Facile synthesis of fructone from ethyl acetoacetate and ethylene glycol catalyzed by SO3H-functionalized Bronsted acidic ionic liquids

Article abstract of DOI:10.1039/c4ra01708k

SO₃H-functionalized Bronsted acidic ionic liquids (BAILs) were synthesized and utilized as highly efficient catalysts for the production of fructone via the acetalization reaction of ethyl acetoacetate with ethylene glycol. In comparison with conventional H₂SO₄ and cation exchange resins, the BAILs N-(4-sulfonic acid) butyl triethylammonium hydrogensulfate ([BSEt₃N][HSO₄]) of strong acidities exhibited excellent catalytic activities. The effects of various parameters such as different BAILs, reaction temperature, catalyst dosage, and molar ratio of the reactants on the conversion of ethyl acetoacetate were investigated in detail. The experimental results indicated that the catalytic performance of BAILs were closely related to their Hammett acidities. Moreover, it was found that [BSEt₃N][HSO₄] could be also recovered easily and used repetitively six times without obvious decline in activity and quantity, showing great potential application in industry. This journal is the Partner Organisations 2014.

Full text of DOI:10.1039/c4ra01708k

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Facile synthesis of fructone from ethyl
acetoacetate and ethylene glycol catalyzed by
SO3H-functionalized Brønsted acidic ionic liquids
Cite this: RSC Adv., 2014, 4, 22520
a
a
a
b
*
Yong Liu, Yi-Tao Wang, Tao Liu and Duan-Jian Tao
SO3H-functionalized Brønsted acidic ionic liquids (BAILs) were synthesized and utilized as highly efficient
catalysts for the production of fructone via the acetalization reaction of ethyl acetoacetate with ethylene
glycol. In comparison with conventional H2SO4 and cation exchange resins, the BAILs N-(4-sulfonic acid)
butyl triethylammonium hydrogensulfate ([BSEt3N][HSO4]) of strong acidities exhibited excellent catalytic
activities. The effects of various parameters such as different BAILs, reaction temperature, catalyst
dosage, and molar ratio of the reactants on the conversion of ethyl acetoacetate were investigated in
detail. The experimental results indicated that the catalytic performance of BAILs were closely related to
their Hammett acidities. Moreover, it was found that [BSEt3N][HSO4] could be also recovered easily and
used repetitively six times without obvious decline in activity and quantity, showing great potential
application in industry.
Received 26th February 2014
Accepted 7th May 2014
DOI: 10.1039/c4ra01708k
www.rsc.org/advances
stability and effortless reusability.8–12 Till now, some acidic ionic
liquids have been successfully used in esterication,13–15 alkyl-
ation,16–18 acetalization,19,20 ketalization,21 hydration,22,23 etc.,
Introduction
Fructone (ethyl-2-methyl-1,3-dioxolane-2-acetate) is a avoring
material with an apple-like smell. It has been widely used in
cosmetics, pharmaceuticals, detergents, and lacquer industries.
Fructone can be synthesized by the acetalization reaction of
ethyl acetoacetate with ethylene glycol in the presence of acid
catalysts (Scheme 1), such as sulphuric acid, p-toluenesulfonic
acid, etc. However, these acids always cause several problems
such as the tedious purication process of the products,
corrosion of equipments, and environmental pollution. To
overcome these drawbacks, various heterogeneous acid cata-
lysts have been developed to replace sulfuric acid catalysts, such
as zeolites,1,2 solid acids,3–5 heteropoly acids (HPA).6,7 However,
these catalysts are not entirely satisfactory due to their inherent
drawbacks such as lower activity and selectivity to the target
product, high cost of catalysts, easy carbon deposition, long
reaction time. Therefore, there was an urgent need to develop
environmentally friendly, high efficient and easily reusable
catalysts for the synthesis of fructone.
