Surfactant-like Br?nsted acidic ionic liquid as an efficient catalyst for selective Mannich reaction and biodiesel production in water

Article abstract of DOI:10.1007/s13738-016-1036-2

Abstract: The current study deals with the applications of a surfactant-like Br?nsted acidic ionic liquid (IL) 1-dodecyl-3-methylimidazolium hydrogen sulfate ([DMIm]HSO₄) for Mannich reaction at room temperature. The reaction was efficiently preceded in water as solvent without using any harmful and expensive organic additives. Our findings showed that the reaction is selective for cyclohexanone and no Mannich product was observed when cyclopentanone was used as starting material. Density functional theory (DFT) calculations were performed to provide an evidence about the nature of reactivity of the cyclohexanone/cyclopentanone. The activity of the catalyst was also tested for biodiesel production of fatty acids with methanol and ethanol at mild thermal condition without applying additional water removal steps such as using additives or performing special methodologies like azeotropic distillation. In both reactions, the IL can be recycled and reused several times with relatively constant efficiency. Graphical Abstract: [Figure not available: see fulltext.]

Full text of DOI:10.1007/s13738-016-1036-2

J IRAN CHEM SOC
DOI 10.1007/s13738-016-1036-2
ORIGINAL PAPER
Surfactant‑like Brønsted acidic ionic liquid as an efficient catalyst
for selective Mannich reaction and biodiesel production in water
Majid Vafaeezadeh1 · Mina Karbalaie‑Reza1 · Mohammad Mahmoodi Hashemi1 ·
Kasra Qasempour Soleimany2
Received: 27 May 2015 / Accepted: 20 December 2016
© Iranian Chemical Society 2016
Abstract The current study deals with the applications of
a surfactant-like Brønsted acidic ionic liquid (IL) 1-dode-
cyl-3-methylimidazolium hydrogen sulfate ([DMIm]HSO4)
for Mannich reaction at room temperature. The reaction
was efficiently preceded in water as solvent without using
any harmful and expensive organic additives. Our findings
showed that the reaction is selective for cyclohexanone and
no Mannich product was observed when cyclopentanone
was used as starting material. Density functional theory
(DFT) calculations were performed to provide an evidence
about the nature of reactivity of the cyclohexanone/cyclo-
pentanone. The activity of the catalyst was also tested for
biodiesel production of fatty acids with methanol and etha-
nol at mild thermal condition without applying additional
water removal steps such as using additives or performing
special methodologies like azeotropic distillation. In both
reactions, the IL can be recycled and reused several times
with relatively constant efficiency.
Electronic supplementary material The online version of this
article (doi:10.1007/s13738-016-1036-2) contains supplementary
material, which is available to authorized users.
* Majid Vafaeezadeh
majidvafaeezadeh@yahoo.com
* Mohammad Mahmoodi Hashemi
mhashemi@sharif.edu
1
Department of Chemistry, Sharif University of Technology,
PO Box: 11155-1639, Tehran, Iran
2
Hasin Technology Company, Tehran, Iran
1 3

J IRAN CHEM SOC
Graphical Abstract
catalyst. Therefore, the need for developing an efficient cat-
alytic system in water with high efficiency and reusability
is exist.
In recent year, the roles of the ionic liquids (ILs) have
been moved beyond their applications as alternative sol-
vents [4]. Several ILs have been designed, synthesized and
applied as catalyst for organic and inorganic transforma-
tions [5]. Brønsted acidic ILs are a large group of com-
pounds which attracts special attention for replacement of
traditional homogeneous acid catalyst [6–8]. These com-
pounds can be readily prepared, reused and separated from
the reaction mixture without releasing noticeable acidic
vapor. An interesting aspect of the ILs is attributed to the
tunable properties. By incorporating a hydrocarbon chain
with various lengths into the structure via simple chemical
reactions, the hydrophobicity/hydrophilicity of the ILs can
be controlled. The ionic nature of IL provides suitable solu-
bility in water. Simultaneously, the hydrophobic nature of
the IL facilitates approaching the organic groups toward IL.
