An efficient, high yielding, and eco-friendly method for the synthesis of 14-aryl- or 14-alkyl-14H-dibenzo[a, j]xanthenes using polyvinylsulfonic acid as a recyclable Bronsted acid catalyst

Article abstract of DOI:10.1007/s00706-011-0537-z

Abstract Aryl or alkyl-14H-dibenzo[a,j]xanthene derivatives were synthesized efficiently by the reaction of 2-naphthol and aromatic or aliphatic aldehydes in the presence of polyvinylsulfonic acid (PVSA) as a reusable Bronsted acid catalyst under aqueous

Full text of DOI:10.1007/s00706-011-0537-z

Monatsh Chem (2011) 142:1259–1263
DOI 10.1007/s00706-011-0537-z
ORIGINAL PAPER
An efficient, high yielding, and eco-friendly method for the
synthesis of 14-aryl- or 14-alkyl-14H-dibenzo[a, j]xanthenes using
polyvinylsulfonic acid as a recyclable Brønsted acid catalyst
Ali Rahmatpour
Received: 11 December 2010 / Accepted: 30 May 2011 / Published online: 24 August 2011
Ó Springer-Verlag 2011
Abstract Aryl or alkyl-14H-dibenzo[a,j]xanthene deriv-
atives were synthesized efficiently by the reaction of
catalyst is the simplification of product workup, separation,
and isolation. In the case of linear polymers, techniques such
as precipitation, sedimentation, and ultrafiltration can be
employed for isolation and washing, although these are by no
means as convenient and readily available in all laboratories
[12]. However, these solid catalysts suffer from disadvan-
tages such undesirable by-product formation because of their
very high acidity or basicity, and often require a high degree
of agitation, which causes rupture of the polymeric matrix.
Hence, the development of a homogeneous and active acid
functionalized polymer catalyst in organic transformations
seems highly desirable.
2
-naphthol and aromatic or aliphatic aldehydes in the
presence of polyvinylsulfonic acid (PVSA) as a reusable
Brønsted acid catalyst under aqueous conditions at 90 °C.
This reaction was studied under different conditions, and
several solvents were examined. In terms of reaction yield
and time, water was found to be the optimum solvent. The
catalytic performance of PVSA was then compared with
various acidic catalysts under optimized reaction condi-
tions. The catalyst is well characterized using IR and DSC
techniques.
Performing organic reactions in aqueous media without
the use of harmful organic solvents has attracted much
attention in recent years, because water would be consid-
erably safe, non-toxic, environmentally friendly, and cheap
compared to organic solvents. Moreover, when a water
soluble catalyst is used, the insoluble products can be
separated by simple filtration, and the catalyst system can
be recycled. Therefore, development of a polymeric
Brønsted acid catalyst that is not only stable in water but
also completely soluble in it is highly desirable [13–15].
Xanthenes, especially benzoxanthenes, are an important
and very useful class of intermediates in organic synthesis
because of their wide range of biological and pharmaceu-
tical properties, such as antibacterial [16], antiviral [17],
and anti-inflammatory activities [18], and being sensitizers
in photodynamic therapy for destroying tumor cells [19].
Also these heterocyclic compounds are widely used as
leuco-dyes [20], pH-sensitive fluorescent materials for
visualization of biomolecules [21], and in laser technology
Keywords Condensation Á Heterocycles Á
Polyvinylsulfonic acid Á Brønsted acid catalyst Á
Functional polymers
Introduction
In recent years, there has been growing interest in the cata-
lytic application of functional polymers in organic synthesis.
