Dual catalysis with magnetic chitosan: Direct synthesis of cyclic carbonates from olefins with carbon dioxide using isobutyraldehyde as the sacrificial reductant

Article abstract of DOI:10.1039/c5dt01012h

Chitosan coated magnetic nanoparticles were synthesized and used as a support for the immobilization of the cobalt(ii) acetylacetonate complex [Co(acac)₂] and quaternary triphenylphosphonium bromide [P⁺Ph₃Br^-] targeting -NH₂ and -OH moieties located on the surface of chitosan. The synthesized material was used as a catalyst for one pot direct synthesis of cyclic carbonates from olefins via an oxidative carboxylation approach with carbon dioxide using isobutyraldehyde as the sacrificial reductant and molecular oxygen as the oxidant. After the reaction, the catalyst was recovered by applying an external magnet and reused for several runs without significant loss in catalytic activity and no leaching was observed during this course.

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Dual catalysis with magnetic chitosan: direct synthesis of cyclic
carbonates from olefins with carbon dioxide using isobutyraldehyde as
sacrificial reductant
Subodh Kumar,a Nikita Singhal,a Raj K. Singh,a Piyush Gupta,b Raghuvir Singhb and Suman L. Jain*a
5
Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX
DOI: 10.1039/b000000x
value products is one of the most challenging areas in current
decades both from economical and environmental points of view.
50 One of the most successful examples in the area of CO2
utilization is the production of five membered cyclic carbonates.8
Cyclic carbonates due to their higher boiling points, low toxicity,
high solubility, and biodegradability have an important market as
aprotic polar solvents and precursors for biomedical applications
55 as well as for engineering plastics.9 Various catalysts including
quaternary ammonium and phosphonium salts, alkali metal salts,
Lewis acids, transition metal complexes, ionic liquids and
organocatalyst have been reported for the coupling reaction of
epoxide and carbon dioxide to yield cyclic carbonate.10 However,
60 such a cycloaddition generally requires the initial synthesis of an
epoxide, which involves toxic or costly reagents and requires a
tedious workup procedure for separation. The direct synthesis of
cyclic carbonates from corresponding olefins and CO2, soꢀcalled
“oxidative carboxylation” constitutes an environꢀeconomic
65 approach due to the low cost and easy accessibility of olefins as
well as avoidance of initial synthesis and separation of epoxides.
The hitherto known methods for oxidative carboxylation of
olefins with O2/CO2 using metal catalysts are associated with the
drawbacks of poor product yields, use of expensive metals such
70 as ruthenium and harsh reaction conditions for example high
temperature and higher CO2 pressure.11
Chitosan coated magnetic nanoparticles were synthesized and
used as support for the immobilization of cobalt(II)
acetylacetonate complex [Co(acac)2] and quaternary
10 triphenylphosphonium iodide [P+Ph3Br-] targeting -NH2 and -
OH moieties located on the surface of chitosan. The
synthesized material was used as catalyst for one pot direct
synthesis of cyclic carbonates from olefins via oxidative
carboxylation approach with carbon dioxide using
15 isobutyraldehyde as sacrificial reductant and molecular
oxygen as oxidant. After the reaction, the catalyst was
recovered by external magnet and reused for several runs
without significant loss in catalytic activity and no leaching
was observed during this course.
20 Bioꢀbased and biodegradable polymers have received
considerable interest in recent decades mainly due to the limited
availability of fossil fuel and growing environmental concerns.
Apart from their wide spread applications in biomedical domain;1
they also have been widely used as catalyst carriers in chemical
25 reactions.2 Among the various known biopolymers, chitosan (CS)
owing to its low cost, non toxicity, biocompatibility, and
multifunctional properties has found extensive applications in
various areas including as catalyst support for chemical
transformations.3 It comprises a great quantity of hydroxyl and
30 amine groups, which can be used for the further functionalization
as well as immobilization of metal complexes through covalent
attachment. This kind of chitosanꢀmetal complexes has been
successfully used as heterogeneous catalysts in plethora of
reactions including hydrogenation, oxidation, adsorption and
35 polymerization.4 Apart from this, chemical instability, lower
surface area, dissolution of chitosan and lower disperse ability are
some major issues associated with the use of chitosan.5 Recently,
employing magnetic Fe3O4 nanoparticles to construct a recyclable
heterogeneous catalyst has led to a particular interest due to the
40 facile and efficient recovery of the catalyst from the reaction
mixture with an external magnetic field.6 Encapsulation of
magnetic nanoparticles with chitosan not only combine the low
cost and biodegradability brought by the natural polymeric
support with a high surface area and facile magnetic separation
45 but also contributes to the amelioration of chemical stability and
disperses ability.7
In the present paper, we describe an efficient heterogeneous
magnetically separable chitosan modified with Co(II)
acetylacetonate and triphenylphosphonium bromide as catalyst
75 for the direct one pot synthesis of cyclic carbonates via oxidative
carboxylation of olefins with carbon dioxide using molecular
oxygen as oxidant and isobutyraldehyde as sacrificial reducing
agent (Scheme 1).
