An efficient and selective conversion of sorbitol in ionic liquids: Use of ion exchange resin as a solid acid catalyst

Article abstract of DOI:10.1016/j.tetlet.2017.07.105

Sorbitol was readily converted by heating in hydrophobic ionic liquids by the presence of ion exchange resins. Chemoseletivity of the dehydration depended on the choice of ion exchange resin; Nafion selectively produced isosorbide while Amberlite gave 1,5-anhydrosorbitol along with unreacted sorbitol. Ionic liquids used in the reaction were readily recovered by simple extraction procedure. With these procedures, we succeeded to prepare isosorbide in pure form, not contaminated with either ionic liquids or acid catalyst, by simple experimental procedure.

Full text of DOI:10.1016/j.tetlet.2017.07.105

Accepted Manuscript
An efficient and selective conversion of sorbitol in ionic liquids: use of ion
exchange resin as a solid acid catalyst
Akio Kamimura, Kengo Murata, Takuji Kawamoto
PII:
S0040-4039(17)30974-7
DOI:
http://dx.doi.org/10.1016/j.tetlet.2017.07.105
TETL 49187
Reference:
Tetrahedron Letters
To appear in:
Received Date:
Revised Date:
Accepted Date:
23 June 2017
25 July 2017
31 July 2017
Please cite this article as: Kamimura, A., Murata, K., Kawamoto, T., An efficient and selective conversion of sorbitol
in ionic liquids: use of ion exchange resin as a solid acid catalyst, Tetrahedron Letters (2017), doi: http://dx.doi.org/
10.1016/j.tetlet.2017.07.105
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An efficient and selective conversion of
sorbitol in ionic liquids: use of ion exchange
resin as a solid acid catalyst
Akio Kamimura,* Kengo Murata and Takuji Kawamoto
Department of Applied Chemistry, Yamaguchi University, Ube 755-8611, Japan

Tetrahedron Letters
journal homepage: www.els evier.com
An efficient and selective conversion of sorbitol in ionic liquids: use of ion
exchange resin as a solid acid catalyst
Akio Kamimura,* Kengo Murata and Takuji Kawamoto
Department of Applied Chemistry, Yamaguchi University, Ube 755-8611, Japan
ARTICLE INFO
ABSTRACT
Article history:
Received
Sorbitol was readily converted by heating in hydrophobic ionic liquids by the presence of ion
exchange resins. Chemoseletivity of the dehydration depended on the choice of ion exchange
resin; Nafion selectively produced isosorbide while Amberlite gave 1,5-anhydrosorbitol along
with unreacted sorbitol. Ionic liquids used in the reaction were readily recovered by simple
extraction procedure. With these procedures, we succeeded to prepare isosorbide in pure form,
not contaminated with either ionic liquids or acid catalyst, by simple experimental procedure.
Received in revised form
Accepted
Available online
Keywords:
Ionic liquids
Biomass conversion
Sorbitol
2009 Elsevier Ltd. All rights reserved
.
Hydrophobicity
Dehydration
1. Introduction
chemoselectivity of the reaction depended on the use of the type
of resin, and achieved selective formation of isosorbide or 1,5-
anhydrosorbitol.
Conversion of biomass to valuable chemicals is of interest to
develop sustainable chemistry.1 Sorbitol is a biomass-derived
chemicals and its conversion to isosorbide is an important
reaction for this purpose.2 The conversion is usually achieved by
heating sorbitol by the presence or absence of an appropriate
catalyst. However, the reaction usually requires high temperature
conditions and long reaction time, the energy consumption of the
process becomes a considerable problem. It is desired to shorten
the reaction time as well as efficient energy delivery to the
reaction pot is required. Ionic liquids are regarded as a novel
reaction solvent for chemical conversions because they have very
unique properties that were never observed in any other solvent.3
The ionic liquids are recyclable and regarded as a green solvent
in the chemical reaction. We recently developed a new use of
ionic liquids for feedstock recycling chemistry and achieved
efficient depolymerization of polyamides and unsaturated
polyesters.4 We also achieved an efficient chemical conversion of
cellulose to glucose.5 We employed hydrophobic ionic liquids for
these purposes because of high iconicity6 that enhanced the
reactivity of the reaction and ready separation of products and
ionic liquids by simple extraction manipulation. For example,
glucose without contamination of ionic liquids was readily
isolated by our procedure.7 This is a point that our methodology
was superior to other methodologies that usually use hydrophilic
ionic liquids. To improve the methodology, we thought that use
of insoluble acid would give simple separation of acid catalyst.
There are many types of ion exchange resin that have been used
in organic synthesis. In this paper we report use of ion exchange
resin for the conversion of sorbitol to isosorbide. We found
2. Results and discussion
We used three types of acidic ion exchange resins, Nafion,
Dowex, and Amberlite, which were readily available
commercially. We first examined Nafion as the catalyst. The
conversion
was
performed
in
[TMPA][NTf2]
(trimethylpropylammmonium bis(trifluoromethylsulfonyl)imide,
Me3NPr+ Tf2N–), a hydrophobic ionic liquid, by the presence of
20 wt% Nafion NR50 (Scheme 1). The results are summarized in
Table 1.
Scheme 1
Table 1. Conversion of sorbitol 1 by the presence of Nafion.
entry
temp (°C) time
(min)
2; yield
(%)a,b
3; Yield
(%)a
0
1
2
3
4
5
180
150
200
230
180
10
10
10
10
20
65c (9)
30 (28)
41 (7)
34 (8)
53 (5)
23
3
2
0
a. Determined by HPLC analyses. b. Recovery of the starting
material 1 is in parentheses. c. Isolated yield.

