Grafting of sulphamic acid on functionalized sawdust: A novel solid acid catalyst for the synthesis of 1,8-dioxo-octahydroxanthenes

Article abstract of DOI:10.1007/s11164-020-04136-5

Abstract: A solid acid catalyst bearing sulphamic acid on sawdust (SA@Sawdust) was designed as a novel heterogeneous catalyst. The structure of prepared catalyst was assessed by various spectroscopic techniques such as FT-IR, field emission scanning elect

Full text of DOI:10.1007/s11164-020-04136-5

Research on Chemical Intermediates
https://doi.org/10.1007/s11164-020-04136-5
Grafting of sulphamic acid on functionalized
sawdust: A novel solid acid catalyst for the synthesis
of 1,8‑dioxo‑octahydroxanthenes
Shrikrishna Karhale1,2
Received: 19 December 2019 / Accepted: 23 March 2020
© Springer Nature B.V. 2020
Abstract
A solid acid catalyst bearing sulphamic acid on sawdust (SA@Sawdust) was designed
as a novel heterogeneous catalyst. The structure of prepared catalyst was assessed
by various spectroscopic techniques such as FT-IR, feld emission scanning electron
microscopy and energy dispersive X-ray, thermogravimetric analysis, solid-state CP/
MAS 13C-NMR spectroscopy, and CHNS analysis. The efciency of prepared cata-
lyst was explored for synthesis of diverse 1,8-dioxo-octahydroxanthene derivatives.
The mild reaction conditions are found to be more compatible with a wide range of
functional groups. The obtained products could be conveniently separated from the
reaction mixture by simple fltration, and the catalyst is recovered and reused for next
cycle without signifcant loss in catalytic efciency. The alluring features of this syn-
thetic route are operational simplicity, shorter reaction time, high conversion, wide
substrate scope, easy work-up procedure, and reusability of catalyst.
Graphic abstract
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s1116
4-020-04136-5) contains supplementary material, which is available to authorized users.
*
Shrikrishna Karhale
sskarhale80@gmail.com
1
Department of Chemistry, Karmaveer Bhaurao Patil Mahavidyalaya (Autonomous), Pandharpur,
Solapur, Maharashtra 413304, India
2
Department of Chemistry, Abasaheb Marathe Arts & New Commerce, Science College,
Rajapur, Maharashtra 416702, India
Vol.:(0123456789)
1 3

S. Karhale
Keywords Renewable bioresources · Sawdust · Xanthene · Green approach
Introduction
Nowadays, the challenges for maintaining ecological balance of our planet are among
the most complicated and daunting ever faced by society. To protect environment,
the research community is highly engaged in facing these challenges fercely through
their systematic improvements and breakthrough innovations. Further, they are trying
to create advanced product by generating the libraries of drug-like organic molecules
involving complex framework [1]. In order to accelerate the innovations and adop-
tion of green metrics, an implementation of green synthetic methodologies plays an
important role in organic synthesis. Such methodologies are the perfect response to
these constraints due to its remarkable performance in designing of recyclability pro-
cess, reduce and valorize the wastes, exceptional synthetic efciency, use of environ-
mentally benign catalyst, high atom economy, and selection of eco-friendly solvents
which are the fundamental aspects of green synthetic methodologies that ultimately
come under the roof of green chemistry [2, 3]. Therefore, a concerted and pervasive
efort is needed for the development and execution of these methodologies.
Presently, petroleum-derived monomers obtained from fossil resources as raw
material are the main source of many polymeric substances. A recent quest towards
the manufacture of polymers using renewable bioresources as a raw material is the
subject of immense curiosity which elegantly attracted the research community [4].
In manufacture of polymer, researchers are engaged in exploring the use of renew-
able bioresources instead of fossil resources. Biomass; being renewable bioresource,
is exploited as a new feedstock material for manufacturing the polymer is defnitely
benefted for both the sustainable development as well as environmental protection
[5]. Recently, severe eforts have been focused on the use of cellulose as biomass-
based polymeric support for designing a variety of heterogeneous catalysts which
efectively catalyzes number of synthetic routes [6–8]. In this regards, efort has
been made to utilize the sawdust as natural source of cellulose instead of refned cel-
lulose for the catalytic support [9]. Sawdust is a renewable bioresource and easily
available natural source of cellulose obtained from wood, owing to presence of num-
ber of active sites on its surface. It ofers the exceptional opportunities for designing
eco-friendly heterogeneous catalyst for mediating signifcant organic transformations
[10, 11]. Our earlier experience with sawdust as catalytic support [12], enthuse us to
investigate its compatibility as support material in preparation of heterogeneous cata-
lyst in the synthesis of biologically privileged heterocyclic scafolds.
Xanthenes are probably one of the most ubiquitous oxygen containing hetero-
cyclic scafold and also well-known versatile synthons due to the presence of reac-
tive inbuilt pyran ring as core unit in the moiety and also exhibit a broad range of
potential applications in the diverse felds [13–18]. Owing to such multifarious bio-
logical and pharmacological applications, the numerous synthetic procedures with
plethora of catalysts have been investigated for the synthesis of 1,8-dioxo-octahy-
droxanthenes [22–36]. Among these, most common approach involves the reaction of
dimedone and aromatic aldehydes. Nevertheless, most of the reported methods sufer
1 3

