A rapid and quantitative synthesis of xanthene derivatives using sulfonated graphitic carbon nitride under ball‐milling

Article abstract of DOI:10.1002/jhet.4327

A truly green, solventless, and fast protocol for the quantitative preparation of biologically active xanthene derivatives with 10 mol% sulfonated graphitic carbon nitride (Sg─CN) as a heterogeneous acidic catalyst was developed. Excellent yields, low cost, solvent‐free conditions, high catalytic activity, reusability of the catalyst, simple workup, and heterogeneous carbon‐based catalyst make the present method particularly attractive from a green chemistry perspective.

Full text of DOI:10.1002/jhet.4327

Received: 28 April 2021
DOI: 10.1002/jhet.4327
Revised: 2 June 2021
Accepted: 8 June 2021
A R T I C L E
A rapid and quantitative synthesis of xanthene derivatives
using sulfonated graphitic carbon nitride under ball-milling
Omid Hosseinchi Qareaghaj | Mohammad Ghaffarzadeh | Najmedin Azizi
Chemistry and Chemical Engineering
Abstract
Research Center of Iran, Tehran, Iran
A truly green, solventless, and fast protocol for the quantitative preparation of
Correspondence
Mohammad Ghaffarzadeh and Najmedin
biologically active xanthene derivatives with 10 mol% sulfonated graphitic car-
bon nitride (Sg─CN) as a heterogeneous acidic catalyst was developed. Excel-
Azizi, Chemistry and Chemical
Engineering Research Center of Iran,
lent yields, low cost, solvent-free conditions, high catalytic activity, reusability
P.O. Box 14335-186, Tehran, Iran.
of the catalyst, simple workup, and heterogeneous carbon-based catalyst make
Email: mghaffarzadeh@ccerci.ac.ir and
the present method particularly attractive from a green chemistry perspective.
azizi@ccerci.ac.ir
Funding information
the Chemistry and Chemical Engineering
Research Center of Iran
1 | INTRODUCTION
excellent method for some organic reactions, such as
oxidations, reductions, polymerization, and metal-
Today, the reinforcement of novel and greener approach
for constructing heterocyclic compounds has continu-
ously gained much attention in recent years [1]. Xan-
thene and its derivatives are the most promising
biologically active compounds with great pharmaceutical
applicability [2–6]. Furthermore, these compounds have
been utilized in local dyes [7], laser technologies [8,9],
and photodynamic therapy [10]. Structures of some bio-
catalyzed bond-forming reactions [19–23]. This mecha-
nochemical technique has more advantages, such as
solvent-free reaction, high yields, low reaction time,
and considerably pure products.
Nanomaterial-based catalysts play a significant role in
various chemical transformations [24–26], due to the
selectivity, low toxicity, good stability, simple surface
functionalization, and magnetic separation [27,28]. Car-
bon materials such as activated carbons, graphene, and
graphitic carbon nitride are environmentally acceptable
and cheap nanomaterials, combining efficient use of
energy and resources in heterogeneous catalysis [29–33].
Sulfonated carbon nitride (Sg─CN) has recently emerged
a new organo-sulfonated heterogeneous acid catalyst pre-
pared via simple calcination of urea [34] and sulfonation
of resulting carbon nitride, respectively. Sg─CN has been
recently used for the synthesis of biodiesel in the efficient
yield [35–37].
Engaged in the development of green chemistry and
following our ongoing research in green organic synthe-
sis [38–40] herein, we investigate the ball-milling
approach in the presence of Sg─CN (10 mol%) as an envi-
ronmentally friendly protocol for the multicomponent
synthesis of xanthene derivatives under solvent-free con-
ditions (Scheme 1).
active
xanthenes
(rhodamine,
amsacrine,
and
RO67-4853) [11] are depicted in Figure 1.
Due to the potential importance of xanthenes, vari-
ous approaches for the symmetrical and unsymmetrical
synthesis of related organic compounds, such as boric
acid [12], PVSA [13], sulfamic acid [14], nano-TiO2
[15], core/shell Fe3O4@GA@isinglass [16], [Et3NSO3H]
Cl [17], and amberlyst-15 [18] reported. Some draw-
backs of these reported procedures have been harsh
reaction conditions, unsatisfactory yields, toxic sol-
vents, tedious workup, and harmful catalysts. From the
green chemistry perspective, it has become essential to
develop sustainable methods for efficient and clean syn-
thesis of xanthene derivatives as bioactive compounds.
In this sense, the mechanochemistry approach for
organic transformations has received significant atten-
tion. Ball-milling is a grinding system that is an
J Heterocyclic Chem. 2021;1–9.
wileyonlinelibrary.com/journal/jhet
© 2021 Wiley Periodicals LLC.
1

