Bi-SO3H-functionalized room temperature ionic liquids based on bipyridinium: Highly efficient and recyclable catalysts for the synthesis of naphthalene-condensed oxazinone derivatives

Article abstract of DOI:10.1039/c3ra00133d

Several bi-SO₃H-functionalized room temperature ionic liquids were synthesized and their catalytic performances for the synthesis of naphthalene-condensed oxazinone derivatives were studied theoretically, as well as experimentally. Compared wit

Full text of DOI:10.1039/c3ra00133d

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Bi-SO H-functionalized room temperature ionic liquids
3
based on bipyridinium: highly efficient and recyclable
catalysts for the synthesis of naphthalene-condensed
oxazinone derivatives
Cite this: RSC Advances, 2013, 3,
9
965
Yuanyuan Wang, Junlong Zhou, Kun Liu and Liyi Dai*
Several bi-SO
performances for the synthesis of naphthalene-condensed oxazinone derivatives were studied
theoretically, as well as experimentally. Compared with traditional single-SO H-functionalized ionic
liquids, less catalyst and higher yields are the key features of this methodology. Hammett function values
and the minimum-energy geometries of bi-SO H-functionalized ionic liquids were calculated and the
3
H-functionalized room temperature ionic liquids were synthesized and their catalytic
3
3
results revealed that the acidities and catalytic activities of ionic liquids in the synthesis of naphthalene-
condensed oxazinone derivatives were influenced by their structures. There are strong hydrogen bond
Received 9th January 2013,
Accepted 10th April 2013
networks in these bi-SO
lengthened to different levels compared with the one in the isolated cation. The ionic liquid
(PS) bPy][OTf] with the shortest H–O bond distance had the strongest hydrogen bond and hence
showed the strongest acidity and the highest catalytic activity.
3
H-functionalized ionic liquids. The H–O bond of the sulfonic acid groups was
DOI: 10.1039/c3ra00133d
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2
2
www.rsc.org/advances
3
of novel bi-SO H-functionalized ILs based on bipyridinium,
which are liquid at room temperature (Scheme 1).
Introduction
Recently, ionic liquids (ILs) have been applied and shown to be
effective in some catalytic conversions. They have important
and unique properties such as negligible vapor pressure,
excellent chemical and thermal stability, potential recover-
ability, and convenience for the separation of products from
Multicomponent reactions (MCRs) have drawn great inter-
est in modern organic synthesis and medicinal chemistry
because of their one-pot processes about bringing together
three or more components, high atom economy and high
15–17
selectivity.
Aromatic-condensed oxazinone derivatives are
1
–4
reactants.
In particular, Brønsted acid functionalized ILs
an important class of heterocyclic compounds, since many of
(
FILs) have been reported as novel ecologically benign catalysts
18
these heterocyclic systems exhibit biological activity. For
5
for some acid-catalyzed reactions. Since Cole et al. firstly
example, naphthalene-condensed 1,3-oxazin-3-ones have been
described a FIL with Brønsted acidity in 2002, the research and
application of various SO H functionalized Brønsted acidic ILs
3
19
reported to act as antibacterial agents.
This class of
compounds has also been used as precursors in the prepara-
have received an increased attention. In most cases, ILs were
functionalized with only one sulfonic acid group and that
resulted in the reduced acidity of the ILs compared to the
20
tion of phosphinic ligands for asymmetric catalysis.
Naphthalene-condensed oxazinone derivatives have been
21
4 2
synthesized through MCRs using HClO –SiO as a catalyst
6
–8
acidities shown by conventional acid catalysts.
years, a series of multi-SO H functionalized ILs have been
reported and shown to be effective, strong acidic catalysts.
