A green route to 1,2-cyclohexanediol via the hydrolysis of cyclohexene oxide catalyzed by water

Article abstract of DOI:10.1007/s11164-012-0544-7

Effective hydrolysis of cyclohexene oxide (CHO) was conducted by heating in water between 100 and 140 °C without another catalyst. It provided 100 % purity and 100 % yield of trans-1,2-cyclohexanediol (1,2-CHD) with five times of H₂O to CHO at 120 °C for 6 h. These intermediates of polyether polyols could be totally decomposed to 1,2-CHD (monomer) by hot water under the same condition. The improved process eliminates the purification and markedly reduces the cost of 1,2-CHD in the follow-up industrial production. The main factors, such as reaction temperature, time, and water volume, were investigated. It was proposed that water acted as a modest acid catalyst, reactant, and solvent in the hydrolysis of CHO and polymers. Springer Science+Business Media B.V. 2012.

Full text of DOI:10.1007/s11164-012-0544-7

Res Chem Intermed (2012) 38:2277–2284
DOI 10.1007/s11164-012-0544-7
A green route to 1,2-cyclohexanediol via the hydrolysis
of cyclohexene oxide catalyzed by water
Qiusheng Yang
•
•
Xue Yang
Haiou Wang Qingyan Cheng
•
Yanji Wang
•
Received: 31 January 2012 / Accepted: 24 March 2012 / Published online: 10 April 2012
Ó Springer Science+Business Media B.V. 2012
Abstract Effective hydrolysis of cyclohexene oxide (CHO) was conducted by
heating in water between 100 and 140 °C without another catalyst. It provided
1
00 % purity and 100 % yield of trans-1,2-cyclohexanediol (1,2-CHD) with five
times of H O to CHO at 120 °C for 6 h. These intermediates of polyether polyols
2
could be totally decomposed to 1,2-CHD (monomer) by hot water under the same
condition. The improved process eliminates the purification and markedly reduces
the cost of 1,2-CHD in the follow-up industrial production. The main factors, such
as reaction temperature, time, and water volume, were investigated. It was proposed
that water acted as a modest acid catalyst, reactant, and solvent in the hydrolysis of
CHO and polymers.
Keywords Hydrolysis Á Water Á Cyclohexene oxide Á 1,2-Cyclohexanediol Á
Polymer
Introduction
1
,2-Cyclohexanediol (1,2-CHD) is an important organic material. It has two
hydroxyl groups, which can participate in dehydration, halogenation, dehydroge-
nation, esterification, etc. 1,2-CHD is not only a kind of top grade diluter of epoxy
resins but is also used to produce the polyester, drugs, plasticizer, pesticides, and so
on. Especially, 1,2-CHD can be converted to catechol by Ni-, Pd-, and Cu-based
catalysts, which is a green route with high yield and less waste [1–3]. Catechol, an
important fine chemical, used to be prepared by hydrolysis of o-chlorophenol
catalyzed by strong base, or hydroxylation of phenol followed by lots of
Q. Yang Á X. Yang Á Y. Wang (&) Á H. Wang Á Q. Cheng
Institute of Green Chemical Technology, Hebei University of Technology, Tianjin 300130, China
e-mail: yqiusheng@sina.com; yjwang@hebut.edu.cn
123

