Bronsted acidic ionic liquids promoted cyclocondensation reaction: Synthesis of 1,8-dioxo-octahydroxanthene

Article abstract of DOI:10.1016/j.crci.2011.04.008

Novel Bronsted acidic ionic liquids bearing hydrogen sulfate and dihydrogen phosphate as anions were designed and successfully applied as catalysts for the one-pot synthesis of 1,8-dioxo-octahydroxanthene in water medium. The sequence of the catalytic act

Full text of DOI:10.1016/j.crci.2011.04.008

C. R. Chimie 14 (2011) 883–886
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Preliminary communication/Communication
Brønsted acidic ionic liquids promoted cyclocondensation reaction:
Synthesis of 1,8-dioxo-octahydroxanthene
P.P. Salvi a, A.M. Mandhare a, A.S. Sartape a, D.K. Pawar a, S.H. Han b, S.S. Kolekar a,
*
a Department of chemistry, Shivaji University, Kolhapur, 416 004 (MS), India
b Inorganic nano-material laboratory, department of chemistry, Hanyang University, Seoul 133-791, South Korea
A B S T R A C T
A R T I C L E I N F O
Article history:
Novel Brønsted acidic ionic liquids bearing hydrogen sulfate and dihydrogen phosphate as
anions were designed and successfully applied as catalysts for the one-pot synthesis of
1,8-dioxo-octahydroxanthene in water medium. The sequence of the catalytic activity
observed in the transformation was in good agreement. In this article, six different ionic
liquids (ILs) such as, [BMIM][BF4], [CMIM][HSO4], [NMP][HSO4], [BMIM][HSO4],
[(CH2)4SO3HMIM][HSO4], [BMIM][H2PO4] were synthesized and used as a catalyst for
synthesis of 1,8-dioxo-octahydroxanthene very first time. The products could be
conveniently separated from the reaction mixture by filtration and the dissolved catalyst
can be regenerated and recycled several times without significant loss of activity.
ß 2011 Acade´mie des sciences. Published by Elsevier Masson SAS. All rights reserved.
Received 23 November 2010
Received in revised form 26 April 2011
Accepted after revision 29 April 2011
Available online 12 June 2011
Keywords:
Brønsted acidic ionic liquids
Green catalyst
Multicomponent reaction
1,8-dioxo-octahydroxanthene
Regeneration of catalyst
1. Introduction
route for one-pot multicomponent reaction (MCR) of 1,8-
dioxo-octahydroxanthene. The xanthene scaffold is prob-
Often, the largest contributor to the environmental
footprint of a chemical process is the solvent used. Solvents
have a significant impact because of the quantity used, e.g.
in pharmaceutical productions they typically account for
between 80 and 90% of the mass utilization of a batch
operation. Consequently, replacing volatile organic sol-
vents with more environmentally benign media, is one of
the central tenets of Green Chemistry and a subject of
significant academic and commercial interest [1]. The use
of task-specific ionic liquids (TSILs) further enhances the
versatility of ILs for the cases in which the reagent and
medium are coupled [2–4]. Brønsted acidic ionic liquids
(BAILs) consist of the useful characteristics of solid acids
and mineral liquid acids and are designed to replace
traditional mineral liquid acids such as sulfuric acid and
hydrochloric acid in chemical procedures. Such BAILs have
potential as dual solvent-catalysts in organic reactions [5].
In a continuation of our catalytic investigation study
[6], herein we report a new, convenient, mild and efficient
ably the most ubiquitous heterocyclic structure in natural
and unnatural compounds that usually have biological
activities [7] and have been used as versatile synthon
because of the inherent reactivity of the pyran ring [8]. The
synthesis of xanthene derivatives has been a major object
of research for several years, and a variety of catalysts [9–
14] were used for the same. However, some of the reported
methods suffer from disadvantages such as prolonged
reaction time, low yield of products, toxic and corrosive
reagents. Therefore, the discovery of clean procedures and
the use of a green and eco-friendly catalyst with high
catalytic activity and short reaction time for the production
of 1,8-dioxo-octahydroxanthene have gained considerable
attention. A slight attempt has been taken in view of green
synthesis [15]. There is some evidence which indicates the
use of BAILs as a catalyst for the synthesis of 1,8-dioxo-
octahydroxanthene [16–19]. Remarkably, the synthesis of
1,8-dioxo-octahydroxanthene using [CMIM][HSO4] as a
catalyst has not been reported yet.
In this article, we have reported synthesis of 1,8-dioxo-
octahydroxanthene (Scheme 1) in presence of water by
developing a conceivable mechanism (Scheme 2) by using
* Corresponding author.
E-mail address: kolekarss2003@yahoo.co.in (S.S. Kolekar).
1631-0748/$ – see front matter ß 2011 Acade´mie des sciences. Published by Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.crci.2011.04.008