Many typical acid- or base-catalyzed reactions using
functional polymers having acidic or basic properties as
catalysts, such as polyanilines [1–3], poly(vinylamine) and
poly(allylamine) [4], polyacrylamide [5], polyvinylpyridine
[
6], polyvinylpyrrolidone [7], and cation and anion exchange
resins [8–11], have been investigated so far. The most
important advantage in using a functionalized polymer as a
A. Rahmatpour (&)
Polymer Science and Technology Division,
Research Institute of Petroleum Industry (RIPI),
14665-1137 Tehran, Iran
e-mail: rahmatpoura@ripi.ir
[
22]. The reported methods for the synthesis of 14-aryl- or
1
4-alkyl-14H-dibenzo[a,j]xanthenes involve the mixing of
2
-naphthol with aldehydes in the presence of an acidic
catalyst such as AcOH-H SO [23], p-TSA [24], sulfamic
2
4
123

1
260
A. Rahmatpour
Scheme 1
SO2 OH
CH2 CH
n
R
OH
(
PVSA, 20 mol%)
+
2 H O
2
+
RCHO
o
Water, 90 C
O
1
2a-2q
R: aryl, alkyl
3a-3q (78-93%)
acid [25], molecular iodine [26, 27], LiBr [28], Amberlyst-
5 [29], silica sulfuric acid [30–32], silica perchloric acid
[55, 56]. The key intermediate for its preparation is the
sodium salt of polyvinylsulfonic acid (Na-PVSA), which
can be prepared from the polymerization of sodium vi-
nylsulfonate monomer using potassium persulfate and
sodium bisulfite as an initiator system (number average
molecular weight 53,000). The free acid (PVSA) was
prepared by ion exchange technique. The DSC thermogram
of Na-PVSA showed thermal stability up to 350 °C. The
FT-IR spectrum of Na-PVSA showed two absorption peaks
1
[
[
31, 32], heteropolyacid [33, 34], wet cyanuric chloride
35], BF ÁSiO [36], Yb(OTf) [37], alum [38], montmo-
3
2
3
rillonite K-10 [39], P O /Al O [40], and ionic liquids
2 3
2
5
[41–43]. In spite of the potential utility of the aforementioned
routes for the synthesis of benzoxanthene derivatives, some
of these methods suffer from at least one or more disad-
vantages, such as a long reaction time, relatively expensive
reagents, use of toxic solvents and catalysts, requirement of
excess of reagents/catalysts, harsh reaction conditions,
unsatisfactory yield, and tedious workup procedures. Thus,
the development of simple, convenient, and environmen-
tally friendly approaches for the preparation of these
pharmaceutically important compounds is still demanding.
In continuation of our interest in the synthesis of organic
compounds from condensation of phenols with dialdehydes
-
1
at 724 and 1,189 cm , which are assigned to the methy-
lene groups (–CH –) in polymer backbone and sulfonate
2
groups, respectively. The absorption bands at 1,448 and
-
2,924 cm are attributed to –CH – bond deformation and
1
2
stretching vibration, respectively.
The synthetic utility of PVSA catalyst was explored by
examining the reaction of 2-naphthol (2 mmol) and
4-chlorobenzaldehyde (1 mmol) as a model substrate in
different solvents, and the results are presented in Table 1.
Initial screening studies identified water at 90 °C and
20 mol% of PVSA catalyst loading as the optimal solvent
for this reaction, and the desired product was obtained in
high yield (93%) within 1 h of reaction time. To show the
[
44–50], we herein report an efficient and green procedure
for the synthesis of aryl- or alkyl-14H-dibenzo[a,j]xanth-
enes using polyvinylsulfonic acid (PVSA) as a novel
Brønsted acid catalyst in aqueous media (Scheme 1). To
the best of our knowledge, synthesis of the title compounds
in water is relatively sparse, and there is only one report on
the application of PVSA catalyst for the Michael addition
reaction in the literature [51]. PVSA has been a known
compound for several decades; however, its catalytic
activities have not been studied in more detail so far. PVSA
is a strong aliphatic polymeric sulfonic acid and has high
solubility in water and lower alcohols [52–54]. PVSA is a
semi-solid material; however, it can be handled easily by
preparing aqueous solutions. This polymeric catalyst is
easily recovered from the reaction mixture, owing to its
complete solubility in water, and it is ready to be used in
further reactions with economic and ecological advantages.
