Solventless synthesis of cyclic carbonates by direct utilization of CO2 using nanocrystalline lithium promoted magnesia

Article abstract of DOI:10.1016/j.mcat.2018.01.012

Cyclic carbonates are industrially important chemicals. In this work, an efficient synthesis of cyclic carbonate was achieved by cyclization of epoxide with CO₂ using nanocrystalline lithium promoted magnesia (Li-MgO), without using any co-catalyst or solvent. A series of Li-MgO were prepared by gel combustion method and well characterized. Li-MgO forms active F-centers (crystallographic defect) due to the difference in valence state of lithium (Li⁺) and magnesium (Mg²⁺) and acts as an active site for CO₂ activation. In the synthesis of 4-(chloromethyl)-1,3-dioxolan-2-one from epichlorohydrin, 0.75% (w/w) Li-MgO was the most active catalyst for CO₂ fixation into cyclic carbonate with excellent conversion (～98%) and selectivity (100%), at 130 °C and 3 MPa of CO₂ pressure. The catalyst showed structural stability and was reused for three cycles without loss of activity. The current synthesis protocol is 100% atom-efficient and thus was extended to a variety of substrates. Langmuir- Hinshelwood-Hougen-Watson (LHHW) type of mechanism was proposed and kinetics studied. Both reactants are strongly adsorbed making the overall reaction zero order with an apparent activation energy of 15.14 kcal/mol.

Full text of DOI:10.1016/j.mcat.2018.01.012

Molecular Catalysis xxx (xxxx) xxx–xxx
Contents lists available at ScienceDirect
Molecular Catalysis
journal homepage: www.elsevier.com/locate/mcat
Solventless synthesis of cyclic carbonates by direct utilization of CO using
2
nanocrystalline lithium promoted magnesia
a
a,⁎
b
b
Kalidas B. Rasal , Ganapati D. Yadav , Rauli Koskinen , Riitta Keiski
a
Department of Chemical Engineering, Institute of Chemical Technology, Nathalal Parekh Marg, Matunga, Mumbai, 400019, India
Department of Mass and Heat Transfer, University of Oulu, Oulu, Finland
b
A R T I C L E I N F O
A B S T R A C T
Keywords:
Carbon dioxide
Lithium promoted magnesia
Cyclic carbonate
Cyclic carbonates are industrially important chemicals. In this work, an efficient synthesis of cyclic carbonate
was achieved by cyclization of epoxide with CO2 using nanocrystalline lithium promoted magnesia (Li-MgO),
without using any co-catalyst or solvent. A series of Li-MgO were prepared by gel combustion method and well
characterized. Li-MgO forms active F-centers (crystallographic defect) due to the difference in valence state of
4
-(Chloromethyl)-1,3-dioxolan-2-one
lithium (Li+) and magnesium (Mg ) and acts as an active site for CO
2+
2
activation. In the synthesis of 4-
Epichlorohydrin
(chloromethyl)-1,3-dioxolan-2-one from epichlorohydrin, 0.75% (w/w) Li-MgO was the most active catalyst for
CO
2
fixation into cyclic carbonate with excellent conversion (∼98%) and selectivity (100%), at 130 °C and
3
MPa of CO pressure. The catalyst showed structural stability and was reused for three cycles without loss of
2
activity. The current synthesis protocol is 100% atom-efficient and thus was extended to a variety of substrates.
Langmuir- Hinshelwood-Hougen-Watson (LHHW) type of mechanism was proposed and kinetics studied. Both
reactants are strongly adsorbed making the overall reaction zero order with an apparent activation energy of
15.14 kcal/mol.
1
. Introduction
supported on MCM-41 [12], Pd/C [13], metal porphyrin [14], qua-
ternized chitosan [15] and protonic ionic liquids [16]. Heterogeneous
catalysis is always preferred over homogeneous systems because of its
well-known attributes. Generally, homogeneous protocols have
common drawbacks like non-reusability of catalyst, toxicity and cost of
the reagents.