O
cat.
O
O
R2
O2/
CHO
CO2
Scheme 1 oxidative carboxylation of olefin
R2
80
Chemical activation and conversion of carbon dioxide to high
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Result and Discussion
Synthesis and characterization of catalyst
The synthetic strategy adopted for the immobilization of
cobalt(II) acetylacetonate complex [Co(acac)2] and quaternary
triphenylphosphonium bromide [P+Ph3Brꢀ] to magnetic chitosan
is shown in Scheme 2. Initially chitosan coated magnetic particles
were prepared via coꢀprecipitation method by mixing
FeCl3.6H2O, FeCl2.4H2O and required amount of chitosan
followed by the addition of aqueous ammonia for 30 min in a
5
10 Teflon coated reactor. After completion of the reaction, the
particles were recovered by external magnet and washed with
deionized water for several times.12 As synthesized magnetic
chitosan i.e. MCS was subsequently used as support for the
immobilization of Co(acac)2 to give Co(acac)2@MCS by using –
15 NH2 groups presented on chitosan. Finally the synthesized
Co(acac)2@MCS
was
treated
with
3ꢀbromoꢀ
propyltrimethoxysilane (BPTMS) followed by the reaction with
triphenylphosphine to give magnetic chitosan immobilized cobalt
acetylacetonate and quaternary phosphonium bromide denoted as
20 Co(acac)2ꢀQPB@MCS catalyst (Scheme 2).
45 Fig. 1 HRTEM image of a) Fe3O4 nano particles; b) MCS; c) Co(acac)2ꢀ
QPB@MCS; d) MCS
Furthermore, XPS analyses was carried out to demonstrate the
successful anchoring of Co(acac)2 and P+Ph3Brꢀ onto MCS. An
apparent indication of anchoring of Co(acac)2 and P+Ph3Brꢀ onto
50 MCS can be deduced by the appearance of C, N, O, Si, Br, P, Fe
and Co elements in the wide scan XPS spectra of Co(acac)2ꢀ
QPB@MCS (Fig 2a). The highꢀresolution XPS spectrum of Fe
2p for MCS showed two peaks at 711.1 and 724.6 eV
corresponding to Fe2p3/2 and Fe2p1/2 in magnetic Fe3O4
55 nanoparticles respectively (Fig 2b).14 However, the intensity of
Fe2p peak is nearly invisible due to the matrix of chitosan. The
split bands in high resolution XPS spectrum of Co2p for
Co(acac)2@MCS at 780.1 and 795.8 eV were observed due to
the Co2p3/2 and Co2p1/2 of homogeneous Co(acac)2 complex.
60 However, the shifting of these bands in the immobilized catalyst
suggested the successful grafting of Co(acac)2 onto chitosan
support via covalent attachment (Fig. 2c).15
H3C
CH3
1. BPTMS
2. PPh3
HO
HO
O
O Si
Co(acac)2
S
C
NH2
N
O
O
Co
O
H2N
PPh
3Br
Toluene,
reflux
Toluene,
reflux
M
HO
HO
O
CH3
H3C
QPB@MCS 3
MCS 1
Co(acac)2@MCS 2
H3C
O
CH3
H3C
CH3
O
O
O
1. BPTMS
2. PPh3
O
O
Co
N
OH
OH
Co
N
Toluene,
reflux
O Si
O
PPh
3Br
O
H3C
H3C
CH3
CH3
Co(acac)2ꢀQPB@MCS 4
2
Scheme 2 Stepꢀwise synthesis of catalyst
The cobalt loading in the synthesized catalyst was found to be
25 0.31 mmol cobalt/g (1.8 wt% Co) as determined by ICPꢀAES
analysis. The amount of phosphorus in the synthesized catalyst
was found to be 0.16 mmol/g as determined by ICP. The possible
reason for the poor loading of phosphorus may be due to lesser
degree of substitution of hydroxyl groups of chitosan with 3ꢀ
30 bromopropyl trimethoxysilane followed by subsequent reaction
with triphenylphosphine.
