Synthesis of 14-aryl-14H-dibenzo[a,j]xanthenes catalyzed by acyclic acidic ionic liquids

Article abstract of DOI:10.1002/jhet.346

Some recyclable acyclic SO₃H-functionalized ionic liquids have been used as novel catalysts for the synthesis of 14-aryl-14H-dibenzo[a,j] xanthenes via the one-pot condensation of β-naphthol and aromatic aldehydes in aqueous medium. The condens

Full text of DOI:10.1002/jhet.346

May 2010
Synthesis of 14-Aryl-14H-dibenzo[a,j]xanthenes Catalyzed by
Acyclic Acidic Ionic Liquids
509
Dong Fanga,b* and Zu-Liang Liub
aJiangsu Provincial Key Laboratory of Coast Wetland Bioresources & Environment Protection,
Yancheng Teachers’ College, Yancheng 224002, People’s Republic of China
bSchool of Chemical Engineering, Yancheng Normal University, Yancheng 224002,
People’s Republic of China
*E-mail: fang-njust@hotmail.com
Received September 1, 2009
DOI 10.1002/jhet.346
Published online 31 March 2010 in Wiley InterScience (www.interscience.wiley.com).
Some recyclable acyclic SO3H-functionalized ionic liquids have been used as novel catalysts for the
synthesis of 14-aryl-14H-dibenzo[a,j]xanthenes via the one-pot condensation of b-naphthol and aromatic
aldehydes in aqueous medium. The condensation reaction was accomplished successfully with various
aromatic aldehydes with good to excellent yields ranged from 86 to 96% within 5–30 min. After the
reaction, the products could simply be separated from the catalysts by filtration. When separated from
the reaction mixture, the catalysts could be recycled and reused for several times without noticeably
reducing catalytic activity. The methodology gives the advantages of high yields, short reaction time,
and easy work-up procedure.
J. Heterocyclic Chem., 47, 509 (2010).
INTRODUCTION
atile liquids, the solvents used in organic synthesis are
high on the list of environmental pollutants. For over-
coming these problems; one approach is to use the
water as the green medium, another approach is to de-
velop new processes involving the solvent-free condi-
tions. In recent years, ionic liquids have been emerged
as a powerful alternative to conventional molecular or-
ganic solvents because of their particular properties,
such as undetectable vapor pressure, wide liquid range,
as well as ease of recovery and reuse, and making them
a greener alternative to volatile organic solvents. Com-
bining the useful characteristics of solid acids and min-
eral acids, Brønsted acidic task-specific ionic liquids
(TSILs) are designed to replace traditional mineral liq-
uid acids, such as sulfuric acid and hydrochloric acid in
chemical processes [17]. Such acidic TSILs have dual
role (solvent and catalyst) in organic reactions [18–21].
In fact, the use of Brønsted-acidic TSILs as catalysts is
an area of ongoing activity; however, development and
exploration of acidic TSILs are currently in the prelimi-
nary stage.
The synthesis of xanthenes derivatives is of much im-
portance because of their wide range of biological and
pharmaceutical properties, such as antiviral, and anti-
inflammatory activities as well as efficacy in photody-
namic therapy [1,2]. Furthermore, these compounds can
be used as dyes [3], pH-sensitive fluorescent materials
for visualization of bimolecular [4] and used in laser
technologies [5]. Recently, many synthetic methods for
synthesis of these compounds have been reported by the
condensation of aldehydes with b-naphthol in the
presence of p-toluenesolfonic acid [6], sulfamic acid [7],
fluoroboric acid/silica-gel [8], cellulose sulfuric acid [9],
zirconium(iv) oxide chloride [10], CBr4 [11], molecular
ionine [12], heteropoly acid [13], silica sulfuric acid
[14], Amberlyst-15 [15], and cyanuric chloride [16] as
catalysts. However, the search for the new readily avail-
able and green catalysts is still being actively pursued.
