A green and efficient hydration of alkynes catalyzed by hierarchically porous poly(ionic liquid)s solid strong acids

Article abstract of DOI:10.1016/j.apcata.2018.07.018

The catalytic conversion of alkynes into ketones via hydration has received considerable attention, because the ketones are very important intermediates in the chemical and pharmaceutical industries. The hydration of alkynes was usually performed with rather complicated processes in presence of liquid acids or highly toxic metal catalysts. We report here a novel metal free and efficient route to conversion of alkynes into ketones catalyzed by hierarchically porous poly(ionic liquid)s solid strong acids, which were synthesized from one-step, template-free copolymerization of divinylbenzene (DVB) with nitrogen containing monomers under solvothermal condition, further by post grafting with strong acid ionic liquid groups. The porous poly(ionic liquid)s solid acids have large BET surface areas, hierarchical nanopores and enhanced acid strength. A variety of alkynes could be effectively transformed into ketones catalyzed by the synthesized porous poly(ionic liquid)s solid acids under green and mild conditions, which were much better than those of Amberlyst 15, phosphotungstic acid and sulfuric acid. Furthermore, the porous poly(ionic liquid)s solid acids also show excellent activities and good reusability in direct hydroamination of amines with phenylacetylene. This work largely expands the wide applications of porous poly(ionic liquid)s solid strong acids in hydration and hydroamination, which develops a green, efficient and cost effective approach for conversion of low cost alkynes into high-value added ketones.

Full text of DOI:10.1016/j.apcata.2018.07.018

Accepted Manuscript
Title: A green and efficient hydration of alkynes catalyzed by
hierarchically porous poly(ionic liquid)s solid strong acids
Authors: Duan-Jian Tao, Fujian Liu, Lin Wang, Lilong Jiang
PII:
S0926-860X(18)30341-7
DOI:
Reference:
https://doi.org/10.1016/j.apcata.2018.07.018
APCATA 16744
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Applied Catalysis A: General
Received date:
Revised date:
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30-5-2018
7-7-2018
14-7-2018
Please cite this article as: Tao D-Jian, Liu F, Wang L, Jiang L, A
green and efficient hydration of alkynes catalyzed by hierarchically porous
poly(ionic liquid)s solid strong acids, Applied Catalysis A, General (2018),
https://doi.org/10.1016/j.apcata.2018.07.018
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A green and efficient hydration of alkynes catalyzed by hierarchically
porous poly(ionic liquid)s solid strong acids
Duan-Jian Tao a, Fujian Liu*b , Lin Wang c and Lilong Jiang b
a
College of Chemistry and Chemical Engineering, Institute of Advanced Materials,
Jiangxi Normal University, Nanchang, P. R. China.
b National Engineering Research Center of Chemical Fertilizer Catalyst (NERC-CFC),
School of Chemical Engineering, Fuzhou University, Gongye Road No.523, Fuzhou
350002, Fujian, P. R. China. E-mail: fjliu1982@gmail.com; fjliu@usx.edu.cn
c Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan
430071, P. R. China.
1

GRAPHICAL ABSTRACT
Highlights
One-step solvothermal approach was used to synthesize N doped nanoporous polymers.
Strong acid ionic liquids were post grafted onto the synthesized nanoporous polymers.
Porous polymeric ionic liquids show strong acid strength and adjustable acid contents.
Porous polymeric ionic liquids were very active in hydration and hydroamination of alkynes.
Green and metal-free approach was developed for conversion of alkynes into useful chemicals.
Abstract
The catalytic conversion of alkynes into ketones via hydration has received
considerable attention, because the ketones are very important intermediates in the
chemical and pharmaceutical industries. The hydration of alkynes was usually performed
with rather complicated processes in presence of liquid acids or highly toxic metal
2

