Graphene Oxide Incorporated Strontium Nanoparticles as a Highly Efficient and Green Acid Catalyst for One-Pot Synthesis of Tetramethyl-9-aryl-hexahydroxanthenes and 13-Aryl-5H-dibenzo[b,i]xanthene-5,7,12,14(13H)-tetraones Under Solvent-Free Conditions

Article abstract of DOI:10.1007/s10562-019-02675-0

An efficient, inexpensive and recyclable graphene oxide/strontium nanocatalyst was synthesized and applied in a pseudo three-component, one-pot cyclocondensation of aromatic aldehydes and dimedone/lowson to afford the corresponding 3,3,6,6-tetramethyl-9-a

Full text of DOI:10.1007/s10562-019-02675-0

Catalysis Letters
https://doi.org/10.1007/s10562-019-02675-0
Graphene Oxide Incorporated Strontium Nanoparticles as a Highly
Efficient and Green Acid Catalyst for One-Pot Synthesis of Tetramethyl-
9-aryl-hexahydroxanthenes and 13-Aryl-5H-dibenzo[b,i]xanthene-
5,7,12,14(13H)-tetraones Under Solvent-Free Conditions
Seyyed Rasul Mousavi1 · Hamid Rashidi Nodeh2 · Elham Zamiri Afshari3 · Alireza Foroumadi1
Received: 15 November 2018 / Accepted: 13 January 2019
© Springer Science+Business Media, LLC, part of Springer Nature 2019
Abstract
An efficient, inexpensive and recyclable graphene oxide/strontium nanocatalyst was synthesized and applied in a pseudo
three-component, one-pot cyclocondensation of aromatic aldehydes and dimedone/lowson to afford the corresponding
3,3,6,6-tetramethyl-9-aryl-3,4,5,6,7,9-hexahydro-1H-xanthene-1,8(2H)-diones and 13-aryl-5H-dibenzo[b,i]xanthene-
5,7,12,14(13H)-tetraones in high yields under solvent-free conditions. To the best of our knowledge, there are no literature
reports on applying graphene oxide/strontium as a nanocatalyst for xanthene derivatives synthesis. The key potential ben-
efits of the present method are including high yields, short reaction time, easy workup, recyclability of catalyst and ability
to tolerate a variety of functional groups which gives economical as well as ecological rewards. The nanocatalyst easily
separated from the reaction mixture easily by applying an external magnet and reused at least six times without noticeable
degradation in catalytic activity.
Graphical Abstract
Keywords Xanthene · Lowson · Heterogeneous catalyst · Reusable catalyst · Graphene oxide · One-pot · Magnetic
nanocatalyst
Extended author information available on the last page of the article
Vol.:(0123456789)
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S. R. Mousavi et al.
of MNPs, they provided various potential applications
such as hyper thermal agents, drug delivery, MRI contrast
agents and cell sorting [17–22]. Furthermore, extraction
of selected cells from biological samples and cell cultures
using MNPs has been reported [23].
1 Introduction
In recent years, green chemistry has become a major driv-
ing force for organic chemists to develop environmentally
benign to a myriad of materials [1]. The development of
cleaner technologies is a major subject in green chemistry
[2]. Green chemistry concerns the design of environmen-
tally friendly products and chemical processes while mini-
mizing the usage and generation of hazardous substances.
Organic solvents are a key factor in environmental pollu-
tion and many are carcinogenic and toxic making reactions
which do not require the use of organic solvents desir-
able. Water is an alternative solvent for many chemical
reactions, possessing desirable properties such as ready
availability, chemical stability, nontoxicity, recyclability
and easy handling [3–5]. Moreover, performing of organic
reactions under solvent-free conditions is another strategy
to avoid the use of hazardous organic solvents [6–8]. On
the other hand, one of the arms of green chemistry is the
use of heterogeneous green catalysts. In the last decade,
the synthesis and application of nanoparticles as heteroge-
neous catalysts with different shapes and sizes have been
developed. The catalytic activity of a heterogeneous cata-
lyst is mainly determined by its morphology and particle
size. The catalytic activity can be improved by reducing
the particle size to nanometer scale. Because, nanocata-
lysts exhibit higher activity and selectivity than their cor-
responding bulk materials. They are expected to be suita-
ble candidates for the design of highly active and selective
heterogeneous catalysts for organic synthesis due to their
unique physical, surface chemical and catalytic properties
and large surface-to-volume ratio [9]. Nevertheless, use of
such nanoscales can be increase operating costs but also
increase having negative environmental impacts. Since,
collection and separation of these nanoparticles from the
reaction mixture is almost as difficult as separation using
conventional methods [8]. In recent years, a great deal of
attention has been paid to the preparation of heterogeneous
catalysts by immobilizing magnetic materials on various
solid supports [8, 10–13]. Among the many attempts to
the various support used for the preparation of heteroge-
neous catalyst systems, iron oxide magnetic nanoparticles
(MNPs) has particular importance because of its avail-
ability, high stability and the fact that organic groups can
adjoin to its surface with strong connection [14–16]. More
importantly, due to the magnetic nature of the catalyst,
it could be recovered using an external magnetic field.
