p-Toluenesulfonic acid functionalized imidazole ionic liquids encapsulated into bismuth SBA-16 as high-efficiency catalysts for Friedel-Crafts acylation reaction

Article abstract of DOI:10.1039/d1dt00355k

Bismuth SBA-16 catalyst was synthesized by the hydrothermal method. Four kinds ofp-toluenesulfonic acid functionalized imidazole ionic liquids were prepared by a two-step method and their molecular structures were characterized by¹H NMR and MS. The post-synthesis impregnation method was used to functionalize the Bi(10)-SBA-16 silicon mesoporous material with the ionic liquids and the obtained materials were characterized by FT-IR, XRD, BET, XPS, and TG. The results show that the volume and pore size of SBA-16 were changed by loading Bi and ionic liquids, while the three-dimensional cubic pore structure of SBA-16 was not destroyed. The composite catalyst was evaluated in Friedel-Crafts acylation of anisole with acetic anhydride. The effects of reaction temperature and the ratio of anisole and acylating agent on the acylation of anisole were investigated by experimental design. The results showed that 1.2ILc@Bi(10)-SBA-16 was used as the catalyst, the conversion of anisole was 85.41% and the yield of aromatic ketone was 69.19% under the conditions of a reaction temperature of 100 °C, a catalyst dosage of 0.5 g, a time period of 4 h and a molar ratio of 1?:?1.5. After 5 recycling runs, the reduction in the overall ratio of reactant conversion and product yield did not exceed 7.5%, indicating that 1.2ILc@Bi(10)-SBA-16 has good stability and reusability.

Full text of DOI:10.1039/d1dt00355k

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p-Toluenesulfonic acid functionalized imidazole
ionic liquids encapsulated into bismuth SBA-16 as
high-efficiency catalysts for Friedel–Crafts
acylation reaction†
Cite this: Dalton Trans., 2021, 50,
5871
Guofang Gao, Qian Zhao, Cheng Yang and Tingshun Jiang
*
Bismuth SBA-16 catalyst was synthesized by the hydrothermal method. Four kinds of p-toluenesulfonic
acid functionalized imidazole ionic liquids were prepared by a two-step method and their molecular
1
structures were characterized by H NMR and MS. The post-synthesis impregnation method was used to
functionalize the Bi(10)-SBA-16 silicon mesoporous material with the ionic liquids and the obtained
materials were characterized by FT-IR, XRD, BET, XPS, and TG. The results show that the volume and pore
size of SBA-16 were changed by loading Bi and ionic liquids, while the three-dimensional cubic pore
structure of SBA-16 was not destroyed. The composite catalyst was evaluated in Friedel–Crafts acylation
of anisole with acetic anhydride. The effects of reaction temperature and the ratio of anisole and acylating
agent on the acylation of anisole were investigated by experimental design. The results showed that
1.2ILc@Bi(10)-SBA-16 was used as the catalyst, the conversion of anisole was 85.41% and the yield of aro-
matic ketone was 69.19% under the conditions of a reaction temperature of 100 °C, a catalyst dosage of
0.5 g, a time period of 4 h and a molar ratio of 1 : 1.5. After 5 recycling runs, the reduction in the overall
ratio of reactant conversion and product yield did not exceed 7.5%, indicating that 1.2ILc@Bi(10)-
SBA-16 has good stability and reusability.
Received 1st February 2021,
Accepted 26th March 2021
DOI: 10.1039/d1dt00355k
rsc.li/dalton
metal oxides,4,16,17 heteropoly acids,18,19 solid superacids,8,20
Introduction
ionic liquids,21,22 etc. Due to its high thermal stability, good
Aromatic ketones can be used in the synthesis of spices, dyes, electrical conductivity, and low vapor pressure reverse recovery,
pharmaceuticals and agrochemicals,1–5 which were important ionic liquids have been widely used in organic reactions, such
fine chemical and pharmaceutical intermediates. Friedel– as Friedel–Crafts alkylation, esterification, oxidation, and
Crafts acylation was one of the important reactions of synthetic acetalization,21,22 etc. Tran et al.23 synthesized the imidazole
aromatic ketones,2,6–8 which was widely used because of its ionic liquid catalyst Bi(OTf)3/[BMIM]OTf by the microwave
simple reaction and high selectivity. The acylation reactants radiation method and found that active aromatic hydrocarbons
were generally acyl halides or anhydrides that were introduced and naphthalene can be benzoylated to obtain aromatic
through electrophilic substitution reactions in aromatic rings ketones in a short reaction time. Yeung et al.24 synthesized an
to produce aromatic ketones. Traditional catalysts mainly acidic imidazoline-chloroaluminate ionic liquid that can carry
include Lewis acids9–11 (such as anhydrous ZnCl2, A1Cl3, out the Friedel–Crafts acylation at the C-3 position of indole at
FeCl3, etc.) or Brønsted acids5,11 (such as concentrated sulfuric room temperature. There is no denying that these catalysts are
acid, hydrochloric acid, etc.). However, traditional catalysts more or less flawed. Therefore, it is necessary to develop a cata-
easily cause side reactions that were highly corrosive to equip- lyst that is environmentally friendly, has excellent perform-
ment and cannot be easily recycled. The large amount of ance, and has high economic benefits.