catalysts. We report here a novel metal free and efficient route to conversion of alkynes
into ketones catalyzed by hierarchically porous poly(ionic liquid)s solid strong acids,
which were synthesized from one-step, template-free copolymerization of divinylbenzene
(DVB) with nitrogen containing monomers under solvothermal condition, further by post
grafting with strong acid ionic liquid groups. The porous poly(ionic liquid)s solid acids
have large BET surface areas, hierarchical nanopores and enhanced acid strength. A
variety of alkynes could be effectively transformed into ketones catalyzed by the
synthesized porous poly(ionic liquid)s solid acids under green and mild conditions, which
were much better than those of Amberlyst 15, phosphotungstic acid and sulfuric acid.
Furthermore, the porous poly(ionic liquid)s solid acids also show excellent activities and
good reusability in direct hydroamination of amines with phenylacetylene. This work
largely expands the wide applications of porous poly(ionic liquid)s solid strong acids in
hydration and hydroamination, which develops a green, efficient and cost effective
approach for conversion of low cost alkynes into high-value added ketones.
Keywords: Porous polymeric ionic liquids; Alkynes hydration; Hydroamination; Solid
acids; Green and sustainable chemistry.
3

1. Introduction
Ketones are very important intermediates in the chemical and pharmaceutical
industries, and they are popularly produced by the hydration of alkynes with 100 %
atomic economy. [1,2] However, the traditional alkynes hydration usually employs
mercuric (II) salt, a highly toxic compound, as the catalyst in aqueous sulfuric acid,
which strongly constrain their wide applications in the industry. [3] To overcome the
toxicity of Hg salts, the usage of various organometallic catalysts such as compounds
containing Au, Pt, Ag, Ru, and even biomimetic catalysts have been widely developed.
[4-13] Despite enhanced conversions and selectivities were obtained, these catalysts also
suffered from at least one of the following drawbacks: (1) expensive noble metals (Au, Pt,
Ru, Ag, etc); (2) high reaction temperatures (>100 °C); (3) large excess of water and
additional acidic additives; (4) limited functional group compatibility. Recently, several
Brønsted acids (e.g. TfOH, HNTf2) were found to exhibit very good catalytic activity for
the hydration of alkynes. [14,15] However, the processes usually require stoichiometric
or excess amounts of acids, which lead to the difficulties in separating and recycling of
acid catalysts. Therefore, it is still highly desirable to develop new kind of acid catalysts
with high effectiveness for alkynes hydration under green and mild conditions.
Acidic ionic liquids (ILs), regarded as a new type of green reaction medium, have
been successfully introduced into the area of acid catalysis owing to their unique
properties such as negligible vapor pressure, remarkable solubility, and structural variety
4

[16-19]. To promote separation and reusability of the homogeneous ILs catalysts, the
synthesis of mesoporous polymeric ILs catalysts containing both the acidic sites and the
IL groups has received considerable attention in these years. [20,21] Porous polymeric
ILs, as highly active acid catalysts, should have several characteristics including large
BET surface areas, strong acid strength, and enhanced exposure degree of active sites.
However, many polymeric ILs reported in the previous literatures, have very low
concentrations of acidic sites and rather poor porosities, which constrain them used as
efficient solid acids in various acid-catalyzed reactions, especially in hydration reaction.
[22-25] Therefore, it remains a challenge to prepare porous polymeric ILs with large BET
surface areas, enhanced acid strength, controllable and high contents of acid sites.
Recently, we reported the preparation of strongly acidic ILs functionalized, porous
polymers with unique characteristics such as controllable hydrophilic–hydrophobic
networks, hierarchical porosity, large BET surface areas and strong acid strength, which
exhibit even higher activities than their homogeneous counterparts in biodiesel
production. [20] In this work, we report here the synthesis of sponge-like nanoporous
polymers functionalized with both the sulfonic group and the ionic liquids group (e.g.,
PDVB–[C3VP][SO3CF3], PDVB: polydivinylbenzene, VP: 4-vinyl pyridine, C3:
1,3-propanesultone, SO3CF3: HSO3CF3 anion-exchanger), which were synthesized from
solvothermal copolymerization of divinylbenzene (DVB) with functional monomers of
1-vinylimidazolate (vim) or 4-vinyl pyridine (VP) at 100 °C, followed by formation of
quaternary ammonium salts using 1,3-propanesultone, and finally ion-exchanged with
5