which have showed high catalytic activity and selectivity. In
2001, Deng et al. reported their early work on the acetalization
and ketalization using acidic chloroaluminate ILs as catalyst
with high conversion and selectivity.13 Cole et al.24 had rstly
synthesized SO3H-functionalized Brønsted acidic ionic liquids
(BAILs) and used them for the esterication of acetic acid with
ethanol. They found that these BAILs showed a good catalytic
performance and reusability in the esterication reactions. Yu
et al.25 had further reported the merits of using SO3H-func-
tionalized BAILs for the preparation of plasticizer ester. For the
synthesis of fructone, Dai et al.26 prepared a series of water-
soluble BAILs. Among them, [Hmim]BF4 showed the highest
catalytic activity. Aer reaction, the fructone could be isolated
from the reaction system automatically, and the IL could be
directly reused by simple decantation. Aer that, Lin et al.27
combined aluminium sulfate with ionic liquid to catalyze the
acetalization of ethyl acetoacetate with 1,2-propanediol. The
conversion of ethyl acetoacetate reached 73.9% at 1 h. However,
with so much ILs to do, ILs were still restricted their widespread
practical applications. Herein, we believe that further investi-
gation in need to explore the synthesis of fructone using SO3H-
functionalized BAILs with high activity and selectivity.
In recent years, ionic liquids (ILs) have attracted extensive
research interest as clean catalysts and excellent solvents due to
their unique physical and chemical properties, such as negli-
gible vapour pressure, remarkable solubility, high thermal
aInstitute of Fine Chemistry and Engineering, Henan Key Laboratory of
Polyoxometalate, College of Chemistry and Chemical Engineering, Henan University,
Kaifeng, 475004, China
bJiangxi Inorganic Membrane Materials Engineering Research Centre, College of
Chemistry and Chemical Engineering, Jiangxi Normal University, Nanchang 330022,
China. E-mail: djtao@jxnu.edu.cn; Fax: +86-791-88120843; Tel: +86-791-88121974
Scheme 1 Synthetical route of fructone.
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In this work, a series of SO3H-functionalized BAILs had been
RSC Advances
2-Methylpyridinine hydrogen sulfate ([Hmpy][HSO4])
prepared and used as catalysts for the synthesis of fructone. The
effects of catalytic reaction parameters such as different BAILs,
reaction temperature, catalyst dosage, and molar ratio of reac-
tants were investigated in detail to obtain the optimum condi-
tions. In addition, the Hammett acidity and reusability of BAILs
were also studied, and their acidity-catalytic activity relation-
ships were further discussed.
The synthesis procedure was similar to that of [Hpy][HSO4]. 1H
NMR (300 MHz, DMSO-d6, 25 C, TMS): d (ppm) 2.719 (s, 3H),
ꢁ
7.909 (m, 2H), 8.444 (t, 1H), 8.799 (d, 1H).
N-Tributylammonium hydrogen sulfate ([Et3NH][HSO4])
The preparation method was similar to the procedure of
[Hmim][HSO4]. 1H NMR (300 MHz, DMSO-d6, 25 ꢁC, TMS): d
(ppm) 1.17 (t, 9H), 3.08 (m, 6H), 8.89 (s, 1H).
Experimental
Materials
1-(4-Sulfonic acid) butyl-3-methylimidazolium
hydrogensulfate ([BSmim][HSO4])
1-Methylimidazole (purity $99%), and 1,4-butyl sultone (purity
$99%) were purchased from Aladdin Chemical Reagent Co.
Ltd. (Shanghai, China). The strong acidic cation ion exchange
resin Amberlyst-15 was obtained from Rohm and Haas. Ethyl
acetoacetate, ethylene glycol, sulfuric acid, triethylamine,
1-bromobutane, and acetone were of analytical grade and used
without any further purication.
