Green synthesis of 1-phenyl-1-ortho-xylene ethane in IL and reaction mechanism

Article abstract of DOI:10.1039/c6ra28009a

1-Phenyl-1-ortho-xylene ethane (PXE) in IL was synthesized, and the catalysts used were AlCl₃ in 1-butyl-3-methylimidazolium bromide ([BMIM][Br]) or 1-butyl-3-methylimidazolium chloride ([BMIM][Cl]), and H₂SO₄. When the concentrations of AlCl₃ in IL, ortho-xylene and styrene were 0.35, 0.03 and 0.005?mol, respectively, it could be discovered that ([BMIM][Br]) was the best catalyst. When the mole fraction concentration of AlCl₃/[BMIM][Br] was more than 0.40%, the reaction was able to achieve 100% conversion. When the reaction time was longer than 60 minutes, the percentage conversion of ortho-xylene attained was 100%. The mechanisms of the reaction were investigated by the DFT method at the B3LYP/6-311++G(d, p) level. The potential energy surface (PES) profile indicated that the energy of transition state was 22.59 kcal mol^?1. This indicated that the activation energy of reaction was 28.24 kcal mol^?1, which illustrated that the reaction occurred easily. Vibrational frequencies were observed in FT-IR spectra, the corresponding vibrational modes ν_s(H4-C3Al-H5) and ν_as(H4-C3Al-H5) indicated that an Al³⁺ ion was combined with a C3 atom. In addition, the repeated use of the catalysts was studied; the ionic liquids could still catalyze the reaction and the percentage yield of PXE was larger than 91% after 6 runs.

Full text of DOI:10.1039/c6ra28009a

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PAPER
Green synthesis of 1-phenyl-1-ortho-xylene ethane
in IL and reaction mechanism†
Cite this: RSC Adv., 2017, 7, 14998
a
b
a
a
b
Xuejun Sun, Xinming Zhou, Bobo Cao, Ziping Cao* and Hui Fu*
1
-Phenyl-1-ortho-xylene ethane (PXE) in IL was synthesized, and the catalysts used were AlCl
methylimidazolium bromide ([BMIM][Br]) or 1-butyl-3-methylimidazolium chloride ([BMIM][Cl]), and H
When the concentrations of AlCl in IL, ortho-xylene and styrene were 0.35, 0.03 and 0.005 mol,
respectively, it could be discovered that ([BMIM][Br]) was the best catalyst. When the mole fraction
concentration of AlCl /[BMIM][Br] was more than 0.40%, the reaction was able to achieve 100%
3
in 1-butyl-3-
2 4
SO .
3
3
conversion. When the reaction time was longer than 60 minutes, the percentage conversion of ortho-
xylene attained was 100%. The mechanisms of the reaction were investigated by the DFT method at the
B3LYP/6-311++G(d, p) level. The potential energy surface (PES) profile indicated that the energy of
ꢀ1
transition state was 22.59 kcal mol . This indicated that the activation energy of reaction was 28.24 kcal
ꢀ1
mol , which illustrated that the reaction occurred easily. Vibrational frequencies were observed in FT-IR
Received 10th December 2016
Accepted 23rd February 2017
spectra, the corresponding vibrational modes n (H4–C3Al–H5) and nas(H4–C3Al–H5) indicated that an
s
3+
Al ion was combined with a C3 atom. In addition, the repeated use of the catalysts was studied; the
DOI: 10.1039/c6ra28009a
ionic liquids could still catalyze the reaction and the percentage yield of PXE was larger than 91% after 6
runs.
rsc.li/rsc-advances
spent acids are disadvantages of both processes. To avoid
pollution a more environmentally friendly catalyst is desired.
