Glycerol carboxylation to glycerol carbonate in the presence of rhodium complexes with nitrogen-containing macroligands

Article abstract of DOI:10.1134/S0965544112060060

The carboxylation of glycerol to glycerol carbonate (GC) in the presence of rhodium complexes with N-containing macroligands (polyethyleneimine and chitosan) has been studied. It has been found that the {RhCl³ + chitosan} system is an effective catalyst. It is most effective in the presence of methyl iodide or in the case of introduction of carbonates (dimethyl carbonate, propylene carbonate) into the reaction zone. The carboxylation of glycerol occurs at temperatures of 140-180°C in a methanol solution in a reducing environment under a pressure of 50 atm (40 atm of CO and 10 atm of H₂). The turnover number of the rhodium catalyst for the reaction time is 10 to 120. Pleiades Publishing, Ltd., 2012.

Full text of DOI:10.1134/S0965544112060060

ISSN 0965ꢀ5441, Petroleum Chemistry, 2012, Vol. 52, No. 6, pp. 416–421. © Pleiades Publishing, Ltd., 2012.
Original Russian Text © N.N. Ezhova, I.G. Korosteleva, N.V. Kolesnichenko, E.A. Kuz’min, S.N. Khadzhiev, E.Yu. Sorokina, M.A. Vasil’eva, Z.D. Voronina, 2012, published in
Neftekhimiya, 2012, Vol. 52, No. 6, pp. 448–453.
Glycerol Carboxylation to Glycerol Carbonate in the Presence
of Rhodium Complexes with NitrogenꢀContaining Macroligands
N. N. Ezhova, I. G. Korosteleva, N. V. Kolesnichenko, E. A. Kuz’min, S. N. Khadzhiev,
E. Yu. Sorokina, M. A. Vasil’eva, and Z. D. Voronina
Topchiev Institute of Petrochemical Synthesis, Russian Academy of Sciences, Moscow, Russia
eꢀmail: korosteleva@ips.ac.ru
Received April 22, 2012
Abstract—The carboxylation of glycerol to glycerol carbonate (GC) in the presence of rhodium complexes
with Nꢀcontaining macroligands (polyethyleneimine and chitosan) has been studied. It has been found that
the {RhCl3 + chitosan} system is an effective catalyst. It is most effective in the presence of methyl iodide or
in the case of introduction of carbonates (dimethyl carbonate, propylene carbonate) into the reaction zone.
The carboxylation of glycerol occurs at temperatures of 140–180°C in a methanol solution in a reducing
environment under a pressure of 50 atm (40 atm of CO and 10 atm of H2). The turnover number of the rhodꢀ
ium catalyst for the reaction time is 10 to 120.
DOI: 10.1134/S0965544112060060
Glycerol carbonate (GC) is a material that is beginꢀ activity in the presence of promoters of quaternary or
ning to be actively used in various branches of industry inorganic salts, are promising for using as catalysts for
[1–5]. This is a relatively new chemical compound,
which is potentially important for fine organic chemꢀ
istry [6, 7] and plasticizer industry [1, 8] and can be, in
particular, used as a monomer for the synthesis of new
polymers (polyesters, polycarbonates, polyurethanes,
and polyamides) [9–11].
the carboxylation of glycerol to GC (reaction 1).
These catalyst composites can be used in concentraꢀ
tions that are an order of magnitude lower than the
systems proposed by other authors (organic tin comꢀ
pounds [13, 14] or ceriumꢀcontaining catalysts [15]).
However, these catalysts are not sufficiently effective
We have shown in [12] that rhodium complexes for this process. In addition, the thermodynamics of
with phosphine ligands, which exhibited catalytic this reaction is unfavorable [12, 16]:
HOCH2–CH–CH2OH + CO2
HOCH2–CH–CH2 + H2O.
(1)
O
O
OH
C
O
This study concerns designing catalyst systems nique described in [12]. A catalyst based on a rhodium
based on rhodium complexes and nitrogenꢀcontaining
macroligands (chitosan and polyethyleneimine (PEI))
for the carboxylation of glycerol as well as finding ways
to bypass the thermodynamic barriers to this reaction.