Grafting of sulphamic acid on functionalized sawdust: A novel…
from drawbacks such as tedious catalyst preparation, longer reaction time, high reac-
tion temperature, low yields, excess use of reagents as well as toxic or expensive cata-
lysts. Therefore, the synthesis of medicinally pertinent 1,8-dioxo-octahydroxanthenes
using robust heterogeneous catalyst involving easily adaptable protocol is of prime
importance. Herein, we report the successfully grafted sulphamic acid on functional-
ized sawdust (SA@Sawdust) as a novel heterogeneous solid acid catalyst for synthe-
sis of medicinally acclaimed 1,8-dioxo-octahydroxanthenes.
Experimental
General remarks
Proton and 13C NMR spectra were recorded on Bruker AC NMR Spectrometer using
TMS as an internal standard in CDCl3. The chemical shifts (δ) are expressed in ppm.
The size and morphology of catalyst were observed by using FESEM of MIRA3
TESCAN microscope with 10 kV of an accelerating voltage. Solid-state CP/MAS
13C-NMR spectrum was recorded on JEOL-ECX400 spectrometer under the pre-
scribed operating conditions. FT-IR spectra were measured on Perkin-Elmer Spec-
trum one FT-IR spectrophotometer. Dimedone, (3-aminopropyl)trimethoxysilane,
chlorosulphonic acid and aryl aldehydes were purchased from local supplier and used
without further purifcation.
Preparation of sawdust‑alumina composite (2)
Fresh and clean sawdust was obtained from local timber industry. It was further
washed by excess of distilled water to remove the surface impurities and dried in an
oven at 60 °C. The dried sawdust was then pulverized and allowed to pass through
1 mm sieve to get fne powder. The mixture of fne sawdust powder (1, 15 g) and
AlCl3·6H2O (15 g) in water (100 mL) was stirred for 12 h at room temperature.
Thereafter, mixture was fltered and the residue was exposed to ammonia and washed
frequently with water, dried in vacuum to get sawdust-alumina composite (2).
Preparation of amino‑functionalized sawdust (3)
The sawdust-alumina composite (2, 10.0 g), (7.0 mL, 40.11 mmol) (3-aminopropyl)-
trimethoxysilane was added and resulting mixture was refuxed in toluene (40 mL)
for 24 h. The reaction mixture was cooled, fltered and washed with toluene (20 mL)
and then dried under vacuum to get the amino-functionalized sawdust (3). CHN anal-
ysis observed: %C 37.62, %H 4.66, %N 2.31; Loading: 0.0824 mmol of amino group
per gram of sawdust.
1 3

