this transformation. However, many
of the reported protocols are, although efficient, a few of them suffer from the
drawbacks of tedious preparation of the catalyst, high reaction temperature, longer
reaction time, low yields, excess use of reagents as well as toxic or expensive
catalysts. This spurred us to develop an efficient, green and easily adaptable protocol
for the synthesis of 1,8-dioxo-octahydroxanthenes.
Acridindiones are the polyfunctionalized and symmetrical derivatives of 1,4-
dihydropyridines (1,4-DHPs) which represent a significant class of aza-heterocyclic
compounds having potential biological and pharmacological applications [45–49].
In addition, they are also employed as excellent building blocks for the synthesis of
antitubercular agents [50] and also serve as potential drug candidates for the
treatment of congestive heart failure [51]. The most common approach for the
synthesis of 1,8-dioxo-decahydroacridines involves the reaction of dimedone and
NH4OAc with aromatic aldehydes. A plethora of catalysts have been reported to
catalyze this transformation [52–58]. However, there is a still scope for improve-
ment, especially towards developing a facile protocol using robust heterogeneous
catalyst.
In continuation of our research work in the development of sustainable
methodologies for the bioactive heterocycles [59–61], we report herein an efficient
strategy for the synthesis of 1,8-dioxo-octahydroxanthenes and 1,8-dioxo-decahy-
droacridines using sawdust sulphonic acid as a reusable heterogeneous acid catalyst
(Scheme 1).
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S. Karhale et al.
Ar
O
O
O
Ar
O
O
SD-OSO3H
SD-OSO3H/Ethanol, Reflux
NH4OAc
Ar-CHO
+
Ethanol, Ref lux
O
O
N
4aH-i
3 a-m
1
2
Scheme 1 Sawdust sulphonic acid catalyzed one-pot synthesis of 1,8-dioxo-octahydroxanthenes and
1,8-dioxo-decahydroacridines
Experimental
Dimedone (Thomas Baker), chlorosulphonic acid (Spectrochem) and aldehydes
(Spectrochem and Thomas Baker) were used as received. The NMR spectra were
1
recorded on a Bruker AC (300 MHz for H NMR and 75 MHz for 13C NMR)
spectrometer using TMS as an internal standard in CDCl3. Chemical shifts (d) are
expressed in ppm. Solid state CP/MAS 13C-NMR spectra were recorded on JEOL-
ECX400 spectrometer under prescribed operating conditions. The mass spectra
were recorded on a Shimadzu QP2010 gas chromatograph mass spectrometer. The
FT-IR spectra were measured on a Bruker ALPHA FT-IR spectrometer in between
the frequency range 500–4000 cm-1. The size and morphology of pristine sawdust
and sawdust sulphonic acid were observed by using a FE-SEM of MIRA3 TESCAN
microscope with an accelerating voltage of 10 kV.
General procedure for synthesis of 1,8-dioxo-octahydroxanthenes
A mixture of dimedone (2 mmol), aromatic aldehyde (1 mmol) and sawdust
sulphonic acid (0.05 g) was refluxed in ethanol (3 mL). After completion of
reaction as indicated by thin layer chromatography (TLC), the reaction mixture was
diluted with hot ethanol (5 mL) and filtered to remove the catalyst. After
evaporation of solvent in vacuo, the crude product was recrystallized from ethanol
to afford the desired 1,8-dioxo-octahydroxanthenes.
General procedure for synthesis of 1,8-dioxo-decahydroacridines
To the well-stirred mixture of benzaldehyde (1 mmol) and sawdust sulphonic acid
(0.05 g) in ethanol (3 mL), dimedone (2 mmol) and NH4OAc (1.5 mmol) were
added, and the resultant reaction mixture was refluxed for an appropriate time. After
completion of reaction (monitored by TLC), the reaction mixture was diluted with
hot ethanol (5 mL) and filtered to remove the catalyst. After evaporation of solvent
in vacuo, the crude product was recrystallized from ethanol to afford corresponding
1,8-dioxo-decahydroacridines.