industrial wastewater produced in the reaction process easily
Supported molecular sieves are a type of composite catalyst
causes environmental pollution. Therefore, the study found that load active components on zeolite molecular sieves,25–31
solid acid catalysts such as zeolite molecular sieves,2,12–15 which can not only reduce the amounts of active components
added but also maintain the characteristics of zeolite mole-
cular sieves. Because of its low dosage, high activity and recycl-
School of Chemistry and Chemical Engineering, Jiangsu University, Zhenjiang
ability, it has high research value and application
212013, P. R. China. E-mail: tshjiang@ujs.edu.cn; Tel: +0511-88791800
prospects.32–35 Recently, introducing metal or other acid func-
†Electronic supplementary information (ESI) available. See DOI: 10.1039/
tional groups into pore structures to change the properties of
d1dt00355k
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molecular sieves has become a research hotspot. Madadi reaction temperature, catalyst dosage and the molar ratio of
et al.36 prepared the Co/SBA-16 catalyst by chelating the metal reactants on acylation were studied systematically.
complex impregnation method and applying it to the limo-
nene aerobic epoxidation reaction, which showed high activity
and stable conversion and selectivity in repeatability tests. Dai
Results and discussion
et al.37 synthesized Zr-SBA-15 mesoporous molecular sieves
with different Si/Zr molar ratios by the hydrothermal method
and synthesized several Brønsted-Lewis acidic ionic liquid Zr-
SBA-15/[mim-ps]Cl-ZnCl2 catalysts by the impregnation
method, exhibiting excellent catalytic performance in the ester-
ification reaction of acetic acid with n-BuOH, BnOH and
Naxol. However, the amount of reaction catalyst was large and
the cost of using Zr salt was high. Zhang et al.38 studied the
esterification of oleic acid and short chain alcohol catalyzed by
an acidic ionic liquid composite catalyst supported on Fe-
SBA-15. The results showed that due to the synergistic effect of
the Lewis and Brønsted acid centers, the catalyst exhibits high
catalytic activity in esterification reactions. However, during
the preparation of Fe-SBA-15, the valence state of the Fe
element was unstable and the reaction conditions were harsh.
Therefore, the introduction of ionic liquids into mesoporous
molecular sieves or metal-doped molecular sieves can make
the catalyst have excellent catalytic activity. In recent years,
low-cost non-toxic bismuth compounds have been used as
environmentally friendly mild Lewis acid catalyst systems in
the synthesis by green chemistry.39 Moreover, to the best of
our knowledge, there are fewer research reports on doping
bismuth into SBA-16.
p-Toluenesulfonic acid was widely used in the synthesis of
medicines, pesticides, stabilizers of polymerization and cata-
lysts for organic synthesis (ester, etc.), and is a strong acid
slightly weaker than sulfuric acid. In this study, a Bi-doped
SBA-16 mesoporous molecular sieve (Bi(x)-SBA-16 (x = 5, 10,
and 15)) was prepared for the first time by in situ synthesis and
four imidazole ionic liquids acidified with p-toluenesulfonic
acid were loaded onto the mesoporous molecular sieve. Above,
four composite catalysts with strong acid properties were
obtained. They were applied to the acylation reaction of
anisole with acetic anhydride. The effects of reaction time,
SXRD and WXRD analysis
Fig. 1 displays the small angle X-ray diffraction patterns of the
carrier Bi(x)-SBA-16 (x = 5, 10, and 15) and the composite
material loaded with the ionic liquids (1.2ILs@Bi(x)-SBA-16
(x = 5, 10,and 15)). As shown in Fig. 1a, the diffraction peaks of
SBA-16 at 0.89°, 1.5° and 1.75° were defined as (110), (200) and
(211), respectively, which were similar to that reported in the
literature,40 indicating that the synthesized mesoporous
molecular sieves have ordered a three-dimensional cubic
channel system. According to the Bragg diffraction equation:
nλ = 2d110 sin θ, d110 = 10.57 nm was calculated, due to
pffiffiffi
a0 ¼ 2d110
= 3, the cell parameter a0 = 12.20 nm was further
calculated (n represents the diffraction order, θ represents the
angle between the incoming ray and the sub-ray, d represents
the crystal plane spacing, and λ represents the wavelength).41
The above diffraction peaks still exist in the SXRD patterns of
Bi(x)-SBA-16 (x = 5, 10, and 15), which was little different com-
pared to those of SBA-16, indicating that the incorporation of
Bi and increasing Bi dosage does not affect the mesoporous
ordering of SBA-16. As can be seen from Fig. 1b, the peak
strength of the composite catalyst decreased significantly
when four ionic liquids were introduced into Bi(x)-SBA-16 (x =
5, 10, and 15) mesoporous materials, although it had a meso-
porous structure. This may be due to the ionic liquids occupy
the pore structure. The position of the diffraction peak of the
(110) crystal plane shifts. Combined with the BET pore size
distribution, it was speculated that the introduction of ILs may
lead to the collapse of the pore channels of the molecular
sieve and then lead to the increase of the pore size.42
The wide-angle XRD patterns of Bi(10)-SBA-16 and
1.2ILs@Bi(10)-SBA-16 composite catalysts are shown in
Fig. S1.† All samples showed a broad peak in the range of 10°
to 25°, which was attributed to amorphous silica. No pure
Fig. 1 The SAXD patterns of (a) Bi(x)-SBA-16 (x = 5, 10, and 15) and (b) 1.2ILs@Bi(x)-SBA-16 (x = 5, 10, and 15) (the mass ratio of ILs to Bi(x)-SBA-16
(x = 5, 10, and 15) was 1.2).