Room temperature ionic liquid (IL) systems have many
1
. Introduction
2,3
1-Phenyl-1-ortho-xylene ethane (PXE) and bis(1-phenyl ethanyl)
ortho-xylene (BPXE) are synthesis liquids with excellent perfor- unique properties such as a very large liquid temperature range,
4
mance because of their high boiling points, low viscosity, high and they can be made task-specic for certain applications,
solubility, low melting points, high-color printer's ability, high which include use as solvents in chemical synthesis and catal-
5
–11
12,13
dielectric strengths and electrothermal stability, etc., and are ysis
and separation technology,
as electrolytes in elec-
14–16
widely used in pressure sensitive dye solvents of carbonless trochemical devices,
paper and electrical insulating oil. In addition, they can also uids. In addition, there is a huge range of possible combi-
and as lubricants or as heat-transfer
1
7
be used as a plasticizer, transformer oil, and other high nations of cations and anions, which contribute to the design of
18
boiling point solvents. Current commercial alkylation ILs. However, before these liquids can be used commercially
processes are catalyzed primarily by concentrated sulfuric acid on an industrial scale, the process variables need to be opti-
1
or hydrouoric acid. The reaction equation is as follows:
mized in the laboratory, not only in batch and continuous
The sulfuric acid process produces large amounts of spent reactor systems for maximum reactant conversion, but also the
acid and acid-soluble oils, which cause serious environmental product yield and catalyst selectivity. Previous studies have
problems. Anhydrous HF is highly toxic and its leakage demonstrated that the activity of such systems strongly depends
produces dangerous stable aerosols at the ground level. In on the molar ratio of AlCl
3
/IL. Usually, maximal activity can be
19,20
addition, equipment corrosion, transport, hazard management obtained at a molar ratio of 1.5–2.0 of AlCl
3
to IL.
This study reports that 1-phenyl-1-ortho-xylene ethane (PXE)
is synthesized in IL and the catalysts used are AlCl in 1-butyl-3-
and environmental liability associated with the disposal of
3
methylimidazolium bromide ([BMIM][Br]) or 1-butyl-3-
methylimidazolium chloride ([BMIM][Cl]). The reaction mech-
anism presented in this work is drawn in the following scheme.
The catalytic activity of a Lewis acid-IL is studied under
different experimental conditions, such as different catalysts,
a
School of Chemistry and Chemical Engineering, Qufu Normal University, Qufu
2
73165, Shandong, P. R. China. E-mail: caozp_qfnu@163.com; sxjsunxuejun@163.
com; qufucaobobo@163.com
b
State Key Laboratory of Heavy Oil Processing, College of Science, China University of
Petroleum, Qingdao 266580, Shandong, P. R. China. E-mail: fuhuiupc@163.com; concentrations, temperatures and reaction times. The catalysts
zhouxinming@upc.edu.cn
are facilely isolated from products and effectively recycled. The
mechanism of the reaction is determined using quantum
†
Electronic supplementary information (ESI) available. See DOI:
0.1039/c6ra28009a
1
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chemical calculations and vibrational frequencies are observed 2.3 Computational methods
in FT-IR spectra. The repeated use of the catalysts is also
investigated.
The reactant (R), intermediate (IM) and transition states (TS)
and formed products (P) were fully optimized using the B3LYP/
6-311++G(d, p) basis set, containing polarizable and diffuse
2
. Experiments
functions, and this well described the weak interactions in the
binary systems, especially for intermolecular H-bonded inter-
actions. The interaction energy (DE) was estimated by employ-
ing the counterpoise (CP) method for the Gaussian basis set
2.1 Materials
High-purity ortho-xylene, styrene and anhydrous AlCl
3
were
used in this study and purchased from the Tianjin Damao
Chemical Reagent Factory (Tianjin, China) and Chinese Medi-
cine Group Chemical Reagent Co, Ltd (Beijing, China). [BMIM]
21
superposition error (BSSE). From intrinsic reaction coordinate
(IRC) calculations and the potential surface (PES) energy prole
for the transition state, two desired minima states of the
mechanism were obtained. All the DFT calculations were
[Cl] (CAS no. 79 917-90-1) and [BMIM][Br] (CAS no. 85 100-77-2)
were purchased from the Lanzhou (Lanzhou, China) Center for
Green Chemistry with a purity of 99% and water mass fractions
of less than 10
22
carried out using the Gaussian09 package.
