The transesterification of dimethyl carbonate with phenol over Mg - Al-hydrotalcite catalyst

Article abstract of DOI:10.1021/op0302098

The production of diphenyl carbonate (DPC) by the transesterification of dimethyl carbonate (DMC) with phenol was performed using a variety of solid catalysts. Mg - Al-hydrotalcite was found to have a high activity for this transesterification. A 14.7% yield of DPC and an 11.6% yield of methylphenyl carbonate (MPC) based on DMC were obtained in the presence of Mg - Al-hydrotalcite catalyst. The optimum experimental temperature for this transesterification reaction was between 160 and 180°C, which was in agreement with the thermodynamic analysis. When the transesterification of DMC with phenol was performed at the molar ratio of phenol to DMC of 2:1, reaction time 10 h, 1.0% of 2:1 Mg - Al-hydrotalcite based on the total weight of reactants, and 160-180°C, the total yield and selectivity for DPC and MPC were 26.3 and 82.4%, respectively. The yield of anisole was 5.6%.

Full text of DOI:10.1021/op0302098

Organic Process Research & Development 2004, 8, 372−375
The Transesterification of Dimethyl Carbonate with Phenol over
Mg-Al-hydrotalcite Catalyst
Mei Fuming, Pei Zhi, and Li Guangxing*
Department of Chemistry, Huazhong UniVersity of Science and Technology, Wuhan, Hubei 430074, P.R. China
4
Abstract:
Tundo et al. reported that the equilibrium constant for
-
4
The production of diphenyl carbonate (DPC) by the transes-
terification of dimethyl carbonate (DMC) with phenol was
performed using a variety of solid catalysts. Mg-Al-hydrotalcite
was found to have a high activity for this transesterification. A
eq 1 was 3 × 10 at 180 °C. This indicates that the
transesterification reactions are thermodynamically unfavor-
able, while the O-methylation reaction is thermodynamically
favorable due to the production of gaseous CO
2
. To overcome
1
4.7% yield of DPC and an 11.6% yield of methylphenyl
the thermodynamic limitation of the transesterification reac-
5-12
carbonate (MPC) based on DMC were obtained in the presence
of Mg-Al-hydrotalcite catalyst. The optimum experimental
temperature for this transesterification reaction was between
tions, many processes have been proposed.
Catalysts are
also very important for transesterification reactions. Tradi-
tionally, the homogeneous catalysts for the transesterification
of DMC with phenol are Sn, Ti, Al, and Fe organometallic
1
60 and 180 °C, which was in agreement with the thermody-
1
3-16
namic analysis. When the transesterification of DMC with
phenol was performed at the molar ratio of phenol to DMC of
compounds,
the heterogeneous catalysts are mainly Mo,
1
7-20
Ti, Si, and rare earth metal oxides.
The homogeneous
2
:1, reaction time 10 h, 1.0% of 2:1 Mg-Al-hydrotalcite based
catalysts are unstable and are not easy to separate from the
products in this reaction system. The heterogeneous catalysts
have low catalytic activities and selectivities. We have found
that samarium trifluoromethanesulfonate is an efficient
heterogeneous catalyst for the transesterification of DMC
with phenol, but it is expensive in commercial application.
Therefore, it is desirable to find more efficient and cheap
catalysts for transesterification of DMC with phenol in the
application of commercial production.
on the total weight of reactants, and 160-180 °C, the total yield
and selectivity for DPC and MPC were 26.3 and 82.4%,
respectively. The yield of anisole was 5.6%.
21
1
. Introduction
Transesterification is an important organic transformation
and provides essential synthons for a number of applications
in organic processes. The synthesis of aromatic carbonates
Hydrotalcite-like compounds (HTLCs) consist of brucite-
like layers with positively charged metal oxide or hydroxide
layers with anions located interstitially. HTLCs catalyze
many organic reactions, such as the aldol and Knoevenagel
1
from dimethyl carbonate (DMC) and phenols is one of the
most important tranesterification reactions. It is thought to
be the most effective method now, because DMC is
achieving increasing importance and interest in the chemical
industry, mainly for its versatility as both reagent and solvent
and its nontoxicity for human health and the environment.
Meanwhile, aromatic carbonates, especially diphenyl carbon-
ate (DPC), are precursors for the production of aromatic
2
2,23
24
condensations,
Michael reactions, cyanoethylation of
25
26
27
alcohols and nitroaldol reactions. Watanabe and Tatsumi
found that hydrotalcite-type materials as base catalysts were
2
(
4) Tundo, P.; Trotta, F.; Moraglio, G.; Ligorati, F. Ind. Eng. Chem. Res. 1988,
7, 1565-1571.
5) Nishihira, K.; Tanaka, H.; Yoshida, S. JP 07101908, 1995.
2
(
polycarbonates by the melt polymerization process which is
(6) Inaba, M.; Kohei, S.; Tanaka, T. JP 08188558, 1996.
(7) Murata, K.; Kawahashi, K.; Watabiki, M. EP 591923, 1994.
now the highlight in the polycarbonate industry.3
(8) Inaba, M.; Sawa, K.; Tanaka, T. JP 0959225, 1997.
The reactions of DMC with phenol involved in the
transesterification reactions are shown in eqs 1-3, and the
O-methylation reaction is showed in eq 4:
(9) Harrison, G. E.; Dennis, A. J. WO 18458, 1992.
10) Fukuoka, S.; Tojo, M.; Kawamura, M. JP 04235951, 1992.
11) Kawamura, K. JP 07330687, 1995.
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(
(
(
(
(
(
(
(
(
(
(
(
15) Tatsuya, N. JP 0407035, 1992.
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17) Zihua, F.; Yoshio, O. J. Mol. Catal. A: Chem. 1997, 118, 293-299.
18) Kim, W. B.; Lee, J. S. J. Catal. 1999, 185, 307-313.
19) Hideaki, T.; Masaru, K.; Kenichi, W.; Yoshiyuki, O. WO 9517371, 1995.
20) Terunobu, Y.; Takashi, Y. JP 0959223, 1997.
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468.
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115-121.
(23) Kantam, M. L.; Choudary, B. M.; Reddy, C. V.; Rao, K. K.; Figueras, F.
*
Corresponding author. E-mail: ligxabc@public.wh.hb.cn.
J. Chem. Soc., Chem. Commun. 1998, 439, 1033-1034.
(24) Choudary, B. M.; Kantam, M. L.; Reddy, C. V.; Rao, K. K.; Figueras, F.
J. Mol. Catal. A: Chem. 1999, 146, 279-284.
(25) Krumbhar, P. S.; Valente, J. S.; Figueras, F. J. Chem Soc., Chem. Commun.
1998, 39, 1091-1092.
(
(
(
1) Otera, J. Chem. ReV. 1993, 93, 1449-1470.
2) Shaikh Abbs-Alli, G.; Sivaram, S. Chem. ReV. 1996, 96, 951-975.
3) Delledonne, D.; Rivetti, F.; Romano, U. Appl. Catal., A 2001, 221, 241-
2
51.
3
72
•
Vol. 8, No. 3, 2004 / Organic Process Research & Development
10.1021/op0302098 CCC: $27.50 © 2004 American Chemical Society
Published on Web 04/17/2004