Also, the isolation of the final product can be possible
by a simple decantation. In addition, such catalysts also
showed better efficiency, and superior stability when com-
pared to their other supported and unsupported peers. On
the other hand, due to having strong magnetic moments
Supporting organocatalyst on MNPs is a very hopeful
research area which widely used for chemical synthesis in
organic reactions. Therefore, different organocatalysts were
covalently grafted to the MNPs surface and was used in
organic transformations [15, 24].
Synthesis of heterocyclic compounds have become
an important area of research in organic chemistry [25].
Recently, fused heterocyclic compounds have gained great
attention in the field of medicinal chemistry due to their
significant contribution in the biological profiling of drugs
[26–29]. In this context, of some active carbonyl compounds
such as dimedone, thiobarbituric acid, barbituric acid, mel-
drum’s acid and naphthoquinones with various substrates for
the synthesis of fused heterocycles have been documented
in recent years [27, 29–37]. Among a large variety of fused
heterocyclic compounds, xanthene derivatives are valuable
synthetic scaffolds for both medicinal and synthetic organic
chemists [38–40]. Xanthene derivatives are tricyclic mol-
ecules containing pyran scaffold as central a ring fused to
aliphatic or aromatic rings on both sides [40]. Xanthenes are
an important class of heterocyclic compounds that exhibit
significant biological and pharmaceutical properties. These
compounds were found to be potent anti-inflammatory [41,
42], antimicrobial [43], antioxidant [44], u-opiat agonist
[45], antiproliferative [46], antiviral [47], and antibacte-
rial agents [48]. Xanthene derivatives are also utilized as
antagonists for paralyzing action of zoxazolamine and in
photodynamic therapy [49]. Moreover, these heterocycles
can be widely used in laser technologies, stable dyes, protein
labelling fluorophores and fluorescent sensor due to their
useful spectroscopic properties [40, 41, 50–52]. Due to their
wide range of applications, xanthenes have received a great
deal of attention in connection with their synthesis. In this
context, a large number of catalytic systems is present in the
literature to assemble these interesting scaffolds [1, 39, 42,
47, 53–61]. Most of this recent research though are useful
and convenient but, several of these methods suffer from
certain drawbacks such as prolonged reactions times, tedi-
ous work-up conditions, use of volatile or hazardous organic
solvents, employment of large amount of catalyst and harsh
reaction conditions. Therefore, due to their manifold appli-
cations xanthene derivatives introducing a clean procedure
by the use of green and environmentally friendly catalyst
with high catalytic activity, moderate temperature, and short
reaction time accompanied with excellent yield for the pro-
duction of this class heterocycles is needed. In view of some
previous works, we were thus fascinated by the possibility
of applying nanotechnology to the design of a novel, active,
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Graphene Oxide Incorporated Strontium Nanoparticles as a Highly Efficient and Green Acid…
recyclable, and magnetically recoverable organometallic
catalyst by using graphene oxide.
excellent activity for the synthesis of tetramethyl-9-aryl-
hexahydroxanthenes (4a–l) and 13-aryl-5H-dibenzo[b,i]
xanthene-5,7,12,14(13H)-tetraones (5a–n) in a one-pot,
pseudo three-component under solvent-free conditions was
demonstrated (Scheme 1). This procedure is very simple,
economical and environmentally friendly.
