Ionic liquid brush as an efficient and reusable heterogeneous catalytic assembly for the tosylation of phenols and alcohols in neat water

Article abstract of DOI:10.1039/c7nj00141j

A very efficient and reusable heterogeneous ionic liquid brush assembly was developed. The catalyst exhibits high catalytic activity for the tosylation of phenols and alcohols in neat water. Moreover, the catalyst shows outstanding stability and reusability, and it can be simply and effectively recovered and reused five times without noticeable loss of catalytic activity.

Full text of DOI:10.1039/c7nj00141j

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ISSN 1144-0546
PAPER
Jason B. Benedict et al.
The role of atropisomers on the photo-reactivity and fatigue of
diarylethene-based metal–organic frameworks
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Ionic Liquid Brush as an Efficient and Reusable Heterogeneous
Catalytic Assembly for Tosylation of Phenols and Alcohols in Neat
Water
Received 00th January 20xx,
Accepted 00th January 20xx
Simin Feng,a Jing Li*a and Junfa Wei*a,b
DOI: 10.1039/x0xx00000x
www.rsc.org/
waterꢀsolvent reactions from the standpoint of green chemistry.28ꢀ
A very efficient and reusable heterogeneous assembly of ionic
liquid brush has been developed. The catalyst exhibits high
catalytic activity for tosylation of phenols and alcohols in neat
water. Moreover, the catalyst shows outstanding stability and
reusability, and it can be recovered simply and effectively and
reused five times without noticeable loss of the catalytic activity.
32
However, water is still not commonly used as the sole solvent
for organic transformations in the laboratory and in industry due
to the limited water solubility of organic substrates.33 In the past
decade, although there have been several synthetic methods for
tosylation of phenols and alcohols, to the best our knowledge, the
reported procedures for these variants in water to date have been
rather routine. Tanabe34 reported an effective tosylation of
alcohols in water promoted by KOH and catalytic amines, but it
The pꢀtoluenesulfonylation (tosylation) of alcohols and phenols
has long been recognized as fundamental processes in various
fields of organic syntheses.1ꢀ3 The resulting tosylates are useful
building blocks as well as key intermediates in organic synthesis4ꢀ9 required control of the pH of water to prevent hydrolysis of
and various tosylates have important pharmacological TsCl (Figure 1a). Another procedure reported by Matsubara35
pꢀ
properties.10ꢀ13 In the past decate, impressive efforts have been
devoted to prepare tosylates utilizing various reaction systems
involved solventꢀfree synthesis,14ꢀ16 heteropolyacid17 or metalꢀ
with Nꢀhexadecylimidazole as an efficient homogenous catalyst in
water seems to be attractive, because they supposed that
aggregation of the amphiphilic catalyst carrying a hydrophobic
methylene chain would work as a substitute for organic solvent
(Figure 1b). However, the catalyst was difficult to separate from
catalyzed18ꢀ21 tosylation, and reaction of alcohols with
toluenesufonic acid
ꢀTsOH) using silica chloride22 or
CoCl ·6H
construction of tosylates is treatment of alcohols and phenols with
ꢀtoluenesulfonyl chloride ( ꢀTsCl) in the presence of an amine
base, such as pyridine,3 Et N·HCl, 24 Me 25or
N/Me N(CH NMe
pꢀ
(p
2
2
O23 as catalyst. The most common procedure for the the reaction product, which limits its recycling. Thus there is still
a need to develop more efficient and environmentally friendly
catalysts and procedures for the tosylation transformations.
p
p
3
3
2
2
)n
2
BnNMe2
DABCO26ꢀ27 in an anhydrous organic solvent such as
dichloromethane, acetonitrile or toluene. Although the reaction
systems were well designed, these methods suffer from difficulty
in excess amount of amine, undesired side reaction, complex
workup procedures and organic solvents, which would lead to
chemical waste.
Green. Chem
by Y. Tatabe
ref. 34
a
n-C16H33
N
N
b
c
ROTs
+
ROH
p-TsCl
Org. Lett
by S. Matsubara
ref. 35
ILs Brush
Over the past few years, considerable attention has been paid to
this work
Cl-
OEt
Si
O
O
OH
Cl-
N
SiO2
N
N
C8H17-n
ILs Brush =
N
SiO2-BisILsC8H17[Cl]
Fig. 1. Tosylation of phenols and alcohols in neat water.