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QAREAGHAJ ET AL.
FIGURE 1 Structures of some bioactive
xanthene derivatives
SCHEME 1 One-pot synthesis of
xanthene derivatives using Sg─CN in a
vibration ball-mill
2 | EXPERIMENTAL SECTION
2.3 | Some selected data
2.1 | Reagents and instrumentation
chemicals
2.3.1 | 14-Phenyl-14H-dibenzo[a,j]
xanthene (4a)
Aldehydes, β-naphthol, 1,3-indandione, and other
chemicals were purchased from Merck chemical com-
pany and used without further purification. The Retsch
MM 400 ball mill instrument was used.
IR (KBr): ν = 3058, 2961, 1624, 1426, 1348 cmÀ1 1H
.
NMR (500 MHz, CDCl3) δ = 5.74 (s, 1H, CH), 7.04–7.22
(m, 2H), 7.33–7.46 (m, 4H), 7.76–8.02 (m, 3H). 13C NMR
(CDCl3, 100 MHz): δ = 50.89, 117.70, 123.69, 124.91,
126.25, 127.01, 128.07, 128.24, 128.43, 128.84, 129.77,
131.40, 131.49, 144.74, 147.73, 163.97.
2.2 | Synthesis of 12-aryl-
8,9,10,12-tetrahydrobenzo[a]xanthene-
11-one derivatives (4)
2.3.2 | 14-(4-Chlorophenyl)-14H-dibenzo[a,j]
xanthene (4b)
β-Naphthol (2 mmol), aldehyde (1 mmol), and Sg─CN
(10 mol%) were ball-milled according to Table 1 at
r.t. After reaction completion, the appropriate solvents
(ethanol or ethyl acetate, 10 ml) was added, and the
nanocatalyst was filtered or centrifuged. The reused
nanocatalyst was washed with ethanol and ethyl acetate,
and it was dried at 60ꢀC for 4 h and reused for neat runs.
IR (KBr): ν = 3059, 3022, 2954, 2869, 1594, 1466, 1373 cmÀ1
.
1H NMR (500 MHz, CDCl3) δ = 5.65 (s, 1H, CH), 6.62–6.68
(2H, m), 7.15–7.21 (2H, m), 7.31–7.47 (2H, m), 7.68–8.01 (m,
2H). 13C NMR (CDCl3, 125 MHz): δ = 50.23, 116.06, 117.04,
123.15, 123.46, 125.25, 127.40, 128.67, 129.44, 129.66, 131.01,
131.57, 147.77, 152.13, 166.35.