ꢀ
3
ꢀ1
(g g ). To remove traces of volatile
ꢀ6
3. Results and discussion
compounds, the ILs were kept in a vacuum (about 10 bar) at
343 K for 24 h prior to use.
3.1 Solubility of AlCl in [BMIM][Cl] and [BMIM][Br]
3
A given amount of anhydrous AlCl is slowly added to 3.00 g of
3
2.2 Apparatus and measurements
[BMIM][Cl] and [BMIM][Br] and the mixture is stirred at
An Agilent6890 (Agitent Co. USA) gas chromatograph equipped different temperatures until the catalyst is completely dissolved.
with a ame ionization detector (FID) was employed for anal- AlCl
3
/[BMIM][Cl] and AlCl
3
/[BMIM][Br] ionic liquids are thus
in [BMIM][Cl] and [BMIM][Br]
ꢁ
ysis. The detector temperature was maintained at 240 C. The obtained. The solubility of AlCl
3
ꢁ
column was programmed with an initial temperature of 60 C is shown in Table 1. It can be seen that the solubility of AlCl
3
ꢁ
ꢁ
and this was increased thereaer to 220 C at a rate of 15 C increased with the increase of temperature. The solubility of
ꢀ
1
min . The column used for this purpose was HP-1 with AlCl
3
in [BMIM][Br] is higher than that in [BMIM][Cl]. The
dimensions of 50 m ꢂ 0.25 mm ꢂ 0.50 mm.
saturation points of AlCl in [BMIM][Cl] and [BMIM][Br] are
To support the computational results, Fourier transform around 50 C and 80 C, respectively. Experimental results also
3
ꢁ
ꢁ
infrared (FT-IR) spectra of 2BP8HQ were recorded using show that the solubility of AlCl in [BMIM][Cl] and [BMIM][Br] is
3
ꢀ
1
a Nicolet iS5 FT-IR spectrometer (4000–525 cm ; number of larger in the latter than in the former. Since the catalytic
scans: 250; resolution: 1 cm ) to study the variations of the IR properties of these binary mixtures depend on their acidities,
ꢀ1
spectra of ortho-xylene and styrene, and the reaction processes. we can conclude that the catalytic activity of the latter is
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3
Table 1 Solubility of AlCl in [BMIM][Cl] and [BMIM][Br]
[
BMIM][Cl]
[BMIM][Br]
ꢁ
a
b
a
b
Temp. ( C)
Solution
Content
Solubility (%)
solution
Content
Solubility (%)
2
3
4
5
6
7
8
9
0
0
0
0
0
0
0
0
0.00056
0.00061
0.00068
0.00075
0.00078
0.00078
0.00078
0.00078
0.029792
0.032366
0.035947
0.039501
0.041016
0.041016
0.041016
0.041016
0.0330
0.0350
0.0400
0.0430
0.0450
0.0450
0.0450
0.0450
0.00643
0.00719
0.00824
0.00862
0.00877
0.00900
0.00952
0.00952
0.31936
0.4628
0.5249
0.6015
0.6292
0.6402
0.6570
0.6950
0.6950
0.344118
0.375501
0.386132
0.390229
0.396406
0.409921
0.409921
a
b
The concentration is the mole concentration. Molar content of AlCl
3
(X(AlCl
3
3 3
)) ¼ ([AlCl ]/([AlCl ] + IL)).
stronger than the former, which can be adjusted by the molar and the effect of the different mole fractions of AlCl
3
/[BMIM]
ratio of AlCl /IL. [Br] on the reaction is listed in Table 3. It can be seen that the
3
percentage conversion of ortho-xylene increased with the
increase of the mole fraction of AlCl /[BMIM][Br], and when the
3
3
.2 Effects of different catalysts on the reaction
mole fraction of AlCl
percentage conversion of ortho-xylene attained was 100%. This
shows that as long as the mole fraction concentration of AlCl
BMIM][Br] is more than 0.40%, the reaction will be able to
3
/[BMIM][Br] is larger than 0.40%, the
Different catalysts were added to, under the conditions of stir-
ring, solutions of styrene and ortho-xylene dropwise; the reac-
tion is performed in an 80–85 C oil bath. TLC (petroleum ether
3
/
ꢁ
[
as a solvent) was used to monitor the progress of the reaction.