In this paper, a Brønsted acidic IL, 1-dodecyl-3-meth-
ylimidazolium hydrogen sulfate ([DMIm]HSO4) has been
introduced as an efficient catalyst for selective Mannich
reaction in water. Mannich reaction is a useful synthetic
method for carbon–carbon bond formation reactions for
preparation of various drugs, natural products as well as
biologically active compounds [9, 10]. These β-amino car-
bonyl derivatives are majorly synthesized by using either
Brønsted [11, 12] or Lewis acid catalyst [13, 14]. A signifi-
cant improvement of the reaction was reported by Sharma
and co-workers which used an inorganic–organic hybrid
silica-based tin(II) material as a reusable catalyst for this
reaction at room temperature [15]. Despite introducing
efficient synthetic protocol, these methods typically suffer
from releasing hazardous metal wastes, using chlorinated
solvent or employing highly toxic reagent during the cata-
lyst preparation [16]. Moreover, despite extensive works
which were reported for this reaction, no significant report
focused on the selectivity of the reaction. In our method,
high yield of β-amino carbonyl derivatives was obtained
when cyclohexanone was used as ketone at room tempera-
ture. By replacing cyclopentanone as the starting material,
no product was obtained at ambient temperature which
suggests a meaningful selectivity for this reaction. Density
functional theory (DFT) calculations were performed at
B3LYP/6-311++G** to provide evidence about the reac-
tivity of the starting material.
Keywords Brønsted acidic ionic liquid · Mannich
reaction · Biodiesel · Water · DFT
Introduction
Elimination of organic solvent with hazardous environmen-
tal impacts and industrial cost is a crucial challenge in the
field of chemical reaction engineering. In chemical reac-
tions, “solvent free” or in the best case, selecting water as
solvent is a desire goal in both economical and environmen-
tal point of view [1, 2]. Water is cheap, safe and releases no
volatile harmful compounds. Unfortunately, in most cases
organic substrates do not have desirable compatibility and
miscibility with aqueous media. In some cases, modifica-
tion of the surface of the inorganic solids is an alternative
method for better diffusion of organic substrate on the sur-
face of these materials in water [3]. In this condition, water
“pushes” the organic substrates onto the hydrophobic sur-
face of the catalyst. Despite successful achievements, the
reaction kinetic on the surface of the heterogeneous cata-
lyst is low and the desires yields only obtain in prolong
reaction time.
Amphiphilic reagents which are miscible with water and
can dissolve organic substrates are versatile selection for
improving the reaction efficiency in water. Among them,
surfactant-type Brønsted acids such as p-dodecylbenzene-
sulfonic acid (DBSA) may be a good selection with wide-
spread applications. These compounds form hydrophobic
cores in water and thus can conduct organic reactions in
solution phase with high efficiency. However, these com-
pounds still have very poor recovery and reusability as a
The second section of this paper deals with applica-
tion of the surfactant-like [DMIm]HSO4 IL for acid-cata-
lyzed esterification of fatty acids in both solvent-free and
in aqueous media. Fatty acid methyl or ethyl esters are
known as biodiesel which have received extensive atten-
tion for replacements of fossil fuel [17, 18]. It can tradi-
tionally be prepared via base-catalyzed transesterification
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J IRAN CHEM SOC
of triglycerides with short-chain alcohols such as methanol
or ethanol [19]. Unfortunately, in the case of less expen-
sive feedstock such as waste oil (which contains high
degree of free fatty acids) the process interrupted due to
the soap formation by the reaction between fatty acid and
the applied base catalyst. Additionally, excess amount
of base is needed to neutralize the free fatty acids which
cause releasing large volume of salty waste. Hence, acid
catalyst esterification is the best solution for this reaction
which has compatibility with free fatty acid-containing
feedstock. Several methods based on supported IL [20–24]
or homogeneous IL [25–28] systems have been developed
for this reaction. A relatively good method for esterifica-
tion reaction in water comprises using Brønsted acidic sur-
factant as catalyst [29, 30]. However, the most important
challenge for conducting such reaction is attributed to the
reversibility of the reaction and performing the esterifi-
cation reaction in water since esters are metastable com-
pounds and can readily hydrolyze in water. Additionally,
when Brønsted acidic surfactant was used as catalyst, the
isolation of the products is difficult and hence it is neces-
sary to use ionic solution to breakdown the structure of the
micelles. Consequently, the applied surfactant is not reus-
able in this condition.
stirred (at 800 rpm) at room temperature. The reaction pro-
gress was monitored by thin layer chromatography (TLC).
At the end of reaction, the mixture was filtrated and the
solid product was collected and recrystallized in ethanol/
acetone (v/v = 1:1). The remained solution can be reused
for another reaction run.
