Cyclization of alkanediols in high-temperature liquid water with high-pressure carbon dioxide

Article abstract of DOI:10.1016/j.cattod.2011.07.025

Dehydration of 1,4-butanediol (1,4-BDO) to tetrahydrofuran (THF), 2R,5R-hexanediol (2R,5R-HDO) to 2,5-dimethyltetrahydrofuran (2,5-DMTHF), and 2,5-dimethyl-2,5-hexanediol (2,5-DM-2,5-HDO) to 2,2,5,5- tetramethyltetrahydrofuran (2,2,5,5-TMTHF) proceeded in high-temperature liquid water at 523 K. The formation rates of cyclic ethers were enhanced by high-pressure carbon dioxide (16.2 MPa). The order of dehydration rates in high-temperature water with carbon dioxide was 2,5-DM-2,5-HDO > 2R,5R-HDO > 1,4-BDO (tertiary > secondary > primary alcohols), which was the same order as the stability of corresponding carbocation species.

Full text of DOI:10.1016/j.cattod.2011.07.025

Catalysis Today 185 (2012) 302–305
Contents lists available at ScienceDirect
Catalysis Today
journal homepage: www.elsevier.com/locate/cattod
Cyclization of alkanediols in high-temperature liquid water with high-pressure
carbon dioxide
Aritomo Yamaguchi, Norihito Hiyoshi, Osamu Sato, Masayuki Shirai∗
Research Center for Compact Chemical System, National Institute of Advanced Industrial Science and Technology (AIST), 4-2-1 Nigatake, Miyagino, Sendai 983-8551, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Dehydration of 1,4-butanediol (1,4-BDO) to tetrahydrofuran (THF), 2R,5R-hexanediol (2R,5R-HDO)
to 2,5-dimethyltetrahydrofuran (2,5-DMTHF), and 2,5-dimethyl-2,5-hexanediol (2,5-DM-2,5-HDO) to
2,2,5,5-tetramethyltetrahydrofuran (2,2,5,5-TMTHF) proceeded in high-temperature liquid water at
523 K. The formation rates of cyclic ethers were enhanced by high-pressure carbon dioxide (16.2 MPa). The
order of dehydration rates in high-temperature water with carbon dioxide was 2,5-DM-2,5-HDO > 2R,5R-
HDO > 1,4-BDO (tertiary > secondary > primary alcohols), which was the same order as the stability of
corresponding carbocation species.
Received 30 May 2011
Received in revised form 13 July 2011
Accepted 24 July 2011
Keywords:
Intramolecular dehydration
Cyclic ether
© 2011 Elsevier B.V. All rights reserved.
Carbonic acid
High-temperature liquid water
High-pressure carbon dioxide
1. Introduction
high-temperature liquid water and that the dehydration rates were
enhanced by the addition of high-pressure carbon dioxide [7–13].
The chemical transformation techniques of converting biomass-
derived polyalcohol compounds, such as fructose, sorbitol, and
glycerol, to valuable chemicals are indispensable for establishing
a sustainable society [1–3]. Dehydration reactions of polyalcohol
compounds are important to obtain valuable products with desired
boiling points, water solubilities, octane numbers, and viscosities
[4]. The chemistry of intramolecular dehydration of polyalcohol
compounds provides a key technology for developing an efficient
conversion process of biomass derivatives to useful materials [5,6].
High-temperature liquid water has attracted much attention as
a promising solvent for acid- or base-catalyzed reactions because
self-ionization of water is highly feasible at around 523 K, leading
to high concentrations of proton and hydroxide ion. The addition
of high-pressure carbon dioxide can enhance the concentration of
proton in liquid water because carbon dioxide dissolves in water
to form carbonic acid, as shown below,
In this paper, we investigated the intramolecular dehydra-
tion behavior of alkanediols, such as 1,4-butanediol (1,4-BDO),
(2R,5R)-(−)-2,5-hexanediol (2R,5R-HDO), and 2,5-dimethyl-2,5-
hexanediol (2,5-DM-2,5-HDO), to the corresponding cyclic ethers
in high-temperature liquid water with high-pressure carbon diox-
ide. We compared the dehydration rates of the alkanediols and
discussed the reaction mechanism based on the class of alcohols.
2. Experimental
The reactants, 1,4-BDO, 2R,5R-HDO, and 2,5-DM-2,5-HDO, were
purchased from Wako Pure Chemical Industries, Ltd. and used
without any further purification. The dehydration of alkanedi-
ols was carried out in a batch reactor (inner volume: 6 cm3)
made of a SUS316 tube [14,15]. Aqueous solution (1,4-HDO and
2R,5R-HDO: 1 mol dm−3, 3 cm3; 2,5-DM-2,5-HDO: 0.5 mol dm−3
,
3 cm3) was loaded in the reactor, which was then purged with
argon gas to remove air. Carbon dioxide (10 MPa) was then
loaded in the reactor at 323 K. The reactor was submerged into
a molten-salt bath or a sand bath at the reaction temperature.
The partial pressure values of water and carbon dioxide were
4.0 and 16.2 MPa at 523 K, respectively. After the given reaction
time, the reactor was submerged into a water bath for cooling
to ambient temperature. A mixture of the reactant and products
was taken out from the reactor with distilled water and filtered to
remove solid products by a membrane filter (pore size: 200 nm).
Amount of organic carbon in the liquid fraction was evaluated
2−
H2O + CO2 ꢀ H2CO3 ꢀ H+ + HCO3− ꢀ 2H+ + CO3
.
(1)
The combination of water and carbon dioxide are environmen-
tally benign because the added carbon dioxide can be separated
easily by simple depressurization after the reaction. We have
demonstrated that intramolecular dehydration of several polyal-
cohols, which were the chemical blocks of biomass, proceeded in
∗
Corresponding author. Tel.: +81 22 237 5219; fax: +81 22 237 5224.
E-mail address: m.shirai@aist.go.jp (M. Shirai).
0920-5861/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.cattod.2011.07.025