Recently, our group designed and synthesized a series of
SiO2ꢀsupported bisꢀlayered ionic liquids (ILs) bearing two
imidazolium ions on each of the side chains. We call them
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“ionic liquid brushes” because of their brushꢀlike feature room temperature for 3 h; no any organic coꢀsolvents or other
(Figure 1c). The brush extends the immobilized ILs to the additives were employed. The results are listed in Table 1.
upper spaces outside the surface of SiO2, forming an
Table 1. The brushꢀcatalyzed tosylation of phenol with
water under various conditions.a
pꢀTsCl in
immobilized bisꢀlayered ILs possessing more prominent 3D
characters resembling that of the free ionic liquids. In
comparison with the monolayer ILs, we expect our
immobilized bisꢀlayered ILs, should act as highly active
catalysts, cocatalysts or supports based on the following
points: (1) deeper 3D microenvironment and more flexibility
of the longer branched chains containing imidazoliums for
more molecules of substrates and reagents to be
accommodated; (2) adjustable hydrophobicity for the
substrates and reagents to “be dissolved” in and for the
product and sideꢀproduct to move out of the brushes, and (3)
ability to perform the reaction under organic solventꢀfree
condition or in water without the addition of any phase
transfer catalysts. Based upon such an idea, we have found
that the ionic liquid brush displayed excellent activity and
excellent reusability in several organic transformations with
water as a sole solvent.36ꢀ37Herein, we wish to describe our
preliminary results of the brush as an efficient and reusable
catalyst for tosylation of phenols and alcohols in water.
Entry
Catalyst (mol%)b
Base
Yield (%)c
1
2
ꢀ
Na
2
2
2
2
2
CO
3
3
3
3
3
52
74
85
95
99
68
84
63
72
80
0.5
1.0
1.5
2.0
2.0
2.0
2.0
2.0
10
Na
Na
Na
Na
CO
CO
CO
CO
3
4
5
6
NaHCO
NaOH
3
7
8
Et
DABCO
CO
3N
9
10d
K
2
3
a Conditions: phenol (2 mmol),
O (4 mL) with the brush as catalyst. b Based on the imidazolium
pꢀTsCl (2.4 mmol), base (2 mmol),
H
2
ions. c Isolated yield. d Nꢀexadecylimidazole as catalyst reported in
literature.35 DABCO = 1,4ꢀDiazabicyclo[2.2.2]octane.
The brush catalyst SiO
2
ꢀBisILsC8H17[Cl] was synthesized
through a threeꢀstep route according to the procedure we
previously reported.36ꢀ37 The catalyst of ionic liquid brushes
assembly was prepared via coordination linkage between
As can be seen, the present brush catalyst with
terminal alkyl group was efficient for the tosylation of phenol
with ꢀTsCl in water. In sharp contrast, the control experiment
nꢀoctyl as the
immobilized ionic liquid brushes using cheap SiO
2
as
p
supporter. BET analysis showed the brush has a SBET of 181
m2/g. Elemental analysis reveals that there are 1.27 mmol/g
of imidazolium ions loaded on the dilayer ionic liquid brush,
nearly two times the amount of imidazolium ions on its
monolayer analogue. The brush is stable to air and moisture.
without the catalyst gave the corresponding product in a rather
low yield of 52%, which indicated that the catalyst played an
important role in the reaction (Table 1, Entry 1). The yields of
product increased with the addition of catalyst (Table 1, Entry 2ꢀ
5). A loading of 2.0 mol% (2 mmol imidazolium loaded on the
brush catalyst/100 mmol substrate) of the brush catalyst showed
great efficiency to the reaction, giving the desired product in
nearly quantitative yield without detectable unwanted product
(Table 1, Entry 5), in contrast to the reported yield of 80% for the
same reaction catalyzed by 0.1 equiv. (10 mol% with respect to
substrate) of
Other bases such as NaHCO
N
ꢀhexadecylimidazole in water (Table 1, Entry 10)35.