The synthesis of [BSmim][HSO4] was carried out according to
the literatue.29 0.1 mol 1-methylimidazol and 0.1 mol 1,4-butane
sultone were charged into a 100 mL round-bottom ask. Then,
the mixtures were stirred at 80 ꢁC for 12 h. The white solid
zwitterion was washed repeatedly with ether (2 ꢂ 5 mL) to
remove any unreacted materials and dried in vacuum. Then, a
stoichiometric amount of concentrated sulfuric acid was added
ꢁ
and the mixture stirred for 6 h at 60 C during which time the
Synthesis and characterization of SO3H-functionalized BAILs
solid zwitterion dissolved/liqueed, resulted in the formation of
[BSmim][HSO4]. The BAILs phase was then washed repeatedly
with dichloromethane and ether to remove non-ionic residues,
and dried in vacuum. Then [BSmim][HSO4] of yellow viscous
liquid was obtained. 1H NMR (300 MHz, D2O-d2, 25 ꢁC, TMS); d
(ppm) 1.605 (m, 2H), 1.888 (m, 2H), 2.809 (t, 2H), 3.754 (s, 3H),
4.110 (t, 2H), 7.305 (s, 1H), 7.364 (s, 1H), 8.60 (s, 1H).
Six kinds of SO3H-functionalized BAILs composed of [HSO4]
anion and different cations were prepared in this work (Fig. 1).
The detailed synthesis procedure and 1H NMR (Bruker
DPX-300) of these BAILs were as following:
Pyridinium hydrogen sulfate ([Hpy][HSO4])
The synthesis procedure of [Hpy][HSO4] was as following: 0.1
mol pyridine was placed in a three-necked ask and immersed
in a water bath. 2.0 mol Lꢀ1 sulfuric acid solution in water
(50 mL) was added slowly while stirring and cooling to keep the
temperature at 0–5 ꢁC. The mixture was stirred for 5 h to
complete the reaction. Aer drying under vacuum (<10 mmHg)
at 95 ꢁC, the colourless liquid was obtained. 1H NMR (300 MHz,
DMSO-d6, 25 ꢁC, TMS): d (ppm) 8.037 (d, 2H), 8.558 (t, 1H), 8.909
(d, 2H).
N-(4-sulfonic acid) butyl triethylammonium hydrogensulfate
([BSEt3N][HSO4])
The preparation method of [BSEt3N][HSO4] was similar to the
synthesis of [BSmim][HSO4]. 1H NMR (300 MHz, D2O-d2, 25 ꢁC,
TMS); d (ppm) 1.122 (t, 9H), 1.679 (m, 4H), 2.825 (t, 2H), 3.08
(t, 2H), 3.178 (q, 6H).
UV-vs determination of acidity
The Brønsted acidity is an important property of BAILs, and
Hammett function (H0) is oen used to assess the acidity of
BAILs in organic solvents using an UV-visible spectroscopy.30,31
4-Nitroaniline which acted as a Hammett indicator was
respectively added to the same concentration solution of BAILs
or sulfuric acid dissolved in ethanol solution (80 mmol Lꢀ1).
The Hammett function (H0) can be calculated by the equation
below:
1-Methylimidazole hydrogen sulfate ([Hmim][HSO4])
The synthesis procedure was according to the literature.28 1H
NMR (300 MHz, D2O-d2, 25 ꢁC, TMS): d (ppm) 3.563 (s, 3H),
7.083 (s, 2H), 8.307 (s, 1H).
H0 ¼ pK(ln)aq. + log([I]s/[IH+]s)
where pK(I)aq. is the pKa value of the indicator referred to an
aqueous solution. [I]s and [IH+] are the molar concentrations of
the unprotonated and protonated forms of the indicator in the
BAILs, respectively. The maximal absorbance of unprotonated
form of 4-nitroaniline was observed at 371 nm, and the pK(I)aq.
value of 4-nitroaniline is 0.99. The results are shown in Table 1,
Fig. 1 Structure of six Brønsted acidic ionic liquids.