In recent
22
or by the use of MW irradiation. Although these methods are
quite useful, they have limitations, such as low yields, tedious
work-up procedures and harsh reaction conditions. To the best
of our knowledge, there are few reports using ILs as catalysts
for the synthesis of naphthalene-condensed oxazinone deriva-
3
9
–11
However, most of those multi-SO H functionalized ILs are
3
solid at room temperature and could not be administered as
pure liquids, which have restricted their applications. In
continuation of our studies on the preparation and application
tives. We have reported the effective catalytic results of single
12–14
SO H-functionalized ILs to some organic reactions,
so we
3
1
2–14
of SO
3
H-functionalized ILs,
we herein report the synthesis
3
predicted that our bi-SO H-functionalized ILs could also
catalyze the synthesis of naphthalene-condensed oxazinone
derivatives efficiently (Scheme 2).
Shanghai Key Laboratory of Green Chemistry and Chemical Process, Department of
Chemistry, East China Normal University, Dongchuan Road 500, 200240, Shanghai,
PR China. E-mail: lydai@chem.ecnu.edu.cn; Fax: +86 21 62602447;
Tel: +86 21 62233037
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Scheme 1 Structures of the bi-SO H-functionalized ILs used in this paper.
[
(BS)
2
bPy][H
2
PO
4
]
2
.
[PSPy][HSO
4
]
.
[PSPy][OTf]
.
Results and discussion
[(PS) bPy][H PO ] . [(BS) bPy][HSO ] . [(PS) bPy][HSO ]
2
2
4 2
2
4 2
2
4 2
3
The measurement of the acidic scale of bi-SO H-functionalized
ILs was conducted on an Agilent B453 UV-vis spectrophot-
ometer with a basic indicator, crystal violet. With the
increase of the acidic scale of the ILs, the absorbance of the
unprotonated form of the basic indicator decreased, whereas
the protonated form of the indicator could not be observed. It
.
2 2 2 2
[(BS) bPy][OTf] . [(PS) bPy][OTf] . The acidity order of
these SO H-functionalized ILs is accompanied by the following
H
3
2
3
0
values (Table 1): [(PS)
bPy][OTf] (20.0799) . [(PS)
2
bPy][OTf] (20.3873)
2
.
[
[
[
[
(BS)
2
2
2
bPy][HSO ] (20.0411) .
4 2
(BS) bPy][HSO ] (0.0329) . [(PS) bPy][H PO ] (0.2033) .
PSPy][OTf]
(BS) bPy][H PO ] (0.7320) . [PSPy][H PO ] (1.0958). The
2
4 2
2
2
4 2
(0.2087)
.
[PSPy][HSO
4
]
(0.5707)
.
is because of its small molar absorptivity and its location. The
2
2
4 2
2
4
+
[
I]/[IH ] (I represents indicator) ratio could be determined
results indicated that the acidity of ILs became stronger with
the increase of the number of SO H-functionalized groups.
The acidity of bi-SO H-functionalized ILs depended on the
from the measured absorbance differences after the addition
of ILs and the Hammett function (H ) was calculated by using
3
0
3
eqn (1). This value could be considered as the relative acidity
of the ILs.
characteristics of both cations and anions. The ILs with a
+
[
[
(PS) bPy] cation had stronger acidities than those with a
2
+
(BS)
2
bPy] cation. When the cations of the ILs were the same,
+
H
0
= pK(I)aq + log([I]/[IH ])
(1)
the dependence of the acidity of the IL on the anion was
significant. The acidities of the bi-SO H-functionalized ILs
3
H
0
values of bi-SO
3
H-functionalized ILs were calculated
2
2
4
with [OTf] were stronger than those of the ILs with [HSO ]
2
1
with the same concentration of crystal violet (5 mg L , pK
.8) and IL (25 mmol L ) in distilled water. For comparison,
a
=
2
and [H
2 4
PO ] anions (Table 1, entries 1–6).
2
1
0
The minimum-energy geometries of bi-SO
3
H-functionalized
we also determined the H values of single-SO H-functiona-
0
3
ILs were determined by performing ab initio geometry
optimizations at the RHF/6–31(d, p) level. The fully optimized
geometries of these ILs were presented in Fig. 2 and 3 and
Table 2. It is obvious that a strong hydrogen bond network is
lized ILs based on pyridium. The maximal absorbance of the
unprotonated form of the indicator was observed at 590 nm.