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Green and cost effective protocol for the synthesis of…
Fig. 1 Preparation of sawdust sulphonic acid
Result and discussion
Our initial strides began with the preparation of sawdust sulphonic acid by adopting
the literature procedure [19]. In general, sawdust obtained from the local timber
industry was washed with a copious amount of distilled water to remove the adhered
surface impurities and dried at 60 °C for 24 h. The dried sawdust was finely
pulverized and passed through 1 mm sieve to get fine powder. The sulphonic acid
groups were introduced with the help of hydroxyl groups in sawdust by reacting
with chlorosulfonic acid in dichloromethane at 0 °C. The product obtained was
filtered, washed with diethyl ether, dried and further pulverized to get the desired
sawdust sulphonic acid as fine powder (Fig. 1).
Sawdust sulphonic acid was characterized on the basis of FT-IR, solid state 13C
CP-MAS, FE-SEM and EDX techniques. In the FT-IR spectrum (Fig. 2), cellulose
and hemicellulose units are present in sawdust sulphonic acid displaying C–H
stretching vibrations at 2940 and 2891 cm-1 while the phenyl ring of lignin showed
C=C stretching peaks at 1660 and 1625 cm-1. In addition, the FT-IR spectrum also
displayed characteristic peaks at 3327 cm-1 (OH stretching of SO3H), 1157,
Fig. 2 The FT-IR spectrum of sawdust sulphonic acid
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S. Karhale et al.
Fig. 3 Solid state CP-MAS 13C-NMR spectrum of sawdust sulphonic acid
1025 cm-1 (asymmetric and symmetric stretching of SO2), 896 cm-1 (S–OH
bending) and 663 cm-1 (S–O symmetric stretching) indicating the successful
grafting of sulphonic acid in the matrix of sawdust.
The solid state 13C CP-MAS spectrum (Fig. 3) of sawdust sulphonic acid
displayed peaks at 105.12 (bs, cellulose-C1), 89.32 (bs, cellulose-C4), 72.48–75.38
(m, cellulose-C2, C3, C5), 65.73 (bs, cellulose-C6) which is in concordance with the
proposed catalyst.
The elemental mapping of pristine sawdust and sawdust sulphonic acid was done
by using energy dispersive X-ray (EDX) analysis. The EDX analysis of sawdust
(Fig. 4a) revealed carbon and oxygen as the major elements while that of sawdust
sulphonic acid recognized the peaks for carbon, oxygen and sulfur as shown in
Fig. 4b. The presence of sulfur in its respective energy position at 2.30 keV also
Fig. 4 EDX: a pristine sawdust; b sawdust sulphonic acid
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Green and cost effective protocol for the synthesis of…
Fig. 5 SEM images: a pristine sawdust; b sawdust sulphonic acid
supports the formation of sawdust sulphonic acid. The loading of SO3H as
determined by EDX was found to be 0.123 mmol/g of sawdust.
The surface morphology of pristine sawdust and sawdust sulphonic acid was
studied by scanning electron microscopy (SEM). The SEM images (Fig. 5a, b)
clearly indicate irregular morphology having a particle size in the micrometer range.
The sawdust sulphonic acid (Fig. 5b) exhibits smooth and uniform particles with
sufficient voids having a shape mimicking pristine sawdust.
The acidic sites on sawdust sulphonic acid were quantified by the ion exchange
method and were found to be 1.88 mmol H?/g of catalyst [62].
Initially, the catalytic potential of sawdust sulphonic acid has been screened for
the synthesis of 1,8-dioxo-octahydroxanthenes. In this regard, the dimedone and
4-cyanobenzaldehyde were chosen as model substrates for optimization of reaction
conditions. In order to optimize the solvent, a model reaction in the presence of
sawdust sulphonic acid (0.05 g) was carried out in various organic solvents at
different temperature conditions (Table 1). High yield was achieved in the presence
of ethanol under reflux conditions (Table 1, entry 11). Since, it is relatively safe and
can be used to dissolve many organic compounds. Unfortunately, the model reaction
afforded lower yields of desired product in toluene, chloroform, dichloromethane,
acetonitrile, EDC, THF, DMF, and acetone (Table 2, entries 1–8). Furthermore, use
of n-propanol gave the desired product in moderate yield (Table 2, entry 9). On the
contrary, the reaction gave the desired product in trace amount in n-butanol
(Table 2, entry 10).