and the acidity order is as follows: [BSmim][HSO4] z
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Table 1 Hammett acidity function (H0) values of H2SO4 and different Table 2 The conversion of ethyl acetoacetate in the presence of
BAILs
different catalystsa
Entry
BAILs
Amax
[I]%
[IH]%
H0
Conversion
of ethyl
1
2
3
4
5
6
7
8
—
1.03
100
90
80.6
87.7
93.4
51.5
52.2
52.6
0
10
—
acetoacetate
(%)
Isolated
yields (%)
[Hmim][HSO4]
[Hpy][HSO4]
[Hmpy][HSO4]
[Et3NH][HSO4]
[BSmim][HSO4]
[BSEt3N][HSO4]
H2SO4
0.927
0.830
0.903
0.963
0.530
0.538
0.542
1.94
1.61
1.84
2.14
1.02
1.03
1.10
19.4
12.3
6.6
48.5
47.8
47.4
Entry Catalyst
1 h
2 h
1 h
2 h
Solvent
1
[BSEt3N][HSO4]
59.7
59.5
34.4
33.3
9.5
10.0
60.5
48.8
96b
61.6
60.0
43.9
41.2
14.4
16.2
71.2
49.6
—
53.4 56.6 Without
52.9 55.7 Without
30.9 39.6 Without
29.8 36.2 Without
8.0 12.1 Without
8.6 13.7 Without
54.1 63.8 Without
43.5 44.1 Without
2
3
4
[BSmim][HSO4]
[Hmpy][HSO4]
[Hpy][HSO4]
5
6
7
[Et3NH][HSO4]
[Hmim][HSO4]
H2SO4
[BSEt3N][HSO4] > H2SO4 > [Hpy][HSO4] > [Hmpy][HSO4] >
[Hmim][HSO4] > [Et3NH][HSO4].
8
9
10
11
Amberlyst-15
USY-3 zeolites
Copolymerization
30%Cs2.5/DUSY
—
—
—
—
—
—
Toluene
Cyclohexane
Without
—
71.6d
97.4c
—
Apparatus and procedure
a
The catalytic activity was carried out in the liquid-phase ace-
talization of ethyl acetoacetate with ethylene glycol to synthesize
fructone in a three-necked ask (100 mL) equipped with a
magnetic stirrer, and a condenser. In a typical run, ethyl ace-
toacetate (0.1 mol) and ethylene glycol (0.1 mol) were charged
into the reactor. The reaction temperature was raised to the
desired value, followed by the addition of catalyst (BAILs, H2SO4
or Amberlyst-15). Aer the reaction was completed, the reaction
mixture was taken out from the reactor at regular intervals. The
sample was cooled to room temperature. The system formed a
liquid–liquid biphase automatically, and lower phase contain-
ing BAILs could be easily separated from the reaction mixture by
simple decantation. Aer that, about 0.2 mL of liquid sample in
the upper phase was taken out, and detected by (Shimadzu GC-
17A) using a DB-17 capillary column (30 m ꢂ 0.544 mm ꢂ
1.0 mm) with a hydrogen ame ionization detector (FID). The
temperature of the inlet and the detector were set to be
553.15 K, and 573.15 K, respectively. Then the conversion and
selectivity were calculated according to the area of each chro-
matograph peak.
Reaction conditions: the reactions were conducted at the temperature
of 353.15 K, with ethyl acetoacetate to ethylene glycol molar ratio of
1 : 1.5, and catalyst dosage of 1.0 wt% (based on the mass of all
b
reactants). No byproducts were found by GC. Ref. 1: temperature of
146 ꢁC, 7.4 wt/wt% (based on ethyl acetoacetate), ratio toluene/ethyl
c
acetoacetate of 26.6, selectivity of 97%. Ref. 3: reuxed temperature,
0.02 mol ethyl acetoacetate, catalyst 0.05 g, cyclohexane 10 mL,
d
selectivity of 99.3%. Ref. 6: temperature of 343 K, catalyst dosage of
0.5 wt%, reaction time of 0.5 h.
60.0% at 2 h using the SO3H-functionalized BAILs [BSEt3N]-
[HSO4] and [BSmim][HSO4] as catalysts. Isolated yields of fruc-
tone were 55.7% and 56.6% at 2 h. By comparison, in the
presence of weak acidic catalyst [Hmim][HSO4] and [Et3NH]-
[HSO4], the conversions of ethyl acetoacetate at 2 h were only
16.2% and 14.4%, respectively, [Hmpy][HSO4] and [Hpy][HSO4]
also induced relatively low conversions of ethyl acetoacetate at 2
h, due to their weakly acidic cations. Therefore, it was demon-
strated that varying the cationic structure of BAILs can change
its acidity conveniently, and the catalytic activity order of the
BAILs is consistent with the acidities order. Moreover, these
experimental observations could be validated by a two-step
reaction mechanism for acetalizaiton.1,2 The reaction mecha-
nism indicates that the rst step in the reaction is the formation
of a hemiacetal, followed by the removal of a water molecule.