Aer the completion of the reaction, the reaction liquid was le
standing and allowed to cool; the lower layer was separated. The
ionic liquid catalyst is rapidly added to small amounts of ortho-
xylene for the next use. ortho-Xylene is distilled and recovered,
achieve 100% conversion, and moreover, the rates of formation
of PXE and BPXE increased with the increase of the mole frac-
1
tion of AlCl to [BMIM][Br]. The H NMR spectrum for a mixture
3
of PXE and BPEX with a 1 : 0.36 ratio is shown in Fig. S1 (ESI†).
1
3
H NMR (500 MHz, CDCl ): d 7.35–7.20 (m, 3 + 2.13H), 7.20–7.10
ꢁ
and the distillation product is collected at 208–214 C.
(
4
3
m, 4 + 1.42H), 7.08–6.90 (m, 1 + 0.71H), 4.27 (q, J ¼ 7.2 Hz, 1H),
3
When the concentration of AlCl in IL, ortho-xylene and
.12 (q, J ¼ 7.2 Hz, 0.71H), 2.29 (s, 3H), 2.21 (s, 2.13H), 2.18 (s,
H), 1.63 (d, J ¼ 7.2 Hz, 2.13H), 1.58 (d, J ¼ 7.2 Hz, 3H). The
styrene are 0.35, 0.03 and 0.005 mol, respectively, the reactions
ꢁ
are performed at 30 C, the effects of different catalysts on the
results are in agreement with the data in ref. 23.
reaction are shown in Table 2. It can be seen that the orders of
yield are AlCl
SO (56%), which indicated that the yields of AlCl
Cl] and [BMIM][Br] are larger than that of H SO , especially, the
yield of AlCl /[BMIM][Br] reaches 99%. This illustrates that
AlCl /[BMIM][Br] is the best catalyst for the alkylation reaction
of ortho-xylene and styrene. Hence, AlCl /[BMIM][Br] is used as
the catalyst in the following experiments.
3
/[BMIM][Br] (99%) > AlCl
3
/[BMIM][Cl] (73%) >
H
[
2
4
3
in [BMIM]
3
.4 Effects of different temperatures on the reaction
When the amount of ortho-xylene and styrene was 0.03 and
.005 mol, respectively, the reaction time was 60 minutes and
2
4
3
0
3
the mole fraction of AlCl /[BMIM][Br] was 0.40%. The reactions
3
3
were carried out, and the effects of different temperatures on
the reaction are given in Table 4. It can be seen that the
percentage conversion of ortho-xylene increased with the
increase of temperature, and when the temperature is higher
3.3 Effects of different mole fractions of AlCl
3
/[BMIM][Br] on
the reaction
ꢁ
than 60 C, the percentage conversion of ortho-xylene attained is
ꢁ
When the amount of ortho-xylene and styrene is 0.03 and 100%. This illustrates that 60 C is enough for the reaction. At
ꢁ
0
.005 mol, respectively, the reactions are carried out at 30 C, the same time, the rates of formation of PXE and BPXE
a
Table 2 Effects of different catalysts on the reaction
Selectivity (%)
PXE
Conversion
(%)
b
Entry
Catalyst
Time (min)
BPXE
Yield (%)
1
2
3
H
AlCl
AlCl
2
SO
4
60
60
60
45
85
100
47.6
57
69
9.5
16
30
56
75
98
c
c
3
/[Bmim][Cl]
3
/[Bmim][Br]
a
ꢁ
b
c
3
Reaction conditions: ortho-xylene (0.03 mol), styrene (0.005 mol) and catalyst (0.5 g) at 30 C. GC yield was shown. The mole ratio of AlCl to IL is
0
.35.