The morphological features of the synthesized MCS and
Co(acac)2ꢀQPB@MCS were determined by transmission electron
microscopy (TEM) (Fig. 1). As shown in Fig 1, the MCS
35 exhibited spherical (Fig. 1b) whereas Co(acac)2ꢀQPB@MCS
revealed spheroidal morphology (Fig. 1c). The average size of the
Co(acac)2ꢀQPB@MCS nanoꢀcomposite spheres was found to be
in the range of 50ꢀ100 nm. The appearance of black spot
indicated the uniformly ingrained iron nanoparticles in the matrix
40 of chitosan. The lattice fringes for Fe3O4 phase with an interꢀ
planar dꢀspacing of 0.235 nm, corresponding to the (311) plane
can be clearly seen in the HRTEM image of an individual particle
of MCS (Fig. 1d).13
Fig. 2 a) wide scan XPS spectra of Co(acac)2ꢀQPB@MCS; Highꢀ
65 resolution XPS spectrum of b) Fe 2p for MCS; c) Co 2p for
Co(acac)2@MCS
2
|
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The FTIR spectra of MCS, Co(acac)2@MCS and Co(acac)2ꢀ
solvent at 100 ºC (Scheme 3).
QPB@MCS are given in supporting information (Fig. S1). FTIR
spectrum of MCS displayed characteristic peaks at 3400ꢀ3500
cm−1 (NꢀH, OꢀH), 2800ꢀ3000 (CꢀH), 1620 (NꢀH), 1050 cmꢀ1 (Cꢀ
OꢀC) and 595 cmꢀ1 (FeꢀO). After the Schiff condensation of
cobalt complex, and anchoring of P+Ph3Brꢀ moiety, the significant
changes in the FTIR spectra of chitosan were observed. There are
new bands at 1724, 1450 and 780 cmꢀ1 are corresponding to the
C=O, C=C (aromatic) and CꢀH (aromatic) stretching.
XRD pattern of as synthesized materials and chitosan is shown
in Fig. 3. XRD pattern of chitosan shows two characteristics peak
at 2θ = 11.2 and 21.8 while in case of Co(acac)2ꢀQPB@MCS,
two new peaks of lower intensity are appeared due to the
ingrained nanoparticles of Fe3O4 in chitosan matrix at 2θ =35.3
15 and 38.1 corresponding to the (311) and (222) planes
respectively.16 Peaks at 2θ = 11.2 and 21.8, have also become
sharper than native chitosan, it might be because of the phase
transformation of synthesized material from amorphous to
crystalline nature by the precipitation reaction of iron and
20 chitosan. It is to be noted that owing to the low concentration of
Co loaded on MCS, we could not see the signature of Co.
CHO
O
i) 4, PO2= 5 bar
O
O
5
ii) 4, PCO2= 30 bar
100oC, 10 h
acetonitrile
Scheme 3 Oxidative carboxylation of styrene
10
40
In an effort to find the best catalytic system, various catalysts (2
mol %) such as MCS, Co(acac)2@MCS, QPB@MCS, and
Co(acac)2ꢀQPB@MCS were screened. The results of these
experiments are summarized in Table 1. To our delight,
45 Co(acac)2ꢀQPB@MCS catalyst showed high efficiency for this
reaction under described conditions. The reaction was found to be
very slow in the absence of any catalyst or using MCS and
QPB@MCS as catalyst (Table 1, entry 1, 2, 3 and 4). The use of
physical mixture of Co(acac)2@MCS and QPB@MCS (1:1) as
50 catalyst provided lower yield of the product (Table 1, entry 6).
These results suggested that the covalent grafting of Co(acac)2
and P+Ph3Brꢀ moieties to MCS had a significant effect on
catalytic activity (Table 1, entry 5).