A. Yamaguchi et al. / Catalysis Today 185 (2012) 302–305
303
Scheme 1.
Fig. 2. Yields of 2,5-DMTHF (sum of cis and trans forms, closed symbols) and 2R,5R-
HDO (open symbols) as a function of elapsed time for the 2R,5R-HDO dehydration
reactions at 523 K in water (initial 2R,5R-HDO concentration: 1.0 mol dm−3, carbon
dioxide partial pressure: 0 (circles) and 16.2 MPa (triangles)).
with an increase in reaction time. After 5 h, 16% of THF yield was
obtained.
The addition of 16.2 MPa of carbon dioxide enhanced the
intramolecular dehydration rate. THF was the solo liquid product
from the 1,4-BDO dehydration even when high-pressure carbon
dioxide was added. The THF yield in water for 30 min was 16% with
high-pressure carbon dioxide. After 5 h, the THF yield was 88%. The
high dehydration rate could be obtained by the catalysis of protons
derived from carbonic acid.
Fig. 1. Yields of THF (closed symbols) and 1,4-BDO (open symbols) as a function
of elapsed time for the 1,4-BDO dehydration reaction at 523 K in water (initial 1,4-
BDO concentration: 1.0 mol dm−3, carbon dioxide partial pressure: 0 (circles) and
16.2 MPa (triangles)).
using a total organic carbon analyzer (Shimadzu, TOC-VCSN). The
quantitative analysis of the liquid products was conducted by
gas chromatography with a flame ionization detector (GC-FID)
equipped with a DB-WAX capillary column (Agilent Technologies)
using 1-propanol as an internal standard material. The products
were identified by their retention times of the GC-FID analysis,
compared with those for known materials: tetrahydrofuran (THF,
Wako Pure Chemical Industries), 2,5-dimethyltetrahydrofuran
(2,5-DMTHF, Aldrich, a mixture of cis and trans forms), and
2,2,5,5-tetramethyltetrahydrofuran (2,2,5,5-TMTHF, Alfa Aesar).
The products, cis-2,5-DMTHF and trans-2,5-DMTHF, were analyzed
by two discriminable peaks of GC-FID and spectra of 1H and 13C
NMR. Initial formation rates of the products were estimated from
the initial slopes of the fitting curves of their yields.
3.2. Dehydration of 2,5-hexanediol (2,5-HDO)
Dehydration behavior of chiral 2R,5R-HDO (1.0 mol dm−3) in
water was also investigated in the absence and presence of carbon
dioxide at 523 K (Scheme 2).
Intermolecular dehydration of chiral 2R,5R-HDO also proceeded
in water at 523 K (Fig. 2). 2,5-DMTHF (mixture of cis and trans forms)
was the sole liquid product from the intramolecular dehydration
of 2R,5R-HDO. The dehydration of 2R,5R-HDO to 2,5-DMTHF was
also enhanced by the addition of high-pressure carbon dioxide.
It is notable that the dehydration rate of 2R,5R-HDO was larger
than that of 1,4-BDO in high-temperature water (523 K) with high-
pressure carbon dioxide (16.2 MPa) (Figs. 1 and 2).
The selectivities to cis-2,5-DMTHF were more than 85% in the
total product 2,5-DMTHF independently of both conversion and
carbon dioxide pressure. It is reported that the 2R,5R-HDO dehy-
dration proceeded by concentrated sulfuric acid at 293 K to produce
a mixture of cis- and trans-2,5-DMTHF and the selectivities to cis
and trans forms were both 50% [16,17], indicating that the 2,5-HDO
dehydration proceeded via SN1 mechanism by concentrated sul-
furic acid. The 85% of cis-selectivity was obtained in our reaction
conditions, indicating that intramolecular dehydration proceeded
mainly via an SN2 pathway in high-temperature liquid water or
high-temperature liquid water with high-pressure carbon dioxide
[9].
3. Results and discussion
3.1. Dehydration of 1,4-butanediol (1,4-BDO)
Dehydration behavior of 1,4-BDO (1.0 mol dm−3) in water was
investigated in the absence and presence of carbon dioxide at 523 K
(Scheme 1).
Intermolecular dehydration to THF proceeded slowly in water
at 523 K (Fig. 1). The material balance was more than 95% inde-
pendently of the 1,4-BDO conversion. The dehydration proceeded
Scheme 2.