Fatty acid esterification in water or solvent‑free
conditions
A mixture of fatty acid (2 mmol), methanol or etha-
nol (1.1–1.2 mL) and [DMIm]HSO4 was added to a
round-bottom flask equipped with a reflex condenser
and stirred in indicated times and temperatures. In the
case of the reaction in water, 2 mL of distilled H2O
was added to the reaction media. After the reaction ter-
mination, the biodiesel was extracted from the mixture
by adding n-hexane (2 × 15 mL). The small amount of
the residual fatty acid was neutralized with 5% aqueous
solution of NaHCO3 (4 mL). Then the resulted mixture
was dried over Na2SO4, and the n-hexane was evapo-
rated under reduced pressure to afford the corresponding
pure biodiesel.
Theoretical calculations
Experimental
The initial structures were built and optimized at B3LYP/6-
311++G** using Spartan software [31]. The imaginary
frequencies were checked for all optimized structures. Both
of the transition states have imaginary frequencies related
to the corresponding vibrational modes for bond forma-
tion and bond dissociation. The imaginary frequencies con-
firmed that whether the structures are ground state or tran-
sition state.
Preparation of [DMIm]HSO4
In a typical procedure, 20 mmol of 1-methylimidazol and
22 mmol of 1-bromododecane were refluxed in toluene for
8 h. After the termination of the reaction, the mixture was
cooled to room temperature. The resulted white precipitate
was collected and washed separately with toluene and die-
thyl ether to produce 1-dodecyl-3-methylimidazolium bro-
mide. The anion exchange was performed by adding equi-
molar amount of H2SO4 in super dry toluene. After 16 h,
the solvent was evaporated and the [DMIm]HSO4 was iso-
lated as viscous oil. The IL was dried in oven in the pres-
Results and discussion
Mannich reaction
1
ence of P2O5. H NMR (500 MHz, CDCl3): 0.73 (t, 3H),
The [DMIm]HSO4 was simply prepared from the reaction
between 1-methylimidazol and 1-bromododecane and sub-
sequent anion exchange by H2SO4. In this condition, HBr
was released during the reaction. The reaction was con-
tinued until the generation of HBr was finished. Then the
[DMIm]HSO4 IL was isolated and was stored in a refrig-
erator. The schematic illustration of the synthesis of IL is
shown in Scheme 1a.
1.09 (broad, 18 H), 1.69 (broad, 2H), 3.79 (s, 3H), 4.06 (t,
2H), 7.29 (s, 1H), 7.41 (s, 1H), 8.86 (s, 1H) and 10.01 (s,
1H). 13C NMR (125 MHz, CDCl3): 14.52, 23.09, 26.74,
29.53, 29.78, 29.91, 30.04, 30.07, 30.09, 30.58, 32.33,
36.97, 50.40, 122.36, 124.31, 137.03.
Mannich reaction in water
The activity of the IL was investigated for three-com-
ponent Mannich reaction of benzaldehyde, aniline and
cyclohexanone as a bench reaction (Scheme 1b). At the first
step, we started to optimize the reaction temperature and
solvent which are two important parameters in chemical
A mixture of benzaldehyde (4 mmol), cyclohexanone
(4 mmol), aniline (4 mmol) and [DMIm]HSO4 (0.5 mmol)
was added to a 25-mL round-bottom flask. Then 6 mL of
distilled water was added, and the mixture was vigorously
1 3

J IRAN CHEM SOC
Scheme 1 Schematic prepara-
tion of [DMIm]HSO4 (a) and
Mannich reaction (b)
transformations. H2O was selected as an environmen-
tally benign and cheap solvent. Surprisingly, we found that
the reaction could be efficiently proceeded in water and at
ambient temperature. In this condition, 91% of product was
obtained when 0.5 mmol of the IL was used. Decreasing the
amount of IL led to a significant drop of the reaction product.
Under this mild and clean condition, we then set up
experiments to study the scope and limitation of our cata-
lytic system. The results are summarized in Table 1.
Based on our finding, various available benzaldehydes
undergo Mannich reaction with cyclohexanone and ani-
line in high yield at room temperature after 6 h (Table 1,
entry 1–6). Moreover, 69% of the three-component Man-
nich derivative by using acetophenone as ketone was also
obtained in this condition (Table 1, entry 7). It was found
that the reaction with aniline derivative with electron-
donating group was facilitated and 94% of product was
obtained in our catalytic system (Table 1, entry 8).