When an acidic IL was added, the absorbance of the
unprotonated form of the indicator decreased. As is shown
in Fig. 1, the absorbance of the unprotonated form of the
present in the bi-SO
3
H-functionalized ILs. Taking the IL
[
(PS) bPy][HSO as an example, the anions were located on
2
4 2
]
2 4
indicator on nine ILs decreased as follows: [PSPy][H PO ] .
the side of the propyl sulfonic acid groups, and interacted with
the propyl alkyl sulfonic acid group and bipyridinium ring in
…
…
the form of C(N)–H O or O–H O (hydrogen bonds). There
were eight hydrogen bonds in the IL [(PS) bPy][HSO , which
were shorter than the van der Waals distance of 2.67 Å. These
2
4 2
]
2
4
18…
16…
included the hydrogen bonds C15–H
O
54, C12–H
O
54 and
57 (bond distances are 2.474 Å, 2.181 Å and 2.392 Å)
between the anions and the bipyridinium ring, as well as the
6…
C
1
–H
O
26…
35…
32…
C
22–H
O
52, C31–H
O
57 and C30–H O57 (bond distances
Scheme 2 The synthesis of naphthalene-condensed oxazinone derivatives via
are 2.150 Å, 2.242 Å and 2.770 Å) hydrogen bonds between the
anions and the alkyl sulfonic acid chain. Most importantly, the
the condensation reaction of an aldehyde, 2-naphthol and urea catalyzed by ILs.
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3
Fig. 1 Absorbance spectra of crystal violet for various SO H-functionalized ILs in distilled water.
strongest interactions between the anions and the sulfonic
acidity sequence. When the anion of the ILs was the same, the
H–O bond distances of bi-SO H-functionalized ILs with the
cation were shorter than those with the
bPy] cation. Taking ILs with the [H PO ] anion as
examples, the H–O bond distance of the sulfonic acid group of
…
…
acid proton were O –H
O51 and O –H
46
O58 (bond
3
4
7
48
45
2
+
distances are 1.435 Å and 1.388 Å). The other five bi-SO
3
H-
[(PS)
[(BS)
bPy]
2
2
+
functionalized ILs also exhibited similar strong interactions
between the anions and the sulfonic acid groups. Those
interactions could make the H–O bond of the sulfonic acid
groups lengthen to different levels compared with the one in
the isolated cation. When the cation of the ILs was the same,
2
2
4
these ILs decreased as follows: [(PS)
1.131 Å, H48–O47 = 1.147 Å) , [(BS)
2
bPy][H
bPy][H
2
PO
PO
4
]
2
(H46–O45
] (H43–O42
4 2
=
=
2
2
1.209 Å, H54–O53 = 1.204 Å), which was also the reverse of their
acidity sequence. The formation of a hydrogen bond was
caused by a process of sharing the lone electron pair of the O
or F atom with the H atom. As the hydrogen bond is stronger,
the potential energy surface for the shared hydrogen is
flattened, hence causing the delocalization of the shared
proton, which most likely in this case, increases the acidity of
the H–O bond distance of the bi-SO H-functionalized ILs
3
decreased as follows: [Cation][H
Cation][OTf] . Taking ILs based on the [(PS)
examples, the H–O bond distance of the sulfonic acid group of
2 4 2 4 2
PO ] . [Cation][HSO ] .
+
[
2
2
bPy] cation as
these ILs decreased as follows: [(PS)
2
bPy][H (H46–O45
4 2
bPy][HSO ] (H48–O47
2
PO
4
]
2
=
=
1.131 Å, H48–O47 = 1.147 Å) . [(PS)
1.088 Å, H46–O45 = 1.105 Å) . [(PS)
1.063 Å, H48–O47 = 1.073 Å), which was the reverse of their
2
2
5–28
2
bPy][OTf]2 (H46–O45 =
the ionic liquids.