884
P.P. Salvi et al. / C. R. Chimie 14 (2011) 883–886
O
O
CHO
O
BAILs
+
2
CH3
CH3
70 oC,
water
3HC
3HC
CH3
CH3
O
O
Scheme 1.
-
-
HSO4
HSO4
+
N
+
N
O
Ar
O
O
N
O
N
COOH
COOH
O
OH
Ar
..
O
..
O
H
3
4
2
O
1
..
O
O
Ar
O
O
Ar
O
O
H
H2O
..
OH
..
O
..
H
5
Ar
O
O
O
Ar
OH
O
Ar
O
H+
H+
..
+
O
H
O
OH
H2O
O H
..
O
H
OH
6
O
Ar
O
O
Ar
O
H
O
O
O
+
H
H
7
Scheme 2.
-
-
HSO4
-
HSO4
+
N
BF4
+
N
+
COOH
N
N
N
N
SO3H
[CMIM][HSO4]
[(CH2)4SO3HMIM][HSO4]
[BMIM][BF4]
-
H2PO4
+
-
-
HSO4
HSO4
+
+
N
N
N
N
N
O
H
[BMIM][HSO4]
[BMIM][H2PO4]
[NMP][HSO4]
Scheme 3.

P.P. Salvi et al. / C. R. Chimie 14 (2011) 883–886
885
Table 1
Table 2
Effect of different BAILs as catalyst for 1,8-dioxo-octahydroxanthene
synthesis.
Results of 1,8-dioxo-octahydroxanthene synthesis using [CMIM][HSO4]
as catalyst under different conditions.
Entry
Ionic liquids
Molar
Time
(h)
Yield
(%)
Entry
Molar ratio (%)
Time (h)
Yield (%)
87
ratio (%)
a
b
c
d
e
f
5
5
2
1
[BMIM][BF4]
20
10
20
10
20
10
20
10
15
20
10
15
20
3
8.9
56
2.5
2.5
3
90
2
[(CH2)4SO3HMIM][HSO4]
[(CH2)4SO3HMIM][HSO4]
[NMP][HSO4]
3
10
10
15
15
15
20
95
3
2.5
3
63.1
68
94
4
2.5
3
91
5
[NMP][HSO4]
2.5
2.5
2.5
2.5
2
70
91
6
[BMIM][H2PO4]
[BMIM][H2PO4]
[CMIM][HSO4]
[CMIM][HSO4]
[CMIM][HSO4]
[BMIM][HSO4]
[BMIM][HSO4]
[BMIM][HSO4]
65.8
71
g
h
4
89
7
3
90
8
95
All reactions were run using 5 mmol aldehyde and 10 mmol dimedone.
All reactions were preceded at 70 8C.
9
90.8
90.2
93
10
11
12
13
2
2.2. Effects of different reaction conditions using
[CMIM][HSO4] as a catalyst
2
2
92
2.5
89
Initially, to optimize the amount of ionic liquid, the
reaction of dimedone (10 mmol) and aldehyde (5 mmol)
was performed in 10 ml water at 70 8C in the presence of
different quantities of [CMIM][HSO4] (Table 2). As shown
in Table 2, the yield of product g using high amounts of
[CMIM][HSO4] was comparatively low and the reaction
time was long (Table 2, entries f-h). No improvement in the
reaction rate was observed by decreasing the amount of
ionic liquid from 15 to 5 mol % but the yield of product c in
the presence of 10 mol % of [CMIM][HSO4] was higher than
the others (Table 2, entries c,d). A conceivable mechanism
for formation of 1,8-dioxo-octahydroxanthene is proposed
(Scheme 2).
All reactions proceeded at 70 8C.
BAILs (Scheme 3). The reaction proceeded smoothly and,