CO is a key contributor to global warming due to its increasing
2
concentration in the atmosphere [1] but can be used for a variety of
purposes. It is a cheap, abundant, and non-toxic renewable C1 energy
resource [2,3]. Nowadays, from the green chemistry point of view
utilization of CO
2
into value-added chemicals has achieved significance;
Yamaguchi et al. [17] used Mg-Al hydrotalcite as catalyst for direct
for instance, in the synthesis of formic acid, methanol, dimethyl car-
bonate (DMC), etc. [4,5]. It also been used as a green alternative to
phosgene and thionyl chloride [6]. For the past few decades the utili-
2
utilization of CO into cyclic carbonate using DMF as solvent as well as
co-catalyst. Since then various reports are published on the solventless
synthesis of cyclic carbonates using heterogeneous catalysts (Table 1)
such as nitrogen doped carbon monolith, methyl imidazole (ionic li-
quid, IL) supported on cellulose [18], IL supported on polystyrene [19],
polystyrene supported organometallic catalyst [20], MgO using DMF as
solvent [21], and salen complexes with different metals like Zn, Cu, Co
and Cr [22–24]. However, there is scope for improving methodology
and economic aspect of the processes for synthesis of cyclic carbonates.
Table 1 lists various routes of preparation of cyclic carbonates.
2
zation CO in the synthesis of cyclic carbonate has been extensively
studied because the process is 100% atom efficient. Cyclic carbonates
have wide applications as solvents or precursors in many fields such as
lithium ion battery, pharmaceutical chemistry, biomedical and biode-
gradable plastic industry, fine chemicals, etc.
CO
2
has a linear structure with zero dipole moment and is thermally
and kinetically a stable molecule [7]. To overcome the stability of CO
2
,
there is a need to develop cost-effective catalyst for its activation [8,9].
Several reports are published on the synthesis of cyclic carbonates from
Li-MgO was used as a basic catalyst for oxidative coupling of me-
thane [26], synthesis of cyclic carbonates using dimethyl carbonate
(DMC) [25], aldol condensation [27] and transesterification reaction
coupling of CO
2
and epoxides using different catalysts; for instance,
+
phosphonium based ionic liquid supported on polymer nanoparticle
[28]. In the case of Li-MgO, the atomic radii size of Li (∼76 pm) and
[
10], 2-pyridinemethanol [11], magnetically separable ZnBr
2
magnesium Mg2+ (∼72 pm) in their oxide form [29] allow easy
⁎
Corresponding author.
E-mail address: gd.yadav@ictmumbai.edu.in (G.D. Yadav).
https://doi.org/10.1016/j.mcat.2018.01.012
Received 4 August 2017; Received in revised form 9 January 2018; Accepted 10 January 2018
2468-8231/ © 2018 Elsevier B.V. All rights reserved.
Please cite this article as: Rasal, K.B., Molecular Catalysis (2018), https://doi.org/10.1016/j.mcat.2018.01.012

K.B. Rasal et al.
Molecular Catalysis xxx (xxxx) xxx–xxx
Table 1
Literature review for synthesis of cyclic carbonates.
#
Catalyst
Epoxide mmol
CO
2
Pressure MPa
Temp. °C
Time h
Yield%
Sel%
Epoxide per g-cat mol/g
Ref.
1
2
3
4
5
6
7
8
9
Metalated porous porphyrin polymer
Imidazolium based polymer supported ionic liquid
Bifunctional quaternary phosphonium salt catalyst
Chiral Co(III) complexes
12.5
54
0.2
86
10
10
1
54
10
52
10
21.5
10
0.5
127
0.1
0.8
0.1
5
4
1
30
100
60
24
6
24
24
24
3
2
6
6
6
16
2.5
4
24
4
95
91
85
80
95
97
96
100
90
96
84
98
60
90
97
99
100
–
99
99
99
99
90
–
99
–
98.5
–
0.25
0.11
–
[33]
[34]
[35]
[36]
[37]
[38]
[39]
[40]
[41]
[42]
[43]
[19]
[21]
[44]
This work
50
–
Silica grafted ammonium salts
100
120
120
130
100
140
150
130
135
100
130
0.016
0.011
–
[Heemim][ZrCl
5
]
Heteropolyacid-based ionic liquid@SiO
Imidazole supported on silica
Phosphorus ylide
2
1
1.5
0.1
2
5
1.2
2
–
0.055
–
4
1
1
1
1
1
1
0
Polystyrene@quaternized ammonium salt
Nitrogen@porous carbon monolith
Bis-ammonium@ polystyrene
MgO (DMF solvent)
Mg-Al HT (DMF solvent)
Li-MgO
1
2
3
4
5
–
0.005
0.008
0.254
1
3
96
99
replacement of anion of Mg2+ and Li+ in the periclase structure of the
theoretical equation of formation of Li-MgO catalyst (F/O ratio 2) is as
follows [28,45]:
2
+
+
catalyst [27,30]. The replacement of Mg
vacancy or structural defect (F center) in order to maintain crystal
neutrality. That F-center acts as active sites of catalyst for CO activa-
with Li creates oxygen
9
.99 Mg(NO
3
)
2
.6H
2
O + 0.01LiNO3(S) + 20NH
O + 40CO2(g) + 20.004 N
2
CH
2
COOH(S) →
2
9.99MgO + 0.005Li
2
2
↑
(g) + 109.94H O
2 (g)
tion [31,32]. Thus, Li-MgO was considered as the most promising cat-
alyst which needed further insight including its method of synthesis.