In order to confirm the formation of epoxide during the
55 reaction and to establish the mechanism, we performed the
reaction of styrene in the absence of carbon dioxide under
otherwise identical experimental conditions. The progress of the
reaction was monitored by GC, which confirmed the formation of
styrene epoxide as the major product along with about 17 % of
60 benzaldehyde as the byꢀproduct (Table 1, entry 7). Based on these
studies and in analogy to the existing report we proposed a
plausible mechanistic pathway for the reaction.17 The reaction
might involve the formation of isopropylacyl radical from
isobutyraldehyde via an electron transfer to the cobalt (II)
65 complex which subsequently added with oxygen to give oxoꢀ
metalꢀcomplex radical and then peroxideꢀmetalꢀcomplex radical.
These reactive peroxoꢀmetal intermediates reacted with olefin to
give styrene oxide and benzaldehyde. The styrene oxide further
reacted with carbon dioxide to give corresponding cyclic
70 carbonate.
Fig. 3 a) XRD spectra; b) TGA spectra
The thermal stability of the chitosan and Co(acac)2ꢀQPB@MCS
25 was determined by TGA analysis as shown in Fig. 3. The thermo
gram of Co(acac)2ꢀQPB@MCS catalyst exhibits a first stage
mass loss of 3ꢀ5 % below 150 ºC due to the loss of the occluded
solvents both on the surface and in the pores of the particles. The
second stage continuous mass loss starts around 220 ºC due to the
30 decomposition of organic moieties presented on the surface of the
catalyst and chitosan itself. The variation in thermal events of
chitosan and Co(acac)2ꢀQPB@MCS proved the formation of the
new material.
Catalytic Activity
35 The synthesized catalyst was first tested for the synthesis of
styrene carbonate from O2/CO2 and styrene using acetonitrile as
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Table 1 Catalytic activity of various catalystsa
S.N.
Catalyst
Styrene
CC
SO
Banzaldehyde
Selectivity (%)
CC
Yield (%)
TOF
(hꢀ1)
ꢀ
ꢀ
ꢀ
0.01
9.25
7.10
ꢀ
Conversion (%) Selectivity (%) Selectivity (%)
1.
2.
3.
4.
5.
6.
7b
ꢀ
1
2
3
4
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
8.1
ꢀ
ꢀ
ꢀ
15.5
92.3
5.4
95.2
87
7.4
52.7
1.1
1.4
8.9
76.2
39.6
2.6
20.7
15.7
16.9
1.7
73.1
62.4
ꢀ
0.1
69.6
54.3
ꢀ
2 + 3
4*
93.1
a
⁰
Reaction conditions: styrene (20 mmol, 2.28 mL), catalyst (0.5 g ), acetonitrile (10 mL), isobutyraldehyde (25 mmol, 2.28 mL) at 100 C, 5 bar pressure
of O2 and 30 bar pressure of CO2 for 10 h. TOF : Turn Over Frequency (hꢀ1), CC: Cyclic Carbonate, SO: Styrene Oxide; bIn the absence of carbon dioxide
The effect of other parameters, such as CO2/O2 pressure, reaction 25 Furthermore, the reusability of the catalyst was examined for
5
temperature and reaction time was also investigated (Fig. 4). At
ambient temperature (25 C) the reaction rate was found to be
slow and depended on the O2/CO2 pressure applied. The yield of
the product was found to be increased with increasing O2 and
subsequent four runs under described experimental conditions
(Fig. 4). The yield of styrene carbonate was found to be almost
same in all cases, indicating that the catalyst is highly stable and
can be recycled for several runs with consistent catalytic activity.
º
CO2 pressure. It was found that efficient and selective conversion 30 These results clearly indicated the merits of the developed
º
10 of styrene could be achieved at 100 C, 5 bar pressure of O2 and
30 bar pressure of CO2 (Fig. 4). Further increase in temperature
and reaction pressure did not affect the catalytic activity to any
heterogeneous catalyst.
Once the optimal conditions for this reaction were established, we
looked at examining the utility of this methodology. Thus, the
scope of the reaction was tested with respect to other substituted
significant extent. Similarly, the reaction was found to increase
with reaction time at 100 C, 5 bar pressure of CO2 and 30 bar 35 olefins and the results of these experiments are summarized in
º
15 pressure of CO2 and showed the highest yield in 10 h. Further
increase in reaction time did not improve the results to any
significant extent. When other solvents such as dichloromethane,
DMF and toluene were used in place of acetonitrile the yield of
product was found to be decreased significantly (Fig. 4).