S. Karhale
Preparation of SA@Sawdust (4)
In 25-mL RB fask, amino-functionalized sawdust (3, 5 g) in diethyl ether (20 mL),
chlorosulfonic acid (2.33 g, 20 mmol) was added dropwise over 20 min via a syringe
at 0 °C. The reaction mixture was stirred at room temperature for 30 min; brown pow-
der was obtained which was again washed with diethyl ether (10 mL). The resultant
solid was dried under vacuum at 60 °C for 4 h to get desired SA@Sawdust (4). FT-IR
(KBr) (cm−1): 3347, 3245, 2885, 1228, 1025, 885, 837, 696, 632, 581; 13C CP-MAS
NMR (500 MHz): δ 105.64 (s, cellulose-C1), 89.48-84.27 (d, cellulose-C4), 75.56-
65.64 (m, cellulose-C2, C3, C5), 56.84 (s, cellulose-C6), 43.68 (s, N–CH2), 22.32
(s, N–CH2–CH2–CH2), 11.12 (bs, CH2–Si); EDAX analysis: %C 19.03, %O 40.81,
%Al 12.05, %Si 26.03, %S 2.08; CHNS analysis observed: %C 27.93, %H 5.09, %N
2.36, %S 5.71; Loading: 0.130 mmol of sulphonic group per gram of sawdust.
The covalent grafting of chlorosulphonic acid on amino-functionalized sawdust is
shown in Fig. 1. Initially, aluminium oxide was highly dispersed on the surface of
sawdust (1) with high degree of adhesion to form sawdust-alumina composite (2).
This composite was then allowed to react with (3-aminopropyl)trimethoxysilane at
refux in toluene to form amino-functionalized sawdust (3) with good degree of orga-
nofunctionalization. Afterwards, chlorosulfonic acid was covalently grafted in the
matrix of functionalized sawdust using free aminopropyl group resulting in the for-
mation of desired catalyst acronymed as SA@Sawdust (4).
General procedure for synthesis of 1, 8‑dioxo‑octahydroxanthenes
In 25-mL RB fask, the mixture of dimedone (2 mmol) and aryl aldehyde (1 mmol)
in presence of SA@Sawdust (0.05 g, 0.0075 mmol) was refuxed in ethanol (5 mL).
Upon the completion of reaction (TLC monitored), reaction mixture was diluted with
hot ethanol (5 mL) and fltered to remove the catalyst. The evaporation of solvent in
OH
OH
OH
OH
OH
Al
l
A
AlCl3.6H2O
Water, RT
Sawdust
(3-Aminopropyl)trimethoxysilane
Toluene, Reflux
Sawdust
1
2
H3CO
Si
H3CO
NH2
Si
NHSO3H
O
O
OH
O
O
OH
OH
OH
OH
OH
Al
Al
Chlorosulphonic Acid
Diethyl ether, 0 °C
l
A
l
A
Sawdust
Sawdust
4
3
Fig. 1 Preparation of heterogeneous solid acid catalyst SA@Sawdust
1 3