Based on the above fundamental understandings and
in continuing our ongoing research towards the develop-
ment of eco-friendly and green multicomponent reactions
[28, 37, 62–64], a magnetically recyclable graphene oxide
catalyst was assembled using magnetic nanoparticles as
the support, and the combined convenient recyclability and
As shown in Scheme 2, the catalyst (MSrGO NCs) was
prepared via a simple route and method from inexpensive
commercially materials.
Scheme 1 Synthesis of xanthene derivatives using immobilized graphene oxide on magnetic strontium nanoparticles (MSrGO NCs)
Scheme 2 Graphical route for
synthesis of MSrGO nanocata-
lyst
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S. R. Mousavi et al.
via the condensation reaction between aromatic aldehydes
and dimedone/lawsone. The reaction conditions have been
optimized by the reaction of benzaldehyde 1 (1 mmol),
and dimedone 2 (2 mmol) as model reaction to result
in, 3,3,6,6-tetramethyl-9-phenyl-3,4,5,6,7,9-hexahydro-
1H-xanthene-1,8(2H)-dione 4a. The model reaction was
optimized in terms of various parameters such as effect of
solvent, catalyst amount, and influence of temperature. A
summary of the optimization experiments is provided in
Table 1. At the beginning, two uncatalyzed reactions were
tested under solvent-free conditions (One at room tem-
perature and another at 80 °C) but no significant yield was
obtained even after 24 h (Table 1, entries 1 and 2). Then,
the test reaction was studied in the presence of 5 mg under
solvent-free conditions, as well as with different solvents
such as EtOH, MeOH, EtOAc, CH2Cl2, CH3CN and H2O
to assess the solvent effect on the reaction rate at 80 °C
(Table 1, entries 3–9). It was observed that the reaction
proceeds moderately in the presence of various solvents,
but when the reaction was carried out under solvent-free
reaction conditions, maximum yield (75%) was obtained at
2 Results and Discussion
2.1 Evaluating the Catalytic Activity of the MSrGO
NCs
Following our interest to designing and developing a
new efficient and environmental friendly heterogeneous
catalysts for organic transformations, the MSrGO NCs
was initially synthesized [65] according to procedure as
shown in Scheme 2. Then, the synthesized catalyst was
fully characterized by means of different techniques, such
as Fourier transform infrared spectroscopy (FT-IR), small-
angle X-ray diffraction (XRD) and field emission scanning
electron microscopy (FE-SEM). The results obtained from
these techniques confirmed the successful preparation of
the new mesoporous catalyst. The present study overcomes
some drawbacks of the previous methods, such as longer
reaction times, separation of catalyst, hazardous solvents
and expensive catalyst required for the green, one-pot,
pseudo three-component synthesis of xanthene derivatives
Table 1 Optimization of conditions for the synthesis of 4a
Entry
Catalyst (mg)
Solvent
Temperature (°C)
Time (h)
Yield (%)a
1
2
3
4
5
6
7
8
–
–
5
5
5
5
5
5
–
–
RT
80
80
80
80
80
80
80
80
80
80
80
80
80
40
60
100
110
24
24
5
5
5
5
5
5
5
–
–
EtOH
MeOH
EtOAc
CH2Cl2
MeCN
H2O
–
–
–
–
–
–
–
–
65
65
56
47
66
45
75
85
92
92
90
91
53
68
90
91
9
5
10
11
12
13
14
15
16
17
18
10
15
20
25
30
15
15
15
15
3
2.5
2.5
3
3
8
8
3
2.5
–
–
aYield refers to the pure isolated product
1 3

Graphene Oxide Incorporated Strontium Nanoparticles as a Highly Efficient and Green Acid…
80 °C (Table 1, entry 8). Following choice of solvent-free
conditions, the effect of the catalyst loading on yields of
the reaction was assessed (Table 1, entries 9–14). Vari-
ous sets of reactions were carried with different catalyst
concentrations ranging from 5 to 30 mg at 80 °C. It was
observed that with increasing the catalyst concentration,
yield of the product increases. Maximum yield (92%)
was obtained when 15 mg of catalyst was used (Table 1,
entry 11). Further increase in the catalyst loading (25 and
30 mg) had no significant effect on the yield of the reaction
(Table 1, entries 13 and 14).
shorter reaction times without formation of any byproducts
(Table 2). The investigation of results shows that the nature
of substitutions on aromatic aldehydes has no significant
effect on the reaction time and yields under the above opti-
mal conditions (Table 2, entries 2–12).