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Bi2O3 phase was found in the wide-angle XRD spectrum, tion of Bi atom has no significant effect on the uniform pore
which indicates that the bismuth oxide can be well dispersed structure of the carrier. After loading the ionic liquids, the
on the surface of the silica and cannot be detected by the composite catalyst exhibits the same physical properties as the
wide-angle XRD spectrum.43,44 The high dispersibility of carrier.
bismuth on the surface of silica makes the active center close
Table 1 summarizes the corresponding textural properties
to the reactant molecules during the reaction. The nature of of all the samples, including specific surface area, average
this intermetallic compound will be determined later by XPS pore size and pore volume. The results show that the specific
characterization.
surface area, average pore size and pore volume of Bi(x)-SBA-16
(x = 5, 10, and 15) decreased with increasing Bi dosage. As
shown in Table 1, ILc@Bi(10)-SBA-16 has the lowest specific
surface area among ILs@Bi(10)-SBA-16. According to the
literature,45,46 upon comparing the density of imidazole cation
salts with different substituents, the density has a linear
relationship with the length of the N-alkyl chain on the imid-
azole cation. As the organic cation becomes larger, the density
of the ionic liquid becomes smaller. Compared to Bi(10)-
N2 adsorption–desorption analysis
The N2 adsorption–desorption isotherms of SBA-16, Bi(x)-
SBA-16 (x = 5, 10, and 15) and 1.2ILs@Bi(10)-SBA-16 are
shown in Fig. 2. According to IUPAC, all samples show typical
type IV adsorption isotherms and have H2 type hysteresis
loops, demonstrating that SBA-16 is a mesoporous material
with a uniform pore size distribution, and that the introduc-
Fig. 2 N2 adsorption–desorption isotherms and pore size distribution of (a and b) Bi(x)-SBA-16 (x = 5, 10, and 15), (c and d) 1.2ILs@Bi(x)-SBA-16 (x
= 5, 10, and 15).
Table 1 The textural properties of Bi(x)-SBA-16 (x = 5, 10, and 15) and 1.2ILs@Bi(x)-SBA-16 (x = 5, 10, and 15)
Catalyst
Surface area (BET) [m2 g−1
]
Total pore volume [cm3 g−1
]
Pore size (BJH ads) [nm]
SBA-16
Bi(5)-SBA-16
Bi(10)-SBA-16
Bi(15)-SBA-16
1.2ILa@Bi(10)-SBA-16
1.2ILb@Bi(10)-SBA-16
1.2ILc@Bi(10)-SBA-16
1.2ILd@Bi(10)-SBA-16
884
852
838
829
353
329
256
392
0.714
0.691
0.553
0.462
0.228
0.263
0.279
0.281
2.722
3.170
3.048
2.845
3.499
3.917
3.853
3.686
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SBA-16, the immobilization of ionic liquids greatly reduced the on the spectra of the composite catalyst, which proved that the
specific surface area of the composite catalyst but the average ionic liquid was successfully compounded with the support.
pore size was relatively increased. This may be due to the fact
SEM analysis
that the ionic liquids blocked the microporous channel (in
Fig. S2,†) The pore size of Bi(10)-SBA-16 is 0.6988 nm and the
pore volume is 0.08037 cm3 g−1. After loaded with ionic
liquids, the pore size was 0.7522 nm and the pore volume was
0.02503 cm3 g−1 due to the blockage of micropores, making
the overall pore size of Bi(x)-SBA-16 (x = 5, 10, and 15) larger,
which further indicates that the ionic liquid has been success-
fully loaded on the carrier.35,37
SEM was used to observe the particle size and particle mor-
phology of the synthesized sample. As shown in Fig. 4b, Bi
(10)-SBA-16 was composed of the aggregated nanoparticles
with a size range of 30–60 nm. Similar to SBA-16 (in Fig. 4a),
Bi(10)-SBA-16 has the characteristics of a spherical shape, and
the particle size was relatively uniform and the surface was
smooth. After the ionic liquids were encapsulated (in Fig. 4c
(1.2ILa@Bi(10)-SBA-16), Fig. 4d (1.2ILb@Bi(10)-SBA-16),
Fig. 4e (1.2ILc@Bi(10)-SBA- 16) and Fig. 4f (1.2ILd@Bi(10)-
SBA-16)), the surface of the carrier became rough, floccus and
particulate matter appeared and the morphology became irre-
gular. However, the overall morphology and size did not
change significantly, indicating that the ionic liquid has been
encapsulated on the carrier. In addition, the existence and dis-
persion of Bi ions in Bi(10)-SBA-16 samples were studied by
EDS. Fig. S3† shows the EDS spectra of all samples, verifying
the existence of the Bi element.
FT-IR analysis
The FT-IR spectra of all samples are illustrated in Fig. 3. As
shown in Fig. 3a, the absorption peak of SBA-16 at 463 cm−1
was the bending vibration peak of Si–O–Si bonds. The charac-
teristic peaks at 805 cm−1 and 1087 cm−1 correspond to the
symmetrical stretching vibrations and asymmetric stretching
vibrations of the silicon–oxygen tetrahedron, respectively. The
absorption band around 3464 cm−1 corresponds to Si-OH on
the surface of the molecular sieve. Compared to SBA-16, the
infrared spectrum of Bi(10)-SBA-16 has undergone significant
changes. The decrease in the characteristic peak intensity at
805 cm−1 may be due to the formation of the Si–O–Bi bonds.47
The absorption peak near 953 cm−1 was considered as the
stretching vibration of Si-OH. In the metal loaded sample, the
peak was designated as the stretching vibration of the surface
hydroxyl group (Si-OH) disturbed by the nearby metal species.