Table 1 The effect of solvent on the reaction of 2-naphthol and
4
9
-chlorobenzaldehyde (2d) in the presence of 20 mol% of PVSA at
0 °C
a
d
Entry
Solvent
Time/h
Yield/%
1
2
3
4
5
6
7
8
9
a
EtOH
8
8
41
35
29
26
33
25
93
60
0
MeOH
DMSO
DMF
8
8
i-PrOH
8
CH
3
CN
8
2
H O
1
Results and discussion
b
–
4
c
2
H O
10
Polymeric sulfonic acid is a strong polybasic acid compa-
rable to sulfuric acid, and protons are considered to be
localized along the polymer chain. Hence, the proton
density in solutions may be locally concentrated, unlike in
mineral acid. PVSA was prepared in two steps according to
the known literature procedure with slight modification
3
3
cm solvent
The reaction was run under solvent-free conditions at 90 °C
The reaction was run in the absence of PVSA under reflux
b
c
conditions
d
Isolated yield
1
23

Synthesis of 14-aryl- or 14-alkyl-14H-dibenzo[a,j]xanthenes
1261
effect of polyvinyl sulfonic acid, the reaction of 2-naphthol
and 4-chlorobenzaldehyde (molar ratio 2:1) was examined
in the absence of the catalyst. However, this reaction did
not proceed, and hardly any product was detected after
obtained low to moderate yields in water (Table 2). All the
reactions were run in the same reaction conditions, and
similar amounts of catalysts (20 mol%) were used. As can
be seen in Table 2, PVSA catalyzes the reaction better than
other catalysts, and satisfactory results were obtained only
with PVSA (entry 12). The reason is that a huge excess of
acidic groups is present along the polymer chain of PVSA,
and the proton density in solution is locally concentrated;
as a result, the reaction takes place only in the neighbor-
hood of the polymer molecule.
1
0 h under reflux conditions in water (Table 1, entry 9).
Based on the optimized conditions in the reaction of
-naphthol and 4-chlorobenzaldehyde using PVSA as cat-
2
alyst, we also tested the catalytic activity of different acidic
catalysts for comparing the efficiency of PVSA, and we
Encouraged by the remarkable results obtained with the
above reaction conditions, and in order to show the gen-
erality and scope of this new protocol, we used several
aromatic and aliphatic aldehydes and 2-naphthol in the
presence of PVSA in water. The results obtained are
summarized in Table 3. Aromatic aldehydes carrying dif-
ferent functional groups were subjected to the reaction, and
in all cases the desired product was synthesized in high
yields and short reaction times (Table 3, entries 1–13).
Another advantage of this method is its efficiency for the
high yield synthesis of 14-alkyl-14H-dibenzo[a,j]xanthenes
from aliphatic and cycloaliphatic aldehydes (Table 3,
entries 14–17). The workup procedure is simple and
includes filtration of the mixture to separate the product,
and the aqueous solution was saved for the next reaction.
Compared with traditional homogeneous Brønsted acid
catalysts, it is easy for PVSA to be reused, which is prior to
the conventional homogeneous acid catalysts. Hence, we
Table 2 Effect of acidic catalyst (20 mol%) on the reaction of
2-naphthol (1, 2 mmol) and 4-chlorobenzaldehyde (2d, 1 mmol) in
water
Entry
Catalyst
NH Cl
Time/h
Yield/%
1
2
3
4
5
6
7
8
9
4
8
8
8
8
8
4
8
6
8
8
8
1
22
NaHSO
NaHSO
3
4
18
21
4
(NH )
2
HPO
4
Trace
Trace
90
Fe(HSO
KAl(SO
p-TsOH
4
)
)
3
2
a
4
2
.12H O
51
Silica sulfuric acid
64
I
2
Trace
35
1
1
1
a
0
1
2
Montmorillonite K-10
SO
H
2
4
20
PVSA
93
5
0 mol% was used
Table 3 Synthesis of 14-aryl- or 14-alkyl-14H-dibenzo[a,j]xanthenes 3a–3q catalyzed by PVSA using different aldehydes 2 and 2-naphthol (1)
a
Entry
R
Time/h
Prod.