The scope and generality of the present protocol were also
extended by condensation of two equivalents of 2-hydrox-
ynaphthalene-1,4-dione and one equivalent of aryl aldehydes
containing the electron-withdrawing or electron-donating
substituents (Scheme 1). The reaction progressed smoothly
with both electron-withdrawing and electron-donating aro-
matic aldehydes to get higher yields of the corresponding
13-aryl-5H-dibenzo[b,i]xanthene-5,7,12,14(13H)-tetraones
in shorter reaction time (Table 3). The position of the sub-
stituent on the phenyl ring of aryl aldehydes showed no sig-
nificant effect on the yield and time of the reaction.
During the optimization of the reaction conditions, the
effect of temperature on the pilot reaction was also evaluated
at 40, 60, 80, 100 and 110 °C to test their efficiency under
solvent-free conditions (Table 1, entries 11 and 15–18). It
was observed that the yield of the product is maximum at
80 °C (Table 1, entry 11). Hence, 80 °C was chosen as opti-
mum temperature for the reaction. Therefore, as shown in
Table 1, using 15 mg MSrGO NCs under solvent-free and
80 °C gave the highest yield of 3,3,6,6-tetramethyl-9-phenyl-
3,4,5,6,7,9-hexahydro-1H-xanthene-1,8(2H)-dione 4a in the
shortest time.
In order to assess the efficiency of this methodology, the
obtained result from the reaction of 4-methyl benzaldehyde
with 2-hydroxynaphthalene-1,4-dione for the synthesis of
13-(p-tolyl)-12H-dibenzo[b,i]xanthene-5,7,12,14(13H)-
tetraone (5b) by this procedure has been compared with
those of the previously reported in the literature. As shown
in Table 4, the use of MSrGO NCs leads to an improved pro-
tocol in terms of compatibility with environment, reaction
time, yield of the product, and amount of the catalyst when
compared with other catalysts.
With these encouraging results in hand, the general-
ity of this reaction was examined using various aromatic
aldehydes containing electron-donating as well as electron-
withdrawing groups. All the substrate variants reacted well
and afforded higher yields of 3,3,6,6-tetramethyl-9-aryl-
3,4,5,6,7,9-hexahydro-1H-xanthene-1,8(2H)-diones in
The end in order to make the procedure economically
and environmentally more viable, we also carried out a
Table 2 Synthesis of 3,3,6,6-tetramethyl-9-aryl-3,4,5,6,7,9-hexahydro-1H-xanthene-1,8(2H)-diones by SrFeGO nanocomposite
Entry
R
Product
Time (h)
Yield (%)a
M.p (°C)
M.p (°C) [References]
1
2
3
4
5
6
7
8
H
4-CH3
2-Br
2-Cl
4-Cl
2-NO2
3-NO2
4-NO2
4-N(CH3)2
4-OCH3
3,4-(OCH3)2
3,4,5-(OCH3)3
4a
4b
4c
4d
4e
4f
4g
4h
4i
2.5
3
1
1
1
0.9
4
1.5
5
1.5
1.5
0.8
92
89
97
90
92
91
93
96
80
94
93
90
199–200
211–213
227–229
226–228
232–234
248–250
170–172
220–222
220–222
240–242
181–183
190–192
198–200 [1]
212–214 [66]
226–229 [60]
226–228 [67]
230–232 [68]
248–249 [69]
171–173 [66]
221–223 [67]
221–223 [66]
239–241 [70]
182–184 [1]
192–194 [71]
9
10
11
12
4j
4k
4l
aIsolated yield
1 3