In this context, we report a solvent-free synthesis of cyclic carbonate
by direct utilization of CO
synthesized by simple gel combustion method using glycine as fuel
25]. A variety of loading of Li on MgO was used to determine the most
active and selective catalyst vis-à-vis several others. Synthesis of a
cyclic carbonate, (4-(chloromethyl)-1,3-dioxolan-2-one) from epi-
2
in the presence of Li-MgO. The catalyst was
2.3. Experimental procedure for cyclization of epichlorohydrin and CO2
[
Epichlorohydrin (1a) 127 mmol (10 mL) and catalyst 0.05 g/cm3
(0.5 g) were taken in 50 mL autoclave (Amar Equipments, Mumbai,
India) with pressure and temperature regulators. The reactor was flu-
chlorohydrin and CO
2
was studied systematically using Li/MgO
(
Scheme 1). The effect of lithium loading on crystallite size and mor-
shed twice with CO to remove air and temperature set at 130 °C; After
2
phology was studied which will have a direct bearing on conversion and
selectivity. Reaction mechanism and kinetics are also presented for the
first time.
reaching the temperature the reactor was charged with CO2 and pres-
surized to 3 MPa which was maintained throughout the experiment.
Reaction progress was monitored by GC. After completion of the reac-
tion, the reactor was cooled down to 10 °C through coolant and slowly
depressurized.
2. Experimental
2.1. Chemicals
3. Results and discussion
The following chemicals were procured from the reputed firms
Since 0.75% (w/w) Li-MgO was the most active catalyst for CO
2
(
(
Merck, Sigma Aldrich, etc.) and used without further purification: Mg
NO LiNO , epichlorohydrin, propylene oxide, cyclohexene oxide,
fixation into cyclic carbonate, its complete characterization is provided
in comparison with other loadings of Li on MgO and pure MgO. To find
out if any structural changes had taken placed, reused catalyst was also
characterized.
3
)
2
3
glycidol, styrene oxide, ethylene oxide etc.
2
.2. Li-MgO preparation
The catalyst was prepared by gel combustion method using glycine
3
3
.1. Catalyst characterization
as fuel as per our previously published report [25]. The stoichiometric
mixtures of precursors like Mg(NO ·6H O, Li(NO ) and glycine were
3
)
2
2
3
.1.1. XRD
dissolved in minimum quantity of deionized water (†ESI, Table S1).
Then, this homogenized solution was heated at ∼100 °C to form a
transparent gel which was transferred to muffle furnace at 350 °C for
combustion at autoignition temperature of glycine. Combustion was
completed in a few seconds; the powdered mass was further calcined at
XRD patterns of fresh and reused Li-MgO were analyzed in the range
of 10−80° 2θ using Bruker AXS, D8 discover instrument (USA) with
Cu-Kα (1.54 Å) radiation. Pure MgO gives sharp peaks at 2θ values
3
6.8°, 42.8°, 62.2°, 74.3° and 78.6° which correspond to (111), (200),
(
202), (311), (222) diffraction planes, respectively. Its diffraction pat-
5
50 °C for 3 h in air to get pure and nanocrystalline Li-MgO. Rapid high-
temperature combustion allow the formation solid defects (F centers)
due to the evolution of gases (mainly CO , N2, and H O). The
tern matches with periclase cubic type structure of MgO, confirmed by
standard JCPDS data card # 45-0946 [46]. Diffraction peaks related to
pure MgO were broader than those for Li- MgO samples; the broadening
indicates smaller crystallite size [25,31]. Up to 0.5% (w/w) lithium
loading has no significant effect in XRD patterns (Fig. 1). It indicates
that the material with less than 0.5% lithium loading shows cubic na-
2
2
2 3
nocrystalline MgO phase. In Li-MgO catalyst the Li CO phase (JCPDS
card # 22-1141) was observed at 0.5% of lithium loading (2θ = 33°).