The rate-determining step of the formation of acetals or ketals is
the formation of a cation from the protonated hemiacetal. The
strongly acidic reaction media can effectively promote the
protonation of any hemiacetal formed, and sufficiently polar to
allow the stabilization of the cationic intermediate. Thus, it is
generally accepted that the BAILs of strong acidity can induce a
relatively high yield of acetals.
Results and discussion
Catalyst performance
The acetalization reaction of ethyl acetoacetate with ethylene
glycol to synthesize fructone using different BAILs composed of
various cations was conducted to assess their catalytic activities
at the temperature of 353.15 K, with ethyl acetoacetate to
ethylene glycol molar ratio of 1 : 1.5, and catalyst dosage of
1.0 wt% (based on the mass of all reactants). The results were
summarized in Table 2. As seen from Table 2, combined with
the Brønsted acidity values from Table 1, it was obvious that
these six BAILs catalysts exhibited different catalytic activities,
and the catalytic performance of BAILs were closely relevance to
their Brønsted acidities. The BAIL possessing strong acidity can
induce a higher catalytic activity.31,32 For example, compared
with other four BAILs, [BSmim][HSO4] and [BSEt3N][HSO4]
beared with an butyl sulfonic acid exhibited the strongest
acidities. The conversion of ethyl acetoacetate were 61.6% and
For comparison, the acetalization reaction was also investi-
gated in the presence of H2SO4 and strong acidic cation
exchange resin Amberlyst-15. As seen from Table 2, the stron-
gest acidity enabled H2SO4 to induce remarkable conversion of
ethyl acetoacetate. However, H2SO4 would cause severe equip-
ment corrosion and environmental pollution. It was also indi-
cated that the catalytic performance of Amberlyst-15 resin was
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lower than that of [BSEt3N][HSO4] and [BSmim][HSO4]. break the bonds and form products and thus result in higher
Compared with the homogeneous catalysis of BAILs, the conversion of ethyl acetoacetate. However, the conversion of
heterogeneous catalysis of Amberlyst-15 existed high transfer ethyl acetoacetate increased gradually when the temperature
resistance and led to relative lower catalytic activities.28 was further increased to 363.15 K and 368.15 K. These results
Furthermore, we compared the catalytic performance of show that the optimal reaction temperature is 353.15 K using
[BSEt3N][HSO4] with the results of other catalysts which pub- the [BSEt3N][HSO4] as catalyst.
lished in the literatures (entries 9–11). It was found that water-
The effect of catalyst dosage varied from 0.5 wt% to 2.0 wt%
carrying agent used in the acetalization reaction could obtain on the conversion of ethyl acetoacetate was investigated at
considerable conversion of ethyl acetoacetate. However, there temperature of 353.15 K and with ethyl acetoacetate to
exited many disadvantage such as solvent recycling, high energy ethylene glycol molar ratio of 1 : 1.5. The results were given in
consumption. By contrast, without the aid of water-carrying Fig. 3. It can be seen from Fig. 3 that the conversion of ethyl
agent, [BSEt3N][HSO4] and [BSmim][HSO4] also display the acetoacetate raised with the catalyst dosage. This increase can
comparable catalytic performance in comparison with H2SO4 be attributed to an increase in the availability of the number of
and those catalysts under mild conditions. Aer reaction, the catalytically active sites. However, it was noted that the
system formed a liquid–liquid biphase automatically, and lower conversion of ethyl acetoacetate at 2 h was improved with a
phase containing BAILs could be easily separated from the limited extent (from 61.6% to 65.1%) when the amount of
reaction mixture by simple decantation. In addition, the [BSEt3N][HSO4] catalyst was further enhanced from 1.0 wt% to
preparing process of [BSEt3N][HSO4] is simple and low-cost in 2.0 wt%, which implies that there are sufficient catalytic active
comparison with that of [BSmim][HSO4]. Thus [BSEt3N][HSO4] sites available for the substrate ethyl acetoacetate under the
was considered to be promising substitutes in the synthesis of experimental conditions. Therefore, considering the reaction
fructone and chosen as the catalyst for the following factor rate and the cost of the experiment, we choose 1.0 wt% as the
experiments.
dosage of [BSEt3N][HSO4].