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a
3
Table 3 Effects of different mole fractions of AlCl /[Bmim]Br on the reaction
Selectivity (%)
PXE
AlCl
(mole ratio)
3
/[Bmim][Br]
Conversion
(%)
b
Entry
Time (min)
BPXE
Yield (%)
1
2
3
4
5
6
0.28
0.32
0.35
0.38
0.39
0.40
60
60
60
60
60
60
24
26
30
84
97
100
24
28
35
59
67
70.6
1.3
1.6
3.5
6.9
21
17
21
25
70
92
98
24
a
ꢁ
b
Reaction conditions: ortho-xylene (0.03 mol), styrene (0.005 mol) and catalyst (0.5 g) at 30 C. GC yield is shown.
a
Table 4 Effects of different temperatures on the reaction
3
are 0.03 and 0.005 mol, respectively, the mole fraction of AlCl /
[
BMIM][Br] is 0.40%, the reaction time is 60 minutes and the
Selectivity (%)
ꢁ
reactions are carried out at 70 C.
Temperature
( C)
Conversion
(%)
ꢁ
b
Entry
PXE
BPXE
Yield (%)
3
.6 Reaction mechanism
1
2
3
4
5
6
10
30
50
70
90
100
15
97
99
100
100
100
14
67
69
69
69
69
0.6
21
28
30
30
30
12
92
96
98.3
98.6
99
3.6.1 Mechanism of the reaction. Quantum chemical
calculations are a useful tool to predict the reaction mecha-
nisms and kinetics of the alkylation reaction. Styrene (R1) and
ortho-xylene (R2) have been fully optimized at the B3LYP/6-
311++G(d, p) level, the geometrical parameters involving
a
Reaction conditions: ortho-xylene (0.03 mol), styrene (0.005 mol) and various species of R1, R2, IM, TS and P are shown in Fig. 1 and
AlCl
3
/[Bmim][Br] (0.5 g, mole ratio: 0.40) at the indicated temperature
b
S2 (ESI†), and the important geometrical parameters are given
in Table 6. It can be seen that styrene has a P
for 60 minutes. GC yield is shown.
8
8
conjugated
structure; for R, the bonds of C1–C2 and C2–C3 are averaged
3
+
ꢀ
which are 1.390 and 1.486 (A), respectively. When an Al ion is
increased with temperature, which do not vary when the
3
+
combined with a C3 atom in styrene, the length of C3–Al is
ꢁ
temperature is 60 C.
ꢀ
2
.101 (A), and the obtained IM joined with ortho-xylene. This
3
+
illustrates that the Al ion plays an important role in the
alkylation processes of styrene and ortho-xylene. From IRC
3
.5 Effects of different reaction times on the reaction
When the amount of ortho-xylene and styrene is 0.03 and calculations for the transition state (TS), we obtain two desired
.005 mol, respectively, and the mole fraction of AlCl /[BMIM] minima states of the process. This indicates a transition state,
0
3
ꢀ1
ꢁ
[
Br] is 0.40%, the reactions are carried out at 70 C, and the and it has an imaginary frequency (ꢀ182.63 cm ), the
effects of different reaction times on the reaction are shown in geometrical parameters of the TS are shown in Fig. 1. In the TS,
Table 5. It can be seen that the percentage conversion of ortho-
xylene increased with reaction time, and when the reaction time
is longer than 60 minutes, the percentage conversion of ortho-
xylene attained is 100%. Consequently, according to the above
results, the synthesis conditions for obtaining 1-phenyl-1-ortho-
xylene ethane are that the amounts of ortho-xylene and styrene
a
Table 5 Effects of different reaction times on the reaction
Selectivity
(
%)
Reaction time
(min)
Conversion
(%)
b
Entry
PXE
BPXE
Yield (%)
1
2
3
4
5
10
30
60
90
100
18
97
100
100
100
15
67
69
69
69
1.8
21
28
30
30
15
92
97.5
98.6
99
a
Reaction conditions: ortho-xylene (0.03 mol), styrene (0.005 mol) and
3
ꢁ
b
AlCl /[Bmim][Br] (0.5 g, mole ratio: 0.40) at 70 C. GC yield is shown. Fig. 1 Geometrical parameters of the TS.