HSO3CF3, similar to the method we previously reported. The combination of structural
characteristics such as large BET surface areas, hierarchical nanopores and much
enhanced acid strength, the synthesized nanoporous polymer ionic liquid solid acids show
extraordinary catalytic activities and improved reusability in both hydration of alkynes
into ketones and hydroamination of amines with phenylacetylene, which were better than
those of Amberlyst 15, phosphotungstic acid and sulfuric acid. This work largely expands
the wide applications of porous poly(ionic liquid)s solid strong acids in hydration and
hydroamination, which develops a green, efficient and cost-effective approach for the
conversion of raw feedstocks into high value-added chemicals in the industry.
2. Experimental details
2.1 Chemicals and reagents
All reagents were of analytical grade and used as purchased without further
purification. Divinylbenzene (DVB), 1-vinylimidazole, 4-vinyl pyridine Amberlyst 15
were purchased from Sigma-Aldrich Co. Azobisisobutyronitrile (AIBN), ethyl acetate,
1,3-propanesultone, HSO3CF3, H2SO4, HCl, trifluoroethanol, toluene, phosphotungstic
acid and CH2Cl2 were obtained from Beijing Chemical Agents Company.
2.2. Samples preparation
Nanoporous polymers could be synthesized from crosslinking of 1-vinylimidazolate
(vim) or 4-vinylpyridine (VP) with DVB under solvothermal condition at 100 °C, where
6

ethyl acetate was employed as the solvent. After quaternary ammonization and
anion-exchange treatment, ILs functionalized nanoporous polymers were obtained. [21]
In a typical synthesis of PDVB-VP-0.5 support, 2.0 g of DVB and 0.5 g of VP were
introduced into a solution containing 0.07 g of AIBN and 30 mL of ethyl acetate. After
stirring at room temperature for 3 h, the mixture was solvothermally treated at 100 °C for
24 h, followed by slow evaporation of the solvent at room temperature for 2 days. The
product of PDVB-VP-0.5 with monolithic morphology was obtained. Correspondingly,
PDVB-VP-0.2 could be synthesized with similar procedures, where 0.2 g of VP
functional monomer was introduced into the mixture. Meanwhile, PDVB-vim-0.2 support
could also be synthesized with similar procedure as that of PDVB-VP-0.2, where 0.2 g of
vim functional monomer was introduced into the mixture.
PDVB-[C3VP][SO3CF3]-0.5 (C3 stands for quaternary ammoniation reagent of
1,3-propanesultone) were synthesized by quaternary ammoniation of pristine
PDVB-VP-0.5 support with 1,3-propanesultone, followed by ion exchanging with
HSO3CF3. Typically, 1.0 g of PDVB-VP-0.5 was added into 25 mL of toluene under
vigorous stirring, followed by addition of 0.25 g of 1,3-propanesultone. After quaternary
ammoniation at 100 °C for 24 h, the product was collected by filtration, washing with
abundant ethanol and drying at 60 °C. The resultant sample was then treated with
HSO3CF3 in toluene solvent for 24 h at room temperature, washed with abundant CH2Cl2
and dried at 80 °C for 8 h under vacuum condition, to give the final solid acid of
PDVB-[C3VP][SO3CF3]-0.5. Correspondingly, PDVB-[C3VP][SO4H]-0.5 could also
7

synthesized with similar procedures, where the exchange acid was sulfuric acid.
PDVB-[C3vim][SO3CF3]-0.2 was prepared in a similar way, and PDVB-SO3H was
prepared as literature for comparison. [26]
2.3. Characterizations
Nitrogen isotherms were measured using a Micromeritics ASAP 3020M system. The
samples were outgassed for 10 h at 150 °C before the measurements. The pore-size
distribution was calculated by using Barrett-Joyner-Halenda (BJH) model. FT-IR spectra
were collected by using a Bruker 66V FT-IR spectrometer. SEM images were performed
on JEOL 6335F field emission scanning electron microscope (FESEM) attached with a
Thermo Noran EDX detector. Transmission electron microscopy (TEM) images were
performed on a JEM-2100F electron microscope (JEOL, Japan) with an acceleration
voltage of 200 kV. CHNS elemental analysis was performed on a Perkin-Elmer series II
CHNS analyzer 2400. XPS spectra were performed on a Thermo ESCALAB 250 with Al
Kα radiation at y = 901 for the X-ray sources, the binding energies were calibrated using
13
the C1s peak at 284.9 eV. C solid state NMR experiments were carried out on a Varian
Infinityplus-300 spectrometer at resonance frequencies of 75.38 MHz. The experiments
were recorded using a 4 mm double-resonance MAS probe at a spinning rate of 10 kHz.
13
The pulse width (π/2) for C was measured to be 4.1 μs. A contact time of 4 ms and a
recycle delay of 3 s were used for the 13C CP/MAS measurement.
8