QAREAGHAJ ET AL.
3
TABLE 1 Optimization of the reaction condition for the synthesis of 5a
Entry
Amount Sg─CN (Mol%)
No catalyst
Conditions/temperature (ꢀC)
EtOH/reflux
Time (min)
Yield (%)a
1
60
70
60
45
40
50
30
12
10
10
10
0
2
No catalyst
H2O/reflux
0
3
No catalyst
Ball-milling
0
4
Sg─CN (5 mol%)
Sg─CN (10 mol%)
Sg─CN (5 mol%)
Sg─CN (5 mol%)
Sg─CN (5 mol%)
Sg─CN (10 mol%)
Sg─CN (15 mol%)
g-C3N4 (10 mol%)
EtOH/reflux
40
35
40
55
75
99
99
21
5
H2O/reflux
6
CH3CN/reflux
EtOH/Ball-milling/r.t
Ball-milling/r.t
Ball-milling/r.t
Ball-milling/r.t
Ball-milling/r.t
7
8
9
10
11
aIsolated yields.
2.3.3 | 14-(p-tolyl)-14H-dibenzo[a,j]
xanthene (4c)
and it was dried at 60ꢀC for 4 h and reused for neat runs.
After that, the crude product was further purified by
recrystallization from EtOH to afford the pure product.
IR (KBr): ν = 3063, 1595, 1369 cmÀ1. 1H NMR (500 MHz,
CDCl3) δ = 2.57 (s, 3H, CH3), 5.69 (s, 1H, CH), 6.62–6.69
(m, 2H), 7.15–7.21 (m, 2H), 7.32–7.47(m, 3H), 7.68–7.99
(m, 3H). 13C NMR (CDCl3, 125 MHz): δ = 20.30, 51.06,
116.96, 117.83, 123.76, 124.90, 126.97, 128.38, 128.77,
129.53, 129.66, 131.36, 131.50, 137.30, 147.65, 154.04,
163.94.
2.5 | Selected compounds
2.5.1 | 13-Phenylbenzo[f]indeno[1,2-b]
chromen-12(13H)-one (5a)
IR (KBr): ν = 3065, 2956, 2945, 1698 (C═O), 1608 cmÀ1
.
1H NMR (500 MHz, CDCl3) δ = 5.06 (s, 1H, CH), 7.02–
7.05 (m, 1H), 7.11–7.19 (m, 1H), 7.46–7.60 (m, 2H), 7.84–
7.93 (m, 3H), 8.02–8.08 (m, 3H), 8.48 (d, J = 6.8 Hz, 2H).
13C NMR (CDCl3, 125 MHz): δ = 48.86, 102.89, 111.15,
117.39, 118.07, 121.35, 123.42, 124.82, 124.91, 128.48,
128.67, 128.76, 128.86, 129.65, 130.17, 130.27, 131.56,
132.11, 134.06, 134.13, 135.24, 154.25, 195.22.
2.3.4 | 14-(4-Nitrophenyltrophenyl)-14H-
dibenzo[a,j]xanthene (4d)
IR (KBr): ν = 3063, 1596, 1300 cmÀ1. 1H NMR (500 MHz,
CDCl3) δ = 5.76 (s, 1H, CH), 7.08–7.23 (m, 3H), 7.37–7.47
(m, 5H), 7.81–7.82 (d, J = 7.0 Hz, 2H), 7.97–8.01 (d,
J = 7.0 Hz, 2H). 13C NMR (CDCl3, 125 MHz): δ = 57.06,
11,698, 117.71, 123.71, 124.89, 126.26, 127.0, 128.26,
128.38, 128.50, 128.84, 131.39, 131.49, 145.09, 147.78,
165.63.
2.5.2 | 13-(3-Chlorophenyl)benzo[f]indeno
[1,2-b]chromen-12(13H)-one (5b)
IR (KBr): ν = 3058, 2951, 2901, 1686 (C═O), 1607 cmÀ1
.
2.4 | General procedure for the synthesis
of 5
1H NMR (500 MHz, DMSO-d6) δ = 5.12 (s, 1H, CH),
6.63–6.94 (t, J = 8.0 Hz, 4H), 6.93–6.97(d, J = 8 Hz, 1H),
7.13–7.16 (d, J = 7.0 Hz, 1H), 7.57–7.62 (t, J = 7.5 Hz,
3H), 7.73–7.75 (d, J = 8.0 Hz, 1H), 8.02–8.16 (d, J = 8 Hz,
2H), 8.10–8.12 (d, J = 7.2 Hz, 2H). 13C NMR (DMSO-d6,
125 MHz): δ = 48.85, 115.79, 116.79, 118.62, 123.60,
124.06, 125.82, 126.64, 130.02, 131.27, 133.48, 135.64,
139.17, 142.27, 144.90, 146.47, 147.50, 148.62, 149.81,
151.78, 152.94, 154.49, 156.33, 158.57, 159.53, 164.67,
188.30.
β-Naphthol
(1 mmol),
aldehyde
(1 mmol),
1,3-indandione (3, 1 mmol), and Sg─CN (10 mol %) was
ball-milled for the appropriate time (Table 1) at room
temperature. After reaction completion, the suitable sol-
vents (ethanol or ethyl acetate, 10 ml) were added, and
the nanocatalyst was filtered or centrifuged. The reused
nanocatalyst was washed with ethanol and ethyl acetate,