It can also be observed from Fig. 3b that there were absorption
peaks at 563 cm−1 and 667 cm−1 for 1.2ILs@Bi(10)-SBA-16,
indicating the existence of sulfonate and hydrogen sulfonate.
The para-vibration band peak of the benzene ring was at
814 cm−1, which can identify p-toluenesulfonate. The peak at
1464 cm−1 was ascribed to the vibration band of the benzene
TEM analysis
Fig. 5 illustrates the TEM images of SBA-16 and the composites
with bismuth doped and loaded ionic liquids. Fig. 5b–f show
the TEM images of SBA-16, 1.2ILa@Bi(10)-SBA-16, 1.2ILb@Bi
(10)-SBA-16, 1.2ILc@Bi(10)-SBA-16 and 1.2ILd@Bi(10)-SBA-16
perpendicular to the pore axis. Upon combining with the
small angle XRD and BET data, it is proved that the SBA-16
and Bi(10)-SBA-16 materials have good ordering. When com-
pared with the carrier, the pore size of the composite catalyst
obtained by loading the ionic liquid was decreased, indicating
that the ionic liquid was well encapsulated in the cage struc-
ture of Bi(10)-SBA-16.
ring framework. The absorption peaks around 1539 cm−1
1657 cm−1 and 3672 cm−1 were caused by the stretching
,
XPS analysis
vibrations of CvN, CvC and C–H on the imidazole ring, Fig. 6a demonstrates X-ray photoelectron spectroscopy of
respectively.48 The absorption vibration peaks of the ionic SBA-16, Bi(10)-SBA-16 and 1.2ILa@Bi(10)-SBA-16. The binding
liquid and functional groups of Bi(10)-SBA-16 were observed energy, which can be obtained by using a curve fitting
Fig. 3 The FT-IR spectra of (a) SBA-16, Bi(10)-SBA-16 and (b) 1.2ILs@Bi(10)-SBA-16.
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Fig. 4 The SEM images of (a) SBA-16, (b) Bi(10)-SBA-16, (c) 1.2ILa@Bi(10)-SBA-16, (d) 1.2ILb@Bi(10)-SBA-16, (e) 1.2ILc@Bi(10)-SBA-16, and (f)
1.2ILd@Bi(10)-SBA-16.
Fig. 5 The TEM images of (a) SBA-16, (b) Bi(10)-SBA-16, (c) 1.2ILa@Bi(10)-SBA-16, (d) 1.2ILb@Bi(10)-SBA-16, (e) 1.2ILc@Bi(10)-SBA-16, and (f)
1.2ILd@Bi(10)-SBA-16.
program, and relative strength were used to determine the 1.2ILa@Bi(10)-SBA-16 characterizes N1s (401.51 eV) and S2p
types and chemical properties of each element. Fig. 6b and c (167.81 eV) and the peak value of C1s (284.65 eV) became stron-
show the high-resolution spectrum of 1.2ILa@Bi(10)-SBA-16. ger when compared to that of Bi(10)-SBA-16, which was sup-
As can be seen from the figure Bi(10)-SBA-16 contains the posed to be caused by the introduction of ionic liquids.
typical peaks of SBA-16: C1s (284.65 eV), O1s (532.85 eV), Si2p
1H NMR analysis
(103.85 eV) and other peaks: Bi4f5/2 (159.65 eV) and Bi4f7/2
1
(164.95 eV). The difference between the two peaks of Bi4f was The H NMR (400 MHz, D2O, ppm, δ) spectrum (see the ESI,
about 5.3 eV, which corresponds to the binding energy of Bi3+
.
Fig. S4†) of the four kinds of ILs were shown as follows:
ILa: 8.39(s, 1H), 7.55–7.52(m, 2H), 7.23–7.18(t, J = 20 Hz,
It was inferred that Bi exists in the form of Bi2O3. C1s may be
caused by air and instrument pollution. The spectrum of 4H), 3.72(s, 3H), 2.23(s, 4H).
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Fig. 6 XPS spectra of samples: (a) the XPS full survey spectra of SBA-16, Bi(10)-SBA-16 and 1.2ILa@Bi(10)-SBA-16 and (b and c) Bi4f, S2p and N1s of
1.2ILa@Bi(10)-SBA-16.
ILb: 8.48(s, 1H), 7.55–7.53(m, 2H), 7.27–7.19(m, 4H), of ILc [HSO3-PMIM]+. Fig. S3d1† shows an ion peak at m/z
3.99–3.96(t, J = 12 Hz, 2H), 3.70(s, 3H), 2.24(s, 4H), 1.69–1.61 224.60 that may be the cation structure of ILd [HSO3-BMIM]+.
(m, 2H), 1.19–1.10(m, 2H), 0.79–0.75(t, J = 16 Hz, 3H).