The solid-state 31P NMR spectra over nanoporous polymer based solid acids were
performed as the following procedures: prior to the sorption of trimethylphosphine (TMP)
and trimethylphosphine oxide (TMPO) probe molecules, the samples were placed in glass
tubes, which were connected to a vacuum line for dehydration. The samples were kept at
a final temperature at 453 K for 24 h, with the pressure below 10-3 Pa. Then, they were
cooled. The preparation of TMPO adsorbed samples was performed according to the
method proposed by Zheng and coworkers. [27] Prior to the NMR experiments, the
sealed sample tubes were opened and the samples were transferred into NMR rotors with
31
a Kel-F end cap under a dry nitrogen atmosphere in a glove box. P NMR experiments
were performed on a Bruker Ascend-500 spectrometer at a resonance frequency of
202.34 MHz for 31P nucleus, with a 4 mm triple-resonance MAS probe at a spinning rate
31
31
of 12 kHz. Pulse width (π/2) for P was measured to be 4.5 μs. P MAS NMR spectra
with high power proton decoupling were recorded with a recycle delay of 30 s. The
chemical shift of 31P resonance was externally referenced to 1 M aqueous H3PO4.
2.3. Reaction procedures
A typical procedure for the ketone from alkynes hydration is as follows: Catalyst (44
mg) was added into the mixture of phenylacetylene (0.4 mmol) and deionized water (0.8
mmol) in trifluoroethanol (2.0 mL) in a 12 mL microwave tube. The resulting mixture
was vigorously stirred at 1000 rpm at controlled temperature. After reaction for 18 h, the
reaction mixture was centrifuged and the liquid was transferred to a bottle. Qualitative
9

analyses of products were examined by a Thermo Trace 1300 GC-ISQ, and quantitative
analyses were carried out by a GC-FID (Agilent 7890B). A capillary column HP-5
(methyl polysiloxane, 30 m×0.32 mm×1 μm) was used to determine the composition of
the samples with nitrogen as the carrier gas at a flow rate of 3 mL/min. The temperature
of the column, the inlet and the detector was kept at 453, 473, and 523 K, respectively.
3. Results and discussion
3.1 Structural characterizations
Figure 1 shows N2 sorption-desorption isotherms at 77 K and pore size distribution
of the synthesized PDVB-[C3vim][SO3CF3]-0.2, PDVB-[C3VP][SO3CF3]-0.2 and
PDVB-[C3VP][SO3CF3]-0.5. Interestingly, all the samples show typical type-IV
isotherms with relatively high volume adsorption, which increases steeply at the relative
pressure of 0.85–1.0, indicating that abundant meso–macropores were formed in these
samples. The pore size distribution cover a wide range from 0 to 300 nm, indicating
hierarchical nanopores were formed in these samples. The calculated textural properties
of the synthesized POPs are illustrated in Table 1, PDVB based poly(ionic liquid)s solid
strong acids show large BET surface areas ranged from 92 to 698 m2/g, the corresponding
pore volumes were ranged from 0.27 to 1.49 cm3/g. The pore size distributions curves of
PDVB based poly(ionic liquid)s shows dual peaks centered at around 30 and 120 nm,
which were distributed in the range of meso-macroporous scale. Combination of large
BET surface areas and abundant meso-macropores in PDVB based poly(ionic liquid)s,
10