S. R. Mousavi et al.
Table 3 Construction of 13-aryl-5H-dibenzo[b,i]xanthene-5,7,12,14(13H)-tetraone derivatives in the presence of MSrGO NCs
Entry
R
Product
Time (h)
Yield (%)a
M.p (°C)
M.p (°C) [Ref]
1
2
3
4
5
6
7
8
H
4-CH3
2-Br
5a
5b
5c
5d
5e
5f
5g
5h
5k
5l
2.5
2
1
0.8
2.5
2
90
92
96
94
89
92
91
95
93
90
88
89
304–306
303–305
282–284
>310
262–264
>310
272–274
>310
>310
305–307 [72]
304–307 [73]
283–285 [72]
>320 [74]
263–264 [55]
320–322 [54]
273–277 [55]
340–342 [58]
>330 [55]
4-Br
2-OCH3
4-OCH3
2-NO2
3-NO2
4-NO2
2-Cl
2
1.75
1.5
1.75
2
9
10
11
13
306–308
279–281
>310
304–306 [54]
280–282 [55]
330–332 [58]
3-Cl
4-Cl
5m
5n
1.75
aIsolated yield
Table 4 Comparative study of the present methodology with others reported in the literature for the synthesis of compound 5b
Entry
Catalyst
Reaction conditions
Time (min)
Yield (%)a
[References]
1
2
3
4
5
6
7
8
ChCl/itaconic acid
[Msim]Cl
[Hmim]HSO4
[Et3N–SO3H]Cl
[Et3NH][HSO4]
H2SO4
bmim[HSO4]
p-TSA
80 °C
120
7
7
8
9
150
90
420
240
60–132
120
91
88
90
90
89
91
84
70
78
84
92
[55]
[53]
[53]
[53]
[53]
[54]
[54]
[58]
Solvent-free, 80 °C
Solvent-free, 80 °C
Solvent-free, 80 °C
Solvent-Free, 80 °C
EtOH, reflux
−
80 °C
Solvent-free/80 °C
Solvent-free/100 °C
75 °C
9
10
11
p-TSA
TMGT/TFA
MSrGO NCs
[73]
[47]
This work
Solvent-free/80 °C
aIsolated yield
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Graphene Oxide Incorporated Strontium Nanoparticles as a Highly Efficient and Green Acid…
100
3.2 Preparation of MSrGO Nanocomposite
92
91
89
89
88
88
80
60
40
20
0
Magnetic nanoparticles doped graphene oxide (M–GO) was
prepared by dissolving of proper amount of FeCl3.6H2O
(200 mg), FeCl2.4H2O (400 mg) and grapheme oxide
(500 mg) in distilled water (50 mL). To get homogenize
solution the mixture was sonicated for 30 min then ammo-
nia solution (2 mL, 25%) was added drop-vise and stirred
vigorously for 5 h. The dark black product was collected
by assistance of external magnet and washed with excess
distilled water and oved dried at 80 °C for 24 h. For fur-
ther experiment, M–GO nanocomposite was modified with
strontium nanoparticles to get MSrGO nanocatalyst. Conse-
quently, strontium nitrate solution (0.1 M) was prepared in
distilled water then 500 mg of M–GO powder was added and
sonicated for 30 min. Then, reaction temperature was set at
45 °C followed by addition of 1 M ammonia solution (drop-
wise) to set solution pH at 9–10 under vigorous stirring for
1 h. finally, solution was transferred to autoclave and kept
for 24 h at 120 °C. Product was washed with excess distilled
water and oven dried at 80 °C for 24 h before using.
Yield (%)
Time (h)
6
5
4
3
3
2
1
2
3
4
5
6
Run
Fig. 1 Recyclability studies of MSrGO NCs in the synthesis of the
product 5b
reaction to inspect reusability of MSrGO NCs. As soon as
the reaction was complete, the catalyst was separated eas-
ily by an external magnetic field and washed with ethanol
for several times and dried. The catalytic activity of recy-
cled MSrGO NCs was tested under optimal reaction con-
ditions for the synthesis of 13-(p-tolyl)-12H-dibenzo[b,i]
xanthene-5,7,12,14(13H)-tetraone (5b), and it was found
that recycled MSrGO NCs furnished the product in good
to high yield. Likewise, this catalyst can be reused in six
more consecutive runs (Fig. 1) with only a modest loss in
catalytic activity.
3.3 Catalyst Characterization
3.3.1 FT-IR Spectroscopy
FT-IR spectroscopy (Fig. 2) is represent the characteristics
functional groups of as prepared M-GO and MSrGO nano-
catalyst. The M–GO spectrum provided several IR bands at
3431, 1636, 1378, 1097 and 592 cm−1 that are correspond-
ing to O–H stretching, C=O, C–C/C–O (epoxy), C–OH
and F–O, respectively. As can be seen, after modification
of M–GO with strontium nanoparticles some IR bands are
appeared and disappeared in MSrGO spectrum. Hence, the
3 Experimental
3.1 General
All solvents, chemicals and reagents were research grade
and purchased from Merck, Fluka and Sigma Aldrich
chemical companies and used without further purifica-
tion. All reactions and the purity of the products were
monitored by thin-layer chromatography (TLC) on F254
aluminium plates coated with silica gel (Merck) using
petroleum ether/ethyl acetate (8:2) as the eluent solvent.