Furthermore, in order to optimize the catalyst loading, the model reaction was
carried using different quantities of sawdust sulphonic acid (Table 2). It was
observed that the optimum amount of catalyst turns out to be 0.05 g in order to
obtain the best result (Table 2, entry 5). However, a catalyst quantity lower than
0.05 g did not lead to quantitative yield of the product (Table 2, entries 1–4).
Furthermore, an increase in catalyst quantity beyond 0.05 g did not increase the
yield of product significantly (Table 2, entry 6).
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S. Karhale et al.
Table 1 Solvent optimization in the synthesis of 1,8-dioxo-octahydroxanthenes
CN
CN
O
O
O
Sawdust sulphonic acid
Solvent, Reflux
2
+
O
O
CHO
Entry
Reaction condition
Reaction time (min)
Isolated yield (%)
1
Toluene/Reflux
Chloroform/Reflux
DCM/Reflux
30
30
30
30
30
30
30
30
30
30
30
25
2
28
3
30
4
Acetonitrile/Reflux
EDC/Reflux
33
5
35
6
THF/Reflux
37
7
DMF/Reflux
43
8
Acetone/Reflux
n-propanol/Reflux
n-butanol/Reflux
Ethanol/Reflux
58
9
53
10
11
Trace
92
Reaction conditions: Dimedone (2 mmol), 4-cyanobenzaldehyde (1 mmol) and sawdust sulphonic acid
(0.05 g, 0.0061 mmol) in solvent (3 mL) at given condition
Table 2 Catalyst loading studies in the synthesis of 1,8-dioxo-octahydroxanthenes
CN
CN
O
O
O
Sawdust sulphonic acid
Ethanol, Reflux
2
+
O
O
CHO
Entry
Catalyst amount (g)
Reaction time (min)
Isolated yield (%)
1
2
3
4
5
6
0.01
0.02
0.03
0.04
0.05
0.10
30
30
30
30
30
30
59
62
70
85
92
93
Reaction conditions: Dimedone (2 mmol), 4-cyanobenzaldehyde (1 mmol) and catalyst in ethanol
(3 mL) at reflux condition
To explore the scope of the present protocol, several structurally diverse
aldehydes were treated with dimedone under optimized reaction conditions, and the
results are summarized in Table 3. In all the cases, reaction proceeded smoothly,
affording corresponding 1,8-dioxo-octahydroxanthenes as the sole products and no
anomalies like tetraketones were noted [63]. The aromatic aldehydes bearing
electron-donating as well as electron-withdrawing substituents reacted efficiently
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Green and cost effective protocol for the synthesis of…
Table 3 Sawdust sulphonic acid catalyzed synthesis of 1,8-dioxo-octahydroxanthenes from dimedone
and aryl aldehydes
Ar
O
O
O
SD-OSO3
H
Ar-CHO
+
Ethanol, Reflux
O
O
3 a-m
2
1
Entries
Aryl aldehyde (2)
Product (3)
Time (min)
Yield (%)a
Mp (°C)
1
Benzaldehyde
3a
3b
3c
3d
3e
3f
50
30
45
50
35
55
50
45
50
40
50
55
55
88
92
82
85
90
88
88
83
80
86
80
81
82
200–202
218–222
230–233
238–240
226–230
249–252
217–220
246–248
160–162
248–251
171–173
206–208
162–165
2
4-Cyanobenzaldehyde
4-Chlorobenzaldehyde
4-Bromobenzaldehyde
4-Nitrobenzaldehyde
3
4
5
6
4-Hydroxybenzaldehyde
4-Methylbenzaldehyde
4-Methoxybenzaldehyde
3-Methoxybenzaldehyde
2-Nitrobenzaldehyde
7
3g
3h
3i
8
9
10
11
12
13
3j
2,5-Dimethoxybenzaldehyde
3k
3l
3,4,5-Trimethoxybenzaldehyde
Thiophene-2-carboxaldehyde
3m
Reaction conditions: Dimedone (2 mmol), aryl aldehyde (1 mmol) and sawdust sulphonic acid in
ethanol (3 mL) at reflux condition
a
Isolated yield
forming 1,8-dioxo-octahydroxanthenes in good to excellent yields (80–92%)
highlighting general applicability of the protocol (Table 3, entries 2–5 and 6–9).