With the increasing public concern over environmen-
tal degradation and future resources, it is of great im-
portance for chemists to come up with new approaches
that are less hazardous to human health and environ-
ment. Being used in large amounts and are usually vol-
We are especially interested in developing the poten-
tial use of efficient, simple, and inexpensive TSILs
C
V
2010 HeteroCorporation

510
D. Fang and Z.-L. Liu
Vol 47
Table 1
Table 2
Reusing of the ionic liquid [TMPSA][HSO4].a
Synthesis of 14-phenyl-14H-dibenzo[a,j]xanthenes catalyzed
by acidic ionic liquids.a
Entry
Run
Isolated yield (%)
TSILs
(mol %)b
Time
(min)
Yields
(%)c
1
2
3
4
5
6
7
Fresh
93
94
93
91
92
90
90
Entry
Catalyst
1
2
3
4
5
6
1
2
–
–
1
180
60
30
5
–
[TMPSA][HSO4]
[TMPSA][HSO4]
[TMPSA][HSO4]
[TMPSA][HSO4]
[TMPSA][HSO4]
[TMPSA][HSO4]
[TEPSA][HSO4]
[TBPSA][HSO4]
[TMBSA][HSO4]
[TEBSA][HSO4]
[PyPSA][HSO4]
[MIMPSA][HSO4]
[bmim][HSO4]
80
86
93
94
95
94
90
92
94
93
91
93
85
3
4
3
5
5
6
7
9
5
5
a 5 mmol benzaldehyde, 10 mmol b-naphthol, 0.25 mmol catalyst,
7
15
5
5
5
100ꢀC, 5 min.
8
9
5
5
10
11
12
13
14
5
5
5
5
absence of ionic liquids (entry 1), which indicated that
the catalyst was absolutely necessary for this condensa-
tion reaction. All the prepared eight TSILs proved to be
very active, leading to 86–95% yield of 14-aryl-14H-
dibenzo[a,j]xanthenes in the presence of 5% TSILs
(entries 4, 8–14). In addition, ionic liquids containing
the shorter length of alkyl chain are relatively cheaper.
Further, the better immiscibility of the resulted xan-
thenes with the shorter length of alkyl chain should
facilitate the separation in work-up procedure. Hence,
[TMPSA][HSO4] should be the best catalyst for this
condensation among the five acyclic TSILs, and the
optimized reaction conditions were presented in Table 1
(entry 4).
5
5
5
5
30
5
a 5 mmol benzaldehyde, 10 mmol b-naphthol, water is used as a
solvent.
b Molar ratio of TSILs to benzaldehyde.
c Isolated yields.
catalysts. In our previous work, some novel and rela-
tively cheap SO3H-functional halogen-free acidic ionic
liquids that bear an alkane sulfonic acid group in an
acyclic trialkylammonium cation have been synthesized
and their catalytic activity for acid-catalyzed reactions
have also been investigated [22–24]. In continuation of
our work in studying acid-catalyzed reactions in ionic
liquids, we report here the synthesis of 14-aryl-14H-
dibenzo[a,j]xanthenes in acidic ionic liquids.
Compared with the traditional methods, use of vola-
tile solvents and catalysts, which is complex, and time
and energy consuming, and environmentally malign, the
easy recycling is an attractive property of the TSILs for
the environmental protection and economic reasons. So,
the recycling performance of [TMPSA][HSO4] in the
same model condensation reaction was subsequently
explored. After the reaction, the products were isolated
from the catalytic system by filtration, the catalyst was
reused in the next run directly without further
RESULTS AND DISCUSSION
For the beginning of this study, benzaldehyde and
b-naphthol were used as the model reactants to compare
the catalytic performance of the TSILs. As shown in
Table 1, nearly no xanthenes could be detected in the
Table 3
Synthesis of 14-aryl-14H-dibenzo[a,j]xanthenes catalyzed by [TMPSA][HSO4].a
Entry
Ar
Product
Time (min)
m.p. (ꢀC) [lit.]