The effect of ethyl acetoacetate to ethylene glycol molar ratio
on the reaction in the presence of [BSEt3N][HSO4] as catalyst
was revealed in Fig. 4. It can be found that the conversion of
ethyl acetoacetate is inuenced by the molar ratio of reactants.
With the amount of glycol increased, the conversion of ethyl
acetoacetate was rapidly improved when the initial molar ratio
of ethyl acetoacetate to ethylene glycol increased from 1 : 1 to
1 : 1.5. It due to that increasing the amount of ethylene glycol
was benecial to the forward reaction because the acetalization
of ethyl acetoacetate with ethylene glycol is a reversible reaction.
However, when the amount of ethylene glycol was further
increase to 1 : 2, the conversion of ethyl acetoacetate decreased
because of the dilute effect of the reaction mixture. So the
optimal molar ratio of ethyl acetoacetate to ethylene glycol was
preferred to be 1 : 1.5.
Effect of other parameters on conversion of ethyl acetoacetate
The reaction temperature was one of the important inuence
factors for the synthesis of fructone. The effect of the reaction
temperature on the conversion of ethyl acetoacetate was studied
in the presence of [BSEt3N][HSO4] as catalysts under the
condition of ethyl acetoacetate to ethylene glycol molar ratio of
1 : 1.5, and catalyst dosage of 1.0 wt% (based on the mass of all
reactants). As seen from Fig. 2, the conversion of ethyl acetoa-
cetate increased with the increase of reaction temperature. The
conversion of ethyl acetoacetate at 2 h increased from 56.1% to
61.6% with the rise of temperature from 333.15 K to 353.15 K.
This indicates that higher temperature generates greater
conversion of ethyl acetoacetate. It is due to that the increase of
reaction temperature brings more effective collisions. These
effective collisions have sufficient energy (activation energy) to
Fig. 2 Effect of reaction temperature on the conversion of ethyl Fig. 3 Effect of catalyst dosage on the conversion of ethyl acetoa-
acetoacetate using [BSEt3N][HSO4] as catalysts at temperature (-) cetate using [BSEt3N][HSO4] as catalysts at temperature of 353.15 K,
333.15 K; (C) 343.15 K; (:) 353.15 K; (;) 363.15 K; (+) 368.15 K, with with ethyl acetoacetate to ethylene glycol molar ratio of 1 : 1.5, with
ethyl acetoacetate to ethylene glycol molar ratio of 1 : 1.5, and catalyst catalyst dosage of (-) 0.5 wt%; (C) 0.8 wt%; (:) 1.0 wt%; (;) 1.2 wt%;
dosage of 1.0 wt% (based on the mass of all reactants).
(+) 2.0 wt%.
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Fig. 4 Effect of ethyl acetoacetate to ethylene glycol molar ratio on
the conversion of ethyl acetoacetate using [BSEt3N][HSO4] as catalysts
at temperature of 353.15 K, with catalyst dosage of 1.0 wt%, with ethyl
acetoacetate to ethylene glycol molar ratio of (-) 1 : 1; (C) 1 : 1.2; (:)
1 : 1.5; (;) 1 : 2.
Fig. 6 The recycle test of [BSEt3N][HSO4] catalyst at 2 h.
ascribed to the effect of static hindrance of bulk carbon chain
which can inhibit the diffusion of the reactants.