Remarkably, good yields (80–86%) were obtained with the sterically hindered
aldehydes such as 2-nitrobenzaldehyde and 2,5-dimethoxybenzaldehyde under the
optimized reaction condition (Table 3, entries 10–11). Interestingly, highly
substituted aromatic aldehyde such as 3,4,5-trimethoxybenzaldehyde (Table 3,
entry 12) was also well tolerated furnishing comparatively moderate yield (81%) of
the desired product. Fascinatingly, hetero-aromatic aldehyde like thiophene-2-
carbaldehyde (Table 3, entries 13) was found to be equally effective furnishing the
anticipated product in good yields (82%).
The tentative mechanism for sawdust sulphonic acid catalyzed synthesis of 1,8-
dioxo-octahydroxanthenes is outlined in Scheme 2. Initially, sawdust sulphonic acid
protonated aryl aldehyde (I) and undergoes facile knoenvengel condensation with
dimedone to form intermediate (II). Next, Michael addition of another dimedone
molecule on (II) forms intermediate (III) which on further cyclodehydration
furnishes the desired 1,8-dioxo-octahydroxanthenes.
The hot filtration test was carried out to validate the heterogeneous nature of
sawdust sulphonic acid. After the 50% completion (GC) of the model reaction of
1,8-dioxo-octahydroxanthenes, catalyst was removed from the reaction mixture by
simple filtration and the filtrate was refluxed for an additional 1 h. The reaction did
not push forward beyond 50% of product yield. This clearly indicates that during the
123

S. Karhale et al.
Scheme 2 Plausible mechanistic pathway for the formation of 1,8-dioxo-octahydroxanthenes
Table 4 Sawdust sulphonic acid catalyzed synthesis of 1,8-dioxo-decahydroacridines
O
Ar
O
O
SD-OSO3H/Ethanol, Reflux
NH4OAc
Ar-CHO
+
O
N
H
1
2
4a-i
Entry
Aryl aldehyde (2)
Product (4)
Time (min)
Yield (%)a
Mp (°C)
1
2
3
4
5
6
7
8
9
Benzaldehyde
4a
4b
4c
4d
4e
4f
50
30
45
50
35
55
50
45
55
88
92
82
85
90
88
86
83
81
190–192
[300
4-Cyanobenzaldehyde
4-Chlorobenzaldehyde
4-Bromobenzaldehyde
4-Nitrobenzaldehyde
4-Hydroxybenzaldehyde
4-Methylbenzaldehyde
4-Methoxybenzaldehyde
3,4,5-Trimethoxybenzaldehyde
297–299
241–243
283–285
[300
4g
4h
4i
[300
298–300
260–262
Reaction conditions: Dimedone (2 mmol), aryl aldehyde (1 mmol), NH4OAc (1.5 mmol) and sawdust
sulphonic acid in ethanol (3 mL) at reflux condition
a
Isolated yield
course of reaction, SO3H units are held firmly to the cellulosic matrix of sawdust
and are not being leached out. This confirms that catalytic process takes place
exclusively under heterogeneous conditions.