Table 2. All the substrates either containing electron donating or
withdrawing groups were found to be nearly equally reactive and
afforded moderate to good product yields (Table 2). All the
experiments were carried out in a stainless steel (15 ml) autoclave
40 equipped with a stirrer. After completion of the reaction, the
reaction mixture was cooled to room temperature and the
heterogeneous catalyst was easily recovered by applying external
magnate. The obtained organic layer was concentrated under
reduced pressure to give crude product. The crude product was
45 further purified using column chromatography to give the desired
product.
Pressure (bar)
10 15 20 25 30 35 40
100
80
100
Temp.
Press.
80
60
40
20
0
PO2=5bar
PO2=3bar
60
40
20
0
PO2=1bar
2
4
6
8
10 12 14 16 18 20
20
40
60
80 100 120 140
Temerature (oC)
Time (hrs)
100
80
60
40
20
0
Dichloromethane
DMF
Toluene
Acetonitrile
80 100
0
20
40
60
1
2
3
4
Run
Yield (%)
20
Fig. 4 a) effect of O2 pressure on the yield; b) effect of temperature and
pressure on the yield; c) effect of solvent on the yield; d) recyclability of
catalyst
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Table 2: oxidative carboxylation of various olefins catalyzed by catalyst
30 FTIR Spectra was recorded on Perkin–Elmer FTꢀIR Xꢀ1760 IR
spectrophotometer using potassium bromide. TEM analysis is
done using FEIꢀTecnai G2 Twin TEM operating at an
acceleration voltage of 200 kV. For TEM a very dilute aqueous
dispersion of catalyst was deposited on carbon coated copper
35 grid. Thermo gravimetric analyses (TGA) of samples were
carried out using a thermal analyzer TAꢀSDT Qꢀ600. Analysis
was carried out in the temperature range of 40 to 600 °C under
nitrogen flow with heating rate 10 °C/min. For determining Co
content of catalyst, ICPꢀAES analysis was carried out by
40 Inductively Coupled Plasma Atomic Emission Spectrometer
(ICPꢀAES, DRE, PSꢀ3000UV, Leeman Labs Inc, USA). XRD
pattern of this sample was obtained with a Bruker AXS D8
Advanced SWAX Diffrectometer using CuKa (1=0.15406 nm
radiation). Xꢀray photoelectron spectroscopy (XPS, JPSꢀ
45 9010TRX, JEOL Ltd.) measurements were carried out using thin
films of developed catalyst deposited on carbon tape. All XPS
measurements were executed using a MgKα line as the Xꢀray
4.a
Entry
1
Epoxide
Product
Conv.
(%)b
CC
CC
Selec. Yield
(%)b
(%)c
O
O
O
O
95.2
96.1
69.6
67
O
O
2
72.4
70
O
O
O
3
4
5
96.3
96.0
98.1
78.2
80.1
87.3
76
78
85
O
O
O
O
O
O
1
source. The H NMR spectra were recorded on a Bruker Avance
O
O
O
500 Spectrometer in CDCl3 as a standard and the chemical shifts
50 are expressed in parts per million (ppm) relative to
tetramethylsilane (TMS) as the internal standard.
6
7
8
96.6
97.4
98.1
79.6
82.5
88.3
76
80
85
O
Cl
O
O
O
Detailed experimental procedure for the preparation of
Co(acac)2-QPB@MCS
Cl
O
O
Modified magnetic chitosan particles (MCS) were obtained by
55 coꢀprecipitation method as following the literature procedure.12
Coꢀprecipitation reaction was carried out by mixing 1.0%(w/v)
chitosan in the mixture of FeCl3.6H2O (0.32M) and FeCl2.4H2O
(0.2M) at 50 ºC followed by addition of liquid ammonia. Cobalt
acetylacetonate Co(acac)2 was immobilized on the magnetic
60 chitosan via Schiff condensation utilizing –NH2 moiety. 2.0 g of
modified magnetic chitosan was treated with 0.5 g of Co(acac)2
in 25 ml of toluene under refluxing condition for 24 h. The
Co(acac)2 functionalized magnetic chitosan Co(acac)2@MCS was
then first reacted with 3ꢀbromopropyl trimethoxysilane (2 mL)
65 and further with triphenylphosphine (1.0 g) in toluene for
immobilizing QPBr utilizing –OH moieties under refluxing
condition for 24 h to get Co(acac)2ꢀQPB@MCS. The solid
material thus obtained was separated by external magnate and
thoroughly washed with ethanol and dried under vacuum.