Yields (%)b
1
2
3
C6H5
o-ClC6H4
p-ClC6H4
2,4-ClC6H3
p-FC6H4
o-NO2C6H4
m-NO2C6H4
p-NO2C6H4
p-CH3C6H4
p-CH3OC6H4
3a
3b
3c
3d
3e
3f
3g
3h
3i
5
10
5
184–185 [8]
213–215 [6]
286–288 [6]
228–229 [10]
238–239 [6]
213–215 [8]
211–212 [6]
310–312 [8]
227–229 [6]
202–204[6]
93
92
96
95
95
90
91
95
92
86
4
10
5
10
10
5
5
6
7
8
9
10
10
30
3j
a 5 mmol benzaldehyde, 10 mmol b-naphthol, 0.25 mmol catalyst, 100ꢀC.
b Isolated yields.
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

May 2010
Synthesis of 14-Aryl-14H-dibenzo[a,j]xanthenes Catalyzed by Acyclic
Acidic Ionic Liquids
511
Scheme 1
In conclusion,, it was demonstrated that some readily
available, economic TSILs have been used as recyclable
catalysts for the condensation of benzaldehydes and
b-naphthol to synthesis 14-aryl-14H-dibenzo[a,j]xan-
thenes. The merit of this methodology is that it is sim-
ple, high efficient, and eco-friendly.
EXPERIMENTAL
Melting points were determined on X-6 microscope melting
1
apparatus. H NMR spectra were recorded on Bruker DRX300
(300 or 500 MHz) and 13C NMR spectra on Bruker DRX300
(75.5 MHz) spectrometer. Mass spectra were obtained with
automated FININIGAN Trace Ultra-Trace DSQ GC/MS spec-
trometer. All chemicals (AR grade) were commercially avail-
able and used directly without further purification.
Synthesis of SO3H-functional halogen-free acidic ionic
liquid (TSILs). All acyclic SO3H-functionalized halogen-free
acids, such as [TMPSA][HSO4], [TEPSA][HSO4] were synthe-
sized according to our previous methods [18], the pyridine,
imidazole-based SO3H-functionalized ionic liquids for compar-
ison were obtained according to reported methods [16]. The
structures of TSILs were analyzed by 1H NMR, 13C NMR,
and MS spectral data (Scheme 1).
The selected spectral data for SO3H-functionalized halo-
gen-free TSILs.
ammonium hydrogen sulfate [TMPSA][HSO4]. H NMR (300
MHz, D2O): d 3.22 (t, J ¼ 7.2 Hz, 2H, NACH2ACACASO3),
N,N,N-trimethyl-N-propanesulfonic acid
1
2.90 (s, 9H, NACH3), 2.73 (t,
J
¼
7.8 Hz, 2H,
purification. As shown in Table 2, the catalyst can be
reused at least six times without appreciable decrease in
yield and reaction rate, and the yield ranged from 94–
90%.
NACACACH2ASO3), 1.99 (m, 2H, NACACH2ACASO3).
13C NMR (75.5 MHz, D2O): d 65.00, 52.51, 47.89, 18.85. MS
(m/z): 279.05 (Mþ), 182.14(100).
N,N,N-triethyl-N-propanesulfonic acid ammonium hydro-
1
gen sulfate [TEPSA][HSO4]. H NMR (300 MHz, D2O): d
The condensation reactions of other substituted ben-
zaldehydes and b-naphthol in the presence of
[TMPSA][HSO4] were accomplished under the opti-
mized reaction conditions described above and the
results are presented in Table 3. It can easily be seen
that all aromatic aldehydes with either electro-withdraw-
ing or electro-donating substituents, such as nitro and
methoxy groups gave reasonable to good yields ranged
from 85–96% with 30 min. However, aromatic alde-
hydes with electron-withdrawing group are more
actively than that with electro-donation one. Their phys-
ical properties were determined and structures were con-
3.22–3.05 (m, 8H, (6H þ 2H), NACH2ACH3, NACH2A
CACASO3), 2.85 (t, J ¼ 7.2 Hz 2H, NACA CACH2ASO3),
1.97 (m, 2H, NACACH2ACASO3), 1.12 (t, 9H, NACACH3).