For detailed study of the catalytic performance, we
then set up experiment by using cyclopentanone as start-
ing material (Table 1, entry 9). Our attempt to perform
the reaction at room temperature led to achieve poor yield
of Mannich product (8%). Having this interesting data in
hand, in the next stage we investigated the possibility of
chemoselective reaction of cyclohexanone in the presence
of cyclopentanone (Scheme 2).
As shown in Scheme 2, a 1:1 mixture of cyclohexanone
and cyclopentanone was allowed to react with aniline and ben-
zaldehyde in the presence of [DMIm]HSO4 as catalyst. After
6 h stirring of the reaction mixture at room temperature and
the product isolation, it was observed that only cyclohexanone
participated in the reaction and the corresponding Mannich
product of cyclopentanone was not obtained. This observation
suggests an interesting selectivity toward cyclohexanone in the
presence of cyclopentanone. On the other hand, by increasing
the reaction temperature to 50 °C cyclopentanone was sim-
ply converted to its corresponding Mannich product. Conse-
quently, the above catalytic system established the chemose-
lectivity at room temperature (22–25 °C).
The reaction mechanism comprises initial formation of
an iminium ion from the reaction of aniline and the benzal-
dehyde. At the second step, the iminium ion attacked by the
enol form of the applied ketone. Hence, the reactivity of the
cyclic ketone is attributed to the rate of enol formation of
cyclopentanone and cyclohexanone. Computational meth-
ods are fruitful techniques to provide evidence about reac-
tivity and energetic of the reactions. To provide evidence
about the origin of selectivity for cyclohexanone and cyclo-
pentanone in Mannich reaction, we optimized the initial
structure of cyclopentanone, cyclohexanone and their cor-
responding enol forms using B3LYP/6-311++G** level
of calculation. Then the transition state of each enol–keto
transformation was obtained at the same level of calcula-
tion (Scheme 3).
As shown in Scheme 3, in the transition state an H
atom is moving from the α-carbon atom to the oxygen of
carbonyl. Both of the imaginary frequencies are belong
to this H-shift and occurred at 2249.7 cm−1 for cyclopen-
tanone and at 2203.3 cm−1 for cyclohexanone. The higher
value of the H-shift frequency for cyclopentanone may be
interpreted that this tautomerization is more energetic than
that in cyclohexanone. Moreover, the activation energy
for conversion of cyclopentanone to its enol tautomer is
approximately 6.7 kcal/mol higher than that of cyclohex-
anone. Accordingly, at lower temperature, the energy for
cyclohexanone tautomerization could be better supplied
than cyclopentanone. By increasing the reaction tempera-
ture to 50 °C, the energy for cyclopentanone was supplied,
and thus, 79% of Mannich product from this ketone was
obtained (Table 1, entry 9).
The possibility of the recovery for the IL for Mannich
reaction was also investigated. For this purpose, the aque-
ous solution which was obtained from the first reaction run
was subjected to another reaction at the identical condi-
tion for Mannich reaction from benzaldehyde, aniline and
cyclohexanone (Table 1, entry 1). It was found that the
catalytic system can be reused at least for four times with
relatively constant activity.
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J IRAN CHEM SOC
Table 1 Catalytic activities of [DMIm]HSO4 for Mannich reaction at
room temperature in water
Fatty acid esterification reaction
Entry Product
Yield (%)a,b
m.p. (°C)
References
The high activity of the [DMIm]HSO4 encouraged us to turn
our attention for esterification of fatty acid. The reaction of
fatty acids with short-chain alcohol such as methanol or etha-
nol is one of the most important acid-catalyzed esterifications
since the products are used as biodiesel. As discussed above,
the limitations of this work are attributed to using organic
solvent and utilizing dehydration techniques to remove water
by-product to shift the reaction toward completion.
1
91 (90, 88, 85)c 115–116
114–115 [16]
O
Ph
N
H
2
86
122–124
119–120 [16]
CH3
O
To investigate the efficiency of the catalyst, the solvent-
free esterification of stearic acid with methanol was tested
as the sample reaction. At the first step, the amount of IL
was optimized for this reaction. As shown in Table 2, by
increasing the amounts of IL, the yield of ester was signifi-
cantly increased.
However, increasing the amounts of IL did not show
significant improvement in the reaction. For example, by
increasing the amounts of IL from 0.20 to 0.30 g, a negligi-
ble improvement for the reaction was observed. To increase
the reaction efficiency, the amounts of methanol decreased
to 1.1 mL. Surprisingly, it was found that the yield of prod-
uct reached 94% (isolated yield) in the presence of 0.1 g of
IL. It can be concluded that reducing the amounts of alco-
hol has positive effect on the reaction efficiency.