Sorbitol was smoothly converted into isosorbide 2 in 65%
yield by treatment with [TMPA][NTf2] in the presence of 20 wt%
of Nafion, although small amounts of sorbitol 1 remaining was
detected after the reaction (entry 1).8 The reaction progressed
very fast under these conditions and was almost complete within
10 minutes. When the reaction temperature was set to 150 °C, the
reaction rate was decelerated and the yield of isosorbide 2
decreased to 30% along with 28% of remaining sorbitol 1. Note
that the formation of 1,5-anhydrosorbitol 3 increased to 23%
(entry 2). Higher reaction temperature did not change the results
very much and isosorbide 2 was formed in slightly lower yields
(entries 3 and 4). This is probably due to the decomposition of
isosorbide during the reaction because of too high temperature
conditions. To consume all of sorbitol we exposed the reaction
mixture for 20 minutes, but the results were not very different.
of the change of the selectivity, but 1,5-anhydrosorbitol tends to
become the major products when sorbitol 1 was treated less
acidic or much milder conditions. For example, simple heating
conditions conducted compound 3 as the kinetic product.
Treatment of sorbitol 1 at lower temperature also formed 3 as a
side product (Table 1, entry 2). We assume that the selective
formation of 3 occurred because Amberlite is less acidic catalyst
than Nafion and offers much milder conditions.
In the end, we examined reuse of the ionic liquids and the
resin catalyst (Scheme 3).
Isolation and purification of isosorbide 2 was very simple. The
reaction mixture was diluted with water and then filtered to
remove resin catalyst. The filtrate was then extracted with
organic solvent to remove the ionic liquids. The recovery of ionic
liquids reached 98% after drying and evaporation of the organic
solvent. 13C NMR spectrum of the recovered ionic liquids
indicated a sharp quartet signal coming from the NTf2 group.
This result clearly suggested that the group survived during the
manipulation and its amounts was maintained in almost the same
level of the virgin ionic liquids. Finally concentration of the
remaining water phase in vacuo afforded desired isosorbide 2 in
almost pure form.
Scheme 3
Unfortunately the recovered ionic liquids provided sluggish
progress of the reaction and isosorbide 2 was obtained only 38%
yield. Note that we observed the formation of 1,5-
anhydrosorbitol in 38% yield. We are not sure the reason why the
recovered ionic liquids did not work well for the conversion
although the recovered ionic liquids showed almost complete
spectra in 13C NMR. The reuse of the resin catalyst was not
effective because the reaction did not progressed well and most
of sorbitol 1 remained in the reaction mixture. This is probably
because Nafion was decomposed during the first reaction and the
catalytic activity as an acid was spoiled. Or the cation exchange
between [TMPA] cation and proton could progress in the resin
surface, and this exchange spoiled the reactivity of recovered
Nafion. So we concluded that recycling use of ionic liquids is not
really effective and the acid resin tolerates only one-time use.
Even so, we feel the present modification is effective because
almost pure isosorbide was obtained by simple extraction and
filtration manipulation.
We then examined DOWEX HCR W-2 and Amberlite IR-
120B for the reaction (Scheme 2). The results are summarized in
Table 2.
Scheme 2
Table 2. Conversion of sorbitol 1 by the presence of DOWEX
or Amberlite.
entry
resin
pre-
treatment
-
2; Yield
(%)a,b
3; Yield
(%)a
0
In conclusion, we examined effective conversion of sorbitol to
isosorbide, an important reaction of biomass conversion, under
various conditions. Ionic exchange resin, especially Nafion,
serves as an effective catalyst for the conversion and almost pure
isosorbide was isolated in 65% by simple manipulation. The
present methodology avoids contamination of acid catalysis such
as TsOH in the product. Less acidic resin prefers to form 1,5-
anhydrosorbitol selectively. This information will give important
information for further improvement of the reaction.
1
2
3
4
5
DOWEX
Amberlite
DOWEX
DOWEX
Amberlite
0 (100)
0 (100)
50 (1)
0 (100)
5 (32)
-
0
18
0
6M HCl
AcOH
1M HCl
62
a. Determined by HPLC analyses. b. Recovery of the starting
material 1 is in parentheses.
We firstly examined the both resin for the reaction, but no
formation of isosorbide was observed (entries 1 and 2). This was
probably because their capability as an acid catalysis was not
sufficient to promote the reaction progress. To enhance the
activity as the acid catalysis, we pretreated the resins with acid.
Treatment of DOWEX with HCl enhanced the catalytic activity
to consume sorbitol 1 quickly and desired isosorbide 2 was
obtained in 50% along with the formation of 1,5-anhydrosorbitol
3 in 18% yield (entry 3). On the other hand pretreatment with
acetic acid did not enhance the catalytic activity and no reaction
occurred under the same conditions (entry 4). Pretreatment of
Amberlite with HCl also improved the activity, however, 1,5-
anhydrosorbitol 3 was formed as the major product in this
reaction although starting sorbitol 1 remained in 32% (entry 5). It
was interesting that changing the resin catalyst controlled the
chemoselectivity of the reaction. We are not sure the exact reason
Acknowledgments
This work was partially supported by Grant-in-Aid for
Scientific Research (A) (24241023).
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1
sorbitol 2 in 65% yield (98.4 mg). H NMR (500 MHz, D2O) δ
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- Efficient conversion of sorbitol to isosorbide in
hydrophobic ionic liquids.
- Microwave heating achieved very rapid
conversion.
- perfect separation of product from ionic liquids
and catalyst was accomplished by simple extraction
manipulation.