Yield/%
M.p./°C
Lit. m.p./°C
1
2
3
4
5
6
7
8
9
C
6
H
5
1.5
2
3a
3b
3c
3d
3e
3f
91
90
90
93
90
92
90
90
91
88
86
91
90
83
82
79
78
184–185
228
185 [33]
4-MeC
6
H
4
229 [33]
4-MeOC
6
4
4
H
4
1.5
1
203–204
289–290
214–216
310–311
213–214
297–298
261–262
293–294
309–310
249–250
238–239
149–150
154–155
152–153
173–174
204 [33]
4-ClC
2-ClC
6
H
H
289 [33]
6
1.5
2
215 [33]
4-O
2-O
2
NC
NC
6
H
4
310 [33]
2
6
H
4
2.5
2
3g
3h
3i
213 [33]
4-BrC
4-HOC
4-NCC
4-OHCC
4-MeO CC
4-FC
6
H
4
297 [33]
6
H
4
1.5
1.5
2
263 [28]
10
11
12
13
14
15
16
17
6
H
4
3j
291–292 [37]
309–312 [39]
249–250 [42]
238–240 [38]
152 [43]
6
H
4
3k
3l
2
6
H
4
1.5
1.5
2.5
3
6
H
4
3m
3n
3o
3p
3q
CH
CH
3
CH
CH
2
2
3
CH
2
155–157 [36]
152–154 [36]
174–175 [57]
(CH
3
)
2
CH
3
C
H
6 11
4.5
3
Reaction conditions: aldehyde 2 (1 mmol), 2-naphthol (1, 2 mmol), PVSA (20 mol%), 3 cm water, 90 °C
a
Isolated yields
123

1
262
A. Rahmatpour
Table 4 Reuse of PVSA for synthesis of 3d
14-alkyl-14H-dibenzo[a,j]xanthene derivatives using PVSA
that can be prepared by a simple operation from commer-
cially available and relatively cheap starting monomer. The
notable advantages of this methodology are short reaction
times, the easy purification of the products by simple fil-
tration and crystallization, generality, and the use of water
as solvent. The unique acid properties, easy handling, and
catalytic performance of PVSA as a Brønsted polymeric
acid catalyst will allow the development of methods for a
variety of organic transformations. To the best of our
knowledge, this protocol is the first report on the synthesis
of the title compounds using polymeric Brønsted acid
catalyst in aqueous media. Recovery and reuse of PVSA
catalyst are also satisfactory, demonstrating the cost
effectiveness and green aspect of our methodology.
Run
1
2
3
4
5
a
Yield/%
93
91
89
87
84
Reaction conditions: 2d (1 mmol), 2-naphthol (1, 2 mmol), and
3
PVSA (20 mol%) in 3 cm water at 90 °C
a
Isolated yield
decided to study the catalytic activity of recycled Brønsted-
acidic PVSA for the synthesis of 3d. After the separation of
product, the filtrate containing catalyst was evaporated to
remove water, and the resulting catalyst was reused directly
for the next run. As shown in Table 4, the Brønsted-acidic
PVSA can be recycled at least five times without any
treatment and without a significant decrease in catalytic
activity. The yields ranged from 93 to 84%.
We also studied the reaction between terephthaldialde-
hyde (1 mmol) and excess amounts of 2-naphthol
Experimental
(
4 mmol); we expected that both of the formyl groups on
the aromatic ring of terephthaldialdehyde would react with
-naphthol. However, we observed that one of the formyl
The monomer and starting materials were purchased from
Fluka and Merck chemical companies and used without
purification. PVSA was prepared according to the reported
procedure with slight modification [55, 56]. Viscosity
measurements were carried out using an Ubbelohde vis-
cometer. Differential scanning calorimetry (DSC) was
performed on a Stanton STA-625 instrument. FT-IR
spectra were run on a Shimadzu FTIR-8300 spectropho-
2
groups was condensed with 2-naphthol and another group
was intact because of steric effects between o-hydrogens of
the benzene ring and the xanthene ring (Scheme 2).
Based on the experimental results and by referring to the
literature [24, 25, 30], the mechanism of the dibenzo-
xanthene formation proceeds by the usual pathway pro-
posed using acidic catalysts.
1
13
tometer. H NMR and C NMR spectra were recorded on
a Bruker Avance DPX instrument (250 MHz) using TMS
as internal standard. The progress of the reactions was
followed by TLC on silica gel Polygram SIL/UV 254
plates. Elemental analyses were performed using a Heraeus
CHN-O-Rapid analyzer, and the results agreed favorably
with calculated values.