Ph
N
H
3
83c
145–147
–
Ph
O
Ph
N
H
4
76
78
118–120
127–129
116–117 [16]
OEt
Ph
O
N
H
5
–
Cl
Ph
O
N
H
Table 3 shows the effect of temperature on the esterifica-
tion reaction of stearic acid with methanol.
6
79d,e
121–122
123–125 [32]
NO2
As can be deduced from these experiments, the esteri-
fication was smoothly proceeds at room temperature and
73% of the corresponding biodiesel was obtained after
10 h. Performing the esterification reaction at room tem-
perature without using water removal techniques is an
interesting issue especially in the industrial point of view.
By increasing the temperature, the yield of the reaction
was reached 94% at 60 °C and even to its highest value at
70 °C.
The kinetic of the mentioned reaction was also inves-
tigated (Fig. 1). In this regard, several experiments for
esterification of stearic acid and methanol were per-
formed. The results showed that after 10 h, the amount of
product was reached its maximum value and increasing
the reaction time did not show a significant improvement
of the reaction.
O
Ph
N
H
7
69
130–132
134–135 [32]
O
Ph
N
H
8
94
169–171
110–112
168–169 [16]
CH3
O
Ph
N
H
9
8 (79)e,f
–
O
Ph
N
H
Performing the esterification in water is the most
promising issue of the reaction. According to the Le
Chatelier’s principle, by using water as solvent the reac-
tion equilibrium tends to relief the effect of the additional
H2O and readjusts to form initial acid and alcohol in the
presence of the acidic catalyst. However, our screen-
ing about this issue revealed that even in the presence
of water, high yield of biodiesel could be obtained. The
yields of ester in the presence of various amounts of
water are listed in Table 4.
a
Reaction conditions: aldehyde (4 mmol), ketone (4 mmol), amine
(4 mmol), [DMIm]HSO4 (0.5 mmol) and distilled H2O (6 mL) at
room temperature for 6 h, unless otherwise stated
Yields refer to isolated pure product and gave satisfactory 1H NMR
b
c
Recovery experiments for the 2nd, 3rd and 4th runs of the reaction,
respectively
d
1 mL ethanol was added as co-solvent
e
Reaction time: 8 h
f
Reaction temperature: 50 °C
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J IRAN CHEM SOC
Scheme 2 Chemoselective
Mannich reaction of cyclohex-
anone in the presence of cyclo-
pentanone in water
Table 3 Optimization of the temperature for esterification of stearic
acid and methanol catalyzed by [DMIm]HSO4
Entry
Temperature
Yield (%)a,b
1
2
3
4
5
r.t.
40
50
60
70
73
80
90
94
97
Yields refer to isolated pure product and gave satisfactory 1H NMR
Reaction condition: stearic acid (2 mmol), methanol (1.1 mL) IL
a
b
(0.1 g) and 10 h
Scheme 3 The relative energies for enol–keto tautomerization for
cyclopentanone and cyclohexanone. The values of energies are stated
in kcal/mol
Table 2 Optimization of the amount of [DMIm]HSO4 for esterifica-
tion of stearic acid and methanol
Fig. 1 Kinetic of solvent-free esterification of stearic acid and methanol
at 60 °C in the presence of 0.1 g IL, 2 mmol stearic acid and 1.1 mL
methanol
Entry
Amount of IL (g)
Yield (%)a,b
1
2
3
4
5
0.10
0.15
0.20
0.30
0.10
76
76
82
84
94c
The highest amount of the product (90%) was obtained
when 2 mL of water was added to system. Worthy to note
that in this condition the water may exist in the form of
both solvent and impurity of the starting material. For
example, in most esterification reaction it is necessary
to use absolute ethanol or methanol which increases the
reaction cost. However, our investigation showed that the
a
Yields refer to isolated pure product and gave satisfactory 1H NMR
Reaction condition: stearic acid (2 mmol), methanol (2.5 mL)
b
60 °C and 10 h, unless otherwise stated
c
The reaction was performed in the presence of 1.1 mL methanol
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J IRAN CHEM SOC
Table 4 Effect of water on esterification of stearic acid and methanol
Table 5 Data for catalytic performance for biodiesel production
from esterification of fatty acids in both solvent free and water as sol-
vent
Entry
H2O (mL)
Yield (%)a,b
1
2
3
4
5
2
90
80
75
70
64
Entry
Fatty acid
Alcohol
Yield (%)a
2.5
3
Solvent condition
Solvent freeb H2Oc
3.5
5
1
2
3
4
Stearic acid
Methanol 76
Ethanol 80
Methanol 85
Ethanol 81
Palmitic acid Methanol 74
Ethanol 84
Methanol 77
Ethanol 90
90 (85, 86, 81)d
84
96
87
83
86
80
95
a
Yields refer to isolated pure product and gave satisfactory 1H NMR
Reaction condition: stearic acid (2 mmol), methanol (1.1 mL) IL
Lauric acid
b
(0.1 g), 60 °C and 10 h
current protocol is applicable with high efficiency even in
the presence non-absolute alcohols.