therefore, the purification of products was fairly simple.
Furthermore, BAILs were conveniently separated from the
products and easily recycled for another round of reaction.
This will significantly reduce the effect of the reaction on
the environment and thus pave a way for large scale
applications.
2. Results and discussion
2.1. Promoting effect of BAILs
2.3. Reusability of [CMIM] [HSO4]
Our efforts were focussed on investigating the synthesis
of 1,8-dioxo-octahydroxanthene using BAILs as the new
catalyst. The promoting effect of BAILs for the synthesis of
1,8-dioxo-octahydroxanthene is summarized in Table 1.
Acidity and the structure of ILs, molar ratio of IL/substrate
and reaction time all have significant effects on the
reaction. The reaction hardly occurred in the presence of
[BMIM][BF4] (Table 1, entry 1) while the reaction conver-
sion was enhanced from 8.9 to 95%, when BAILs with a
ÀSO3H group in the anions were used as promoters. As an
exception [(CH2)4SO3HMIM][HSO4], [NMP][HSO4] and
[BMIM][H2PO4] showed a relatively weaker promoting
effect (Table 1, entries 2–7) than [CMIM][HSO4] and
[BMIM][HSO4].These results imply that the performance
of BAILs is dependent upon the character of the side chain
of the cation and the N-heterocyclic ring. These initial
investigational results showed that the change of BAILs
concentration would increase the reaction rate, and the
change of acid group introduced into the imidazolium
cation would affect the acidic activity. In this method,
BAILs plays an important role in enhancing the reactivity as
well as reducing formation of by-products. The use of these
BAILs in this reaction can be considered as new green
alternative.
One of the most effective BAIL, [CMIM][HSO4] was
selected to investigate the possibility of reusability (Fig. 1).
The product is insoluble in water and it was collected by
simple filtration, while the ionic liquid is completely
soluble in water. The dissolved IL could be recovered easily
by rotary evaporator and directly reused for subsequent
runs. As shown in Fig. 1, slight decrease was observed with
the recovered IL. 1H NMR spectrums of IL before the run
and after fifth run exhibits almost same values which
100
95
95
94
94
95
90
85
80
93
1
2
3
4
5
Number of runs
Fig. 1. Reusability of [CMIM][HSO4].