which was favorable for the fast diffusion of various substrates, enhancement of
accessibility of acidic sites in these samples. The acid contents of PDVB based poly(ionic
liquid)s were ranged from 0.95 to 1.83 mmol/g (Table 1), which were lower than
variously traditional acid catalysts such as Amberlyst 15 (4.7 mmol/g), H3O40PW12 (3.5
mmol/g), and H2SO4 (10.1 mmol/g).
Figure
2
shows SEM images of PDVB-[C3vim][SO3CF3]-0.2 and
PDVB-[C3VP][SO3CF3]-0.2. Both samples showed monolith morphology with rather
rough surface and sponge-like characteristics, and abundant macropores were found in
these samples. The pore sizes were larger than 100 nm, which was in consistent with N2
adsorption results. On the other hand, TEM images of the synthesized samples were also
systematically studied. TEM is a reliable technique for characterization the internal
nanopores of porous materials. Figure
3
shows the TEM images of
and
PDVB-[C3vim][SO3CF3]-0.2, PDVB-[C3VP][SO3CF3]-0.2
PDVB-[C3VP][SO3CF3]-0.5. Interestingly, all the samples showed the hierarchical
meso-macropores characteristics, which are in consistent with N2 adsorption and SEM
results. The mesopore sizes were distributed in the range from 20 to 40 nm, in good
agreement with N2 adsorption results.
Figure 4 shows 13C solid state NMR spectrum of PDVB-[C3VP][SO3CF3]-0.2.
Notably, the chemical shifts at around 41 and 46 ppm should be assigned to methylene
bridges in PDVB-VP support and C3 alkyl chain. The chemical shift at around 138 ppm
should be assigned to the carbon atom connected with nitrogen in pyridinic ring. The
11

chemical shifts at around 129, 145 and 150 ppm should be assigned to the carbon atoms
in DVB and pyridinic ring without connecting with nitrogen. The 13C NMR spectrum
confirms the successful grafting of strong acid ionic liquids onto the network of
PDVB-VP, which gives PDVB-[C3VP][SO3CF3]-0.2 solid acids.
To further confirm the acidity of the synthesized nanoporous poly(ionic liquid)s solid
acids. Various characterization of FT-IR, XPS and 31P solid state NMR spectra were
investigated. Figure 5 shows FT-IR spectra of PDVB-[C3vim][SO3CF3]-0.2,
PDVB-[C3VP][SO3CF3]-0.2, PDVB-[C3VP][SO3CF3]-0.5 and five times recycled
PDVB-[C3VP][SO3CF3]-0.5. Notably, the vibration at around 1036 and 1220 cm−1
associated with the C–S and S=O vibrations could be observed in these samples. The
vibration at around 1170 cm−1 associated with the C–F and S-O vibration could also be
observed in these samples, indicating the successful introduction of acid ionic liquid and
sulfonate groups in these samples. [20,26,28,29]
Figure
6
shows
X-ray
photoelectron
spectroscopy
(XPS)
of
PDVB-[C3VP][SO3CF3]-0.5 and PDVB-[C3vim][SO3CF3]-0.5. The samples show the
signals of C1s, N1s, O1s, S2p and F1s. The signal of S2p associated with sulfonate group
was centered at around 168.5 eV. The C1s peaks at around 284.6, 286.2, and 291.9 eV are
assigned to C−C, C−N, and C-F bond. [20] The N1s peaks are centered at around 401.9
eV, which indicates the successful quaternary ammonization of N atom in VP and vim
building units with 1,3-propanesultone. [20] The O1s peaks at around 533.0 and 535.0 eV
are assigned to the oxygen atoms in the -SO3H and -SO2CF3, respectively. [20] The F1s
12

peaks at around 535.0 eV are assigned to -SO2CF3 group. [20] The above results further
confirm the successful grafting of acidic ionic liquid and sulfonate groups in the
synthesized PDVB-VP and PDVB-vim.
To further study the acidity of the synthesized solid acids, 31P MAS NMR spectra of
trimethylphosphine (TMP) and trimethylphosphine oxide (TMPO) adsorbed on the
31
synthesized samples was investigated. It is well known that P MAS solid state NMR
spectra is a state of the art technique for acidity characterization of various acid catalysts,
and such approach has been extensively used to determine the acidic properties (i.g.,
acidic type, acidic strength and acidic amount) of various solid acids, including zeolites,
sulfated mesoporous metal oxides and heteropolyacids. [27,30-35] Figure 7a shows room
temperature 31P MAS NMR spectra of TMP adsorbed on PDVB-[C3VP][SO3CF3]-0.5. 31P
NMR of adsorbed TMP has been demonstrated to be a sensitive and reliable technique for
the determination of the Brønsted and Lewis acid sites in the solid acids. The adsorption
of TMP on the Brønsted acid will give rise to 31P resonances in a rather narrow range (ca.
-2 ~ -5 ppm), and TMP bound to Lewis acid sites, may result in 31P peaks in the range of
ca. -20 ~ -60 ppm. [29,30] As shown in Figure 7a, using TMP as a probe molecule, the
31P resonance at -3.3 ppm was assigned to the protonated adducts, [(CH3)3P-H]+,
31
attributed by the reaction of TMP and the Brønsted acidic protons. The P resonance at
-62 ppm was assigned to the physical absorbed TMP in the sample. [34] The 31P
resonance at 26.8 ppm should be attributed to the signal of mobile TMP in the sample.
[34]
13