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Q. Yang et al.
by-products. So, the preparation of 1,2-CHD has drawn wide attention of
researchers. Although current interest is on direct oxidation to 1,2-CHD from
cyclohexene with H O as the oxidant catalyzed by acetic acid, tungsten compound
2
2
[
4] and Ti- and Zr-silicates [5–7], the one-step method has many disadvantages,
such as low yield, non-recyclable catalyst, more by-products (over oxidation) [8],
solvents and wastes. Cyclohexene oxide (CHO) is another source of 1,2-CHD. Ring
opening of epoxides is a pivotal synthetical protocol for making useful chemicals
such as vicinal diols and amino alcohols [9]. Hydrolysis is normally catalyzed by
either acid or base to vicinal diols in the presence of added catalysts. Mostly, CHO
has been hydrolyzed to 1,2-CHD using inorganic acid [10, 11], DMF [12], Lewis
acid [13, 14], and metal complexes [15–17] as catalysts. Some catalysts were
corrosive and these processes required many solvents, such as acetone, alcohol [18],
acetonitrile [19], and water, increased costs of solvent and catalyst, plus the
difficulty of post-processing. In addition, many kinds of solvents and catalysts led to
solvolytic reactions associated with by-products [9, 18–20].
Water, an ideal solvent, has been used as an acidic catalyst in many reports.
,2-CHD can be attained by increasing the water amount in order to avoid the
1
polymerization or form a homogeneous system, but too much water causes more
organic solvent for extraction or energy for concentration to increase the isolated
yield due to 1,2-CHD solubility in water [21]. For example, under the optimized
conditions, the molar ratio of water and 1,2-CHD was 40:1 [22]. According to our
knowledge, neither temperature effect nor water volume has so far been reported
on the synthesis of 1,2-CHD from CHO. In this paper, a new process of hydrolysis
from CHO to 1,2-CHD catalyzed by hot water was designed to assure high
yield and high purity of 1,2-CHD and eliminate the purification process in the
follow-up industrial production. A possible mechanism of the process was also
proposed.
Experimental section
CHO and 1,2-CHD (purity [99 %) were both obtained from Yueyang Changde
Chemical, (China). Distilled water was obtained from our laboratory. GC analysis
was performed on a SP 3420 chromatograph with a flame ionization detector
equipped with a PEG-20000 capillary (i.d. 0.25 mm 9 30 m). The data listed were
determined by area %.
These reactions were carried out in a magnetic stirring stainless autoclave of
0 mL. The vessel was immersed in an oil bath, which was maintained at the
5
desired temperature with an accuracy of ± 0.5 °C. A typical procedure of CHO
hydrolysis was as follows: CHO (100 mmol, 9.80 g) and distilled water (500 mmol,
9
.00 mL) were mixed in a 50-mL stainless autoclave; the resulting suspension was
stirred vigorously at 120 °C for the indicated time. After reaction completion, the
sample for GC analysis was obtained at 60–70 °C. The remaining mixture was
concentrated under vacuum to afford a dry white powder with mp 101.3–102.5 °C)
[
22: mp 101–103 °C].
1
23

A green route to 1,2-cyclohexanediol via the hydrolysis
2279
Results and discussion
Epoxides with a three-membered ring are significantly more reactive than other
ethers. They have a high thermodynamic driving force, usually [20 kcal/mol
because of the three-membered strained heterocycle [23]. The hydrolysis procedures
for epoxide ring opening, an endothermic reaction, can be based on nucleophilic or
protic/Lewis acid-mediated electrophilic mechanism. The reaction often results in
many by-products, such as polymer, ethers, and cycloalkene [24].
Water, a green medium, is not an inert medium but an active participant in the
above reaction. It has special properties such as high dielectric constant, high heat
capacity, and hydrogen bond formation between water and reactants as well as acid
or base characters from the self-ionization of water. Kotsuki’s group reported a
catalyst-free hydrolysis of epoxides in the mixed solvent of acetone and water at
4
6
0 °C under 10 bar [25]. Other researchers used only water without another solvent
and catalyst during the same reaction (2100 °C), but the reaction required an excess
of water, [60 mol equiv, and time, [12 h, to drive 1,2-CHD formation because of
the insolubility of the reactants and the incompatibility of the reaction intermediates
[
21]. Water acted in three roles as follows: reactant, solvent, and catalyst in the
procedure. Water molecules act as a proton relay, thereby facilitating the formation
and cleavage of bonds that leads to the products. In general, an acid-catalyzed
mechanism was proposed based on the observed selectivity of the reactions in
water. CHO was hydrolyzed with excellent stereoselectivity since only trans-vicinal
diols were detected.
The effect of temperature
Generally, temperature has a significant influence on the reaction rate. A superior
yield of 1,2-CHD was obtained and the reaction rate reached a maximum at a higher
temperature (Fig. 1). The highest yield of 98.6 % was obtained at 120 °C. The
conversion was increasing and the selectivity was 100 % from 100 to 120 °C. The
selectivity data of 100 % means no detectable by-products were found by GC. The
selectivity was decreasing and conversion is 90.5 % at 130 °C, while the conversion
was up to 100 % and the selectivity was 97.6 % at 140 °C.
The hydrolysis of CHO in water was influenced by two mechanisms (Scheme 1):
?
direct hydrolysis and two-step hydrolysis from CHO. H came from dissociation of
water and 1,2-CHD. This system had a gas phrase and two liquid phrases (water and
organic layers) above 100 °C. Direction hydrolysis mainly happened in the water
and gas phrases. Otherwise, the two-step method included polymerization in the
organic layer and polymer hydrolysis in the water layer. The polyether polyols of
different degrees was made in the organic layer and it could be gradually
decomposed to 1,2-CHD (monomer) in hot water.
Direct hydrolysis of CHO to 1,2-CHD was endothermic and the increase of
temperature was beneficial to the conversion from dynamics and thermodynamics. It
was also favorable for the rate constant by modifying the free energy of activation
and the transmission coefficient. With increasing temperature, hydrogen bonding in
water becomes weaker and less persistent while the density and the average cluster
123