886
P.P. Salvi et al. / C. R. Chimie 14 (2011) 883–886
confirmed that the IL is structurally stable even after fifth
run.
[BMIM][BF4]: 1H NMR (DMSO-d6):
d 0.72 (t, J = 7.2 Hz,
3H), 1.11 (m, 2H), 1.67 (m, 2H), 3.89 (s, 3H), 4.17 (s, 2H),
7.85 (s, 1H), 7.94 (s, 1H), 9.63 (s, 1H).
3. Conclusion
[(CH2)4SO3HMIM][HSO4]: 1H NMR (DMSO-d6):
d 1.49 –
1.59 (m, 2H), 1.82 – 1.92 (m, 2H), 2.51 – 2.58 (m, 2H), 3.85
(s, 3H), 4.18 (t, J = 7.2 Hz, 2H), 7.59 (s, 2H), 7.72 (s, 1H), 7.78
(s, 1H), 9.16 (s, 1H).
Several BAILs with different acidic scales were synthe-
sized. Their acidity was infuenced by the structures of both
the anion and the cation. In particular, the presence of a
SO3H group in the anions of BAILs might be responsible for
[CMIM][HSO4] (before any run): 1H NMR (DMSO-d6):
d
3.63 (s, 3H), 4.84 (t, J = 3.0 Hz, 2H), 7.20 (s, 2H), 8.49 (bs,
a
higher acidity, which brought about
a
signicant
1H).
promoting effect on the formation of 1,8-dioxo-octahy-
droxanthene. The product yield attained a plateau when
the reaction was promoted with BAILs. Further study of
[CMIM][HSO4] with similar reaction shows discrimination
in the good to excellent yield. The reusability of ILs has
given the green touch to the research.
[CMIM][HSO4] (after fifth run): 1H NMR (DMSO-d6):
d
3.82 (s, 3H), 5.11 (t, J = 2.9, 2H), 7.76 (s, 2H), 9.0 (bs, 1H).
[BMIM][HSO4]: 1H NMR (DMSO-d6):
0.86 (t, J = 7.2 Hz,
d
3H), 1.25 – 1.18 (m, 2H), 1.73 (s, 2H), 3.84 (s, 3H), 4.15 (s,
2H), 7.41 (bs, 1H), 7.72 (s, 1H), 7.80 (s, 1H), 9.31 (s, 1H).
[BMIM][H2PO4]: 1H NMR (DMSO-d6):
d 0.87 (t, J = 7.2,
3H), 1.22 (m, 2H), 1.74 (s, 2H), 3.84 (s, 3H), 4.16 (s, 2H), 7.71
(s, 1H), 7.78 (s, 1H), 9.28 (s, 1H), (H of H2PO4 not seen).
4. Experimental
[NMP][HSO4]: 1H NMR (DMSO-d6):
d 1.83 – 1.91 (m,
4.1. Materials and methods
2H), 2.15 (t, J = 7.8 Hz, 2H), 2.65 (s, 3H), 3.27 (t, J = 6.9 Hz,
2H), 9.78 (bs, NH, HSO4).
All the chemicals were purchased from Sigma Aldrich
and used as received without further purication. The IR
spectra was run on a Perkin–Elmer, FTIR-1600 spectro-
photometer and expressed in cmÀ1 (KBr). 1H and 13C NMR
spectra were recorded on Bruker Avance (300 MHz)
spectrometer. An LC-MS spectrum was obtained with
Shimadzu LC-MS–2010 equipped with electrospray ioni-
zation interface.
Acknowledgments
The authors P.P.S. and S.S.K., thanks to DAE–BRNS, New
Delhi (India) for the research fellowship and financial
assistance respectively.
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The round-bottomed flask was charged with benzalde-
hyde (5 mmol), dimedone (10 mmol) and [CMIM][HSO4]
(10 mol %). Unfortunately, as the [CMIM][HSO4] is very
viscous, water (10 mL) was used as sequester. The mixture
was then stirred at 70 8C for an appropriate time (Table 1).
On completion of reaction (monitored by TLC), the
precipitated crude product was collected by filtration to
get a product in excellent yield (95%). The product was
identified by IR, 1H NMR, 13C NMR and LC-MS with those
reported in the literature.
3,3,6,6-Tetramethyl-9-phenyl-3,4,5,6,7,9-hexahydro-
2H-xanthene-1,8-dione (3):
mp 202-204 8C; IR (KBr): 2960 cmÀ1 (-CH3 stretching),
2874 cmÀ1 (Ar C – H stretching), 1665 cmÀ1
(a, b –
unsaturated carbonyl group), 1622 and 1453 cmÀ1 (Ar C –
C stretching); 1H NMR (300 MHz, CDCl3):
0.9 (s, 6H), 1.1
(s, 6H), 2.2 (s, 4H), 2.4 (s, 4H), 4.7 (s, 1H), 7.1 – 7.3 (m, 5H);
13C NMR (300 MHz, CDCl3):
27.3, 29.2, 31.8, 32.1, 40.8,
d
d
50.7, 115.6, 126.3, 128.0, 128.3, 144.0, 162.2, 196.2; M/
z = 351 (M + 1); Purity by LC-MS = 100%.
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