The increase in crystallinity was proportional to the lithium loading in
Li-MgO.
Scheme 1. Synthesis of cyclic carbonate (4-(chloromethyl)-1,3-dioxolan-2-one).
2

K.B. Rasal et al.
Molecular Catalysis xxx (xxxx) xxx–xxx
Fig. 1. XRD diffraction patterns of Li- MgO with different loadings.
3
.1.2. FT-IR spectra
Fig. 2 shows FT-IR of CO adsorbed species on the surface of 0.75%
2
Lewis-acid–Brönsted base [M2+O2−] type forms bidentate carbonate
species. It shows symmetric and asymmetric OeCeO stretching at 1319
−
1
(
w/w) Li-MgO. CO
2
was adsorbed on the surface of the catalyst in three
and 1621 cm
,
respectively. The surface eOH group forms bicarbonate
different ways; unidentate, bidentate and bicarbonate [25,27]. The free
species. It shows symmetric and asymmetric OeCeO stretching at 1442
2
−
−1
−1
O
species of unidentate carbonate shows symmetric OeCeO
and 1638 cm , respectively. The band observed at 1087 cm
is due
−
1
−1
−1
stretching at 1384 cm
and asymmetric stretching at 1504 cm
.
2
to the absorbed CO and the broad spectrum at 645 cm is attributed
Fig. 2. FITR spectrum of 0.75% (w/w) Li-MgO.
3

K.B. Rasal et al.
Molecular Catalysis xxx (xxxx) xxx–xxx
Fig. 3. SEM images of (a) 0.75% (w/w) Li-MgO fresh and (b) reused catalyst 0.75 (w/w) Li-MgO and (c) TEM image of fresh 0.75% (w/w) Li-MgO.
−
to MgeOeMg bending vibrations. The IR spectra of reused catalyst
were recorded after third reuse. It does not show a considerable change
in nature of IR spectrum thereby proving the stability of catalyst (†ESI
Fig. S1).
valency in their oxide forms. It is stabilized by O species and so there
is formation of [Li+
O ] defect or F center in the crystal lattice [31].
Lithium-doped impurity tries to persist on the surface of the catalyst so
as to maintain its low co-ordination number for the stability of crystal
−
[
51]. However, with an increase in dopant lithium, there is subsequent
3
.1.3. SEM and TEM
Samples of MgO and 0.75 (w/w) Li-MgO were analyzed by SEM and
increase in the oxygen valency to maintain the neutrality of crystal
lattice. The addition of this dopant impurity changes all morphological
features of the catalyst such as crystallite size, surface area, pore size,
and pore volume. During combustion synthesis, due to the addition of
dopant i.e. lithium (Li), the basicity of Li-MgO was enhanced by for-
mation of crystallographic defect (F-center). Thus 0.75 (w/w) Li-MgO
showed excellent conversion per unit mass of catalyst, in synthesis of
cyclic carbonate. The reaction conditions were as follows; temperature
(130 °C), pressure (3 MPa) and reaction time (4 h) (Scheme 1). To study
the efficiency of this process, we have calculated the conversion ratio of
substrate per gram of catalyst in synthesis of cyclic carbonate, it gives
comparatively good conversion in terms of moles (substrate) per gram
of catalyst (Table 1).
TEM to observe the morphology of MgO, fresh and reused Li-MgO. The
fresh catalyst shows highly porous and uneven distribution of fine
particles. The rapid evolution of gases in combustion synthesis results in
the formation of pores and voids with uneven distribution. The porous
structure of fresh and reused Li-MgO was analyzed by SEM. The mor-
phology had somewhat changed in the reused catalyst with slight ag-
glomeration as compared to the fresh catalyst (Fig. 3).
3
.1.4. BET surface area
MgO and 0.75 (w/w) Li-MgO show type IV adsorption isotherm that
indicates the formation of mesoporous material and H3 type hysteresis
loop that suggests slit-shaped pores or plate-like particles (†ESI Fig. S2).