Melting points were recorded on an Electrothermal 9100
apparatus. Ultraviolet light was used for spots identifica-
tion during the reaction process. Functional groups of the
products were characterized using FT-IR spectroscopy and
spectra were recorded in the range of 400–4000 cm−1 by
a Bruker Equinox 55 FT-IR spectrometer (Bremen, Ger-
many). Bruker NMR-500 MHZ spectrometer applied for
1
recording of H NMR spectra. Elemental composition
and morphology of the magnetic nanocatalyst were stud-
ied using TESCAN MIRA3 FE-SEM equipped with EDX
analyzed (Prague, Czech Republic).
Fig. 2 FT-IR spectrum of the synthesized MSrGO NCs
1 3

S. R. Mousavi et al.
IR bands for MSrGO are as following 3620, 3434, 2921,
1769, 1620, 1450, 1208, 690, 556 and 460 cm−1. The peaks
at 3620 cm−1 and 1620 cm−1 are enhancing the O–H stretch-
ing and bending. The characteristics bands at 2921, 1769,
1450, 1208 are corresponding to C–H, C=O, C=C/C–C and
C–OH, respectively. The presence of strontium nanoparti-
cles on the nanocatalyst can be claimed with two peaks at
690 cm−1 and 460 cm−1 that attribute the Sr–O band. Finally,
the IR signal at 556 cm−1 confirm the presence of magnetic
iron oxide substance (Fe–O) on the nanocatalyst.
3.3.3 XRD Diffractometer
The crystalline structure of MSrGO NCs was investigate
through small-angle XRD analysis. The XRD signals for
both magnetic Fe3O4 nanoparticle and MSrGO NCs are
depicts in Fig. 4. Both patterns are showing the various
XRD signals at different angle (2 theta) that directly reflect
the crystalline structure of bot materials. The characteristics
signals for magnetic Fe3O4 nanoparticles are approximately
observed at 25°, 30.2°, 35.4°, 43.1°, 53.6°, 57° and 63° and
for strontium are approximately at 28°, 33°, 38, 42°, 48,
50, 52, 55°, 67°. The sharp signal at 18° (002) is reflecting
the graphene oxide skeleton. Thus, it can be claim that the
MSrGO NCs is possessing crystalline structure that it is suit-
able for catalyst purposes.
3.3.2 FESEM Microscopy
Surface micrograph of the MSrGO nanocatalyst was stud-
ied with FESEM microscopy technique. Hence, the FESEM
micrograph (Fig. 3) shows the sheet like layers with some
dispersed nanoparticles. Probably the flake sheets are cor-
responding to grapheme oxide layers and nanoparticles are
corresponding to the strontium and iron oxide nanoparticles.
It is noteworthy that the nanoparticles are well dispersed on
the surface of graphene sheets. The particle size was moni-
tored with Image J software for 60 particles and average size
obtained was 71.9 nm. These are provided the successful
synthesis of the nanocatalyst. The expected elements on the
nanoctalyste were analyzed with energy-dispersive X-ray
spectroscopy technique and C, O, Fe and Sr, elements were
as 32, 23, 29 and 14%, respectively.