Through the above data analysis, it can be seen that the molar
ILc: 8.52(s, 1H), 7.52–7.49(d, J = 12 Hz, 2H), 7.31–7.30(t, J = anions and cations in the ionic liquid were consistent with the
4 Hz, 1H), 7.24–7.23(t, J = 4 Hz, 1H), 7.18–7.16(d, J = 8 Hz, 2H), theoretical value, indicating that the four ionic liquids have
4.16–4.13(t, J = 12 Hz, 2H), 3.69(s, 3H), 2.76–2.72(m, 2H), 2.20 been successfully synthesized.
(s, 4H), 2.16–2.09(m, 2H).
ILd: 8.55(s, 1H), 7.54–7.53(m, 2H), 7.32–7.31(t, J = 8 Hz,1H),
7.26–7.25(t, J = 4 Hz, 1H), 7.22–7.20(d, J = 8 Hz, 2H), 4.08–4.04
(t, J = 16 Hz, 2H), 3.72(s, 3H), 2.81–2.77(m, 3H), 2.24(s, 4H),
1.89–1.81(m, 3H), 1.63–1.55(m, 3H).
TG-DSC analysis
The thermogravimetric (TG) curves of Bi(10)-SBA-16 and
1.2ILs@Bi(10)-SBA-16 are shown in Fig. 7. As can be seen from
the figure that the mass of all the samples decreased signifi-
cantly from room temperature to 100 °C, which may be due to
the evaporation of crystal water in the sample. With the rise of
MS analysis
Fig. S3a–d† (see the ESI, Fig. S3†) shows the positive and nega- temperature, the TG curve of Bi(10)-SBA-16 tends to be stable,
tive ion peaks of the electrospray mass spectra of the four while the four composite catalysts 1.2ILs@Bi(10)-SBA-16
ionic liquids in the positive and negative ion modes, providing experience secondary weight loss. When the temperature
a basis for identifying the molecular structure, molecular increases from 350 to 600 °C, the mass of the ionic liquids in
weight, and the presence of anions and cations of the syn- Bi(10)-SBA-16 decreased by 11.361%, 13.819%, 21.528% and
thesized ionic liquids. First, we found that there were ion 15.558%, respectively. Compared to Bi(10)-SBA-16, it was
peaks at m/z 176 in the negative ion mode, which was consist- found that this phenomenon should be caused by the degra-
ent with the molar weight of our anion structure [p-TSA]−. In dation of ionic liquid. It also can be seen from the figure that
addition, the ion peak at m/z 169.02 shown in Fig. S3a1† was the loading rate of ILc was the highest under the same load.
assumed to be the cation structure of ILa [COO(CH2)3-MIM]+. According to the literature, the melting point is a key para-
As shown in Fig. S3b1,† the ion peak at m/z 144.82 may be the meter to evaluate the characteristics of ionic liquids. The
cation structure of ILb [BMIM]+. As shown in Fig. S3c1,† the melting point of ionic liquids is closely related to the compo-
ion peak at m/z 210.57 was inferred to be the cation structure sition of cations and anions, and increases with the improve-
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Fig. 7 TG-DSC curves of (a) Bi(10)-SBA-16 and (b–e) 1.2ILs@Bi(10)-SBA-16.
ment in the degree of cation symmetry and intermolecular
force.49–51 The TG curve of the composite material does not
change significantly as the temperature continues to rise. The
TG analysis showed that the ionic liquid was successfully
encapsulated in Bi(10)-SBA-16 and had good thermal stability.
Table 2 Performance of various catalysts in Friedel–Crafts acylation
reaction
Conversion of
anisole (%)
Yield of aromatic
ketones (%)
Catalyst
Blank
45.19
65.30
52.93
55.11
52.40
60.09
62.17
69.85
61.23
23.61
48.22
35.67
40.13
36.55
46.36
47.55
50.41
45.20
Catalytic activity evaluation
Concentrated sulfuric acid
Bi(5)-SBA-16
Bi(10)-SBA-16
Effect of different catalysts on Friedel–Crafts acylation.
Table 2 lists the conversion rates of the reactants and the
product yields of all samples involved in the acylation reaction
of anisole with acetic anhydride. The main product of the reac-
tion is p-methoxybenzophenone (p-MAP) and the by-product is
o-methoxybenzophenone (o-MAP). p-MAP was the target
product of the reaction.52,53 The reaction mechanism is shown
in Fig. S6.† The results of the blank experiment and that with
concentrated sulfuric acid as a catalyst are also listed in
Table 2. The reaction conditions for all the catalytic reactions
listed in Table 2 are as follows: temperature = 80 °C, n(AN)/
Bi(15)-SBA-16
1.2ILa@Bi(10)-SBA-16
1.2ILb@Bi(10)-SBA-16
1.2ILc@Bi(10)-SBA-16
1.2ILd@Bi(10)-SBA-16
Reaction conditions: (n(anisole)/n(acetic anhydride) = 1 : 1.5, catalyst
dosage = 0.3 g, temperature = 80 °C, and time = 3 h).