Grafting of sulphamic acid on functionalized sawdust: A novel…
vacuo, aforded crude product which was recrystallized from ethanol to obtain the
desired 1,8-dioxo-octahydroxanthenes.
Result and discussion
Fourier transform infrared (FT-IR), feld emission scanning electron microscopy
(FESEM), energy dispersive X-ray (EDX), thermogravimetric analysis (TGA), and
cross-polarization magic angle spinning (CP-MAS) 13C-NMR spectroscopy were
employed to monitor the structure of SA@Sawdust.
The FT-IR spectrum of the catalyst was recorded on Perkin-Elmer Spectrum one
FT-IR spectrophotometer and is depicted in Fig. 2. The FT-IR spectrum of SA@Saw-
dust displays O–H stretching of sulphonic group at 3375 cm−1 while N–H stretching
appears at 3242 cm−1. The peak obtained at 2854 cm−1 is attributed to C–H stretching
vibration of methylene groups of propyl unit present in the catalyst. The SO2 sym-
metric and asymmetric stretching vibrations appeared at 1242, 1022 cm−1, respec-
tively. The peaks at 888 and 752 cm−1 belong to S–OH bending vibration, whereas
S–O symmetric stretching bands appeared at 625 and 583 cm−1 confrms the forma-
tion of desired catalyst.
The formation of SA@Sawdust was further corroborated by recording cross-
polarization magic angle spinning (CP-MAS) 13C-NMR spectroscopy (Fig. 3) which
demonstrated the peaks at 105.64 (s, cellulose-C1), 89.48–84.27 (d, cellulose-C4),
75.56–65.64 (m, cellulose-C2, C3, C5), 56.84 (s, cellulose-C6), 43.68 (s, N–CH2),
22.32 (s, N–CH2–CH2–CH2), 11.12 (bs, CH2–Si) which is in well agreement with
proposed structure.
The EDX analysis of desired catalyst is shown in Fig. 4. Figure 4a pristine sawdust
revealed carbon and oxygen as the major elements where as Fig. 4b indicates the
peaks for carbon, oxygen, aluminium and silicon for amino-functionalized sawdust.
Further, SA@Sawdust recognized the peaks for carbon, oxygen, aluminium silicon
and sulfur as shown in Fig. 4c. Presence of sulfur at its respective energy position at
Fig. 2 FT-IR Spectrum of heterogeneous solid acid catalyst SA@Sawdust
1 3

S. Karhale
Fig. 3 Solid state CP/MAS 13C-
NMR spectrum of SA@Sawdust
Fig. 4 EDX: a Pristine Sawdust, b amino-functionalized sawdust, c SA@Sawdust
2.30 keV also suggests the successful grafting of chlorosulfonic acid on amino-func-
tionalized sawdust. The loading of sulphonic group as determined by EDX analysis
was found to be 0.15 mmol/g of sawdust.
Field emission scanning electron microscopy (FESEM) is used for the studying
the particle size and surface morphology of catalyst (Fig. 5). FESEM image clearly
shows that the catalyst particles exhibit fbrous morphology having length ranging
from couple of hundred nanometres to few micrometres.
The thermal stability of prepared catalyst was assessed using thermogravimetric
analysis (TGA) in the temperature range 25–1000 °C under nitrogen atmosphere
(Fig. 6). Initial weight loss of 18.62% displayed by the catalyst due to removal
of physically absorbed water associated with catalyst through the hydrogen bond-
ing. The second weight loss of 22.48% at 312 °C is attributed to the loss of com-
bustible organic moieties [19]. Further, the combined weight loss of 24.22%
and 21.11% is assigned to the pyrolytic decomposition of major constituents of
1 3

Grafting of sulphamic acid on functionalized sawdust: A novel…
Fig. 5 FESEM of SA@Sawdust
Fig. 6 TGA analysis of SA@Sawdust
sawdust (cellulose, hemicelluloses and lignin), through the formation of levoglu-
cosan and other volatile compounds [20]. Finally, the residual weight of 10.64% is
due to formation of oxides of alumina.
1 3