Chitosan and PEI were chosen as macroligands
because these rhodiumꢀcontaining catalyst systems
have previously proven to be highly effective catalysts
in a number of syntheses of organic compounds [17,
18].
macrocomplex with PEI was prepared as follows: a
methanol solution of RhCl3 was added to a PEI soluꢀ
tion in methanol in small portions under constant stirꢀ
ring using a magnetic stirrer until the formation of a
homogeneous solution. Complexes with chitosan were
prepared in situ. Complexes RhCl(PPh3)3 and
Rh(acac)(CO)2, as well as ettriol phosphite (ETPO),
were synthesized according to known procedures [19,
20]. Commercial chemicals (Fluka) RhCl3, PPh3
,
bis(1,4ꢀdiphenylphosphino)propane (dppp), bis(1,4ꢀ
diphenylphosphino)butane (dppb), and Bu4NI were
used without further purification. Methyl iodide and
monoethanolamine (MEA) were distilled before use.
EXPERIMENTAL
The catalytic interaction of glycerol and СО2 was
run as a liquidꢀphase reaction according to the techꢀ Chitosan, which is a natural polymer, had a molecular
416

GLYCEROL CARBOXYLATION TO GLYCEROL CARBONATE
417
Table 1. Carboxylation of glycerol to glycerol carbonate in the presence of catalyst systems based on RhCl3 and a nitrogenꢀ
containing PEI macroliganda
Catalyst turnꢀ Glycerol conꢀ GC concentraꢀ
No.
Ligand
Promoter
T, °C
over number
version, %
tion, mmol/L
1
2
3
4
5
6
PEI
PEI
PEI
–
–
140
180
140
140
180
140
140
140
0
0
0
0
0
0
Bu NI
0
0
0
4
PPh + PEI
–
–
0
0
0
3
PPh + PEI
0
0
0
3
PPh + PEI
Bu NI
2.72
8.06
1.00
0.08
0.24
0.03
4.9
14.5
1.8
3
4
b
7
PPh + PEI
Bu NI
4
3
8
PPh
Bu NI
3
4
Equilibrium at 140–180°C [1]
0.24
15.0
a
–3
Note: Fifty atmospheres (40 atm of CO , 10 atm of H ), the solvent is methanol; [Rh] = 1.8
× 10 gꢀat/L; [PEI] = 2.7 g/L;
2
2
[glycerol] = 6.3 mol/L; P/Rh = 9; chitosan/Rh = 1.6; Bu NI/Rh = 30; 20 h.
4
b
59 h.
weight of about 60 000; PEI with the [–CH2–CH2–
NH–]nꢀ structure was used with a molecular weight of
All the component ratios in this study are mole
ratios.
about 10 000.
Liquid reaction products were identified by IR
spectroscopy and gas–liquid chromatography (GLC).
IR spectra were recorded in the absorption region of
carbonate (1820–1840 cm–1), hydroxyl (3410 cm–1),
and carbamate groups (1680 and 1540 cm–1). For
RESULTS AND DISCUSSION
The results of the carboxylation of glycerol to GC
in the presence of catalysts based on rhodium chloride
and PEI are shown in Table 1.
GLC analysis, a capillary column (9 m
×
0.53 mm
×
It is evident from these data that RhCl3 in combiꢀ
nation with PEI is not active at 140 and 180°С
(entries 1, 2). However, this catalyst system exhibits a
sufficient activity after the simultaneous introduction
0.3 m) coated with the OVꢀ225 stationary phase was
µ
used. The accuracy of the chromatographic analysis
was 5% rel %.
6
5
I
II
III
IV
4
3
2
1
0
5
10
15
20
Reaction time, h
Effect of the component concentration of the {RhCl + PEI + PPh + Bu NI} catalyst system on the yield of GC: (I) PPh /Rh =
3
3
4
3
3, Bu NI/Rh = 3; (II) PPh /Rh = 9, Bu NI/Rh = 30; (III) PPh /Rh = 3, Bu NI/Rh = 30; and (IV) without PEI, PPh /Rh =
4
4
3
4
3
4
3
9, Bu NI/Rh = 30.
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418
EZHOVA et al.