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n(AA) = 1 : 1.5, catalyst dosage = 0.3 g, and time = 3 h. As 70 °C to 110 °C was explored. It can be seen from the figure
shown in Table 2, the SBA-16 carrier with 10% Bi doping has that the conversion and yield improve with the increase in
better catalytic performance compared to other doping temperature, which may be due to the enhancement of the
amounts. With Bi(10)-SBA-16 as the carrier and doped with an molecular collision and miscibility of reactants. When the
ionic liquid, 1.2ILc@Bi(10)-SBA-16 showed the best catalytic temperature was 100 °C, the conversion and yield up
performance under the above reaction conditions, the conver- were 78.94% and 57.52%, respectively. Obviously, the conver-
sion rate of anisole was 69.85% and the product yield was sion and yield change a little when the temperature was
50.41%. It may be due to that the structure of cations has a increased from 100 °C to 110 °C, possibly due to the pro-
certain influence on the acidity and solubility of the ionic duction of by-products (such as 2-methoxyacetophenone and
liquids. The acidity and solubility of the ionic liquids are phenol).52,53,57,58
closely related to their catalytic activity. The mutual solubility
Effect of molar ratio on Friedel–Crafts acylation. The effect
of ionic liquids and reaction products determines the difficulty of the molar ratio of anisole to acetic anhydride on acylation is
of phase separation, and phase separation performance has a shown in Fig. 9. Under the reaction conditions of the tempera-
great influence on the catalytic effect. Although the ionic ture of 100 °C, the catalyst dosage of 0.3 g and the reaction time
liquid with a propane sulfonate group has the same activity as of 3 h, the influence of the molar ratio from 1 to 2 on the cata-
the traditional concentrated sulfuric acid catalyst, it has more lytic performance was studied. Apparently, conversion and yield
advantages in terms of product selectivity, product separation increase significantly in the molar ratio range of 1 to 1.5, but
and reuse.54–56
decrease slightly in the range of 1.5 to 2. This may be because
Table S1† presents some catalytic activity data collected anisole was diluted with excessive acetic anhydride as the
from different articles of various catalysts for Friedel–Crafts amount of acetic anhydride increased, which results in the inhi-
acylation. Using HPW/MCM-41(60% loading) as a catalyst, bition of the effective collision between the two reactants.52,55,56
although the reaction conditions were mild, the catalytic effect So the best molar ratio of anisole with acetic anhydride was 1.5.
was negligible. With Nanocrystalline ZSM-5 of 90 nm particle
Effect of catalyst dosage on Friedel–Crafts acylation. The
size as the catalyst, more acetic anhydride was needed, which influence of catalyst dosage on acylation is shown in Fig. 10.
is not economical and good for the environment, and the cata- The amount of reaction variable catalyst is 0.2, 0.3, 0.4, 0.5
lytic effect is not obvious. The same was true with HPA/SiO2 as and 0.6 g, respectively. The reaction conditions were as
the catalyst. When 20%IL/MIL-101 was used as the catalyst, the follows: the temperature was 100 °C, the reaction time was 3 h,
catalytic performance was higher but the amount of the cata- and the molar ratio was 1.5. As can be seen from the figure,
lyst needed was higher.
the conversion and yield of the reaction increase as the catalyst
Effect of reaction temperature on the Friedel–Crafts acyla- dosage increased from 0.2 to 0.5 g. It can be inferred that the
tion. Fig. 8 reveals the effect of temperature on the acylation of augment of catalytic activity enhances the effective collision of
anisole with acetic anhydride. Based on the above results, the reactants. As the amount of the catalyst continues to
1.2ILc@Bi(10)-SBA-16 was selected as the catalyst, the molar increase, the conversion and yield decrease slightly, which
ratio of anisole to acetic anhydride was 1.5, the catalyst dosage may be due to the excessive amount of catalyst leading to the
was 0.3 g, and the reaction time was 3 h. The change in cata- occurrence of deep reaction.52,53 Therefore, the optimal
lytic performance at different reaction temperatures from amount of catalyst was 0.5 g.
Fig. 8 The effect of temperature on acylation of anisole with acetic
anhydride over 1.2ILc@Bi(10)-SBA-16 catalyst (reaction conditions:
n(AN)/n(AA) = 1 : 1.5, catalyst dosage = 0.3 g, and time = 3 h).
Fig. 9 The effect of molar ratio on acylation of anisole with acetic
anhydride over 1.2ILc@Bi(10)-SBA-16 catalyst (reaction conditions:
temperature = 100 °C, catalyst dosage = 0.3 g, and time = 3 h).
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Fig. 10 The effect of catalyst dosage on acylation of anisole with acetic
anhydride over 1.2ILc@Bi(10)-SBA-16 catalyst (reaction conditions:
temperature = 100 °C, n(AN)/n(AA) = 1 : 1.5, and time = 3 h).
Fig. 12 The reusability of the 1.2ILc@Bi(10)-SBA-16 catalyst (reaction
conditions: temperature = 100 °C, n(AN)/n(AA) = 1 : 1.5, catalyst dosage
= 0.5 g, and time = 4 h).
performance of the regenerated catalyst was observed by a
repeated performance test. The results are shown in Fig. 12.
After 5 recycling runs, the conversion of the reactant and the
yield of product decreased, but the overall ratio did not exceed
7.5%, indicating that 1.2ILc@Bi(10)-SBA-16 has good stability
and reusability. The reduction in conversion may be due to the
loss of catalyst quality during regeneration.