S. Karhale
Determination of acidic site
Acidity of catalyst can be determined by using pH measurement. SA@Sawdust
(0.5 g) was added to 25 mL of aq. 1 M sodium chloride (pH 5.4) and resultant mix-
ture was stirred for 2 h at room temperature. The pH of solution decreased to 1.42
which equal to loading 1.86 mmol [H+] per gram of catalyst [21].
Our next task was to explore the catalytic potential of SA@Sawdust in the syn-
thesis of 1, 8-dioxo-octahydroxanthenes. In this regards, the dimedone and benzal-
dehyde were chosen as a model substrates for optimization of reaction conditions. In
order to optimize the solvent, the template reaction in the presence of SA@Sawdust
(0.05 g, 0.0075 mmol) was carried out in diferent organic solvents at refux condi-
tion (Table 1). The reaction marches sluggishly in solvents such as toluene, chloro-
form, dichloromethane, acetonitrile, EDC, THF, and acetone, afording correspond-
ing 1,8-dioxo-octahydroxanthene (7a) in lower yields (Table 1, entries 1–7). The
high yield was acquired in presence of ethanol under refux condition (Table 1, entry
10). Further, in order to optimize the loading of catalyst, the model reaction was car-
ried out using various quantities of catalyst (Table 1). It was observed that the opti-
mal amount of catalyst was 0.05 g (0.0075 mmol) in order to obtain the best result
(Table 1, entry 10). Further decrease in catalyst quantity lower than 0.05 g did not
increase the yield of the product signifcantly (Table 1, entries 8 and 9).
Table 1 Optimization of reaction condition for synthesis of 1, 8-dioxo-octahydroxanthenes
O
CHO
O
O
SA@Sawdust
Solvent, Reflux
+
O
O
Entry
Catalyst quantity (g) Reaction condition
Reaction time (min) Isolated
yield (%)a
1
2
3
4
5
6
7
8
9
10
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.01
0.03
0.05
Toluene/refux
Chloroform/refux
DCM/refux
Acetonitrile/refux
EDC/refux
50
50
50
50
50
50
50
50
50
50
32
38
42
47
48
51
53
72
84
92
THF/refux
Acetone/refux
Ethanol/refux
Ethanol/refux
Ethanol/refux
Reaction conditions: Dimedone (2 mmol), benzaldehyde (1 mmol) and SA@Sawdust in solvent (5 mL)
at given condition
a In all reaction 100% conversion were obtained
1 3

Grafting of sulphamic acid on functionalized sawdust: A novel…
To explore the scope and limitations of this protocol, we focused our attempts on
the synthesis of 1, 8-dioxo-octahydroxanthene derivatives (7) using dimedone (5)
with variety of substituted aryl aldehydes (6) under the optimal condition and the
results are summarized in Table 2. In all cases 1, 8-dioxo-octahydroxanthenes were
obtained as the sole product. Aromatic aldehydes carrying the both electron-with-
drawing and electron-donating (Table 2, entries 2–5 and 6–9) furnishes the corre-
sponding 1, 8-dioxo-octahydroxanthenes in good to excellent yields. Surprisingly,
the signifcant yields were obtained with the sterically crowded aldehydes, such as
2-nitrobenzaldehyde, 2,5-dimethoxybenzaldehyde and 3,4,5-trimethoxybenzaldehyde
under optimized reaction condition highlighting the general applicability of present
Table 2 SA@Sawdust catalyzed reaction between dimedone and aryl aldehydes
R
CHO
O
O
O
SA@Sawdust
Ethanol, Reflux
+
O
R
O
5
6
7a-m
Entries Aryl aldehyde (6)
Product (7) Time (min) Yield (%)a Mp (°C) [lit.]
References
1
2
3
Benzaldehyde
7a
50
35
40
92
93
85
200–202 [201–203] [23]
218–222 [217–218] [23]
230–233 [230–232] [23]
4-Cyanobenzaldehyde 7b
4-Chlorobenzalde-
7c
hyde
4
4-Bromobenzalde-
hyde
7d
50
86
238–240 [240–242] [23]
5
6
4-Nitrobenzaldehyde 7e
40
55
94
88
226–230 [228–230] [23]
249–252 [250–251] [24]
4-Hydroxybenzalde- 7f
hyde
7
8
9
4-Methylbenzalde-
7g
50
45
50
86
85
80
217–220 [219–221] [23]
246–248 [248–250] [25]
160–162 [161–162] [24]
hyde
4-Methoxybenzalde- 7h
hyde
3-Methoxybenzalde- 7i
hyde
10
11
2-Nitrobenzaldehyde 7j
45
50
84
80
248–251 [249–250] [25]
171–173 [172–174] [26]
2,5-Dimethoxybenza- 7k
ldehyde
12
13
3,4,5-Trimethoxyben- 7l
55
60
82
80
206–208 [205–208] [27]
162–165 [164–165] [24]
zaldehyde
Furfural
7m
Reaction conditions: dimedone (2 mmol), aryl aldehyde (1 mmol), and SA@Sawdust in ethanol (5 mL)
were stirred at refux condition
aIsolated yield of purifed products
1 3