Table 2. Carboxylation of glycerol to GC in the presence of MEA (involving reaction 2) and methanol (involving reaction 3) usꢀ
ing a catalyst system based on RhCl3 and PEIa
Product concentration, mmol/L
Glycerol
conversion, %
Turnover number
Rh
No.
1
Ligands
GC
GC derivative
–
Calculated data [1]
0.24
15.0
–
GC conversion by reaction 2b
2
PPh
0.38
4.5
19.5 *
13.0
3
GC conversion by reaction 3c
3
4
5
6
7
PPh
0.51
0.57
0.35
0.33
0
3.1
1.2
0.8
0.5
0
28.9 **
35.9**
22.1**
20.8**
0
17.8
20.0
12.3
11.6
0
3
dppp
dppb
ETPO
–
a
–3
One hundred and forty degrees Celsius; 40 atm of CO ; 10 atm of H ; the solvent is methanol, [Rh] = 1.8 × 10 gꢀat/L; [PEI] = 2.7 g/L;
2
2
[glycerol] = 6.3 mol/L; 20 h.
b
In the presence of Bu NI; Bu NI/Rh = 30; P/Rh = 9.
4
4
c
In the presence of CH I; CH I/Rh = 300; P/Rh = 3; dppp (bisꢀdiphenylphosphinopropane) = (C H ) P(CH ) P(CH H ) ; dppb (bisꢀ
3
3
6
5 2
2 3
6 5 2
diphenylphosphinobutane) = (C H ) P(CH ) P(CH H ) ; ETPO (ettriol phosphite) = P(OCH ) CC H .
6
5 2
2 4
6
5 2
2 3
2 5
Notes: * carbamate.
** methyl ester of GC.
of a phosphine ligand (PPh3) and a quaternary ammoꢀ PPh3 + Bu4NI} composite is almost inactive (curve I).
nium salt (Bu4NI) into its structure (entries 6, 7). In A tenfold increase in the salt concentration and a
the presence of this catalyst system, the concentration of threefold increase in the phosphine concentration
GC achieves an equilibrium value after 59 h (entry 7).
Each of the components of the {RhCl3 + PEI +
PPh3 + Bu4NI} system has a crucial effect on catalytic
activity: thus, upon the exclusion of PEI from its comꢀ
position, the turnover number of the rhodium site (for
the reaction time) decreases almost threefold (entry
8); without phosphine or without the quaternary salt,
the composite does not work at all (entries 3–5).
The effect of the phosphine and quaternary salt
lead to the formation of a relatively stable catalyst
(curve II). In addition, the action of the quaternary
salt is more effective than that of phosphine, which
stabilizes the active site, but increases the duration of
its formation (cf. curves II and III). PEI enhances the
action of both phosphine and Bu4NI (i.e., accelerates
the formation of an active site and increases its stabilꢀ
ity): in the absence of PEI, the reaction occurs with an
induction period and its rate decreases (curves I, IV).
It should be noted that, in the presence of the
concentration in the composition of the {RhCl3
+
{
RhCl3 + PEI + PPh3 + Bu4NI} catalyst system, the
PEI + PPh3 + Bu4NI} catalyst system on its activity is
shown by the data in the figure. It is evident that the
duration of formation of an active site under the reacꢀ
tion conditions depends on the presence of each comꢀ
ponent in the composition of this catalyst system; durꢀ
only product of the conversion of СО2 and glycerol is
GC, and an equilibrium conversion of glycerol is
achieved (0.24%).
The conversion of glycerol in the reaction with СО2
ing the carboxylation of glycerol, in some cases, the can be increased via converting the product (GC) to
catalyst is deactivated (curves I, III). Excess phosꢀ another compound under the reaction conditions (in
phine and quaternary salt hinder the deactivation. situ). The carboxylation of glycerol was combined with
Thus, at low concentrations of PPh3 and Bu4NI the conversion of GC to carbamate through the interꢀ
(P/Rh = 3 and Bu4NI/Rh = 3), the {RhCl3 + PEI + action with MEA (reaction 2):
O
HOCH2–CH–CH2 + H2N–CH2–CH2–OH
CH2–CH–CH2–O–C
(2)
NHCH CH OH
.