Conclusion
In conclusion, we successfully developed a new, efficient,
and eco-friendly method for the preparation of 14-aryl- or
CHO
SO2 OH
CH2 CH
(86%)
n
O
OH
(20 mol%)
+
OHC
CHO
o
Water, 90 C, 2 h
4
mmol
1 mmol
O
O
(
0%)
Scheme 2
1
23

Synthesis of 14-aryl- or 14-alkyl-14H-dibenzo[a,j]xanthenes
1263
Preparation of sodium salt of polyvinylsulfonic acid
(
16. El-Brashy AM, Metwally ME, El-Sepai FA (2004) II Farmaco
5
9:809
7. Jamison JM, Krabill K, Hatwalkar A (1990) Cell Biol Int Rep
4:1075
Na-PVSA)
1
1
A mixture of 20 g sodium vinylsulfonate solution (50%
w/w, 10 g of sodium vinylsulfonate), 0.088 g potassium
persulfate, and 0.033 g sodium bisulfite was made in a
Teflon vessel. The vessel was evacuated and pressured
repeatedly with nitrogen, and then sealed. The sealed
Teflon vessel was rotated in a bath at 15 °C for 48 h. The
18. Chibale K, Visser M, Schalkwyk DV, Smith PJ, Saravanamuthu
A, Fairlamb AH (2003) Tetrahedron 59:2289
1
9. Ion RM, Frackowiak D, Wiktorowicz K (1998) Acta Biochim Pol
5:833
4
2
0. Bhowmik BB, Ganguly P (2005) Spectrochim Acta Part A
61:1997
21. Knight CG, Stephens T (1989) Biochem J 258:683
3
22. Ahmad M, King TA, Cha BH, Lee J (2002) J Phys D Appl Phys
resulting viscous oil was dissolved in 45 cm water and
3
5:1473
3. Sarma RJ, Baruah JB (2005) Dyes Pigment 64:91
24. Khosropour AR, Khodaei MM, Moghannian H (2005) Synlett 955
3
precipitated with 60 cm methanol. Na-PVSA (7.54 g) was
2
obtained after drying in vacuo over P O .
2
5
2
2
2
5. Rajitha B, Kumar BS, Reddy YT, Reddy PN, Sreenivasulu N
2005) Tetrahedron Lett 46:8691
6. Pasha MA, Jayashankara VP (2007) Bioorg Med Chem Lett
7:621
7. Das B, Ravikanth B, Ramu R, Laxminarayana K, Rao BV (2006)
J Mol Catal A Chem 55:74
28. Saini A, Kumar S, Sandhu JS (2006) Synlett 1928
9. Ko S, Yao CF (2006) Tetrahedron Lett 47:8827
0. Seyyedhamzeh M, Mirzaei P, Bazgir A (2008) Dyes Pigment
76:836
(
General experimental procedure for the synthesis
of 14-aryl- or 14-alkyl-14H-dibenzo[a,j]xanthenes
1
A mixture of 2-naphthol (2 mmol), aldehyde (1 mmol), and
3
4
3.2 mg PVSA (50% w/w, 20 mol%, 0.2 mmol) in 3 cm
2
3
water was heated at 90 °C with stirring for the time shown in
Table 3. The progress of the reaction was monitored by TLC
(
n-hexane/ethyl acetate, 3/1). After completion of the reac-
tion, the reaction mixture was cooled to room temperature,
31. Shaterian HR, Ghashang M, Hassankhani A (2008) Dyes Pigment
6:564
7
3
2. Bigdeli MA, Heravi MM, Mahdavinia GH (2007) J Mol Catal A
Chem 275:25
and the precipitated product was filtered and finally washed
3
with 2 9 20 cm of cold and hot water, respectively. The
33. Amini MM, Seyyedhamzeh M, Bazigir A (2007) Appl Catal A
Gen 323:242
xanthene product obtained was recrystallized from ethanol.