S. Karhale
R
SA@Sawdust
O
H
H
O+
O
O
O
Knoenvengel Condensation
H
H
SA@Sawdust
R
R
H
O
O
(I)
R
R
R
R
O
O
H
O
O
O
O
O
O
H
O
O
Cyclization
-H2
O
O
O
O
OH
OH
(II)
(III)
Scheme 1 Plausible mechanistic pathway for formation of 1,8-dioxo-foctahydroxanthenes
Fig. 7 Reusability of SA@
Sawdust for the synthesis of
1,8-dioxo-octahydroxanthenes
protocol (Table 2, entries 10 and 12). Fascinatingly, heteroaromatic thiophene-2-car-
baldehyde (Table 2, entries 13) was examined and found to be well tolerated provid-
ing comparatively moderate yields of the anticipated product.
Mechanistic pathway for the synthesis of 1,8-dioxo-octahydroxanthenes cata-
lyzed by SA@Sawdust is depicted in Scheme 1. We propose that one molecule of
dimedone was frstly underwent knoenvengel condensation with an activated alde-
hyde (I) to aford intermediate (II). Then, another molecule of dimedone reacted with
intermediate (II) via michael addition to give the intermediate (III) which fnally on
cyclodehydration furnishes the expected 1,8-dioxo-octahydroxanthenes.
The fundamental aspect of this study has to establish a reusability procedure for
the synthesis of 1,8-dioxo-octahydroxanthenes (7a) in presence of SA@Sawdust
under optimized reaction condition as shown in Fig. 7. The catalyst was easily recov-
ered from reaction mixture by simple fltration, washed, dried and reused for next
1 3

Grafting of sulphamic acid on functionalized sawdust: A novel…
Table 3 Comparison of efciency of SA@Sawdust catalyst with reported methods for the synthesis of
1,8-dioxo-octahydroxanthenesa
Entry
Catalyst used
Reaction condition
Time
Yield (%)
References
1
2
3
4
5
6
7
8
9
SA@Sawdust (0.05 g)
l-Proline (40 mol%)
CaCl2 (20 mol%)
Montmorillonite K-10 (0.3 g)
[Bmim]HSO4 (0.1 g)
[Hmim]TFA (0.1 g)
SmCl3 (20 mol%)
[Cmmim][BF4] (200 mg)
PMA-SiO2 (0.1 mol%)
InCl3·4H2O (10 mol%)
Ethanol/refux
Dichloroethane/refux
DMSO/90 °C
Solvent-free/100 °C
Solvent-free/80 °C
Solvent-free/80 °C
Solvent-free/120 °C
Methanol/ultrasound
Acetonitrile/refux
[Bmim][BF4]/80 °C
50 min
6 h
4 h
2 h
3 h
3 h
9 h
50 min
4 h
4 h
92
83
85
82
85
85
98
87
95
87
This work
[28]
[29]
[30]
[31]
[32]
[33]
[34]
[35]
10
[36]
aBased on benzaldehyde
cycle. It was observed that catalyst could be reused for three times without signifcant
decrease in the yield of desired product.
In order to show the advantages of SA@Sawdust in comparison with other cata-
lysts, we have summarized several results for the synthesis of 1,8-dioxo-octahydrox-
anthenes (Table 3). A comparison of the results reveals that SA@Sawdust is well
efcient catalyst in terms of reaction time and product yield despite of other reported
catalyst.
Conclusions
In summary, we have reported highly efcient and cost-efective approach towards
the synthesis of 1,8-dioxo-octahydroxanthenes in the presence of SA@Sawdust as
an eco-friendly catalyst. The advantages of present procedure is short reaction time,
cleaner reaction profle, high yields, eco-friendly solvent, operational simplicity, easy
preparation of catalyst and its reusability.
Acknowledgements SSK is gratefully acknowledged APD Section, University of Mumbai, Mumbai for
providing the fnancial assistance (Research Project No. 417, dated: 27th March 2019). Author is also
thankful to the Principal, Abasaheb Marathe Arts & New Commerce, Science College, Rajapur, Ratnagiri,
for encouragement during the course of research work.
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