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Table 6 Important geometrical parameters of the R, IM, TS and P (A) vibration of (C2–C3) in styrene. When AlCl
Paper
ꢀ
3
in [BMIM][Br] is
added to styrene and ortho-xylene, the symmetrical stretching
Transition
state
ꢀ1
vibration of (C2–C3) in styrene is red shied from 1710.33 cm
Bond length
Reactant
Intermediate
Product
ꢀ
1
3+
to 1106.60 cm , which illustrates that the Al ion combines
C1–C2
C2–C3
C2–H4
C3–H5
C3–H6
C7–H8
C3–Al9
C2–C7
C2–H8
C7–H4
C10-A9
1.390
1.486
1.090
1.100
1.081
1.087
1.395
1.460
1.098
1.100
1.087
1.087
2.101
1.473
1.460
1.097
1.097
1.088
1.086
2.101
2.319
2.585
2.562
1.553
1.576
1.091
1.091
1.097
1.110
1.965
1.600
with the C3 atom and decreases the C2–C3 bond strength. The
ꢀ
1
infrared peaks 3165.10 and 3247.26 cm
are attributed to
n
s
(H5–C3–H6) and nas(H4–C3–H5), respectively, which are also
ꢀ1
red shied to 3026.38 and 3067.59 cm , the corresponding
vibrational modes are n
s
(H4–C3Al–H5) and nas(H4–C3Al–H5),
3
+
respectively. This indicates that the Al ion joins to form a C3–
3
+
Al bond, which weakens the C3–H4 and C4–H5 bonds. In the
product (PXE) the infrared vibrational frequencies 3045.83 and
ꢀ1
3119.25 cm
s
correspond to the vibrational modes n (H5–
2.054
C3H7–H6) and nas(H5–C3H7–H6), respectively, and the blue
3
+
shis of these vibrational frequencies illustrate that Al has
ꢀ
1
been substituted for H7. The infrared peak at 991.48 cm is the
symmetrical stretching vibration of (C2–C3), which may be due
to further weakening caused by product formation. The
a C2–H4–C7–H8 four-membered ring is formed, the distances
of the bonds are 1.097, 2.562, 1.086 and 2.585 (A), respectively,
which provides helpful information on the formation of the C2–
C7 bond. The bond lengths of C1–C2, C2–C3 and C2–C7 are
ꢀ
ꢀ1
appearance of the vibrational frequency at 3053.79 cm
,
assigned to the symmetrical stretching vibration of (C2–C7),
demonstrates a new bond formation between styrene and ortho-
xylene.
ꢀ
1.553, 1.576 and 1.600 (A), respectively, which indicates that
those bonds are stretched by steric effects of two benzene rings.
The potential energy surface (PES) prole is depicted in
Fig. 2. The energy of the IM is lower than that of the reactant by
ꢀ
1
5.65 kcal mol , we can also nd that the energy of the P is
ꢀ
1
higher than that of the IM by 15.69 kcal mol . This result 3.7 Repeated use of the catalyst
indicates that the IM is more stable than the P. The energy of
When the amount of ortho-xylene and styrene is 0.03 and
ꢀ1
the TS is 22.59 kcal mol , and this indicates that the activation
0
.005 mol, respectively, and the mole fraction of AlCl
3
/[Bmim]
ꢀ
1
energy of the alkylation reaction is 28.24 kcal mol . This
illustrates that the reaction occurs easily, which is in agreement
with the experimental results.
