1
26
D. Li et al. / Applied Catalysis A: General 510 (2016) 125–133
which showed some limitations in catalytic activities. For exam-
ples, Al-MCM-41 presented well reusability for rearrangement of
cyclohexanone oxime, but showed a low conversion of 50.6% [25].
Titanium-exchanged montmorillonite demonstrated well catalytic
conversion (96%) and selectivity (74%) for rearranging cyclodode-
canone oxime, but required very long reaction time (20 h) [26]. Cs
salt of phosphotungstic acid was a recyclable heterogeneous cat-
alyst for rearrangement of cyclohexanone oxime, which however
oxime (98 wt.%), 2,2-azobisisobutyronitrile (AIBN), hydrogen per-
oxide (H O , 30 wt.%), sodium acetate trihydrate (CH COONa,
99 wt.%), tetrahydrofuran (THF, 99 wt.%) and hydroxylamine
2
2
3
hydrochloride (NH OH·HCl, 98.5 wt.%) were purchased from
2
Sinopharm Chemical Reagent Co., Ltd. Sodium p-styrene sulfonate
(90 wt.%), divinylbenzene (DVB, 80 wt.%) and styrene (ST, 99 wt.%)
were provided by Aladdin Chem. Co., Ltd. Acetophenone (98 wt.%),
concentrated sulfuric acid (H SO , 98 wt.%) and chlorosulfonic acid
2
4
◦
needed the high temperature (150 C) and long time (6 h) to reach
(ClSO H) were supplied by Shanghai Lingfeng Chemical Reagent
3
the moderate conversion (80.8%) [27]. Heteropolyanion-based ILs
materials demonstrated high activity for the rearrangement of
various ketoximes; nevertheless, a co-catalyst such as ZnCl2 was
indispensible and a sluggish deactivation was observed in recycling
tests [28,29].
Co., Ltd. Acetophenone oxime (98 wt.%), benzophenone oxime
(97 wt.%) and cyclopentanone oxime (97 wt.%) were acquired from
Tianjin Heowns Co., Ltd.
2.2. Catalyst preparation
Sulfonic acid group ( SO H) functionalized polymer materials
3
have been developed as effective catalysts for many acid-catalyzed
reactions [30–32]. As the typical commercial strong acidic cation
exchange resin, Amberlyst-15 has a small surface area and low ther-
mal stability, which limits its practical application in catalysis. For
Beckmann rearrangement of cyclohexanone oxime, mesoporous
Sulfonic acid group-functionalized polymer H-PDVB-SO H was
prepared through two steps (Scheme 1) according to the Ref. [34].
3
In the first step, H-PDVB-SO Na was synthesized from copolymer-
3
ization of DVB and sodium p-styrene sulfonate under solvothermal
condition. In detail, 2.0 g of DVB was added into a solution con-
taining 0.05 g of AIBN and 20 mL of THF, followed by addition of
polymers functionalized with SO H have been designed and used
3
as heterogeneous catalysts. For example, meso-structured poly-
2
.0 mL of water and 3.17 g of sodium p-styrene sulfonate. After stir-
mers FDU-14-SO H demonstrated the conversion of 91.4% and
3
ring at room temperature for 3 h, the mixture was solvothermally
selectivity of 85.8% (yield 78.4%) for liquid-phase Beckmann rear-
rangement of cyclohexanone oxime, and could be reused for several
times with slight decrease of conversion [31]. Hypercrosslinked
organic polymer HBS-4 [33] showed the high yield of 83.4% to -
caprolactam with the reaction time of 6 h and its reusability was
unclear. Generally, these polymeric solid acids avoid the utiliza-
tion of any metals that may leach in catalytic systems, thus being
ecologically sustainable and noncorrosive. However, only post-
sulfonated polymers were tested in the Beckmann rearrangement
of cyclohexanone oxime and no study is related to their substrate
compatibility.
◦
treated at 100 C for 24 h. The solvent in the product mixture was
evaporated slowly at room temperature, washed successively with
◦
water, ethanol and diethyl ether, and dried at 80 C for 12 h to give
the product H-PDVB-SO Na.
3
In the secondary step, H-PDVB-SO Na compound was further
3
−1
treated by using 1 M (mol L ) sulfuric acid, giving the sample H-
PDVB-SO H. In a typical run, 1.0 g of H-PDVB-SO Na was dispersed
3
3
in 10 mL ethanol, and then 5 g sulfuric acid (1 M) was added drop-
wise. After stirring for 24 h at room temperature, the solid was
obtained by filtration, washed with water until the filtrate was neu-
◦
tral, and then dried at 80 C for 12 h. (Elemental analysis Calcd: C
In this paper, sulfonic group is in situ incorporated into poly-
meric skeleton, giving a non-post-sulfonated polymer material
6
5.09 wt.%; H 6.06 wt.%; S 8.19 wt.%.)
For comparison, two other control solid acids, post-sulfonated
(
H-PDVB-SO H) that is used as a heterogeneous solid acid cat-
3
mesoporous polymer (P(DVB-ST)SO H), sulfonic acid-modified
3
alyst for liquid-phase Beckmann rearrangements for the first
mesoporous silica SBA-15 (SBA-15-SO H) were prepared according
3
time. H-PDVB-SO H with large surface area and high content
3
to the previous literatures (details are in Supporting Information)
of the sulfonic group is prepared through copolymerization of
divinylbenzene (DVB) and sodium p-styrene sulfonate, followed
by an ion-exchange. Optimization of reaction conditions, catalytic
reusability, and comparison with various control catalysts are
systematically investigated. The catalyst is also assessed in the rear-
rangement of various other ketoximes to evaluate the substrate
[
35].
2
.3. Characterization
Fourier transform infrared spectroscopy (FT-IR) was recorded on
−
1
a Nicolet iS10 FT-IR instrument (KBr discs) in the 4000–400 cm
compatibility. The results show that H-PDVB-SO H is highly active
3
region. Lewis acid sites and Brønsted acid sites of the typical
sample were measured by the pyridine adsorption FT-IR spec-
trum [36]. Thermogravimetry (TG) analysis was carried out with
a STA409 instrument in dry air at a heating rate of 10 C min
Scanning electron microscope (SEM) images were performed on
a HITACHI S-4800 field emission scanning electron microscope.
in transforming aromatic oximes, especially cyclohexanone oxime,
to the corresponding amides. The advantages of this heterogeneous
catalysis system include the very short reaction time of 1 h, easy
recovery and steady reuse of the solid acid catalyst, and no need of
any co-catalysts.
◦
−1
.
Nitrogen (N ) adsorption isotherms and Brunauer–Emmett–Teller
2
2
. Experimental
(
BET) surface areas were measured at the temperature of liquid
◦
nitrogen (−196 C) by using a BELSORP-MINI analyzer. The sam-
2.1. Materials
◦
−3
ples were degassed at 120 C for 3 h to a vacuum of 10 Torr before
analysis, and pore size distribution curves were calculated using the
Barrett–Joyner–Halenda (BJH) model. CHNS elemental analysis was
All chemicals and solvents were commercially available and
used as received without further purification. Cyclohexanone
Scheme 1. Preparation process of sulfonic acid group-functionalized polymer H-PDVB-SO3H.