In order to expand the scope of protocol, the reactions of dimedone, and NH4OAc
with different aldehydes for the synthesis 1,8-dioxo-decahydroacridine derivatives
were undertaken in the presence of sawdust sulphonic acid (0.05 g) and the results
are shown in Table 4. The aromatic aldehydes having electron-poor as well as
electron-rich groups form corresponding 1,8-dioxo-decahydroacridines in good to
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Green and cost effective protocol for the synthesis of…
92
90
88
86
84
82
80
78
1,8-dioxo-
octahydroxanthenes (%)
1,8-dioxo-
decahydroacridines (%)
76
Fresh 1st 2nd 3rd
Run Run Run
No. of Cycles
Fig. 6 Reusability of sawdust sulphonic acid in synthesis of 1,8-dioxo-octahydroxanthenes and 1,8-
dioxo-decahydroacridines
Table 5 Comparison of the efficiency of sawdust sulphonic acid with reported catalysts for the synthesis
of 1,8-dioxo-octahydroxanthenes and 1,8-dioxo-decahydroacridinesa
Entry Catalyst used
Reaction
condition
1,8-dioxo- 1,8-dioxo-
octahydroxanthenes decahydroacridines
Ref.
Time
Yield (%) Time
Yield
(%)
1
2
Sawdust Sulphonic acid
(0.05 g)
Ethanol/
Reflux
50 min 88
55 min 90
This
work
SmCl3 (20 mol %)
Solvent-free/
120 °C
Solvent-free/
9 h
2 h
3 h
6 h
–
98
82
32
95
–
–
–
[39]
[42]
[43]
[64]
[55]
[56]
3
4
5
6
7
Montmorillonite K-10
(0.3 g)
–
–
100 °C
HClO4–SiO2 (0.05 g)
Solvent-free/
140 °C
Cellulose Sulphonic acid Solvent-free/
–
–
–
–
(0.05 g)
110 °C
Ethanol:water/
KH2PO4 (5 mol %)
5 h
94
120 °C
Solvent-free/
Saccharose
(20 mol %)
–
–
35 min 77
80 °C
8
9
Silica bonded N-propyl
sulfamic acid (0.03 g)
Ethanol/
Reflux
–
–
–
–
2 h
86
[57]
[58]
[Et3NH][HSO4]
(10 mol %)
Solvent-free/
20 min 88
110 °C
a
Based on benzaldehyde
excellent yield highlighting general applicability of the present protocol (Table 4,
entries 2–8). Interestingly, good yields were obtained with the sterically hindered
aldehyde such as 3,4,5-trimethoxybenzaldehyde under the optimized reaction
conditions (Table 4, entry 9).
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S. Karhale et al.
The reusability of catalyst is an important attribute from the perspective of green
chemistry. The reusability sawdust sulphonic acid was investigated for synthesis of
3a and 4a under an optimized reaction condition (Fig. 6). The catalyst was easily
recovered from the reaction mixture by simple filtration and reused for three times
without significant decrease in the yield of the desired product. The slight decrease
in the observed yield is attributed to inadequate recovery of the catalyst due to the
attrition during filtration.
In order to show the advantage of sawdust sulphonic acid in comparison with
other reported catalysts, we have summarized some of the previous reports for the
preparation of 1,8-dioxo-octahydroxanthenes and 1,8-dioxo-decahydroacridines
(Table 5). The comparison of results clearly proves that sawdust sulphonic acid is
a highly effective catalyst in terms of reaction time and yield than other reported
catalysts.
Conclusions
In summary, we have reported a highly efficient and cost-effective approach for the
synthesis of 1,8-dioxo-octahydroxanthenes and 1,8-dioxo-decahydroacridines in the
presence of environmentally benign sawdust sulphonic acid as a catalyst. The
advantages of the present protocol includes high yields, short reaction time, eco-
friendly solvent, cleaner reaction profile, operational simplicity, ease of preparation
of the catalyst and facile reusability.
Supporting Information
A supplementary material which includes some of the scan copies of FT-IR,
1H-NMR, 13C-NMR and Mass analysis for this article can be accessed on the
publisher’s website.
Acknowledgements One of the authors (SSK) is indebted to UGC, New Delhi for a Teacher Fellowship
[F. No. 30-35/14 (WRO) dated: 11th June 2014] under the Faculty Development Programme. SSK is also
thankful to the Principal, Abasaheb Marathe Arts & New Commerce, Science College, Rajapur,
Ratnagiri, for encouragement and the Sophisticated Instruments Facility Centre, IISc, Bangalore, for
providing spectral facilities.
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