Surface area Li-MgO catalysts decrease with increase in lithium loading
The activity of various loadings of lithium over MgO was tested for
the synthesis of 4-(chloromethyl)-1,3-dioxolan-2-one from epi-
chlorohydrin and CO . The XRD data show the formation of Li CO
2 2 3
phase after 0.75%, (w/w) of lithium loading; up to 0.75% lithium can
exchange magnesium in the crystal lattice, thereafter the excess of li-
(
Table 2). The reused catalyst 0.75 (w/w) Li-MgO shows no significant
change in BET surface area.
thium forms lithium oxide on the surface of the catalyst. It forms Li
2 3
CO
3
.1.5. Basicity by CO
Basicity of pure MgO and Li-MgO samples were analyzed for CO
2
-TPD
phase when it adsorbs atmospheric CO . This blocks the pores of cat-
2
2
-
alyst and reduces its surface area. Thus, 0.75% was found to be op-
timum loading for the synthesis of cyclic carbonate (Fig. 4).
TPD. It gives an idea about strength and nature of basic sites of the
catalyst. It shows that total number of basic sites Li-MgO were more
than that of pure MgO. The number of basic sites increase with increase
in lithium loading but at the same time, the surface area decreases.
Thus, total number of accessible basic sites also decrease (Table 2). The
basicity of fresh and reused catalyst remains nearly the same.
2
3.3. Effect of CO pressure on cyclization reaction
Cyclization of epichlorohydrin (1a) to 4-(chloromethyl)-1,3-diox-
olan-2-one (1b) as given in Scheme 1 was performed in the range of
0
.5–5 MPa pressure of CO
2 2
. The increases in CO partial pressure from
3.2. Effect of lithium loading
0.5 to 3.0 MPa resulted in the significant increase in epichlorohydrin
conversion; after 3.0 MPa pressure significant decline in conversion was
observed as discussed in previous reports [47,48]. CO2 (G), organic
When lithium is doped in MgO matrix, there is the formation of
+
structural defects [50]. Lithium (Li ) which replaces magnesium
2
+
(
Mg ) results in the formation of F-centers localized into the crystal
lattice. F-center is formed in the crystal lattice due to almost similar
+
2+
sizes of Li (∼76 pm) and Mg
(∼72 pm) ionic radii with different
Table 2
BET analysis and total basicity of pure MgO and lithium promoted magnesia.
Lithium Loading BET surface
Pore size
(nm)
Pore volume
(cm /g)
Total basicity
(mmol/g)
2
3
%
(w/w)
area (m /g)
0
0
0
0
0
1
.00
.10
.25
.50
.75
.00
138.2
119.4
92.3
74.2
52.1
22.5
51.4
7.47
0.38
0.58
0.51
0.26
0.15
0.12
0.14
0.38
0.71
0.65
0.61
0.60
0.52
0.58
12.81
11.23
10.55
13.09
11.05
12.16
Fig. 4. Effect of lithium loading on synthesis of cyclic carbonate.
Reaction conditions: epichlorohydrin 127 mmol; catalyst loading 0.02 g/cm ; reaction
temperature 130 °C; speed of agitation 1000 rpm; time 4 h.
3
Reused 0.75
4

K.B. Rasal et al.
Molecular Catalysis xxx (xxxx) xxx–xxx
2
Fig. 5. Effect of CO pressure on conversion of epichlorohydrin.
Reaction conditions: epichlorohydrin 127 mmol; catalyst loading 0.02 g/cm ; reaction
temperature 130 °C; speed of agitation 1000 rpm; time 4 h.
3
Fig. 7. Effect of temperature on conversion of epichlorohydrin.
Reaction conditions: epichlorohydrin 127 mmol; CO pressure 3 MPa; speed of agitation
000 rpm; time 4 h.
2
1
reactant 1a and product 1b (L) and catalyst (S) forms a triphasic G-L-S
system; at the high CO
organic liquid phase is increased. CO
therefore, there is a formation of the epoxide-CO
concentration on the catalyst sites increases and thus according to the
Langmuir-Hinshelwood-Hougen-Watson (LHHW) the rate decreases
beyond 3 MPa and hence the conversion (Fig. 5).
