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S.-D. Lee et al. / Applied Catalysis A: General 486 (2014) 69–76
In this study, different polystyrene-supported quaternary
(a) PS
ammonium salts were prepared by the reaction of PS and alkyl
diamine followed by quaternization with an alkyl halide, with vary-
ing chain lengths of the alkyl diamine and different cation and
anion of the alkyl halide. The performance of these catalysts in
between the PS and quaternized ammonium group, can activate the
epoxide ring, and therefore, showed better catalytic performance
compared to the PS-supported quaternary ammonium salts with-
out NH– group in the linker [33]. For a better understanding of
the reaction mechanism, DFT studies were performed. The effects
of the catalyst structure, CO2 pressure, and reaction temperature
were also discussed. A recyclability test of the catalyst was carried
out to assess the stability of this catalyst system.
(b) PS-hexyl-diamine
(c) PS-hexyl-MeI
2. Experimental
2.1. Synthetic scheme
4000
3000
2000
1000
Wavenumber (cm-1)
The synthesis of the quaternized ammonium salt anchored to
PS was carried out via two steps as shown in Fig. S1 (Suppor-
ting Information). First, a mixture of PS (Merrifield peptide resin,
Aldrich, 1% DVB, 4.5 mmol Cl/g) and acetonitrile was stirred for 12 h
at 25 ◦C, then alkylene diamine was added with KOH, and this mix-
ture was stirred for 48 h at 80 ◦C to yield alkylenediamine-anchored
PS (PS-alkyl-diamine). The second step is the quaternization of the
PS-alkyl-diamine to form PS-alkyl-AX by its reaction with an alkyl
halide for 72 h at 50 ◦C. The precipitate was filtered and washed
with ethanol and then dried in a vacuum oven for 12 h at 60 ◦C to
prepare PS-alkyl-AX.
Fig. 1. FT-IR spectra of (a) PS, (b) PS-hexyl-diamine and (c) PS-hexyl-MeI.
are summarized in Table 1. The increase in the amount of nitro-
gen from PS to PS-alkyl-diamine indicated that the Cl of the DVB
cross-linked chloromethylated polystyrene reacted with the NH2
of the alkyldiamine to form N C bonds and eliminate HCl during
to 2.7 mmol/g-cat.
2.2. Characterization of the catalyst
The successful immobilization of the quaternary ammonium
salt on the surface of the polystyrene support was confirmed
corresponding to the stretching frequency of the CH2Cl functional
group (1265 cm−1) disappeared in the spectra of PS-hexyl-diamine
and PS-hexyl-MeI, suggesting the complete modification of MPR
[26–28]. New peaks were observed for PS-hexyl-MeI in the regions
1560–1650 and 3400 cm−1, which were absent from the MPR
Elemental analysis (EA) was carried out using Vario EL III. The
samples (2 mg) were heated to 1100 ◦C, and sulfanilic acid was
used as a standard. Fourier transform infrared (FT-IR) spectra were
obtained on an AVATAR 370 Thermo Nicolet spectrophotometer
with a resolution of 4 cm−1. XPS analyses were performed using
an X-ray photoelectron spectrometer (VG, ESCALAB 250) with
monochromatic Al K␣ radiation (hꢀ = 1486.6 eV). The surface mor-
phology was observed using an S-4200 field emission scanning
electron microscope (FE-SEM, Hitachi-3500N).
Further corroboration of the successful quaternization under
microwave irradiation was provided through XPS analyses. The N
1s spectra of PS-hexyl-diamine and PS-hexyl-MeI are presented in
Fig. 2. While PS-hexyl-diamine (Fig. 2b) showed a sole character-
istic amine nitrogen 1s peak at 399.4 eV, the quaternized species
(PS-hexyl-MeI; Fig. 2a) exhibited one additional peak centered at
402.4 eV, which is consistent with the literature data for the 1s
binding energy of quaternized nitrogen (–N+Me3) species. This
observation could be rationalized by the fact that the exposed
amine groups of PS-hexyl-diamine indeed underwent a successful
quaternization. The new peak (402.4 eV) observed in the character-
istic region for the nitrogen atom provided conclusive evidence for
over, the I 3d spectra of PS-hexyl-MeI were acquired to identify the
bonding nature of the halogen associated with the metal species, as
illustrated in Fig. S2. The I 3d peak was observed at 619.6 eV in the
successful immobilization of the quaternized ammonium salt on
the support, as shown in Fig. S1.
2.3. Synthesis of AGC from AGE and CO2
Allyl glycidyl carbonate (AGC) was synthesized by the coupling
reaction of AGE and CO2 in the presence of PS-alkyl-AX. All the
reactions were carried out in a 60-mL stainless-steel batch reac-
tor with a magnetic stirrer at 600 rpm. In a typical batch reaction,
a predetermined amount of catalyst was charged into the reactor
containing 52.3 mmol of AGE. The reaction was carried out under
a constant pressure of CO2 at different temperatures. After the
completion of the reaction, the reactor was cooled to 0 ◦C, and
the products were identified by gas chromatography (Agilent HP
6890 A) with a capillary column (HP-5, 30 m × 0.25 m) using a
flame ionized detector. The product yield was determined using an
internal standard method with biphenyl (0.05 g) as the standard.
3. Results and discussion
3.1. Characterization of the catalysts
The organic compositions of PS, PS-alkyl-diamine, and PS-alkyl-
AX were determined by elemental analysis (EA), and the results
The SEM images of PS, PS-alkyl-diamine, and PS-alkyl-MeI are
presented in Fig. 3. The images show that the diameter of the