3
, NaOH, Et N and DABCO were also
3
investigated, but lower yields of the products were obtained
(Table 1, Entry 6ꢀ9). Finally, the most suitable reaction conditions
were defined as 1.2 equivalents of
pꢀTsCl to phenols or alcohols in
the presence of 1 equivalents of Na
2
CO as an inorganic base
3
under 2.0 mol% of the catalyst at room temperature for 3 h.
To investigate the catalytic ability of the brush to act as
catalysts on the tosylation of phenols and alcohols, different
phenols and
Fig 2. Synthetic route of the brush catalyst.
Initially, we employed the tosylation reaction of phenol with pꢀ
TsCl as a prototypical reaction for discovery of suitable reaction
conditions and the examination of the catalytic activity in neat
water. All of the reactions were carried out by simply stirring a
Table 2 Organic solventꢀfree tosylation of phenols with the brush
as a catalyst.a
mixture of the catalyst, phenol, pꢀTsCl and a base in neat water at
2 | J. Name., 2012, 00, 1-3
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Table 3 Organic solvent free tosylation of alcohols with the brush
as a Catalyst.a
Entry
R
H
Yield (%)b
1
2
99
94
99
91
92
96
4ꢀCH
4ꢀCl
3
Entry
ROH
Yield (%)b
3
1
2
42
57
4
2ꢀNO
4ꢀNO
2
2
5
6c
3
4
5
6
54
69
66
79
4ꢀOH
7
94
a
conditions: The brush (0.04 mmol, based on imidazolium
ꢀTsCl (2.4 mmol), Na CO (2 mmol),
O (4 mL). b Isolated yields. c The brush (0.08 mmol, based on
imidazolium ions), alcohol (2 mmol), ꢀTsCl (4.8 mmol),
Na CO (4 mmol), H O (4 mL).
ions), phenol (2 mmol),
p
2
3
7
55
H
2
8
9
91
82
p
2
3
2
alcohols were mixed with pꢀTsCl in the presence of the brush to
10
73
form the tosylates in neat water. As shown in Table 2, various
phenols bearing electronꢀdonating or electronꢀwithdrawing
substituents were applied to this protocol and the desired
products were obtained in good to excellent yields.
11
12
49c
66c
49c
61a
13
14
Under this organic solventꢀfree condition, a series of alcohols
81
were next pursued with pꢀTsCl into the corresponding tosylates.
As shown in Tables 3, by using the brush as the catalyst, primary,
secondary, benzylic alcohols were all successfully converted to
the corresponding tosylates. In the case of the aliphatic alcohols,
primary alcohols were tosylated in excellent yields compared to
secondary alcohols. For example, 1ꢀpentanol, 3ꢀmethylꢀ1ꢀbutanol,
1ꢀhexanol, 1ꢀoctanol, cyclohexylmethanol and 2ꢀphenylethanol
were transformed into the corresponding tosylates in 66ꢀ91%
yields (Table 3, entries 4ꢀ6, 8, 10 and 14), whereas cyclohexanol
and 2ꢀoctanol were less reactive, which afforded tosylates in only
55% and 82% yields, respectively (Table 3, entry 7 and 9). We
attribute the low yields of ethanol, 1ꢀbutanol and 2ꢀbutanol to
their solubility in water (Table 3, entries 1ꢀ3). Due to the mild
reaction conditions, dihydric alcohols also afforded the
corresponding tosylates (Table 3, entries 11ꢀ13). For unsymmetric
15
16
17
18
19
20
21
R = H
61
95c
77
80
82
89
92
R = 4ꢀOH
R = 4ꢀCl
R = 2ꢀBr
R = 4ꢀBr
R = 2ꢀNO
R = 4ꢀNO
2
2
a
Conditions: The brush (0.04 mmol, based on imidazolium
ions), alcohol (2 mmol), ꢀTsCl (2.4 mmol), Na CO (2 mmol),
O (4 mL). b Isolated yields. c The brush (0.08 mmol, based on
imidazolium ions), alcohol (2 mmol), ꢀTsCl (4.8 mmol),
Na CO (4 mmol), H O (4 mL).
p
2
3
H
2
p
2
3
2
The present heterogeneous catalysts have an advantage that at
the end of reaction the catalyst can be removed from the reaction
stream by simple filtration. To investigate the recyclability of the
diol, such as butaneꢀ1,3ꢀdiol, when 2.4 equivalents of
used, afforded the corresponding product at both primary and
secondary side in 49 % yield; when 1.2 equivalents of ꢀTsCl was
pꢀTsCl was
brush, we carried out the reaction of phenol with
pꢀTsCl
p
repeatedly under the optimized conditions. It is noteworthy that
at the end of the reaction the present catalyst can be recovered by
a simple filtration of the reaction solution and recycled five times.