4
QAREAGHAJ ET AL.
3 | RESULTS AND DISCUSSION
The effect of SO3H groups on the crystalline proper-
ties of g-C3N4 was studied using large-angle XRD analysis
(Figure 3). The g-C3N4 is a crystalline carbon nitride poly-
mer, which supports two crystalline peaks at 27.4ꢀ with
high intensity and 13.1ꢀ with low intensity due to the in-
plane ordering of s-triazine units and the periodic stac-
king of layers of aromatic heterocyclic units, respectively.
The XRD patterns of g-C3N4 and g-C3N4-SO3H (Sg─CN)
were nearly similar, which means that the structure of g-
C3N4 was not destroyed during the functionalization
process.
The Sg─CN nanocatalysts was synthesized using our pre-
vious procedure [24]. The morphology and elemental
analysis of the Sg─CN characterized by SEM and EDX
mapping. As shown in Figure 2A, Sg─CN displayed an
approximate sheet-like porous structure with slight
agglomeration, and the sheets are stacked on each other.
Compositional analysis of Sg─CN using EDX spectro-
scopic studies and elemental analyses confirmed the pres-
ence of C, O, N, and S elements (Figure 2B). The result
indicated that the SO3H groups were successfully
supported on the surface of g-C3N4.
Boehm titration is used to quantify the amount of
sulfonic acid groups on the g-C3N4 before and after the
FIGURE 2 (A) EDX mapping of Sg─CN and (B) SEM images Sg─CN
FIGURE 3 XRD patterns for
g─C3N4 and g─C3N4-SO3H

QAREAGHAJ ET AL.
5
TABLE 2 One-pot preparation 14-aryl-14H-dibenzo[a,j]xanthenes
M.P
Entry
4a
X
Product
Time
Yielda
Found
Reported
H
15
99<
186–184
186–184[41]
4b
4-Cl
10
99<
290–288
288–290[41]
4c
4d
H
20
10
99<
99<
230–228
328–326
227–229[41]
324–327[41]
4-NO2
4e
4f
3-NO2
4-CN
15
10
99<
99<
222–220
338–340
222–220[41]
339–337[41]
4g
4-Br
10
99<
303–304
303–305 [41]
(Continues)

6
QAREAGHAJ ET AL.
TABLE 2 (Continued)
M.P
Entry
4h
X
Product
Time
Yielda
Found
Reported
4-OMe
20
99<
307–308
308–310[41]
4i
4j
4-OH
20
99<
261–262
262–260[41]
2-NO2
2-Cl
15
15
99<
99<
293–294
216–218
294–292[41]
216–218[41]
4f
aIsolated yields.
reaction. The Sg─CN (0.50 g) was added into standard
NaOH solutions (0.01 M, 50 ml) and stirred at room tem-
perature for 4 h. Then, it was back titrated with HCl
(0.01 mol/L). Based on the titration experiments, the per-
centage loading of ─SO3H groups over the Sg─CN surface
is about 5.1 mmol/g which corresponds to about 14.7% of
loading, in good agreement with the atomic percentage of
sulfur (15.9%) determined from EDX analysis and elemen-
tal analysis (14.1%) for Sg─CN. Furthermore, reused
Sg─CN were subject to elemental analysis, and the percent-
age of sulfur was nearly the same as fresh Sg─CN (13.9%),
confirming the stability of our system.
including, catalyst-free, in the presence of Sg─CN cata-
lyst, in different solvents under solvent-free condition.
Additionally, the temperature and amount of Sg─CN in
terms of yield and time period (Table 1) were optimized.
Notably, without catalyst, no desired product was
obtained (Table 1, entries 1–3), while the yield of the
model products improved by employing Sg─CN as a cata-
lyst (Table 1, entries 4–10). Additionally, we also opti-
mized the amount of Sg─CN (5.0, 10.0, and 15.0 mol%)
in the model reaction, and the maximum efficiency in
the presence of 10 mol% of the Sg─CN was obtained
(Table 1, entry 9). It was found that when the amount of
Sg─CN was further increased to 15 mol%, no further
increase in yield was detected. Furthermore, the tempera-
ture parameters were investigated, and results were
shown in Table 1 (entries 4–10).
After preparation and characterization of Sg─CN, to
optimize the reaction parameter, the model condensation
reaction
of
β-naphthol
(2,
2 mmol)
with
4-chlorobenzaldehyde (1 mmol) under various conditions

