S.E. Lyubimov, et al.
Applied Catalysis A, General 592 (2020) 117433
1
Table 1
the reaction mixture according to H NMR. Bearing in mind the possible
a
Synthesis of ethylene carbonate .
formation of oxirane (bp 10.4 ⁰C) in the reaction we have refrigerated
the evolved gases by liquid nitrogen, but no liquid oxirane phase was
observed. We noticed formation of a very small amount of a solid
product which immediately turned gaseous after thawing without
transformation into the intermediate liquid phase, which is typical for
entry
additive
base
T, °C
P, atm
t, h
conversion, %
1
2
3
4
5
6
7
8
9
–
–
–
Na
2
CO
3
110
110
110
110
110
110
110
110
110
110
110
50
56
56
56
56
56
56
56
56
56
10
10
10
10
10
10
10
10
10
10
2
75
44
70
92
91
92
92
0
NaOH
KOH
2
2
1
dry ice. A H NMR spectra of the condensed phase (5 ⁰C) dissolved in
N(Bu)
N(Bu)
N(Bu)
4
4
4
Br
Na
Na
Na
Na
–
2
2
2
2
CO
CO
CO
CO
3
3
3
3
2
I
2
CDCl showed no signals of organic compounds; only traces of water
3
Cl
2
were detected. We also checked the above reaction using K
CO as a
2
3
N(Et)
4
Cl
2
base and N(Bu) Br as an additive without adding silica gel. In this case
4
b
-
2
c
94 % conversion of 2-chloroethanol was obtained, but 41 % of ethylene
glycol was formed in addition to the desired ethylene carbonate. This
fact may be attributed to uncontrolled hydrolysis of 2-chloroethanol to
ethylene glycol under alkaline conditions of the rather hygroscopic
N(Bu)
N(Bu)
N(Bu)
N(Bu)
–
4
Br
4
Br
4
Br
4
Br
–
2
0
10
11
12
13
14
15
16
17
18
19
Na
2
CO
3
2
100
100
81
79
12
10
33
40
K
K
K
2
2
2
CO
CO
CO
3
3
3
2
18
18
18
18
5
50
K
2
CO . The use of silica gel solves the problem with the hygroscopic
3
N(Bu)
–
4
Br
Na
2
Na
2
Na
2
Na
2
CO
3
3
3
3
50
properties of the base due to a higher reaction rate. As reported earlier,
CO
CO
CO
50
–
80
the process is expected to proceed as shown in Scheme 2 but with a few
N(Bu)
–
4
Br
Br
80
5
exceptions [16]. Since the reaction of 2-chloroethanol with K
2
CO is
3
d
K
K
2
CO
2
3
3
80
5
100
unlikely to proceed and no CO evolved as the reaction product, we
2
N(Bu)
4
CO
80
5
100
suppose that K
2
CO can reversibly interact with acidic Si−OH groups
3
a
of silica gel to form a highly alkaline potassium silicate which can
promote the process. It was shown recently that inorganic silicates have
Catalyst
- Acros® Silica gel for chromatography, 0.06-0.2 mm, 60 Ǻ
(
25 mg), additive 5 mg, substrate (0.4 mL)\base = 1\1.1 mol.
b
c
d
the capacity to absorb CO to form carbonates between room tem-
Only silica gel (25 mg) was added.
Only N(Bu) Br (5 mg) was added.
3 % yield, extracted by MeOH.
2
perature and 130 ⁰C, and recoverability of silica gel is the key factor of
4
9
catalytic process [20,21].
From the practical perspective of the reaction process, the eff ;ect of
CO
2
pressure was investigated. Surprisingly, upon decreasing the CO
2
temperature (5 min). The reaction proceeded at 110, 80 or 50 °C for
necessary time. The reactor was cooled to room temperature in a water
pressure from 56 to 10 atm, a noticeable increase in reactivity was re-
gistered (Table 1, entry 10). The use of K
2
CO as a base also showed
3
bath and the CO
2
pressure was released. The reaction products were
complete conversion (Table 1, entry 11) when the same reaction con-
analyzed by NMR after extraction by CDCl
3
(1.5 mL). Spectral char-
dition was tested. Probably, the increased solubility of 2-chloroethanol
acteristics of 2 are in accordance with literature data [15].
in the bulk of hot liquid CO (near-critical conditions) with liquid-liquid
2
phase behavior reduces the reaction rate [22].
3
. Results and discussion
To evaluate effect of temperature on conversion using K
2
CO and
3
Na
2
CO as bases, we studied the process at a lower (50 ⁰C) reaction
3
The cyclization of 2-chloroethanol (1) with CO
2
(56 atm) into
temperature but the same CO
this case, we obtained the product 2 with a good conversion using
CO , while Na CO showed a significantly lower reaction rate
(Table 1, entries 12–15). It should be noted that N(Bu) Br actually
exerted no effect on conversion at this temperature. The reaction of 2-
chloroethanol with CO at a higher reaction temperature (80 ⁰C)
showed again that Na CO gave a lower conversion to 2 compared to
the more basic K CO (Table 1, entries 16–19). Finally, it should be
stressed that K CO alone gives complete conversion of 2-chloroethanol
to desired ethylene carbonate without any assistance from N(Bu) Br,
the latter can only contaminate the product. So, the process requires the
2
pressure (10 atm) and prolonged time. In
ethylene carbonate (2) was first tested using silica gel as a catalyst and
Na
2
CO
3
as a base (Scheme 1).
K
2
3
2
3
At 110 ⁰C, the conversion to the desired carbonate 2 was 75 %
4
(
Table 1, entry 1). The use of KOH or NaOH as a base proved to be less
effective (Table 1, entries 2 and 3). Moreover, the addition of 2-chlor-
oethanol to KOH immediately causes an intensive evolution of ethylene
oxide, which makes the process enough dangerous [17]. In contrast, the
loading of 2-chloroethanol to inorganic carbonates is absolutely safe.
Addition of tetrabutylammonium bromide which practically always is
2
2
3
3
2
2
3
4
used as a co-catalyst in the reaction of CO to form organic carbonates
2
[
14,18,19], resulted in an increase in the catalyst activity (Table 1,
entry 4). In this case conversion reached 92 %. We also checked effi-
ciency of other phase-transfer agents, such as N(Bu) I, N(Bu) Cl and N
Et) Cl, with the result that the same conversion was observed (Table 1,
entries 5–7). It should be noted that the reaction with silica gel or
use of easily available 2-chloroethanol, inexpensive K
2
CO
3
, CO at a
2
sufficiently low pressure (10 atm), a moderate temperature (80 ⁰C), a
pinch of silica gel for column chromatography as a catalyst and lasts for
reasonable time (5 h).
4
4
(
4
tetrabutylammonium bromide without Na
2
CO did not proceed at all
3
(
Table 1, entries 8,9). We also checked the reaction without addition of
4. Conclusions
CO
2
but no product was formed. Only 2-chloroethanol was detected in
In summary, a “green”, simple, technically and economically fea-
sible synthesis of valuable ethylene carbonate under mild reaction
conditions was developed from 2-chloroethanol and CO
2
using K
2
CO
3
as a base and silica gel as a catalyst. Moreover, reuse of insoluble silica
gel and possible utilization of the reaction potassium waste as mineral
fertilizer make the process very ecologically and technology promising
[
16,23]. Testing the industrial application of the process is in progress.
Scheme 1. Synthesis of ethylene carbonate from 2-chloroethanol.
2
Lyubimov, Sergey E.