304
A. Yamaguchi et al. / Catalysis Today 185 (2012) 302–305
Table 1
Initial formation rates of cyclic ethers for dehydration reactions of 1,4-BDO, 2R,5R-HDO, 2,5-DM-2,5-HDO in water.
Reactant
1,4-BDOa
Product
THF
Reaction temperature/K
523
CO2 pressure/MPa
Formation rate/mol dm−3 s−1
0
16.2
0
16.2
0
3.8 × 10−6
1.1 × 10−4
3.4 × 10−6
2.0 × 10−4
>1.2 × 10−4
8.0 × 10−6
2.3 × 10−4
2R,5R-HDOa
2,5-DMTHF
523
2,5-DM-2,5-HDOb
2,2,5,5-TMTHF
523
473
0
14.6
a
Initial reactant concentration was 1.0 mol dm−3
Initial reactant concentration was 0.5 mol dm−3
.
.
b
The material balance, defined as total yield of 2R,5R-HDO and
2,5-DMTHF, decreased with an increase in reaction time for the
dehydration with carbon dioxide. The material balance for the
dehydration of 2R,5R-HDO in the presence of carbon dioxide for
3 h was 60%, which was almost equivalent to the amount of total
organic carbon in the liquid water phase determined by TOC anal-
ysis. These results indicated that the chemicals in the liquid phase
after the 2R,5R-HDO dehydration were only 2,5-DMTHF and 2R,5R-
HDO and that the solid products, such as solid polymers having
more than 200 nm, would be formed at 523 K. We also investi-
gated the stability of 2,5-DMTHF (mixture of cis and trans forms) in
water at 523 K in the same procedure as the 2R,5R-HDO dehydra-
tion reaction by using 0.3 mol dm−3 2,5-DMTHF aqueous solution
instead of 2R,5R-HDO aqueous solution. The formation of 2,5-HDO
(reverse reaction of the 2R,5R-HDO dehydration) was not observed
during the high-temperature water treatment of 2,5-DMTHF and
the recovery yield of 2,5-DMTHF was 50% for 3 h at 523 K under
both conditions with and without carbon dioxide. The total organic
carbon (50%) in the liquid phase after the high-temperature water
treatment of 2,5-DMTHF was almost the same as the recovery yield
of 2,5-DMTHF, indicating that any liquid products were not formed
from 2,5-DMTHF and that solid products would be formed by the
ring-opening polymerization of 2,5-DMTHF.
Fig. 3. Yields of 2,2,5,5-TMTHF (closed symbols) and 2,5-DM-2,5HDO (open sym-
bols) as a function of elapsed time for the 2,5-DM-2,5HDO dehydration reactions at
473 K in water (initial 2,5-DM-2,5HDO concentration: 0.5 mol dm−3, carbon dioxide
partial pressure: 0 (circles) and 14.6 MPa (triangles)).
3.4. Comparison of dehydration rates of primary, secondary, and
tertiary alkanediols
3.3. Dehydration of 2,5-dimethyl-2,5-hexanediol
(2,5-DM-2,5-HDO)
We compared dehydration rates of three kinds of alkanediols
in high-temperature liquid water, estimated from initial slopes of
the fitting curves of the amount of cyclic ethers (Table 1). The ini-
tial formation rates of cyclic ethers were dramatically increased
by the addition of carbon dioxide, indicating that carbonic acid
was the catalyst for the intramolecular dehydration. The order
of cyclic ether formation rate was 2,5-DM-2,5-HDO to 2,2,5,5-
TMTHF > 2R,5R-HDO to 2,5-DMTHF > 1,4-BDO to THF under the