In order to reveal the acid strength of the synthesized PDVB-[C3VP][SO3CF3]-0.5,
TMPO as the probe molecular adsorbed on the surface of PDVB-[C3VP][SO3CF3]-0.5
was also investigated. The corresponding 31P solid-state NMR spectrum was shown in
Figure 7b. Interestingly, multiple 31P resonances at around 66, 83, 87 ppm were observed
in the PDVB-[C3VP][SO3CF3]-0.5, which are assigned to various acid sites with different
strength present in the sample. The resonance peak at around 66 ppm may be assigned to
carboxylic acid site, which was resulted from partially oxidation of polymer networks.
The resonances at around 83 and 87 ppm should be assigned to the grafted sulfonate
group and immobilized acid ionic liquid site, which exhibit strong acid strength in
comparison with variously reported solid acids. [34] Notably, a 31P resonance at -15.5
ppm could be observed in both TMP and TMPO absorbed samples, which may be
attributed to the residual phosphorus in the sample. This signal was not derived from the
interactions between TMP or TMPO and PDVB-[C3VP][SO3CF3]-0.5. The 31P NMR
spectra certified the successful introduction of strong acid ionic liquid group in
PDVB-[C3VP][SO3CF3]-0.5, in good with FT-IR and XPS results.
3.2 Catalytic performance of porous poly(ionic liquid)s solid strong acids
Firstly, the catalytic performance of nanoporous poly(ionic liquid)s solid strong acids
for hydration reaction of phenylacetylene was screened. The results are summarized in
Table 2. It was found that under mild condition of reaction temperature of 40 C for 18 h,
PDVB-[C3VP][SO3CF3]-0.5 had the highest catalytic activity in the hydration reaction of
14

phenylacetylene with a 98 % yield of acetophenone (entries 1-7). This could be directly
assigned to the super acid strength and high acid content of the
PDVB-[C3VP][SO3CF3]-0.5 catalyst. Although PDVB-[C3VP][SO3CF3]-0.2 has larger
BET surface area than PDVB-[C3VP][SO3CF3]-0.5, the limited acid content of
PDVB-[C3VP][SO3CF3]-0.2 results in its lower activity in comparison with of
PDVB-[C3VP][SO3CF3]-0.5. Similar trend could also be found in the
PDVB-[C3vim][SO3CF3] samples. Also, relatively large surface area is favorable for
exposure of catalytically active sites to reactants, and the abundant mesoporosity has an
advantage for mass transfer. Moreover, the hydration of phenylacetylene was also
examined using traditional liquid acids (H2SO4, heteropolyacid) and solid acid
(Amberlyst 15) as catalysts (entries 8-10). It can be seen that PDVB-[C3VP][SO3CF3]-0.5
show much higher catalytic activity than those conventional acid catalysts. It is reasoned
that on the basis of the same amount of acidic sites, PDVB-[C3VP][SO3CF3]-0.5 show
much enhanced acid strength in comparison with these liquid acids. Also, the
heterogeneous catalyst Amberlyst 15 has a relatively large mass transfer resistance, thus
resulting in a low yield of acetophenone. Therefore, the above results demonstrated that
PDVB-[C3VP][SO3CF3]-0.5 is considered to be a promising superacid catalyst with high
activity for hydration of phenylacetylene.
3.3 Optimization of reaction parameters
15