Acetalization of ethyl acetoacetate with other alcohols
Recycling of catalyst
The acetalization of ethyl acetoacetate with other alcohols
(1,2-propanediol and 1,4-butanediol) using the BAILs [BSEt3N]-
[HSO4] as catalysts were further investigated under the above-
mentioned optimized reaction conditions (reaction tempera-
tures of 353.15 K, initial molar ratio of 1 : 1.5, catalyst dosage of
1.0 wt%). The experimental results were given in Fig. 5. It can be
seen that the SO3H-functionalized BAILs [BSEt3N][HSO4] per-
formed high catalytic performances in the acetalization reac-
tions of ethyl acetoacetate with ethylene glycol, 1,2-propanediol
and 1,4-butanediol, affording the corresponding esters in
excellent yields. Compared with the other two diols, 1,2-pro-
panediol possessing an electron-donating methyl group resul-
ted in the highest conversion of ethyl acetoacetate (76%),
showing that the methyl group is benecial to the nucleophilic
ability of 1,2-propanediol and thus the yield of ester. However,
in the case of 1,4-butanediol containing the longest carbon
chain, the conversion was reduced to 19.2% at 2 h. It may be
The feasibility of a catalytic process depends on the recovery and
reuse of catalysts. Thus, the reusability of the BAIL [BSEt3N]-
[HSO4] catalyst in the acetalization of ethyl acetoacetate with
ethylene glycol was investigated under the optimal reaction
conditions (temperatures of 353.15 K, initial molar ratio of
1 : 1.5, catalyst loading of 1.0 wt%, and reaction time of 2 h).
Aer each cycle, the BAIL was separated from the reaction
mixture by simple decantation and then washed with acetone.
Aer being dried under vacuum, it was directly reused in the
successive recycling runs. As shown in Fig. 6, the conversions of
ethyl acetoacetate for six consecutive runs without any signi-
cant decrease in activity, which indicates that the BAIL catalyst
is stable enough and the presence of water produced in the
acetalization reaction has less inuence on the catalytic activity
of [BSEt3N][HSO4]. The gradual decrease in the activities could
be due to the slight loss of [BSEt3N][HSO4] during handling and
transferring of the solution.
Conclusions
In conclusion, six SO3H-functionalized BAILs had been
prepared successfully and applied in the synthesis of fructone.
The experimental results indicated that the SO3H-functional-
ized BAILs [BSEt3N][HSO4] exhibited extremely strong acidities,
and played excellently catalytic activities in the acetalization of
ethyl acetoacetate with ethylene glycol. In addition, it was found
that increasing the reaction temperature, catalyst dosage and
the amount of ethylene glycol could improve the conversion of
ethyl acetoacetate effectively, and the optimal condition was
obtained as follows: temperature of 353.15 K, catalyst dosage of
1.0 wt%, and initial molar ratio of 1 : 1.5. [BSEt3N][HSO4] also
could be recovered easily for six times without signicant
degradation in activities. Therefore, the SO3H-functionalized
BAIL prepared in this work was proved to excellent recyclable
catalysts for the synthesis of fructone, which make it a prom-
ising catalyst for industry.
Fig. 5 Results of the acetalization reaction of ethyl acetoacetate with
various alcohols of (-) ethylene glycol; (C) 1,2-propanediol; (:) 1,4-
butanediol using [BSEt3N][HSO4] as catalysts at temperature of 353.15
K, with catalyst dosage of 1.0 wt%, with ethyl acetoacetate to alcohols
molar ratio of 1 : 1.5.
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RSC Advances
15 D. J. Tao, J. Wu, Z. Z. Wang, Z. H. Lu, Z. Yang and X. S. Chen,
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Acknowledgements
16 X. Nie, X. Liu, L. Gao, M. Liu, C. Song and X. Guo, Ind. Eng.
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This work was supported by the National Natural Science
Foundations of China (no. 21206031), the Foundation of
Education Department of Henan Province of China (no.
13A150091) and the Science & Technology Supporting Programs
and the International Technological Cooperation Programs of
Jiangxi Provincial Department of Science and Technology (no.
20123BBE50081 and 20132BDH80003).
17 Z. S. Qureshi, K. M. Deshmukh, K. P. Dhake and
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