The results obtained from experiments and the minimum-
energy geometries of bi-SO H-functionalized ILs revealed that
3
the acidity and catalytic activity of the ILs were related to their
3
structures. The bi-SO H-functionalized ILs with a shorter H–O
bond had stronger acidity and higher catalytic activity in the
synthesis of b-acetamido ketones.
Table 1 Calculation and comparison of H
0
3
values of different SO H-functiona-
a
lized ILs in distilled water (20 uC)
+
IL
A
max
[I] (%)
[IH ] (%)
H
0
A comparative study on the catalytic activity of the novel bi-
SO
3
H-functionalized ILs with other ILs was carried out using
a:blank
b:[PSPy][H
0.9516
0.6320
0.4389
0.3533
0.1939
0.1920
0.1389
0.1195
0.1109
0.0583
100
0
the reaction of 2-naphthol, benzaldehyde and urea as a model
2
PO
2
4
]
4
]
66.4
46.1
37.1
20.4
20.2
14.6
12.6
11.65
6.1
33.6
53.9
62.9
79.6
79.8
85.4
87.4
88.35
93.9
1.0958
2
9
c:[(BS)
2
bPy][H
PO
4
]
2
0.7320
0.5707
0.2087
0.2033
0.0329
20.0411
20.0799
20.3873
reaction (Fig. 4). Fang et al. reported the application of
pyridinium-based functionalized ILs in the synthesis of 1,2-
dihydro-1-phenylnaphtho[1,2-e][1,3]oxazine-3-one. However,
those procedures encountered the problems of larger usage
of the ILs and a relatively low yield of product. As shown in
Fig. 4, under the same reaction conditions (150 uC, 60 min, 10
mol% IL, solvent-free), the best yield of 1,2-dihydro-1-
phenylnaphtho[1,2-e][1,3]oxazine-3-one was 94% in the pre-
d:[PSPy][HSO
e:[PSPy][OTf]
f:[(PS)
g:[(BS)
h:[(PS)
i:[(BS)
2
bPy][H
bPy][HSO
bPy][HSO
bPy][OTf]
bPy][OTf]
2
PO
4
]
2
2
4 2
]
2
2
4
]
2
2
j:[(PS)
2
2
a
21
21
a
Indicator: crystal violet (5 mg L , pK = 0.8), IL (25 mmol L ).
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2+
2
Fig. 2 Molecular structures of the isolated [(PS) bPy] cation and ILs based on
this cation.
2+
2
Fig. 3 Molecular structures of the isolated [(BS) bPy] cation and ILs based on
this cation.
sence of [(PS)
from 10 to
2
bPy][OTf]
2
. When the amount of IL dropped
5
mol%, the yield of 2-dihydro-1-phenyl-
naphtho[1,2-e][1,3]oxazine-3-one could still reach as high as
2%. When [PSPy][HSO ] was used as a catalyst, the yield was
naphtho[1,2-e][1,3]oxazine-3-one was in good agreement with
the acidity order determined by the Hammett method.
9
4
only 80% (85% reported by Fang et al.). It is very interesting
that the sequence of catalytic activity of SO H-functionalized
ILs observed in the synthesis of 1,2-dihydro-1-phenyl-
Therefore, [(PS)
for further investigation.