Conclusions
In this work, SBA-16 was modified by the in situ synthesis
method for the synthesis of Bi(10)-SBA-16. Four kinds of
p-toluenesulfonic acid functionalized imidazole ionic liquids
were prepared by a two-step method. A series of composite cat-
alysts (1.2ILs@Bi(10)-SBA-16 (ILs = ILa, ILb, ILc, and ILd)) were
obtained by loading the ionic liquids into Bi-doped meso-
porous carriers. After FT-IR, XRD, BET, XPS, MS, TG and other
characterization studies, it was found that the filling of Bi and
ionic liquid changed the pore volume and pore size, while the
three-dimensional cubic pore structure of SBA-16 was not
destroyed. It shows the good catalytic performance in the
Friedel–Crafts acylation reaction of anisole with acetic anhy-
dride. Under ideal conditions, not only the conversion rate of
anisole and the yield of aromatic ketone were high, but also
the repetitive utilization rate of the catalyst was high.
Therefore, the metal-doped mesoporous molecular sieve
coated acidic ionic liquid is of great significance to the pro-
duction and use of industrial aromatic ketones.
Fig. 11 The effect of reaction time on acylation of anisole with acetic
anhydride over 1.2ILc@Bi(10)-SBA-16 catalyst (reaction conditions:
temperature = 100 °C, n(AN)/n(AA) = 1 : 1.5, and catalyst dosage = 0.5 g).
Effect of reaction time on Friedel–Crafts acylation. As shown
in Fig. 11, the 1.2ILc@Bi(10)-SBA-16 was used as the catalyst to
explore the influence of reaction time on acylation under the
corresponding test conditions. The reaction was carried out at
a temperature of 100 °C with a catalyst dosage of 0.5 g and a
molar ratio of 1.5. As can be seen from the figure, the conver-
sion and yield of the reaction increased significantly with the
increase in reaction time. When the reaction time was 4 h, the
conversion and yield reached 85.41% and 69.19% respectively.
However, when the reaction continued for a period of time,
the conversion and yield showed a downward trend, which can
be speculated that adverse reactions have occurred. Therefore,
the optimal reaction time is 4 h.
Reusability of the catalyst. The stability of the catalyst was
studied in the acylation of anisole with acetic anhydride. Under
the optimum reaction conditions (temperature = 100 °C, n(AN)/
n(AA) = 1 : 1.5, catalyst dosage = 0.5 g, time = 4 h), the catalyst
used for the first time was recovered and then washed with
anhydrous ethanol for several times to remove impurities. The
Experimental section
Materials
The Bi-doped SBA-16 mesoporous molecular sieve (Bi(10)-
SBA-16) was synthesized with the Pluronic F127 (poly(ethylene
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oxide)–poly(propylene oxide)–poly(ethylene oxide) tri-block co- with 60 ml of ether. Then, the ionic liquid intermediate
polymer EO106PO70EO106, Maver. = 12 600, Sigma) as the struc- product 1-butyl-3-methylimidazole salt [BMIM]+ can be dried
ture-directing agent and TEOS (tetraethoxysilane, 98%, for more than 12 h under vacuum at 80 °C. The product was
Aldrich) as the silicate source under a hydrochloric acid (36%, light yellow or colorless with high viscosity.
Merck) solution. The ionic liquid was synthesized using
Preparation of ILc intermediate 1-(3-sulfonyl) propyl-3-
N-methylimidazole (99%, Sigma), 1,3-propane sulfonate (99%, methylimidazolium salt [SO3-PMIM]+. The intermediate of
Aldrich), 1,4-butane sulfonate (98%, Aldrich), N-chlorobutane ionic liquid was prepared by a two-step synthesis method:
(99%, Aldrich), and p-toluenesulfonic acid (>99%). Other 30 ml of toluene solvent was measured in a beaker, 6.1 g of
drugs used in the experiment include anisole (99%, Sigma) 1,3-propanesulfonic acid was dispersed in the beaker and 4.1 g
and acetic anhydride (99%, Sigma). All the above commercial of N-methylimidazole was slowly added in an ice water bath,
chemicals were of analytical grade and were purchased from followed by magnetic agitation. Then the temperature was
the Shanghai Chemical Reagent Corporation, China.
slowly raised to 60 °C and continue stirred with a magnetic
stirrer for 5 h. The mixture was filtered to obtain a white solid,
washed with ether for several times and dried at 60 °C for 6 h
Preparation of Bi(x)-SBA-16 (x = 5, 10, 15)
High quality hexagonal ordered mesoporous Bi(x)-SBA-16 (x = 5, to obtain the intermediate 1-(3-sulfonyl) propyl-3-methyl-
10, and 15) was synthesized under acidic conditions using a tri- imidazolium salt [SO3-PMIM]+.
block copolymer as the templating agent. The reaction was
Preparation of ILd intermediate 1-(4-sulfonyl) butyl-3-
carried out according to the reaction ratio F127 : HCl : TEOS : Bi methylimidazolium salt [SO3-BMIM]+. The preparation of ILd
(NO3)3·5H2O = 0.0016 : 1.45 : 0.3841 : 0.0192–0.0576. First, F127 intermediate 1-(4-sulfonyl) butyl-3-methylimidazolium salt
was dissolved in dilute hydrochloric acid and stirred until it was [SO3-BMIM]+ is similar to the preparation of ILc intermediate.