2
pressure the dissolved CO
is acidic and 1a basic and
bond. The CO
2
concentration in
3.6. Catalyst reusability study
2
2
2
After completion of the reaction, the catalyst was separated by fil-
tration, washed with methanol for 2–3 times to remove adsorbed or-
ganic molecules like 1a and 1b from the surface of the catalyst. It was
then refluxed in MeOH at 60 °C for 2 h, filtered and dried at 100 °C for
6
h. The reusability of catalyst was studied up to three cycles at opti-
3
.4. Catalyst loading
mized reaction conditions. It was found that 0.75% Li-MgO catalyst was
robust, recyclable and did not show any significant change even after
the third cycle (Fig. 8).
In the absence of external mass transfer resistance, the conversion of
1
a was proportional to catalyst loading which was studied in the range
3
of 0.01–0.10 g/cm . Increase in catalyst loading proportionally in-
creases the number of active sites (Fig. 6). The initial rate of reaction of
epichlorohydrin increases linearly with catalyst loading.
3.7. Possible reaction mechanism
Based on previously published reports [47,49,52,53] and our ex-
perimental outcomes, we propose a possible reaction mechanism for
fixation of CO with 1a to form 1b. CO has mild acidity which gets
adsorbed on [Li ] (strongly basic) site of the catalyst and 1a is
adsorbed on Lewis acidic sites of catalyst (Mg
justment on the surface of catalyst) as in intermediate (I) (Scheme 2).
After adsorption of CO and 1a on the surface of the catalyst, the linear
structure of CO2 gets disturbed and partial charge separation takes
place. The activated species of CO leads to nucleophilic attack on
sterically less hindered carbon of 1a and opens the ring to form an
intermediate II. The intermediate II further undergoes chemical re-
arrangement to form a CO2 incorporated product and the cyclic car-
bonate (1b) is formed. After formation of the product, it gets desorbed
from the catalyst site (as intermediate III). This catalytic cycle occurs
continuously to get cyclic carbonate as the product.
2
2
+
−
3
.5. Effect of temperature
O
2+
+
or Li ) (located ad-
Effect of temperature for cyclization of epichlorohydrin (1a) with
2
CO was studied in the range of 110–140 °C. From Fig. 7 it clearly in-
2
dicates that temperature plays a crucial role in the conversion of 1a–1b.
From 110–130 °C the conversion increases according to temperature
but thereafter decrease from 1a–1b. Using this experimental data, we
have developed the kinetic model for this reaction.
2
This reaction shows the Langmuir–Hinshelwood–Hougen–Watson
(
LHHW) type mechanism and zero order reaction kinetics. By plotting
Arrhenius plot, we have calculated the apparent activation energy
15.14 kcal/mol). The detailed kinetic study is provided in ESI†.
(
3.8. Reaction kinetics
In the absence of both external mass transfer and intra-paticle dif-
fusion resistances, the reaction is kinetically controlled [56–59].
Langmuir–Hinshelwood–Hougen–Watson (LHHW) mechanism was
used to derive a model for the synthesis of cyclic carbonate. It was
Fig. 6. Effect of catalyst loading on epichlorohydrin.
2
Reaction conditions: epichlorohydrin 127 mmol; CO pressure 3 MPa; reaction tempera-
ture 130 °C; speed of agitation 1000 rpm; time 4 h.
Fig. 8. Reusability of Li-MgO in synthesis of cyclic carbonate.
5

K.B. Rasal et al.
Molecular Catalysis xxx (xxxx) xxx–xxx
Scheme 2. Possible mechanism of synthesis of cyclic carbo-
nate.
observed that CO
weak Lewis acidic sites of the catalyst, respectively.
Assuming that, the catalyst having two different sites (S
adsorption of CO
2
and epichlorohydrin adsorb on strong basic sites and
CT1 = CS1+KACACS1+ KCCCCS1
It was assumed that at equilibrium stage, rate of adsorption and
desorption is the same, concentration of vacant sites can be written
from Eqs. (9) and (10);
(9)
C
T
2
= C
S
+K
B
C
B
C
S
2
(10)
2
1
and S
2
) for
2
and epichlorohydrin.