3.4 General Experimental Procedure for Synthesis
of Xanthene Derivatives
In a topical procedure, a mixture of substituted benzalde-
hydes (1 mmol), and dimedone (2 mmol)/2-hydroxynaph-
thalene-1,4-dione (2 mmol) was stirred at 80 °C utilizing
MSrGO NCs (15 mg) in solvent-free condition for the time
period as indicated in Tables 2 and 3 until the reaction was
complete. Upon completion of the reaction, monitored by
TLC, the mixture was cooled to room temperature. With
completing the reaction, 5 mL ethanol was poured and the
magnetic nanocomposite was removed by an external mag-
net, then the precipitated products were separated by filtra-
tion and recrystallized from ethanol to furnish pure xanthene
derivatives. All products have been reported previously. The
pure products were characterized by conventional spectro-
scopic methods. Physical and spectral data for the selected
compounds 4a, 4e, 4k, 5c, 5f–h, 5l and 5n are shown below:
Fig. 3 SEM image of the synthesized MSrGO NCs
Fig. 4 XRD pattern for MSrGO NCs
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Graphene Oxide Incorporated Strontium Nanoparticles as a Highly Efficient and Green Acid…
3.4.1 3,3,6,6-Tetramethyl-9-phenyl-3,4,5,6,7,9-hexahy-
1H, Ar–H), 7.42 (d, J = 7.8 Hz, 1H, Ar–H), 7.49 (t,
dro-1H-xanthene-1,8(2H)-dione (4a)
J=7.4 Hz, 1H, Ar–H), 7.59 (d, J=7.8 Hz, 1H, Ar–H), 7.68
(t, J = 7.3 Hz, 2H, Ar–H), 7.77 (t, J= 7.3 Hz, 2H, Ar–H),
7.88 (d, J = 7.5 Hz, 2H, Ar–H), 7.95 (d, J = 7.5 Hz, 2H,
Ar–H).
1
White solid, yield: (92%); m.p. 199–200 °C. H NMR
(500 MHz, DMSO): 1.04 (s, 12H, 4CH3), 2.09 (s, 4H, 2CH2),
2.20 (s, 4H, 2CH2), 5.94 (s, 1H, CH), 7.05–7.10 (m, 5H,
Ar–H).
3.4.7 13-(3-Nitrophenyl)-12H-dibenzo[b,i]xan-
thene-5,7,12,14(13H)-tetraone (5h)
3.4.2 9-(4-Chlorophenyl)-3,3,6,6-tetrame-
thyl-3,4,5,6,7,9-hexahydro-1H-xanthene-1,8(2H)-di
one (4e)
1
Orange solid, yield: (95%); m.p. >310 °C. H NMR
(500 MHz, DMSO): 6.65 (s, 1H, CH), 7.49 (t, J =7.9 Hz,
1H, Ar–H), 7.65 (d, J = 7.6 Hz, 1H, Ar–H), 7.71 (t,
J=7.4 Hz, 2H, Ar–H), 7.78 (t, J=7.4 Hz, 2H, Ar–H), 7.91
(t, J=7.2 Hz, 3H, Ar–H), 7.97 (d, J=7.9 Hz, 3H, Ar–H).
1
White solid, yield: (92%); m.p. 232–234 °C. H NMR
(500 MHz, DMSO): 0.98 (s, 6H, 2CH3), 1.02 (s, 6H, 2CH3),
2.08 (s, 4H, 2CH2), 2.24 (s, 4H, 2CH2), 4.49 (s, 1H, CH), 7.17
(d, J=7.5 Hz, 2H, Ar-H), 7.26 (d, J=7.5 Hz, 2H, Ar–H).
3.4.8 13-(2-Chlorophenyl)-12H-dibenzo[b,i]xan-
thene-5,7,12,14(13H)-tetraone (5l)
3.4.3 9-(3,4-Dimethoxyphenyl)-3,3,6,6-tetrame-
thyl-3,4,5,6,7,9-hexahydro-1H-xanthene-1,8(2H)-di
one (4k)
1
Dark green solid, yield: (90%); m.p. 306–308 °C. H
NMR (500 MHz, DMSO): 6.46 (s, 1H, CH), 7.42–7.45
(m, 1H, Ar–H), 7.54 (d, J = 4.0 Hz, 2H, Ar–H), 7.78 (t,
J=7.4 Hz, 2H, Ar–H), 7.83 (t, J=7.6 Hz, 2H, Ar–H), 7.84
(t, J=4.7 Hz, 1H, Ar–H), 7.93 (d, J=7.5 Hz, 2H, Ar–H),
7.98 (d, J=7.5 Hz, 2H, Ar–H),.
1
White solid, yield: (93%); m.p. 181–183 °C. H NMR
(500 MHz, DMSO): 0.75 (s, 6H, 2CH3), 0.89 (s, 6H, 2CH3),
2.06 (s, 4H, 2CH2), 2.19 (s, 4H, 2CH2), 3.35 (s, 3H, OCH3),
3.69 (s,3H, OCH3), 4.98 (s, 1H, CH), 7.67 (s, 1H, Ar-H),
7.40 (d, J=7.8 Hz, 2H, Ar–H).