QAREAGHAJ ET AL.
7
TABLE 3 One-pot preparation 13-phenylbenzo[f]indeno[1,2-b]chromen-12(13H)-ones
M.P
Entry
5a
X
Product
Time
Yielda
>99
Found
Reported
H
10
230–229
229–231[42]
5b
5c
3─Cl
20
20
>99
>99
211–210
196–197
210–212[42]
169–198[43]
4─Me
5d
4─NO2
10
>99
265–267
265–267[43]
5e
5f
4─OCH3
20
10
>99
299–230
254–255
299–230[42]
254–256[42]
4─Br
>99 > 99
aIsolated yields.
Among various conditions, kneading ball-milling in
the presence of 10 mol% Sg─CN at r.t under solvent-free
conditions was the most efficient route for the greener
synthesis of 5b in quantitive yield at 10 min (Table 1,
entry 9). Further reactions were performed under opti-
mized conditions to synthesize two series of xanthene

8
QAREAGHAJ ET AL.
TABLE 4 Comparative study of the catalytic efficiency of Sg─CN
Catalyst
TMSCl1
DBSA2*
Catalyst load (Mol%)
Solvent
Temp. (ꢀC)
Reflux
30
Time (min)
Yield (%)
95[41]
100
10
10
10
10
10
MeCN
420
60
H2O, ultrasound
Solvent-free
Solvent-free
Dioxane, H2O
Solvent-free
89[40]
HCl04─SiO2
SbCl3─SiO2
TBAHS
140
180
50
32[42]
120
93[43]
Reflux
r.t
210
10
88[44]
Sg─CN
99 this work
intermediate (A). Next, the nucleophilic attack of
2-naphthol on the activated carbonyl group due to the
acidic nature of Sg─CN, resulting in Knoevenagel inter-
mediate B formation. Michael addition by the second
2-naphthol or 1,3-indandione molecule resulting from
the desired xanthene derivatives after water
elimination.
In continuation, the recycling and reuse of the
Sg─CN were evaluated in the model reaction (5b), and
the results are shown in Table 5. When the reaction was
completed, hot ethanol was added, and the catalyst
was recovered with centrifuge or filtrations. Then filtered
catalyst was washed with ethanol (10 ml) and ethyl ace-
tate (10 ml) and dried at 60ꢀC. The recovered Sg─CN was
further used for three consecutive cycles, and the
obtained yields are presented in Table 5.
SCHEME 2 The proposed mechanism in the presence
of Sg─CN
4 | CONCLUSION
In summary, a green and straightforward procedure for
the synthesis of various xanthene derivatives was
reported. High yields of products, easy workup proce-
dure, short reaction time, no need for organic solvents,
and high atom economy are the key features of this green
ball-milling procedure. Additionally, the Sg─CN
nanocatalyst is a separable and stable heterogeneous cat-
alyst in this system without activity loss for four runs.
TABLE 5 Reusability of Sg─CN
No of runs
1
2
3
4
Yield
99
99
99
98
derivatives in good to excellent yields (Tables 2). The iso-
lated products were fully characterized by FT-IR,
1HNMR, and 13CNMR spectroscopy. All the compounds
had physical and spectroscopic data identical to those
known xanthenes (Table 3)[41-44].
A comparative study of the catalytic ability of
sulfonated graphitic carbon nitride (Sg─CN) for catalytic
synthesis of 4a with the previously reported procedure is
illustrated in Table 4. Ball milling with Sg─CN acts as an
effective and green procedure concerning reaction time
and yield (Table 4).
ACKNOWLEDGMENTS
The authors express appreciation to the Chemistry and
Chemical Engineering Research Center of Iran to support
this investigation.
DATA AVAILABILITY STATEMENT
The data that support the findings of this study are avail-
able from the corresponding author upon reasonable
request.
A plausible mechanism for the formation of pyran-
annulated heterocycles is depicted in Scheme 2. Reaction
initiates the activation of a carbonyl group of the aro-
matic aldehyde by Sg─CN, which generated the
ORCID
Najmedin Azizi https://orcid.org/0000-0002-1685-038X

QAREAGHAJ ET AL.
9
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How to cite this article: O. H. Qareaghaj,
M. Ghaffarzadeh, N. Azizi, J Heterocyclic Chem
2021, 1. https://doi.org/10.1002/jhet.4327