70
n-Bu
n-Bu
aReaction conditions: substrate (20 mmol), acetonitrile (10 ml), catalyst
⁰
(0.5 g , 0.155 mmol), isobutyraldehyde (2.28 mL, 25 mmol ) at 100 C, 5
5
bar pressure of O2 and 30 bar pressure of CO2 for 10 h; bdetermined by
GCꢀMS using nꢀbutanol as internal standard; ; cIsolated yields
Conclusions
We have demonstrated for the first time the use of magnetically
separable heterogenized homogeneous catalyst prepared by
10 anchoring of Co(acac)2 and P+Ph3Brꢀ on to magnetic chitosan via
covalent attachment for oxidative carboxylation of olefins using
O2/CO2 to give cyclic carbonates. The present method offers a
number of advantages such as use of molecular oxygen as
oxidant, facile recovery of the catalyst by external magnet, higher
15 catalytic activity and higher product yield. The developed
methodology represents the utilization of carbon dioxide in a
sustainable manner which can further be used for large scale
synthesis of carbonates directly from easily available olefins.
Typical experimental procedure for synthesis of styrene
carbonate
Styrene (20 mmol, 2.28 mL), catalyst Co(acac)2ꢀQPB@MCS
(0.5g, 0.155 mmol) and isobutyraldehyde (2.28 mL, 25 mmol)
75 were charged in to the 15 ml high pressure stainless steel reactor
using acetonitrile (10 mL) as a solvent†. The reactor was sealed
and purged with oxygen to replace all others gases. Reactor was
then initially charged with O2 up to 5 bar pressure. The reaction
Experimental
20 Materials
High purity carbon dioxide (99.99%) and oxygen compressed
cylinders were purchased from SigmaꢀGases, India. Chitosan,
triphenylphosphine and 3ꢀbromopropyltrimethoxysilane were
procured from Sigma Aldrich. FeCl3.6H2O, FeCl2.4H2O and
25 Co(acac)2 were purchased from Merck India. Acetonitrile,
ethanol and toluene were indented from Alfa Aesar India. All
other substrates were purchased form sigma Aldrich used as
received and no further purification was done.
°
mixture was stirred for 6 h at 100 C. After this, the reactor was
80 further pressurized with CO2 up to 35 bar and the reaction
mixture was further stirred for next 4 h at 100 ºC. After this the
reactor was placed into ice water and unreacted O2/CO2 gases
were released slowly by passing through a cold trap containing
ethanol. After depressurization, the reaction mixture was
85 transferred in a beaker and the catalyst was separated by applying
external magnate. The obtained organic layer was concentrated
Techniques Used
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F. Quignard , A. Choplin and A. Domard, Langmuir, 2000, 16 ,
9106ꢀ9108.
4. a) T. Vincent, S. Spinelli and E. Guibal, Ind. Eng. Chem.
Res., 2003, 42 , 5968ꢀ5976; b) A. A. Dabbawala, N. Sudheesh and
H. C. Bajaj, Dalton Trans., 2012, 41, 2910ꢀ2917; c) A. Maleki, N.
Ghamari and M. Kamalzare, RSC Adv., 2014,4, 9416ꢀ9423.
65 5. a) M. N. V. Ravi Kumar, Reactive and Functional Polymers, 2000,
46, 1ꢀ27; b) E. Guibal, Prog. Polym. Sci., 2005, 30, 71ꢀ109; c) N. Y.
Gavhane, S. A. Gurav and V. A. Yadav, Int. J. Res. Pharma. Biomed.
Sci., 2013, 4(1), 312ꢀ331.
under reduced pressure to give crude product. Further purification
of the product is done using column chromatography.
†Caution! During the experiments, the high pressures of O2
together with organic substrates (olefin, isobutyraldehyde and
solvent) and oxidation catalyst may give a potentially explosive
mixture.