Considering the reaction,
Li/MgO
A(epichlorohydrin)+ B(CO ) ⎯⎯⎯⎯⎯⎯⎯→ C(cyclic carbonate)
(1)
2
C
T
1
C
C
S
=
=
1
Adsorption of epichlorohydrin (A) and CO
2
(B) was on catalytic site
K
A
C
A
C
S
+K
C
C
C
C
S
1
(11)
1
1 2
S and S respectively;
C
T
2
K
A
S
2
A + S
1
⇄ AS
1
(2)
(3)
B B S2
K C C
(12)
K
B
If surface reaction rate is controlling step, then rate of reaction can
B + S
2
⇄ BS
2
be written as;
Then surface reaction takes place between adsorbed CO
2
and epi-
−
r
A
= kCAS
C
BS − k′CCS
C
S
2
(13)
(14)
1
2
1
chlorohydrin
=
kK
A
C
A
C
S
K
B
P
B
C
S
− k′K
1
C C S S
C C C
2
k
1
2
AS
1
+ BS
2
⇄ CS
1
+ S
2
(4)
(
kKACAKB PB − k′KC CC)CT CT
1
2
=
After reaction completion, product gets desorbed from catalyst site;
(
1 + KB PB)(1 + KACA + KC CC)
(15)
K
D
CS
1
⇄ C + S
1
When reaction is not at equilibrium; the following is obtained
K
D'
(5)
where, w = CT 1 + CT
2
The total concentration of total catalyst sites C
T
expressed as;
kwKB PB KACA
=
(
1 + KB PB)(1 + KACA)
(16)
C
T
= C
T
+C
T
(6)
(7)
(8)
1
2
When the adsorption of CO
2
and epichlorohydrin is strong on catalyst
But, CT = CS + CAS + CCS
1
1
1
1
surface, then (1 + K
B
p
B
< < < K
p ), (1 + K C
B B A A
< < < K
A
A
C ),
then above equation is written as;
C
T
2
= C
S
+CBS
2
2
−
r
A
= kw
(17)
From Eqs. (7) and (8);
6

K.B. Rasal et al.
Molecular Catalysis xxx (xxxx) xxx–xxx
Table 3
substrate scope for synthesis of cyclic carbonate using 0.75 (w/w) Li-MgO.
Sr. no. Substrate
1
Product
% conversion Isolated
yield (%)
98.2
96
2
98.4
95.4
3
4
55.5
90.5
52.4
86.5
A
Fig. 9. Plot of fractional conversion (X ) of epichlorohydrin vs time at different tem-
peratures.
n
This eq . shows zero order kinetics and can be written in fractional
conversion, (X ) as;
A
5
6
95.9
98.9
94.1
96.5
dXA
dt
kw
CA0
=
=
(18)
(19)
dX
dt
A
1
k w
Where,
Reaction conditions: Epichlorohydrin 127 mmol; CO
.1 g/cm ; reaction temperature 130 °C; reaction time 4 h.
2
pressure 3 MPa; catalyst loading
3
0
k
CA0
k1 =
(20)
(21)
δ 44.1, 67.5, 73.5, 154.5.
Integrating above eqn the following is obtained,
1
4-Phenyl-1,3-dioxolan-2-one (entry 2): H NMR (500 MHz, CDCl )
3
δ 7.52–7.40 (m, 3H), 7.40–7.32 (m, 2H), 5.69 (dd, J = 8.5 and 8.0 Hz,
H), 4.81 (dd, J = 8.5 and J = 8.5 Hz, 1H), 4.35 (dd, J = 8.5 and
J = 8.0 Hz, 1H); CNMR: 70.9, 78.1, 126.2, 129.4, 130.2, 137.4,
155.2.
XA = kt
1
13
The plot X
A
vs time shows the straight line (Fig. 9) which means that
the zero order kinetic model shown in Eq. (21) is correct.
1
Arrhenius plot was made from the slopes obtained in Fig. 9 and the
activation energy of reaction was calculated as 15.14 kcal/mol
Fig. 10).
Hexahydrobenzo[d][1,3]dioxol-2-one
(entry
3): HNMR
(500 MHz, CDCl3) 4.65 (t, 1H, J = 3.6 Hz), 1.83–1.91 (m, 4H),
13
(
1.61–1.66 (m, 2H), 1.38–1.48 (m, 2H). C NMR δ = 155.8, 76.1, 26.2,
9.3.
3
4-Methyl-1,3-dioxolan-2-one (entry 4): H NMR (500 MHz, CDCl )
1
1
3
.9. Substrate study
1
3
δ 4.94 (m, 1H), 4.53 (t, 1H), 4.08 (dd, 1H), 1.47 (d, 3H); C NMR δ
Under the optimized reaction conditions the catalyst was found to
19.2, 70.5, 73.9, 155.4.