2 2
bPy][OTf] was chosen as the model catalyst
3
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Table 2 The geometry parameters of isolated cations and bi-SO
3
H-functionalized ILs
+
[
(PS)
2
bPy]
[(PS)
2
bPy][H
2
4
PO ]
2
[(PS)
2
bPy][HSO
4
]
2
2 2
[(PS) bPy][OTf]
H–O bond distance (Å)
H
H
48–O47 = 1.005
46–O45 = 1.006
H
H
H
H
H
H
H
H
46–O45 = 1.131
48–O47 = 1.147
H
H
H
H
H
H
H
H
H
H
46–O45 = 1.105
48–O47 = 1.088
H
H
H
H
H
H
H
H
H
H
46–O45 = 1.063
48–O47 = 1.073
…
…
…
…
…
…
…
Distance between the anion and the sulfonic acid group (Å)
Other hydrogen bonds in the ILs (Å)
48
46
36
O
O
O
50 = 1.306
52 = 1.456
55 = 2.297
48
46
26
18
16
35
32
O
O
O
O
O
O
O
51 = 1.435
48
46
35
O
O
O
52 = 1.495
62 = 1.530
53 = 2.314
…
…
…
…
…
…
58 = 1.388
52 = 2.150
54 = 2.474
54 = 2.181
57 = 2.242
57 = 2.770
…
…
9
O
O
O
50 = 2.558
6
O
53 = 2.596
…
O51 = 2.203
…
…
27
27
52 = 2.472
62 = 2.201
6
…
27
18
18
O
O
O
63 = 2.173
63 = 2.612
64 = 1.979
…
…
…
6
O
57 = 2.392
+
[
(BS)
2
bPy]
[(BS)
2
bPy][H
2
4
PO ]
2
[(BS)
2
bPy][HSO
4
]
2
2 2
[(BS) bPy][OTf]
H–O bond distance (Å)
H
H
43–O42 = 0.989
54–O53 = 0.989
H
H
H
H
H
H
H
H
43–O42 = 1.209
54–O53 = 1.204
H
H
H
H
H
H
H
H
H
H
H
43–O42 = 1.141
54–O53 = 1.105
H
H
H
H
H
H
H
H
H
H
H
H
43–O42 = 1.084
54–O53 = 1.074
…
…
…
Distance between the anion and the sulfonic acid group (Å)
Other hydrogen bonds in the ILs (Å)
43
54
47
17
29
O
O
O
O
O
55 = 1.424
64 = 1.226
58 = 2.162
58 = 1.778
59 = 2.120
54
43
57
56
17
14
30
O
O
O
O
O
O
O
39 = 1.399
43
54
29
56
30
O
O
O
O
O
35 = 1.340
49 = 1.573
50 = 1.975
50 = 2.444
48 = 2.322
…
…
…
…
…
…
…
…
…
…
…
…
…
…
34 = 1.330
35 = 2.670
35 = 2.642
35 = 1.890
36 = 1.935
38 = 2.079
…
…
5
O
59 = 1.697
9
O
O
O
O
O
48 = 2.004
…
…
…
…
64
65
17
14
36 = 2.655
36 = 2.725
36 = 1.871
37 = 1.911
…
6
6
O
38 = 2.647
40 = 1.812
…
O
To extend the preparative utility and generality of this MCR,
several experimental trials illustrating this method for the
synthesis of aromatic-condensed oxazinone derivatives were
conducted. The results are summarized in Table 3.
Benzaldehyde and other aromatic aldehydes containing
electron-withdrawing groups (halide groups) or electron-
donating groups (such as hydroxy, alkoxyl groups) were
employed and were found to react well to give the correspond-
Fig. 4 Synthesis of 1,2-dihydro-1-phenylnaphtho[1,2-e][1,3]oxazine-3-one using different ILs.
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Table 3 Synthesis of various naphthalene-condensed oxazinone derivatives
Table 3 (Continued)
catalyzed by the IL [(PS)
2
bPy][OTf]
2
a
Entry
7
R
Product
Yield (%)
a
Entry
1
R
Product
Yield (%)
92
4-OCH
3
92
H
2
3
2-Cl
4-Cl
94
91
a
Isolated yield. Reaction conditions: 150 uC, 60 min, 5 mol%
bPy][OTf]
[
(PS)
2
2
.
ing 1,2-dihydro-1-arylnaphtho[1,2-e][1,3]oxazine-3-ones in
good yields.