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Q. Yang et al.
conver.
select.
yield
100
8
6
4
0
0
0
100
110
120
130
140
T/°C
Fig. 1 Hydrolysis of CHO in a 5:1 molar ratio mixture of water:CHO under different temperatures
OH
[
H3O+]
O
OH
H3O+]
[H3O+]
[
O
n
HO
O
OH
2
Scheme 1 Hydrolysis mechanism of CHO in the medium of H O
size of water are decreasing. The smaller size of water molecules typically allowed
many water molecules to surround one CHO molecule, which increased the attack
and stabilized the transition states; meanwhile the transmission coefficient was
increasing because of molecular thermal aggravation. The static dielectric constant
of water decreases with increasing temperature, which behaves like a polar organic
solvent. The abovementioned factors were conducive to dissolve CHO. CHO
solubility was increasing sharply above 100 °C [26]. These factors also benefited
the SN reaction which happened during the hydrolysis process. On the other hand,
2
the self-ionization constant (Kw) is another important property of water that varies
considerably with changes in temperature; -logKw value of water at 120 °C is
above 12, which means the concentration of H /OH is 10 times more than that at
?
-
?
2
modest acid, which dominated the direct hydrolysis reaction in high-temperature
5 °C. The higher H from the self-ionization accelerated the hydrolysis rate as a
water.
1
23

A green route to 1,2-cyclohexanediol via the hydrolysis
2281
Besides direct formation of 1,2-CHD, polymerization was the main side reaction
during the hydrolysis, which caused polyether polyols with different degrees
(
Scheme 2). From the beginning of the reaction, the main substances were CHO,
,2-CHD in the organic layer. Little water also coexisted mainly because of its
1
dissolvability in 1,2-CHD. Dissociative alkoxy anion from the self-ionization of 1,2-
CHD attacked the CHO oxonium ion, which resulted in the formation of polyether
polyols in the organic layer. This polymerization rate was slower mainly due to the
complex structures compared to directed hydrolysis in the water layer. Below
1
20 °C, the production of polyether polyols was small and the degree was low. It
was decomposed to 1,2-CHD after 4 h, which resulted in the 100 % selectivity of
CHO. When the temperature was above 130 °C, maybe more CHO (bp 130 °C)
went into the gas phrase. Although the hydrolysis in the gas phrase was
homogeneous like in the water phrase, the reaction in the gas phrase was somewhat
slower than that in the water phrase because of no intensive mixing. Gas remains
including some CHO caused the conversion to decrease to 90.5 % at 130 °C, which
was lower than that at 120 °C. More high degree polymers were formed with more
high temperatures in the organic layer. The generated polymers could not be
hydrolyzed, which caused the 90.7 % selectivity of CHO during the same condition.
This result was also far below that at 120 °C. When the temperature was at 140 °C,
the polymerization and its hydrolysis were all accelerated. Meanwhile, the direct
hydrolysis in the gas phrase also was enhanced. All the CHO was converted, but the
polymers of higher degree still could not be hydrolyzed completely at 140 °C after
4
h. The conversion and selectivity at 140 °C were both improved compared to that
at 130 °C. If the cost was lower, the optimization of reaction temperature was
perhaps 120 °C.
The effect of water amount
Water has a better solubility to 1,2-CHD than CHO because of the hydrogen bond
between water and 1,2-CHD (20 °C, solubility [30 g/100 mL water). We found
that the amount of water had a significant influence on the conversion of CHO
(Fig. 2). As shown in Fig. 2 for the hydrolysis of CHO, the product yield climbed
higher following the increase of the water amount, and the yield went to a plateau
OH
O
H
H
O
OH
OH
O
O
n
HO
O
O
HO
OH
OH
OH
Scheme 2 Polymerization mechanism of CHO in the organic layer
123