4-(hydroxymethyl)-1,3-dioxolan-2-one (entry 5): 1H NMR
(500 MHz, DMSO) δ 5.21 (m, 1H), 4.79–4.70 (m, J = 8.7, 6.0, 3.1 Hz,
1H), 4.45 (t, J = 8.4 Hz, 1H), 4.26 (t, 1H), 3.66–3.61 (m, 1H), 3.47 (dd,
J = 12.7, 3.4 Hz, 1H). 13C NMR: 60.2, 66.1, 77.3, 155.1.
be applicable to various terminal epoxides to provide the corresponding
cyclic carbonates in high yields and selectivity (Table 3). Furthermore,
in the case of an internal epoxide (cyclohexene oxide) as the substrate
(
entry 3), a cyclic carbonate was obtained at lower yield even at longer
1
reaction time (6 h), it may be due to steric hindrance as reported in
previous literature [54,55]. The products were characterized by
1,3-dioxolan-2-one (entry 6): H NMR (500 MHz, DMSO) δ 4.44 (s,
4H).
1
13
GC–MS, HNMR, and CNMR (†ESI).
NMR data;
1
4. Conclusions
3
4-Chloro-1,3-dioxolan-2-one (entry 1): H NMR (500 MHz, CDCl )
13
δ 4.94 (m, 1H), 4.53 (t, 1H), 4.33 (dd, 1H), 3.67–4.02 (d, 2H); C NMR:
In summary, Li-MgO catalyzed simple and cost-efficient protocol for
the synthesis of cyclic carbonates was developed. For this reaction, we
have studied the effect of different lithium loading on cyclization of
epichlorohydrin and CO
2
to form cyclic carbonates. The synthesis of
cyclic carbonates is 100% atom efficient method. Li-MgO has weak
Lewis acidity due to Li+ and Mg
2+
and strong basicity due to the
structural defect in the structure formed by Li-impurity. It was found
that 0.75 (w/w) Li-MgO was the best and reusable catalyst for cy-
cloaddition of CO
,3-dioxolan-2-one under solvent free conditions with excellent con-
version (∼98%) and selectivity (100%), at 130 °C and 3 MPa of CO
2
to epichlorohydrin to synthesize 4-(chloromethyl)-
1
2
pressure. The catalyst showed structural stability and was reused for
three cycles without loss of activity. The current synthesis protocol is
1
00% atom-efficient and thus was extended to a variety of substrates.
2
Fig. 10. Arrhenius plot for cycloaddition of CO to epichlorohydrin.
Cycloaddition of CO to epichlorohydrin follows the LHHW type of
2
7

K.B. Rasal et al.
Molecular Catalysis xxx (xxxx) xxx–xxx
model with both species getting strongly adsorbed leading to zero order
reaction, with an apparent activation energy 15.14 kcal/mol.
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Acknowledgements
polystyrenes with co-catalyzing functional end groups as efficient and reusable
2
heterogeneous catalysts for synthesis of cyclic carbonate from CO and epoxides,
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This work was performed within the collaborative project
Sustainable Catalytic Syntheses of Chemicals using Carbon Dioxide as
“
Feedstock (GreenCatCO )” supported by Department of Science and
2
2
oxiranes and CO to organic cyclic carbonates using a recyclable, bifunctional
polystyrene-supported organocatalyst, Green Chem. 16 (2014) 1552, http://dx.doi.
org/10.1039/c3gc41919c.
Technology (DST), Government of India, and the Academy of Finland to
Professors Ganapati D. Yadav and Riitta Keiski. Kalidas B. Rasal would
like to thank the Academy of Finland (Project nos. 129173 (SUSE) and
[
21] T. Yano, H. Matsui, T. Koike, H. Ishiguro, H. Fujihara, M. Yoshihara, et al.,
Magnesium oxide-catalysed reaction of carbon dioxide with an epoxide with re-
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org/10.1039/a608102i.
1
2
40122 (GreenCatCO )) and the Finnish funding agency for technology
and innovation, Tekes (Project no. 40313/09 (Fermet)) for financial
support. Ganapati D. Yadav also thanks DST for J.C. Bose National
Fellowship and received support from R.T. Mody Distinguished
Professor Endowment.
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1
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in the
online version, at http://dx.doi.org/10.1016/j.mcat.2018.01.012.
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