2
2
O
O
OH OH
C
O
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GLYCEROL CARBOXYLATION TO GLYCEROL CARBONATE
419
Table 3. Carboxylation of glycerol in the presence of catalyst composites comprising a rhodium compound, chitosan, and
methyl iodidea
Product
Yield*, % concentration*,
mmol/L
Rhodium comꢀ
pound
Turnover
number Rh
No.
Additive
P
(H ), atm
T
,
°C
2
1**
2**
3
RhCl
RhCl
RhCl
RhCl
RhCl
RhCl
RhCl
–
–
10
10
10
10
10
10
0
140
180
140
140
140
140
140
140
140
180
0
0
15.0
29.9
3.6
0
8.3
3
3
3
3
3
3
3
0.24
0.47
0.06
0.06
0
–
15.0
2.0
4
LiI
KOH
HI
–
5
3.5
0.2
6
0
0
7
0.01
0.41
0.37
3.40
0.7
0.4
8
RhCl(PPh )
–
10
10
10
25.5
23.3
216.0
14.3
13.0
120.0
3 3
9
Rh(acac)(CO)
–
2
10
RhCl
–
3
a
–ꢀ
3
One hundred and forty degrees Celsius; 40 atm of CO ; 10 atm of H ; the solvent is methanol, [Rh] = 1.8
×
10 gꢀat/L; [chitosan] =
2
2
–2
2.8 × 10 mol/L; [glycerol] = 6.3 mol/L; CH I/Rh = 20; 20 h.
3
Notes: * GC + its methyl ester.
** Without methyl iodide.
The addition of MEA into the reaction zone carbonate is completely destroyed, although a valuable
increases the conversion of glycerol by a factor of 1.6
in comparison with the equilibrium concentration
(Table 2, entries 1, 2). The turnover number of the
rhodium site for 20 h of reaction in the case of the conꢀ
version of GC to carbamate is almost 5 times higher
than in its absence (cf. Table 2, entry 2 and Table 1,
commercial product (an intermediate product of
polyurethane synthesis) is formed.
The structure of carbonate can be preserved via
combining the carboxylation of glycerol and the conꢀ
version of GC to its methyl ester through the interacꢀ
entry 6). However, in this case, the cyclic structure of tion of GC with methanol (reaction 3):
HOCH2–CH–CH2 + CH3OH
CH3OCH2–CH–CH2 + H2O.
(3)
O
O
O
O
C
O
C
O
In this case, the conversion of glycerol is higher iodide [17]). These catalyst systems were studied in the
than the equilibrium conversion of reaction (1) by a
factor of 2.1 (Table 2, entries 1, 3), and the turnover
number of the rhodium site increases almost sevenfold
(see Table 1, entry 5). It should be noted that this effect
is observed only in the presence of methyl iodide, and
the activity of the system with PEI including CH3I
depends on the presence of a phosphorusꢀcontaining
ligand in their composition (entries 3–6).
carboxylation of glycerol. The results are shown in
Table 3. It is evident from these data that the catalyst
with chitosan at 140
(entry 1). However, at 180
°
С
does not mediate the reaction
, the catalyst system is
°С
active, and the reaction achieves an equilibrium conꢀ
centration (entry 2). Upon the addition of CH3I, the
system becomes active even at 140°С and converts
glycerol (to methyl ester of GC) with a turnover numꢀ
Thus, the catalyst system based on rhodium chloꢀ ber of 15.4 (for 20 h of reaction) (entry 3). The presꢀ
ride and PEI is relatively efficient for synthesizing GC
(in the form of its derivatives), but it does not work in
the absence of organophosphorus ligands and promotꢀ
ers, such as quaternary salts or methyl iodide.
There are catalysts based on RhCl3 and chitosan as
a nitrogenꢀcontaining ligand (they are effective in the
ence of ionic compounds (LiI, KOH, HI) decreases
the activity of the catalyst system (entries 4–6).
Hydrogen has a strong effect on the activity of the catꢀ
alyst system: in the absence of Н2, these catalysts
mediate the carboxylation of glycerol at a very low rate
(entry 7), which indicates that the active site is probaꢀ
carbonylation of methanol in the presence of methyl bly hydride. The effectiveness of rhodium–chitosan
PETROLEUM CHEMISTRY Vol. 52
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420
EZHOVA et al.