3.4.9 13-(4-Chlorophenyl)-12H-dibenzo[b,i]xan-
thene-5,7,12,14(13H)-tetraone (5n)
3.4.4 13-(2-Bromophenyl)-12H-dibenzo[b,i]xan-
thene-5,7,12,14(13H)-tetraone (5c)
1
Yellow solid, yield: (89%); m.p. >310 °C. H NMR
1
Yellow solid, yield: (96%); m.p. 282–284 °C. H NMR
(500 MHz, DMSO): 6.47 (s, 1H, CH), 7.04 (d, J=7.5 Hz,
2H, Ar–H), 7.15 (d, J = 7.5 Hz, 2H, Ar–H), 7.63 (t,
J=7.5 Hz, 2H, Ar–H), 7.70 (t, J=7.5 Hz, 2H, Ar–H), 8.02
(d, J=7.5 Hz, 2H, Ar–H), 8.12 (d, J=7.5 Hz, 2H, Ar–H).
(500 MHz, DMSO): 6.85 (s, 1H, CH), 7.36 (t, J =7.3 Hz,
1H, Ar–H), 7.42 (d, J = 7.8 Hz, 1H, Ar–H), 7.49 (t,
J=7.5 Hz, 1H, Ar–H), 7.58 (d, J=7.8 Hz, 1H, Ar–H), 7.68
(t, J = 7.4 Hz, 2H, Ar–H), 7.77 (t, J= 7.4 Hz, 2H, Ar–H),
7.88 (d, J = 7.4 Hz, 2H, Ar–H), 7.95 (d, J = 7.5 Hz, 2H,
Ar–H).
4 Conclusion
3.4.5 13-(4-Methoxyphenyl)-12H-dibenzo[b,i]xan-
thene-5,7,12,14(13H)-tetraone (5f)
In conclusion, we have developed a proficient, magnetic
graphite oxide-based (MSrGO NCs) catalyzed procedure
for the synthesis of xanthene derivatives under solvent-free
reaction conditions. Easy handling of the catalyst, high reus-
ability, shorter reaction time, and solvent-free reaction con-
ditions are the plus points of this methodology which makes
the process ecofriendly, sustainable, and green. Moreover,
high tolerance of this procedure toward various functional
groups, easy work up, exceptionally high yields of desired
products, and easy separation of catalyst by an external mag-
netic field are added advantages for its application to aca-
demic and industrial purposes. We believe this will present a
better and more practical alternative to the existing method-
ologies and will find useful application in organic synthesis.
Red solid, yield: (92%); m.p. >310 °C. 1H NMR (500 MHz,
DMSO): 3.69 (s, 3H, OCH3), 5.94 (s, 1H, CH), 6.75 (d,
J=7.5 Hz, 2H, Ar–H), 7.13 (d, J=7.0 Hz, 2H, Ar–H), 7.78
(d, J=7.0 Hz, 1H, Ar–H), 7.81 (d, J=7.0 Hz, 2H, Ar–H),
7.91 (d, J = 6.5 Hz, 2H, Ar–H), 7.97 (d, J = 6.5 Hz, 2H,
Ar–H).
3.4.6 13-(2-Nitrophenyl)-12H-dibenzo[b,i]xan-
thene-5,7,12,14(13H)-tetraone (5g)
1
Yellow solid, yield: (91%); m.p. 272–274 °C. H NMR
(500 MHz, DMSO): 6.63 (s, 1H, CH), 7.37 (t, J =7.3 Hz,
1 3

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Affiliations
Seyyed Rasul Mousavi1 · Hamid Rashidi Nodeh2 · Elham Zamiri Afshari3 · Alireza Foroumadi1
2
* Alireza Foroumadi
Department of Food science & Technology, Faculty of Food
aforoumadi@yahoo.com
Industry and Agriculture, Standard Research Institute (SRI),
P.O. Box: 31745-139, Karaj, Iran
1
Department of Medicinal Chemistry, Faculty of Pharmacy
3
Department of Chemistry, Faculty of Science, University
of Tehran, Tehran, Iran
and The Institute of Pharmaceutical Sciences (TIPS), Tehran
University of Medical Sciences, Tehran, Iran
1 3