In every case, the catalyst was only recovered by filtration and
washed with ethyl acetate and water, then the experiment
repeated. The result showed almost no significant reduction in
high yields (96ꢀ99 %) (Figure 3). Elemental analysis reveals that
the brush catalyst after 5th cycle has nearly the same content of
nitrogen on the brush. The infrared spectral analysis shows the
main absorption peaks remain unchanged as compared with the
fresh catalyst. All these results indicate the brush catalyst is stable
used, the tosylate almost generated at the primary side in 61 %
yield. Benzylic alcohols, such as benzyl, 4ꢀhydroxybenzyl, 4ꢀ
chlorobenzyl, 2ꢀbromobenzyl, 4ꢀbromobenzyl, 2ꢀnitrobenzyl, 4ꢀ
nitrobenzyl alcohols were all converted to the corresponding
tosylates in 61%ꢀ95% yields (Table 3, entries 15ꢀ21). However,
tertiary alcohol such as
tꢀBuOH was converted to the
corresponding tosylate in less than 10% yield, along with some
undesired impurities, which lead to difficult to isolate and purify
the final product.
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in the reaction. The high recyclability of this catalytic system 11 S. Ullah, M. Saeed, S. Ullah, M. Saeed, S. M. A. Halimi, M.
allows for a more economic and environmentally friendly process.
I. Fakhri, K. M. Khan, I. Khan and S. Perveen, Med. Chem.
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99
98
97
97
96
13 A. Khodairya, S. K. Mohamedb, A. M. Ali, M. T. Elꢀ
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2
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Wassimy and N. S. Ahmed, J. Chem. Pharm. Res., 2015,
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Figure 3. The recycling of catalyst in the tosylation of phenol.
In conclusion, ionic liquid brush has been shown to be an
efficient heterogeneous catalyst for tosylation of phenols and
16 F. Kazemi, A. R. Massah and M. Javaherian, Tetrahedron
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17 R. Fazaeli, S. Tangestaninejad and H. Aliyan, Can. J. Chem.
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alcohols with pꢀTsCl in neat water. The high efficiency, simplicity
of the product isolation, outstanding recyclability, and organic
solventꢀfree and water alone condition makes the catalyst and the
process available in academic laboratories and could find
industrial applications in the future.
18 G. A. Meshram and V. D. Patil, Tetrahedron Lett., 2009, 50
1117.
19 J.ꢀG. Kim, D. O. Jang, Synlett, 2007, 2501.
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Nayyar, U. P. Dhokte, C. W. Doecke, L. M. H. Zollars, E.
Acknowledgements
This work was supported by the National Natural Science
D. Moher, V. Van Khau and B. Košmrlj, J. Am. Chem. Soc.
2002, 124, 3578.
,
Foundation of China (No. 21572124), Natural Science Basic
Research Plan in Shaanxi Province of China (Program No.
2016ZDJC-03) and the Fundamental Research Funds for the
Central Universities (No. GK201603033) are greatly appreciated.
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New Journal of Chemistry
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DOI: 10.1039/C7NJ00141J
Ionic Liquid Brush as an Efficient and Reusable Heterogeneous
Catalytic Assembly for Tosylation of Phenols and Alcohols in Neat
Water
IL Brush
+
p-TsCl
R OH
R OTs
Na2CO3, H2O, rt
R = alkyl and aryl
IL Brush =
OEt
O
Cl-
N
Cl-
N
SiO2
Si
N
C8H17-n
O
N
OH
SiO2-BisILsC8H17[Cl]
An efficient and reusable heterogeneous catalytic assembly-ionic liquid brush
was developed for tosylation of phenols and alcohols in neat water.