It is well-known that the stability and reusability of a
catalyst system are the two key factors that identify whether it
has potential applications in industry. In order to test the
catalyst reusability, the reaction was carried out in the
presence of [(PS) bPy][OTf] (5 mol%) under the optimal
2
2
reaction conditions to synthesize 1,2-dihydro-1-phenyl-
naphtho[1,2-e][1,3]oxazine-3-one. When the reaction finished,
the mixture was cooled to room temperature and washed with
distilled water, then recrystallized from EtOAc–hexane (1 : 3)
4
4-Br
92
to afford the pure product. The catalyst was soluble in H O
2
and could be recovered and reused conveniently after heat
treatment under vacuum at 70 uC for 2 h. The recovered rate of
the catalyst could reach 95–98%. The results are shown in
Fig. 5, and indicated that the isolated yield of the product 1,2-
dihydro-1-phenylnaphtho[1,2-e][1,3]oxazine-3-one was almost
5
4-F
94
consistent after eight runs and [(PS)
reused at least eight times.
2 2
bPy][OTf] could be
Conclusions
3
Several bi-SO H-functionalized room temperature ILs have
been synthesized, and their catalytic performances for the
synthesis of naphthalene-condensed oxazinone derivatives
have been studied by a combination of experimental and
computational techniques. An easier synthesis procedure,
reduced amount of catalyst, higher yield, wider applicability
and reusability are the key features of this methodology. The
results obtained from the experiments and the minimum-
6
4-OH
82
3
energy geometries of bi-SO H-functionalized ILs revealed that
the acidity and catalytic activity of ILs in the synthesis of
naphthalene-condensed oxazinone derivatives were influence
by their structures. The ILs with shorter H–O bond distances
had stronger acidity and higher catalytic activity. These
conclusions will be helpful for the detailed understanding of
3
these bi-SO H-functionalized ILs and will contribute to the
design and synthesis of ILs in a ‘‘task specific’’ way.
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2 2
Fig. 5 Reusability of the IL [(PS) bPy][OTf] .
[
(PS)
colorless liquids.
,49-Bis(4-sulfobutyl) bipyridinium bis(hydrogen sulfate)
[(BS) bPy][HSO ] ), 4,49-bis(4-sulfobutyl) bipyridinium bis(hy-
2 4 2 2 2 4 2 2 2
bPy][HSO ] , [(PS) bPy][H PO ] and [(PS) bPy][OTf] were
Experimental
Synthesis and characterization of ILs
4
(
4,49-Bis(3-sulfopropyl) bipyridinium ((PS) bPy): 4,49-bipyridine
2
4 2
2
drogen sulfate) ([(BS)
bipyridinium bis(trifluoromethanesulfonate) ([(BS) bPy][OTf] ):
under strong vigorous stirring, (BS) bPy (0.01 mol) was dissolved
2
2 2 4 2
bPy][H PO ] ), 4,49-bis(4-sulfobutyl)
(
1.56 g, 0.01 mol) and dimethyl sulfoxide (10 ml) were placed
in a three necked flask with a stirrer. Then 1,3-propane sultone
3.05 g, 0.025 mol) was added slowly within 5 min. After that,
2
2
(
into water (10 ml). 0.02 mol sulfuric acid, phosphoric acid or
trifluoromethanesulfonic acid was dropped slowly into it at room
temperature. After the dropping, the solution was slowly heated up
to 90 uC and stirred for 2 h, then the water was removed under
the reaction mixture was stirred for 6 h at 80 uC. The reaction
mixture was distilled under reduced pressure to remove
dimethyl sulfoxide, then washed with ether five times and
dried at 100 uC for 3 h. The final product (PS) bPy was a white
2
powder.
vacuum at 70 uC for 3 h. The final products [(BS)
(BS) bPy][H PO and [(BS) bPy][OTf] were colorless liquids.