Oleic acid
One plausible explanation for this phenomenon is
attributed to the prevention of ester hydrolysis. The hydro-
phobic nature of the [DMIm]HSO4 led to formation of the
micellar cores in water. The inner part of micelles has high
degree of hydrophobicity which facilitates the transpor-
tation of organic substrates and simultaneous removal of
water by-product. Schematic illustration for the proposed
mechanism for the catalytic efficiency of IL is shown in
Fig. 2.
a
Yields refer to isolated pure product and gave satisfactory 1H NMR
Reaction condition: fatty acid (2 mmol), methanol (1.1 mL) or eth-
b
anol (1.2 mL), IL (0.1 g), 60 °C and 10 h
c
Reaction condition: fatty acid (2 mmol), methanol (1.1 mL) or eth-
anol (1.2 mL), IL (0.1 g), H2O (2 mL), 60 °C and 10 h
d
Recovery experiments for the 2nd, 3rd and 4th runs of the reaction,
respectively
The data for catalytic performance of the [DMIm]HSO4
for direct esterification of various fatty acids and ethanol in
both solvent free and using water as solvent are shown in
Table 5.
As shown in Table 5, various fatty acids efficiently
reacted with methanol and ethanol to produce the cor-
responding biodiesel. In the case of acid-sensitive fatty
acid such as oleic acid, esterification was occurred with-
out hydration of the double bond. Moreover, in all cases
the results of product in water are higher than those in
solvent-free condition. To investigate whether the aque-
ous solution from the first reaction run of esterification
is reusable or not, after the product isolation, the aque-
ous solution of the first run was subjected to other experi-
ments with identical conditions to the first reaction. It
was found that the catalytic system is reusable for four
reaction runs without significant loss of its activity
(Table 5).
Table 6 shows the comparisons among the catalytic effi-
ciency of the [DMIm]HSO4 and some literature reports for
direct esterification reactions. The results indicate that the
catalytic activity of the [DMIm]HSO4 is comparable and
even superior than those which were previously reported
(Table 6).
Fig. 2 Schematic illustration
for esterification reaction in the
[DMIm]HSO4 catalytic system
in water
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J IRAN CHEM SOC
Table 6 Catalytic comparison
of the [DMIm]HSO
Alcohol
Acid
Catalyst
Time (h)/temp. (°C) Yield (%) References
4 for
esterification with some
literature reports
Methanol
Ethanol
Butanol
Butanol
Methanol
Ethanol
Stearic acid
Benzoic acid
Acetic acid
Acetic acid
[DMIm]HSO4
[PSPy][BF4]
10/70
12/78
97
This work
[33]
88.0
98.9
97.4
91.4
82
[(CH2)3SO3HVIm]HSO4 3/89
Poly(VMPS)-PW 1.5/110
[34]
[35]
Caprylic acid [Tshx][HSO4]4
Acetic acid [PSTphP][OTs]
0.5/80
1/175
[36]
[37]
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In this study, we designed and introduced a highly efficient
catalytic system based on surfactant-like IL for Mannich
reaction and biodiesel production in water. High yields
of Mannich products were obtained at room temperature.
Despite the efficiency of [DMIm]HSO4 for Mannich reac-
tion, the selectivity of the IL was also investigated between
cyclopentanone and cyclohexanone. DFT calculation
showed that cyclohexanone is more reactive than cyclopen-
tanone in Mannich reaction. Furthermore, the activity of
the catalyst for solvent-free biodiesel production was fully
studied in various reaction conditions. It was shown that
[DMIm]HSO4 has excellent activity in water and even was
superior than solvent-free condition. Both catalytic systems
(IL + H2O) are capable to reuse for four times without
noticeable loss of activity.
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