2282
Q. Yang et al.
after the molar ratio of water to CHO was raised to 10:1. At 2:1 or 1:1 of water and
CHO, the yield and selectivity of 1,2-CHD were very low mainly because of the
large amount of polymerization and the small amount of direct hydrolysis of CHO.
The water layer was the main place where the direct hydrolysis of CHO took place.
Less water caused less direct hydrolysis in the water layer, which resulted in the low
conversion of CHO. Much CHO was polymerized and insoluble particles of high
degrees were formed at a lower water volume in the organic phrase. The particles
had not disappeared after the reaction at 2:1 or 1:1 of water and CHO. When the
ratio was above 5:1, polymers formed in the organic layer could be hydrolyzed
completely during 4 h. The proper water avoided the form of insoluble high
polymers. It also avoided the by-products of olefin and high polymers catalyzed by
strong acid under those reaction conditions. Above 10:1, the selectivity and yield
were both 100 %, but more water required evaporating to increase the isolated yield.
The effect of reaction time
Time effect was also examined under different times. As shown in Fig. 3, the yield
of 1,2-CHD climbed higher following the reaction time and the yield went to a
plateau after 4 h. When the reaction began, the reaction was nonhomogeneous, 1,2-
CHD was obtained mainly in the water layer and the polymer of low degrees was
formed in the organic layer. The selectivity of 1,2-CHD is low during the first hour.
With increasing time, the polymer of low degrees gradually went into the water
?
layer and was decomposed to 1,2-CHD by an H -catalyzed mechanism (Scheme 1).
Meanwhile, the homogeneous phrase was gradually formed with more 1,2-CHD and
polymers like surfactants. With further development, the polymers were finally
decomposed to 1,2-CHD. When the time was increased to 4 h, no polymer was left.
According to the reaction after 4 h, the selectivity was 100 % and the conversion
conver.
select.
yield
1
00
8
6
4
2
0
0
0
0
0
1:1
1:2
1:5
1:10
1:20
CHO : water (molar rate)
Fig. 2 Hydrolysis of CHO at 120 °C for 4 h under different molar ratios of water and CHO
1
23

A green route to 1,2-cyclohexanediol via the hydrolysis
2283
conver.
select.
yield
1
00
8
6
4
0
0
0
1
2
3
4
5
6
7
8
T/h
Fig. 3 Hydrolysis of CHO at 120 °C in a 5:1 molar ratio mixture of water:CHO at different times
was 98.6 %. That means that no polymer existed while little CHO still remained
after 4 h. This result also implied that two-step hydrolysis was finished earlier than
direct hydrolysis in the water layer and the gas phrase. Perhaps the remaining CHO
existed in the gas phrase. After 6 h, no by-products appeared by GC analysis. No
degradation production was generated even after 8 h. A large-scale experiment
under optimized reaction conditions was carried out (water:CHO = 5:1, 120 °C,
6
h) in a mechanical stirring stainless autoclave. The separated CHD yield was
1
9
7.6 %.
Conclusion
Water is a cheap, safe, and clean solvent. 1,2-CHD was easily obtained by
hydrolysis of CHO with hot water as catalyst, solvent, and reactant. This reaction
included liquid and gas phrases. The liquid phrase had organic and water layers,
which gradually changed into one homogeneous phase. The polyether polyols
formed in the organic layer could be gradually decomposed to 1,2-CHD. A nearly
quantitative yield of 1,2-CHD and simple post-processing were obtained without
any polymers at 120 °C with the molar ratio of 1:5 (CHO:water) for 34 h. This
-
?
method avoided not only extra catalyst but also heteroions except for OH , H and
alkoxy anions formed during the reaction. Very little waste was emitted except
1
A large scale experiment under optimized reaction conditions was carried out in a mechanical stirring
stainless autoclave of 250 mL. CHO (1 mol, 98.0 g) and distilled water (5 mol, 90.0 mL) were mixed and
the resulting suspension was stirred at 900 rpm and at a temperature of 120 °C ± 1 for 6 h. After
completion, the mixture was concentrated under reduced pressure to give 113.2 g solid product. The
separated yield was 97.6 %, mp 101.5–102.3 °C.
123

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Q. Yang et al.
recycled water. The reaction mechanism included acid-catalyzed and low polymers
decomposition mechanisms.
Acknowledgments We acknowledge China National Funds for Distinguished Young Scientists
(21106030) and Hebei Postdoctoral Sustentation Fund for the financial support. We also thank Dr.
Tianyong Zhang from Tianjin University for useful comments and improving the English during the
preparation of this manuscript.
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