clear and transparent; the concentration of dilute hydrochloric
Prepartion of ILa, ILb, ILc, and ILd. The prepared ionic
acid was 1.62 mol L−1. The mixed solution was stirred vigorously liquid intermediate was added to the flask and p-toluenesulfo-
in a 34 °C water bath for 2–3 h, TEOS was added dropwise, and nic acid (p-TSA) was added dropwise according to the ratio of
then Bi(NO3)3·5H2O was added and continuously stirred for 1 : 1 to the intermediate. The ionic liquids were heated to
20 h. The sample was washed after the hydrolysis process and 80 °C in a water bath and stirred for 5–6 h until all ionic liquid
then transferred to a polytetrafluoroethylene reactor. Deionized intermediates were dissolved. After the reaction, the product
water was added to disperse the sample and then the sample was washed with ethyl acetate for three times and dried in a
was hydrothermally crystallized at 100 °C for 24 h. After crystalli- vacuum at 100 °C to obtain sulfonic acid functionalized ionic
zation, the sample was filtered, washed, and dried. The resulting liquids [COOH(CH2)2-MIM]p-TSA (ILa), [BMIM]p-TSA (ILb),
product was calcined at 550 °C to remove the templating agent, [HSO3-PMIM]p-TSA (ILc), and [HSO3-BMIM]p-TSA (ILd).
the heating rate was 1 °C min−1, and the holding time was 6 h.
After the calcination, the white powder was collected to obtain sites. The above four ionic liquids, 1.2 g each, were dissolved
Synthesis of 1.2ILs@Bi(x)-SBA-16 (x = 5, 10, and 15) compo-
Bi(x)-SBA-16 (x = 5, 10, 15).
in 20 ml of deionized water, respectively. The solution was
magnetically stirred at 80 °C in an isothermal oil bath pot.
Then 1 g of Bi(x)-SBA-16 (x = 5, 10, and 15) was added to the
Preparation of ILs
Preparation of ILa intermediate 1-(3-carboxyl)butyl-3-methyl- solution. After 6 h, the water in the mixture was heated and
imidazolium salt [COO(CH2)2-MIM]+. The reaction was carried evaporated to obtain solids that were respectively washed with
out with 1,4-butyrolactone and N-methylimidazole in a molar methanol, ethyl acetate, and anhydrous ether, and then dried
ratio of 1 : 1. First, 8.61 g of 1,4-butyrolactone was added into a in a vacuum for 10 h to obtain 1.2ILs@Bi(x)-SBA-16 (ILs = ILa,
100 ml beaker and then was added 8.21
g
of ILb, ILc, and ILd) (x = 5, 10, and 15) composite catalysts.
N-methylimidazole. The reaction was conducted at room temp-
erature by the solvent free method for 30 min, and then
Catalyst characterization
washed with ethanol. The product was dried in a vacuum at The X-ray diffraction (XRD) patterns of samples were recorded
80 °C to obtain the product intermediate 1-(3-carboxyl) butyl- with an X-ray powder diffractometer made in Germany
3-methylimidazolium salt [COO(CH2)2-MIM]+.
Preparation of ILb intermediate
BRUKER with Cu Kα radiation (λ = 0.15418 nm). It was oper-
1-butyl-3-methyl- ated at 40 kV and 50 mA, the scanning speed was 1° min−1
imidazolium salt [BMIM]Cl+. The reaction was carried out and the scanning was done in the 2 theta range of 0.5–10°.
with 1-chlorobutane and N-methylimidazole in the molar ratio The specific surface area, total pore volume and pore size dis-
of 1.2 : 1. First, 8.2 g of N-methylimidazole was added to three tribution were measured using a Micromeritics Tristar II 3020
flasks and quickly passed into nitrogen for a particular period surface area and pore analyzer. The specific surface area of the
of time and then slowly dripped into 11.1 g of 1-chlorobutane. sample was calculated by the BET (Brunauer–Emmett–Teller)
After all the liquid was added into three batches of burnt pro- formula and the pore size and pore volume of the sample were
ducts, the solution was heated directly to 80–85 °C by the measured by the BJH (Barrett–Joyner–Halenda) formula. The
solvent-free method and then stirred and refluxed for 48 h Fourier transform infrared (FT-IR) spectra of the samples in
under nitrogen conditions. After the reaction, the lower layer the range of 400–4000 cm−1 were obtained using a Nexus
of the pale yellow liquid was separated and washed repeatedly FT-IR 470 spectrometer made by the Nicolet Corporation with
5880 | Dalton Trans., 2021, 50, 5871–5882
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anhydrous KBr as the standard. The particle morphology was the rate of 20 °C min−1, and the injection volume was 2 μl
characterized using a scanning electron microscope (SEM) each time. The product was analyzed by gas chromatography
with a Hitachi S-3400N microscope at 4 kV. EDS allows the using the internal standard method and the internal standard
qualitative and semi-quantitative analyses of samples through used was p-xylene.
the difference in the characteristic energy of the X-ray photons
of the elements. Before analysis, the samples were coated with
gold for a thickness of about 10 nm by cathodic sputtering. A
transmission electron microscopy (TEM) study was performed
Conflicts of interest
using a JEOL JEM 2100 transmission electron microscope There are no conflicts to declare.
operated at 200 kV. The finely powdered samples were sus-
pended in ethanol and dispersed by ultrasound, and then
dried on a porous carbon gate at room temperature for trans-
mission electron microscope observation. The types of surface
Acknowledgements
elements and the chemical states of the surface atoms were This research was supported by the National Natural Science
analyzed and determined using an AXIS-U1tra DLD X-ray Foundation of China (51572115).
photoelectron spectroscope (XPS) from Shimadzu, Japan. The
radiation source was Al-Ka (1486.6 eV). The type of surface
elements was qualitatively determined by XPS and the carbon
pollution peak was found to be 284.8 eV. The chemical
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