ꢁ
[Br] is 0.40%, the reactions are carried out at 70 C with a reac-
tion time of 1.5 hours. Aer the reaction, the supernatant liquid
is poured out. In order to remove ortho-xylene and volatile
organic compounds from the ionic liquid, the reaction vessel
was put under vacuum, and then the weight of the raw materials
was added. The results are listed in Table 8. It can be seen that
the ionic liquid can still catalyze the reaction and the
percentage yield of PXE is larger than 91% aer 6 runs. The
activity of the catalyst decreased gradually aer 6 runs.
3.6.2 Vibrational frequencies. Table 7 lists the main
vibration variations of styrene, styrene + ortho-xylene + AlCl +
3
[BMIM][Br] and PXE as well as the IR intensity observed in FT-IR
spectra; the corresponding infrared spectra are shown in
Fig. S3–S5.† It can be seen that the infrared peak appearing at
ꢀ
1
1710.33 cm
is assigned to the symmetrical stretching
Fig. 2 Energy profiles of the R, IM, TS and P.
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Table 7 Main vibration spectrum variations of styrene, ortho-xylene, styrene + ortho-xylene + AlCl
3
+ [BMIM][Br] and PXE
Frequency
ꢀ
1
Species
Styrene
Vibrational mode assignment
(cm
)
IR intensity
n
n
n
n
n
n
n
n
n
n
n
n
n
n
n
s
s
s
(C2–C3)
(H4–C2)
(H5–C3–H6)
as(H4–C3–H5)
1710
3146
3165
3247
3077
1106
3026
3067
3161
3190
991
9.16
16.20
2.99
14.99
27.10
12.33
26.90
2.28
9.30
7.86
0.50
10.36
23.83
15.26
29.02
ortho-Xylene
s
s
s
(C7–H8)
(C2–C3)
(H4–C3Al–H5)
Styrene + ortho-xylene + AlCl
3
+ [BMIM][Br]
as(H4–C3Al–H5)
s
s
s
s
s
s
(C7–H8)
(H4–C2)
(C2–C3)
(C2–C7)
(H5–C3H7–H6)
(H4–C2)
1084
3045
3053
3119
PXE
as(H5–C3H7–H6)
Table 8 Catalyst performance in ionic liquid for repeated operations percentage conversion of ortho-xylene attained is 100%. The
effects of different reaction times on the reaction are investi-
Selectivity (%)
gated; when the reaction time is longer than 60 minutes, the
Percentage conversion
(%)
Yield
(%)
percentage conversion of ortho-xylene attained is 100%. The
mechanism of the reaction is discussed by quantum chemical
calculations and vibrational frequencies are observed in FT-IR
spectra. In addition, the repeated use of the catalyst is consid-
ered, the ionic liquid can still catalyze the reaction and the
percentage yield of PXE is larger than 91% aer 6 runs. The
activity of the catalyst decreased gradually aer 6 runs. The
activity of the catalyst can be improved by vacuum dehydration,
Run
PXE
BPXE
1
2
3
4
5
6
7
98.5
98.4
98.2
97.8
97.5
96.6
72.3
69.7
69.2
69.1
68.5
68.3
67.9
47.7
28.3
28.3
28.0
27.5
27.4
26.8
20.5
92.8
93.2
92.4
91.8
91.8
91.1
62.0
solvent rinsing and the addition of anhydrous AlCl
being studied.
3
, which is
According to Table 8, the activity of the catalyst began to
decrease aer 3–4 cycles. The main explanations for this are
leaching of AlCl3 from the binary mixture and catalyst Acknowledgements
poisoning by the reaction products and cokes. Measures can be
This work was supported by the National Natural Science
Foundation of China (No. 21206085 and 21203250).
taken to improve the catalytic activity, such as vacuum dehy-
dration, solvent rinsing and the addition of AlCl . Besides this,
3
further study has been carried out by our group aiming to
improve the catalytic efficiency.
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