To optimize the reaction conditions for PDVB-[C3VP][SO3CF3]-0.5 in hydration of
phenylacetylene to prepare acetophenone, the effects of solvent, reaction time, reaction
temperature, and catalyst loading on the yield of acetophenone were investigated. It can
be seen from Table 3 that the solvent has a significant effect on the hydration reaction.
Compared with other solvents, trifluoroethanol (CF3CH2OH) would be much more
favorable to the hydration reaction. Given that alkyne’s hydration is generally via a vinyl
carbocation intermediate, [36] CF3CH2OH has the ability to stabilize a vinyl carbocation
intermediate and thereby cause the hydration reaction to proceed more efficient than
those of reactions occurring in other solvents.[14] Moreover, the effect of reaction
temperature was investigated in the range of 30-60 C. Figure 8a shows that the hydration
could be completely carried out at the optimal reaction temperature of 40 C, and thus the
yield of acetophenone was given to 98 %. This suggests that the favorable temperature in
this work is much milder than those in most of reported literatures. Then, Figure 8b
shows the effect of catalyst loading on the hydration reaction. With an increase in the
relative amount of PDVB-[C3VP][SO3CF3]-0.5, the reaction rate was speeded up and
thus
a
higher yield was obtained. For example, when the dosage of
PDVB-[C3VP][SO3CF3]-0.5 increased from 4 to 10 %, the yield significantly increased
from 63 to 98 %. However, the catalyst loading was further added to 12 %, only a little
increase in the yield was examined. This indicates that over a certain catalyst loading, too
much catalyst amount is not imperative. Thus, in view of the cost of catalyst, 10 wt.% is
taken as the optimum catalyst loading and used in bulk of hydration experiments. Further,
16

the reaction time was examined in the range of 12-24 h as shown in Figure 8c. The yield
of acetophenone gradually increases to 98 % in the first 18 h but keeps no obvious
change at longer reaction times. Thus, 18 h is chosen as the optimal reaction time. The
reusability and stability of catalyst are also the key influential factors for potentially
industrial application. After the completion of a reaction, the system with catalyst
PDVB-[C3VP][SO3CF3]-0.5 was centrifuged. Follow on removing the liquid part and
washing silt substance with dichloromethane, dried it in vacuum oven at 50 °C for 6 h.
After that, there was a step called catalyst activation. The formed suspension, as the ratio
of sample: dichloromethane: triflic acid = 1 g : 25 mL : 2 mL, was stirred at room
temperature for 24 h. Next step, centrifuged, washed and dried, recycled
PDVB-[C3VP][SO3CF3]-0.5 was used in hydration reaction. The above operation was
repeated five times to test its activity as well as stability. As shown in Figure 8d, no
significant decrease in the yield of acetophenone was examined during the five
successive recycles. Thus, the catalyst PDVB-[C3VP][SO3CF3]-0.5 was stable enough to
be recycled for the hydration of phenylacetylene. PDVB-[C3VP][SO3CF3]-0.5 was
considered to be steadily recycled for the hydration reaction.
3.4 Applicability of PDVB-[C3VP][SO3CF3]-0.5 catalyst
The applicability of PDVB-[C3VP][SO3CF3]-0.5 catalyst was examined for
catalyzing hydration of different alkyne substrates. The results were presented in Table 4.
With the substituent electron withdrawing group -Br and electron donating groups -CH3,
17

-OCH3 attached to the aromatic ring, the desired ketones could be obtained with excellent
yields (85-99 %) under mild conditions (entries 1-4). Besides aromatic alkynes, the scope
of this catalytic system was also explored for the hydration of aliphatic alkynes. It was
indicated that the hydration of 1-octyne and 1,2-diphenylacetylene required a relatively
long time and high temperature, resulting in corresponding the target products with 99%
yield (entries 5, 6).
In addition, we tried to inspect the adaptation of PDVB-[C3VP][SO3CF3]-0.5 in a
consecutive reaction, hydroamination of phenylacetylene with different amines (Table 5).
The catalyst PDVB-[C3VP][SO3CF3]-0.5 showed the high activity with a 81% yield of
imine. Notably, the hydroamination of aromatic amines with electron-donating or
withdrawing group was further performed with almost 100 % yields, although the
reaction time prolongs to 50 h. These results demonstrate that poly(ionic liquid)s solid
strong acid catalyst PDVB-[C3VP][SO3CF3]-0.5 exhibits the broad functional group
compatibility in the hydration and hydroamination reactions, showing the potential
industrial synthesis of high-value added ketones and imines.
4. Conclusions
In summary, hierarchically nanoporous poly(ionic liquid)s solid strong acids were
prepared from copolymerization of DVB with nitrogen containing monomers under
solvothermal condition without using additional templates, further by post grafting with
18