reaction conditions with carbon dioxide. The basicity of the sec-
ondary hydroxyl group is higher than that of the primary hydroxyl
group [18]; therefore, the intramolecular dehydration of secondary
alcohol (2R,5R-HDO) by carbonic acid would be faster than that
of primary alcohol (1,4-BDO). The formation rate of cyclic ether
from the tertiary alcohol (2,5-DM-2,5-HDO) dehydration was much
faster than those from the primary (1,4-BDO) and secondary alcohol
(2R,5R-HDO) dehydration. Because carbocation species from proto-
nated tertiary alcohols are stable, the intramolecular dehydration
of tertiary alcohols proceed via SN1 mechanism [18]. Protonated
2,5-DM-2,5-HDO molecules could be easily formed in water with
carbon dioxide because of the high concentration of proton derived
from carbonic acid, resulting that the highest cyclic ether formation
rate was obtained for 2,5-DM-2,5-HDO.
Dehydration behavior of 2,5-DM-2,5-HDO (0.5 mol dm−3) in
water was also investigated at 523 K (Scheme 3).
Intermolecular dehydration of 2,5-DM-2,5-HDO also proceeded
in water at 523 K. The conversion of 2,5-DM-2,5-HDO in water was
more than 60% even for 10 min without carbon dioxide. We inves-
tigated the 2,5-DM-2,5-HDO dehydration at lower temperature of
473 K (Fig. 3) to evaluate the dehydration rate. The 2,2,5,5-TMTHF
yield for 10 min in liquid water at 473 K was 0.9% and increased
to 28% by the addition of 14.6 MPa of carbon dioxide. This result
supports that proton derived from carbonic acid catalyzed the
dehydration of 2,5-DM-2,5-HDO to 2,2,5,5-TMTHF. The material
balance, defined as total yield of 2,5-DM-2,5-HDO and 2,2,5,5-
TMTHF, in water in the presence of carbon dioxide after 3 h was
only 48%, almost equivalent to the amount of total organic carbon
estimated as 50% in the liquid phase. These results also indicated
that the product in the liquid phase was only 2,2,5,5-TMTHF and
that the solid products, such as polymers, were formed during the
dehydration of 2,5-DM-2,5-HDO in high-temperature liquid water.
4. Conclusion
We demonstrated the dehydration of 1,4-butanediol (1,4-BDO),
2R,5R-hexanediol (2,5-HDO), and 2,5-dimethyl-2,5-hexanediol
(2,5-DM-2,5-HDO) to the corresponding cyclic ethers in
Scheme 3.

A. Yamaguchi et al. / Catalysis Today 185 (2012) 302–305
305
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The order of dehydration rate was 2,5-DM-2,5-HDO > 2R,5R-
HDO > 1,4-BDO (tertiary > secondary > primary alcohols), which
was the same order as the stability of corresponding carbocation
species.
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derivatives to useful materials. These reactions are environmen-
tally benign because only water and carbon dioxide are used and
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Acknowledgements
This work has been supported by Special Coordination Funds
for Promoting Science and Technology of Ministry of Education,
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