13C NMR (75.5 MHz, D2O):
d 56.00, 52.95, 48.34,
18.93, 8.04. MS (m/z): 321.05 (Mþ), 322.05, 320.15,
194.05(100).
N,N,N-tributyl-N-propanesulfonic acid ammonium hydro-
1
gen sulfate [TBPSA][HSO4]. H NMR (500 MHz, D2O): d
3.28(t, 2H, J ¼ 4.0 Hz, NACH2ACACASO3), 3.13(t, 6H, J ¼
8.5 Hz, NACH2ACACACH3), 2.85(t, 2H, J ¼ 7.0 Hz,
NACACACH2ASO3), 2.03 (m, 2H, NACACH2ACASO3),
1.56 (m, 6H, NACACH2ACACH3), 1.27 (m, 6H, NACA
CACH2ACH3), 0.84 (t, 9H, J ¼ 7.5 Hz, NACACACACH3).
1
firmed by H NMR spectral data.
Scheme 2
Journal of Heterocyclic Chemistry
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512
D. Fang and Z.-L. Liu
Vol 47
13C NMR (75.5 MHz, D2O): d 58.49, 50.66, 48.42, 23.93,
20.36, 19.16, 14.46. MS (m/z): 405.29 (Mþ), 406.28,
404.28(100).
N,N,N-trimethyl-N-butanesulfonic acid ammonium hydro-
1
gen sulfate [TMBSA][HSO4]. H NMR (300 MHz, D2O): d
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3.24 (t, J ¼ 8.4 Hz, 2H, NACH2ACACACASO3), 2.99 (s,
9H, NACH3), 2.85 (t,
J
¼
7.5 Hz, 2H, NACA
CACACH2ASO3), 1.82 (m, 2H, NACACH2ACACASO3),
1.70 (m, 2H, NACACACH2ACASO3). 13C NMR (75.5 MHz,
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(q, J ¼ 7.2 Hz, 6H, NACH2ACH3), 3.07 (t, J ¼ 8.4 Hz, 2H,
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General procedure for the synthesis of 14-aryl-14H-
dibenzo[a,j]xanthenes derivatives. In a typical experiment, to
a round-bottomed flask charged with b-naphthol (10 mmol) 1,
aldehyde (5 mmol) 2 in 5 mL of water was added to acidic ionic
liquid (0.25 mmol) under stirring. The mixture was then stirred
for a certain time at 100ꢀC (Scheme 2). On completion (moni-
tored by TLC), the precipitated crude product was collected by
filtration and recrystallized from ethanol (95%) to afford pure
14-aryl-14H-dibenzo[a,j]xanthenes 3. The filtrate containing
ionic liquid could be reused directly in the next run without fur-
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The selected data for chalcone 3a.
14-Phenyl-14H-
dibenzol[a,j]xanthene (3a, C27H18O). Colorless crystals; m.p.
184–185ꢀC; IR (KBr, cmꢁ1): 3074, 3020, 2886, 1622, 1591,
1513, 1455, 1430, 1401, 1251, 1152, 1078, 1028, 962, 857,
827, 743, 700. 1H NMR (300 MHz, CDCl3): d 6.46 (s, 1H,
CH), 6.96 (t, J ¼ 7.2 Hz, 1H, Ar-H), 7.12 (t, J ¼ 7.2 Hz, 2H,
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Acknowledgments. This work was financially supported by the
Educational Committee of Jiangsu Province (07KJD530238),
Jiangsu Provincial Key Laboratory of Coastwetland & Environ-
ment Protection (JLCBE 09023) and Professional Elite Founda-
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Journal of Heterocyclic Chemistry
DOI 10.1002/jhet