strong acid ionic liquid groups. The synthesized porous ionic polymer based solid acids
show excellent activities and good reusability in direct hydration of alkynes into ketones
without using any co-catalysts, much better than commercial acids such as Amberlyst 15,
phosphotungstic acid and sulfuric acid. In addition, the synthesized poly(ionic liquid)s
solid acids also show enhanced activities in hydroamination of alkynes with amines. This
work develops efficient porous polymers ionic liquid solid strong acids in hydration and
hydroamination of alkynes, which offers a green and metal free approach for
transformation of low cost alkynes into high-value added ketones in the industry.
Acknowledgements
This work was supported by the National Natural Science Foundation of China
(21573150, 21203122, 21566011, 31570560) and Jiangxi Province Sponsored Programs
for Distinguished Young Scholars (20162BCB23026).
19

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24

Table 1. The textural and acidic parameters of various acid catalysts.
b
c
Samples
Acid content SBET
Vp
Dp (nm) d
(mmol/g) a
0.95
(m2/g) (cm3/g)
PDVB-[C3vim][SO3CF3]-0.2
PDVB-[C3vim][SO3CF3]-0.5
PDVB-[C3VP][SO3CF3]-0.2
PDVB-[C3VP][SO3CF3]-0.5
Amberlyst 15
698
279
196
92
45
-
1.49
0.73
0.61
0.27
0.31
-
32.5&126.5
1.78
29.4&123.3
0.98
30.9&126.5
1.83
28.4&122.1
4.7
40
-
e
H3O40PW12
3.5
e
H2SO4
10.1
-
-
-
a Measured by acid-base titration.
b
Surface area calculated from the BET equation in the relative pressure range of
0.05~0.20.
c Single point total pore volume calculated at the relative pressure of 0.99.
d Pore size distribution estimated from BJH model.
e Calculated from molecular formula.
25

Table 2. Hydration reaction of phenylacetylene over different catalysts a.
Entry
Catalysts
Conversion (%)
Yield (%)
1
2
PDVB-[C3VP][SO3CF3]-0.5
PDVB-[C3VP][SO4H]-0.5
99
90
98
81
3
PDVB-[C3VP][SO3CF3]-0.2
95
89
4
5
6
PDVB-[C3vim][SO3CF3]-0.5
PDVB-[C3vim][SO4H]-0.5
PDVB-[C3vim][SO3CF3]-0.2
96
53
67
90
45
63
7
8
PDVB-SO3H
Amberlyst 15
H3O40PW12
39
18
78
62
35
8
9
56
36
10b
Sulfuric acid
a Reaction condition: Phenylacetylene (0.4 mmol), H2O (0.8 mmol), CF3CH2OH (2 mL),
catalyst (10 wt.% of phenylacetylene), 40 °C, 18 h. b Catalyst (0.0005g).
26

Table 3. Hydration reaction of phenylacetylene over different solvents a.
Entry
Solvent
CF3CH2OH
H2O
Yield (%)
1
2
3
97
<1
<1
CH3CH2OH
4
DMSO
<1
5
6
7
CH3CN
toluene
-
<1
<1
<1
a Reaction condition: Phenylacetylene (0.4 mmol), H2O (0.8 mmol), solvent (2 mL),
PDVB-[C3VP][SO3CF3]-0.5 catalyst (10 wt.% of phenylacetylene), 40 °C, 18 h.
27

Table 4. Hydration of various alkynes catalyzed by PDVB-[C3VP][SO3CF3]-0.5 a.
Entry
Alkyne
Product
Yield (%)
1
2
98
99
85
99
3b
4c
5d
6e
99
99
a Reaction condition: Alkyne (0.4 mmol), H2O (0.8 mmol), CF3CH2OH (2 mL), catalyst
(10 wt.% of alkyne), 40 °C, 18 h. b,c 50 °C. d,e 90 °C, 24 h.
28

Table 5. Hydroamination of phenylacetylene with various amines a.
Entry
1
Amine
Product
Yield (%)
81
2
3
100
100
a Reaction condition: Phenylacetylene (0.4 mmol), H2O (0.8 mmol), amine (0.4 mmol),
CF3CH2OH (2 mL), catalyst (0.048 g), 110 °C, 50 h.
29