Table 4. Effect of promoters on the carboxylation of glycerol to GC in the presence of the {RhCl3 + chitosan} catalyst sysꢀ
tema
Results
[Promoter],
No.
Promoter
[GC],
mol/L
Turnover numꢀ
ber Rh
mol/L
Yield of GC, % Selectivity, %
1
2
3
4
Propylene carbonate
Dimethyl carbonate
0.08
0.08
0.56
0
0.050
0.80
0.50
0.47*
0
100
100
28
18
15
0
0.030
0. 030
0
CH I
2.5
3
–
–
–
Equilibrium
0.015
0.24
–
a
–3
Note: One hundred and forty degrees Celsius; 40 atm of CO ; 10 atm of H ; the solvent is methanol, [Rh] = 1.8
×
10 gꢀat/L; [chiꢀ
2
2
–2
tosan] = 1.8
× 10 mol/L; P/Rh = 9; 48 h.
* GC + its methyl ester.
catalysts depends on the type of the rhodium precurꢀ at least 4 times (compared to an equilibrium value of
sor. A system prepared from RhCl3 is more active than 0.24%) (entry 1). The action of dimethyl carbonate is
that based on Rh(I) complexes, i.e., Rh(acac)(CO)2 less effective: only a twofold increase in the product
and RhCl(PPh3)3 (entries 8, 9). The occurrence of the yield is observed in its presence (entry 2). Similar to
process is strongly affected by temperature. As the the case of addition of methyl iodide into the reaction
temperature increases to 180
alyst increases by almost an order of magnitude (entry makes the system active even at 140
°
С
, the activity of the catꢀ zone (entry 3), the use of carbonates as promoters
°
С
(entries 1, 2),
10): the catalyst makes 120 turnovers and provides the while without them, at the same temperature, the sysꢀ
yield of GC (in the form of its methyl ester) at a level tem does not work (entry 4). In contrast to CH3I, in
of 3.4%. The {RhCl3 + chitosan + CH3I} catalyst sysꢀ the presence of carbonates, the only product of glycꢀ
tem carboxylates glycerol with a 15–30 times higher erol conversion is GC.
turnover number of the active site than that of the
known catalysts [15]. Although the product yield
remains low, it is more than an order of magnitude
higher than the equilibrium conversion of glycerol in
its reaction with СО2 (0.24%).
In this study of the carboxylation of glycerol to GC,
an active catalyst system comprising rhodium chloꢀ
ride, chitosan, and methyl iodide has been found. The
turnover number of {RhCl3 + chitosan + CH3I} (for
20 h of reaction at 180°С) was 120; this is 15–30 times
higher than this parameter value for the catalysts
described in the literature. The combination of the tarꢀ
get reaction with the conversion of GC to methyl ester
has led to a severalfold increase in the yield of the carꢀ
boxylation product.
The introduction of propylene carbonate into the
reaction zone was also effective; in its presence, the
yield of GC increased fourfold, while the structure of
carbonate was fully preserved.
The yield the desired product remains low particuꢀ
larly because the main products of this process are
methyl esters of glycerol rather than GC (or its methyl
ester). It is impossible to suppress the formation of
glycerol esters and to increase the yield of the desired
product because of the rapid consumption of glycerol
in side reactions.
A possible method to increase the yield of GC is the
removal of water from the reaction zone. Convenꢀ
tional methods of using dehydrating agents (e.g., zeoꢀ
lites) were not effective, because the entire adsorbed
water was desorbed at the reaction temperature. The
best results were obtained in the case of the chemical
binding of water, in particular, upon the addition of
organic carbonates—propylene carbonate and dimeꢀ
thyl carbonate—into the reaction zone. These carꢀ
bonates are known to react with water to be converted
to alcohols (propylene glycol and methanol, respecꢀ
tively) [21].
ACKNOWLEDGMENTS
This work was supported by the federal target proꢀ
gram “Research and Development in the Priority
Fields of the Science and Technology Complex of
Russia for 2007–2013.”
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