IR spectra and H NMR spectra data for novel bi-SO
functionalized ILs were shown as follows:
2 4 2
bPy][HSO ] ,
[
2
2
4
]
2
2
2
4
,49-Bis(4-sulfobutyl) bipyridinium ((BS) bPy): 4,49-bipyri-
2
1
H-
dine (1.56 g, 0.01 mol) and dimethyl sulfoxide (10 ml) were
placed in a three necked flask with a stirrer. Then 1,4-butane
sultone (3.40 g, 0.025 mol) was added slowly within 5 min.
After that, the reaction mixture was stirred for 6 h at 80 uC. The
reaction mixture was distilled under reduced pressure to
remove dimethyl sulfoxide, then washed with ether five times
3
2
1
[
(PS)
510, 1452, 1243, 1043, 612. H NMR (500 MHz, D
m, 4H, CH CH CH ), 2.90 (t, 4H, CH SO H), 4.78 (t, 4H,
NCH CH ), 8.44 (d, 4H, py), 9.03 (d, 4H, py).
2 4 2
bPy][HSO ] : IR (KBr, n/cm ): 3433, 3052, 1640, 1566,
1
1
(
2
O) d: 2.40
2
2
2
2
3
2
2
2
1
[
(PS) bPy][H PO ] : IR (KBr, n/cm ): 3429, 3062, 1634, 1559,
and dried at 100 uC for 3 h. The final product (BS)
2
bPy was a
2 2 4 2
1
1
507, 1441, 1224, 1031, 616. H NMR (500 MHz, D
m, 4H, CH CH CH ), 2.85 (t, 4H, CH SO H), 4.76 (t, 4H,
NCH CH ), 8.42 (d, 4H, py), 9.01 (d, 4H, py).
2
O) d: 2.38
white powder.
(
2
2
2
2
3
4
,49-Bis(3-sulfopropyl) bipyridinium bis(hydrogen sulfate)
[(PS) bPy][HSO ), 4,49-bis(3-sulfopropyl) bipyridinium
bis(hydrogen sulfate) ([(PS) bPy][H PO ] ), 4,49-bis(3-sulfopro-
(
2
4
]
2
2
2
2
1
[
(PS) bPy][OTf] : IR (KBr, n/cm ): 3532, 3058, 1640, 1560,
2 2
2
2
4 2
1
1
495, 1452, 1286, 1033, 643. H NMR (500 MHz, D
2
O) d: 2.37
pyl) bipyridinium bis(trifluoromethanesulfonate) ([(PS)
2
bPy]
(
m, 4H, CH CH CH ), 2.85 (t, 4H, CH SO H), 4.73 (t, 4H,
2
2
2
2
3
[
OTf] ): under strong stirring, (PS) bPy (0.01 mol) was
2
2
NCH CH ), 8.39 (d, 4H, py), 9.01 (d, 4H, py).
dissolved in water (10 ml). 0.02 mol sulfuric acid, phosphoric
acid or trifluoromethanesulfonic acid was dropped slowly into
it at room temperature. After the dropping, the solution was
heated up to 90 uC slowly and stirred for 2 h, then water was
removed under vacuum at 70 uC for 3 h. The final products
2
2
2
1
[(BS)
bPy][HSO ] : IR (KBr, n/cm ): 3431, 3065, 1639, 1556,
4 2
2
1
1506, 1446, 1236, 1058. 616. H NMR (500 MHz, D
2
O) d: 1.88
(m, 4H, CH CH CH ), 2.28 (m, 4H, NCH CH ), 3.02 (t, 4H,
2
2
2
2
2
This journal is ß The Royal Society of Chemistry 2013
RSC Adv., 2013, 3, 9965–9972 | 9971

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Paper
RSC Advances
CH SO H), 4.81 (t, 4H, NCH CH ), 8.58 (d, 4H, py), 9.15 (d, 4H,
3 T. Welton, Chem. Rev., 1999, 99, 2071.
2
3
2
2
py).