60
5
Styrene Carbonate.18 1H NMR: δ 4.38ꢀ4.43 (1 H, m), 4.85ꢀ4.89
(1 H, t, J=8.3 Hz), 5.68ꢀ5.72 (1 H, t, J=8.1 Hz), 7.39ꢀ7.49 (5 H,
m); 13C NMR: δ 70.1, 78.1, 126.1, 129.1, 129.7, 136.2, 155.1
10 4-methyl styrene Carbonate.19 1H NMR: δ 2.29ꢀ2.35 (3 H, t),
4.35ꢀ4.41 (1 H, m), 4.82ꢀ4.88 (1 H, t), 5.65ꢀ5.70 (1 H, t), 7.36ꢀ
7.45 (4 H, m); 13C NMR: δ 20.2, 70.0, 77.9, 126.3, 130.2, 130.7,
136.1, 155.2
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Benzyl Carbonate.18 δ 2.45ꢀ2.50 (1 H, m), 2.91ꢀ2.96 (1 H, m),
15 4.48ꢀ4.53 (1 H, m), 4.63ꢀ4.68 (1 H, m), 5.02ꢀ5.09 (1 H, m), 7.07ꢀ
7.11 (2 H, m), 7.17ꢀ7.22 (3 H, m); 13C NMR: 41.1, 70.0, 79.8,
128, 129.2, 130.3, 138.1, 155.7.
Cyclohexene Carbonate.18 1H NMR: δ 1.4ꢀ1.63 (4 H, m), 1.79ꢀ
1.91 (4 H, m), 4.62ꢀ4.81 (2 H, m); 13C NMR: δ 18.9, 26.8, 75.6,
20 155.5
Propylene Carbonate.18 1H NMR: δ 3.8ꢀ4.0 (3 H, d), 4.4ꢀ4.47 (1
H, m), 4.62ꢀ4.66 (1 H, m), 5.1ꢀ5.3 (1 H, m); 13C NMR: δ 43.5,
66.9, 74.2, 154.4
80
85
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1
Cyclohexyl Ethylene Carbonate (Fig. S2 & S3). H NMR: δ
25 1.18 (2H, m), 1.21ꢀ1.32 (1H, m), 1.32ꢀ1.46 (2 H, m), 1.65ꢀ1.76 (4
H, m), 1.89 (2 H, m), 4.36 (1 H, m), 4.51 (1 H, m), 4.73 (1 H, m);
13C NMR: δ 25.99 , 27.26 , 27.74 , 38.38 , 66.04 , 83.61 , 155.19.
Chloropropylene Carbonate.18 1H NMR: δ 3.74ꢀ3.87 (2 H, m),
4.38ꢀ4.43 (1 H, m), 4.60ꢀ4.64 (1 H, m), 5.0ꢀ5.1 (1 H, m); 13C
30 NMR: δ 43.9, 67.1, 74.7, 154.9
1-Butylene Carbonate.18 1H NMR: δ 0.93 (3 H, t), 1.51 (1 H, m),
1.90ꢀ2.02 (1 H, m), 4.45ꢀ4.57 (2 H, m), 4.71 (1 H, t); 13C NMR: δ
8.65, 25.81, 70.05, 81.34, 155.39.
100 14. a) L. Ji, L. Zhou, X. Bai, Y. Shao, G. Zhao, Y. Qu, C. Wang and Y.
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Acknowledgement
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35 The authors, SK and NS thank to Director, CSIRꢀIndian Institute
of Petroleum for granting permission to publish these results. We
acknowledge CSIR, New Delhi for providing research
fellowship. DST, New Delhi is kindly acknowledged for funding.
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Notes and references
40 aChemical Sciences Division, CSIR-Indian Institute of Petroleum,
Dehradun-248005, India; Fax: +91-135-2660202; Tel: +91-135-
2525788; E-mail: suman@iip.res.in
bAnalytical Sciences Division, CSIR-Indian Institute of Petroleum,
Dehradun-248005, India; Fax: +91-135-2660202; Tel: +91-135-
45 2525788.
† Electronic Supplementary Information (ESI) available: [FTꢀIR Spectra
of Catalysts]. See DOI: 10.1039/b000000x/
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6
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DOI: 10.1039/C5DT01012H
Dual catalysis with magnetic chitosan: direct synthesis
of cyclic carbonates from olefins with carbon dioxide
using isobutyraldehyde as sacrificial reductant
5
Subodh Kumar, Nikita Singhal, Raj K. Singh, Piyush Gupta,
Raghuvir Singh and Suman L. Jain
MCS
H3C
H3C
O
CH3
CH3
H3CO
O
O
N
O
H3CO Si
Co
O
BrPh3P
O2/CO2
O
O
PPh3Br
H3C
CHO
R2
CH3
R2
O
N
O
O
Co
Si OCH3
OCH3
O
H3C
CH3
MCS
10
This journal is © The Royal Society of Chemistry [year]
Journal Name, [year], [vol], 00–00 | 7