The filtrate containing the polymeric catalyst was further
evaporated to dryness, and the resulting catalyst was reused
directly for the next run. The reactions using the recycled
catalyst were conducted in a similar manner. All of the
products are known compounds and were characterized by
IR and NMR spectroscopy, and their melting points agreed
with reported values.
3
4. Heravi MM, Bakhtiari K, Daroogheha Z, Bamoharram FF (2007)
J Mol Catal A Chem 273:99
3
5. Mohammad AB, Majid MH, Gholam HM (2007) Catal Commun
8:1595
36. Mirjalili BBF, Bamoniri AH, Akbari A (2008) Tetrahedron Lett
9:6454
4
3
3
7. Su W, Yang D, Jin C, Zhang B (2008) Tetrahedron Lett 49:3391
8. Dabiri M, Baghbanzadeh M, Shakourinikcheh M, Arzroomchilar
E (2008) Bioorg Med Chem Lett 18:436
3
9. Sharifi A, Abaee S, Tavakkoli A, Mirzaei M, Zolfagharei A
(
2008) Synth Commun 38:2958
0. Zarei A, Hajipour AR, Khazdooz L (2010) Dyes Pigment 85:133
1. Kantevari S, Chary MV, Das APR, Vuppalapati SVN, Lingaiah N
4
4
References
(
2008) Catal Commun 9:1575
1
2
. Palanniappan S, John A, Amarnath CA, Rao VJ (2004) J Mol
Catal A Chem 218:47
. Palanniappan S, John A, Amarnath CA, Rao VJ (2004) Catal Lett
42. Pratibha K, Yathindranath V, Chauhan SMS (2008) Synth
Commun 38:637
43. Gong K, Fang D, Wang HL, Zhou XL, Liu ZL (2009) Dyes
Pigment 80:30
9
7:77
3
4
5
6
7
8
9
. Nabid MR, Rezaei S (2009) J Appl Catal A Gen 366:108
. Tamami B, Kolahdoozan M (2004) Tetrahedron Lett 45:1535
. Tamami B, Fadavi A (2005) Catal Commun 6:747
. Jagtap SR, Bhor MD, Bhanage BM (2008) Catal Commun 9:1928
. Iranpoor N, Tamami B, Niknam K (1997) Can J Chem 75:1913
. Alexandratos SP (2009) Ind Eng Chem Res 48:388
44. Rahmatpour A (2010) React Funct Polym 70:923
45. Rahmatpour A (2011) React Funct Polym 71:80
46. Rahmatpour A (2011) Heteroat Chem 22:51
47. Rahmatpour A (2010) J Heterocycl Chem 47:1011
48. Rahmatpour A, Banihashemi A (1999) Tetrahedron 55:7271
49. Rahmatpour A (2002) J Chem Res (S) 118
50. Rahmatpour A, Banihashemi A (1999) J Chem Res (S) 390
51. Ekbote SS, Panda AG, Bhor MD, Bhanage BM (2009) Catal
Commun 10:1569
52. Esenberg H, Mohan GR (1959) J Phys Chem 63:671
53. Distler H (1965) Angew Chem Int Ed 4:300
54. Kutner A, Breslow DS (1986) Encyclopedia of polymer science
and technology, 2nd edn. Wiley, New York
. Harmer AM, Farneth WE, Sun Q (1998) J Am Chem Soc
1
18:7708
0. Bhanushali MJ, Nandurkar NS, Bhor MD (2008) Catal Commun
:425
1. Olah GA, Mathew T, Farnia M, Prakash GKS (1999) Synlett
067
2. Akelah A, Sherrington DC (1981) Chem Rev 81:557
3. Li CJ, Chan TH (1997) Organic reactions in aqueous media.
Wiley, New York
1
1
9
1
1
1
55. Yoshikawa S, Kim OK (1966) Bull Chem Soc Jpn 39:1515
56. Breslow DS, Kutner A (1958) J Polym Sci 17:295
57. Urinda S, Kundu D, Majee A, Hajra A (2009) Heteroat Chem
20:232
1
1
4. Li J (2005) Chem Rev 105:3095
5. Demko ZP, Sharpless KB (2001) J Org Chem 66:7945
123