(BS)
506, 1445, 1234, 1060, 617. H NMR (500 MHz, D
m, 4H, CH CH CH ), 2.30 (m, 4H, NCH CH ), 3.04 (t, 4H,
H), 4.83 (t, 4H, NCH CH ), 8.60 (d, 4H, py), 9.18 (d, 4H,
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1
[
2 2 4 2
bPy][H PO ] : IR (KBr, n/cm ): 3430, 3065, 1640, 1554,
1
1
(
2
O) d: 1.89
5
962.
M. Kumar, K. Sharma and A. K. Arya, Tetrahedron Lett.,
012, 53, 4604.
2
2
2
2
2
6
CH
2
SO
3
2
2
2
py).
(BS)
506, 1447, 1275, 1060, 638. H NMR (500 MHz, D O) d: 1.87
2
1
7 S. Safaei, I. Mohammadpoor-Baltork, A. R. Khosropour,
M. Moghadam, S. Tangestaninejad, V. Mirkhani and
R. Kia, RSC Adv., 2012, 2, 5610.
[
2 2
bPy][OTf] : IR (KBr, n/cm ): 3432, 3049, 1641, 1561,
1
1
2
(
m, 4H, CH CH CH ), 2.28 (m, 4H, NCH CH ), 3.03 (t, 4H,
2 2 2 2 2
8
D. Fang, C. M. Jiao and C. J. Ni, Heteroat. Chem., 2010, 21,
46.
CH SO H), 4.81 (t, 4H, NCH CH ), 8.59 (d, 4H, py), 9.15 (d, 4H,
2
3
2
2
5
py).
UV-vis acidity evaluation
ILs were dissolved into distilled H
9
X. D. Sun, H. Q. Xiao, Y. J. Du, J. J. Zhang, X. Z. Liang and C.
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1
0 X. Z. Liang and J. G. Yang, Green Chem., 2010, 12, 201.
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O and characterized by UV-
vis spectra with an Agilent B453 spectrophotometer.
Computational methods
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475.
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Catal. A: Chem., 2010, 322, 7.
2
The minimum-energy geometries of bi-SO
3
H-functionalized
+
+
ILs and isolated [(PS) bPy] , [(BS) bPy] cations were deter-
2 2
mined by performing ab initio geometry optimizations at the
RHF/6–31(d, p) level using the Gaussian 03 program. A
vibrational analysis was performed to ensure the absence of
negative frequencies and to verify the existence of a true
minimum.
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1
1
5 L. Weber, Drug Discov. Today, 2002, 7, 143.
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7 A. Domling and I. Ugi, Angew. Chem., Int. Ed., 2000, 39,
General procedure for the synthesis of oxazinone derivatives
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A mixture of an aldehyde (1 mmol), 2-naphthol (1 mmol), urea
1
1
8 A. S. Girgis, Pharmazie, 2000, 466.
9 N. Latif, N. Mishriky and F. M. Assad, Aust. J. Chem., 1982,
(
1.3 mmol) and IL (5–10 mol%) was heated at 150 uC with
stirring for one hour. After the completion of the reaction
monitored by TLC), the reaction mixture was cooled to room
3
5, 1037.
0 Y. Wang, X. Li and K. Ding, Tetrahedron: Asymmetry, 2002,
3, 1291.
(
2
2
temperature and washed with distilled water, then recrystal-
lized from EtOAc–hexane (1 : 3) to afford the pure product.
1
1 H. A. Ahangar, G. H. Mahdavinia, K. Marjani and
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Acknowledgements
The authors gratefully acknowledge the National Natural
Science Foundation of China (Nos. 21003049, 21073064) and
the Fundamental Research Funds for the Central Universities
for financial support.
2
4 A. Davoodnia, M. M. Heravi, L. Rezaei-Daghigh and
N. Tavakoli-Hoseini, Monatsh. Chem., 2009, 140, 1499.
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972 | RSC Adv., 2013, 3, 9965–9972
This journal is ß The Royal Society of Chemistry 2013