efficient for the synthesis of dimethyl carbonate from ester
exchange of ethylene carbonate and methanol. In this
contribution on the basis of our studies on the transesteri-
fication of DMC with phenol, we explored Mg-Al-hydro-
talcite as catalyst in the transesterification of DMC with
phenol and found it was efficient for the transesterification
reactions.
Table 1. Thermodynamic properties in the
transesterification of DMC with phenol at atmospheric
pressure
0
0
0
∆
r
H
m
∆
r
S
m
r m
∆ G
-
1
J‚mol ‚K-1
-1
-1
T/°C
kJ‚mol
kJ‚mol
K
eq
-
12
2
5
64.4
49.6
45.9
43.0
-45.2
-41.2
-3.6
65.3
56.0
49.1
-146.1
-133.9
65.4
25.2
22.2
20.8
26.8
28.8
3.5 × 10
2.9 × 10
1.8 × 10
4.0 × 10
1.4 × 10
1.3 × 10
-4
1
1
1
2
00
50
80
20
-
-
-
-
3
3
3
3
2. Experimental Section
2.1. Reagents. DMC (Ube Chemicals, Japan) was frac-
250
tionally distilled and stored over molecular sieves (4Å).
Phenol was of laboratory reagent grade and subjected to
Table 2. Thermodynamic properties in the O-methylation of
phenol with DMC at atmospheric pressure
28
drying and purification by a standard procedure. TiO
and MoO /SiO were prepared according to the literature.
MgO, R-Al , and Sm were used as received.
.2. Preparation of Mg-Al, Calcined Mg-Al-hydro-
talcites. The Mg-Al-NO -hydrotalcite (Mg-Al-HT) with
:1 atom ratio of Mg to Al was prepared in a nitrogen
2
/SiO
2
7
1
3
2
0
0
0
∆
r
H
m
∆
r
S
m
r m
∆ G
-
1
J‚mol ‚K-1
-1
-1
O
2 3
O
2 3
T/°C
kJ‚mol
kJ‚mol
K
eq
2
5
6
6
6
6
7
2
5
25.9
10.7
13.4
52.5
10.7
14.8
192.9
151.1
158.2
247.6
154.9
165.6
-32.6
-45.7
-53.5
-59.7
-65.7
-71.8
5.1 × 10
2.5 × 10
4.1 × 10
7.6 × 10
9.1 × 10
1.5 × 10
3
1
1
1
00
50
80
2
atmosphere to avoid carbonation in air. Magnesium nitrate
hexahydrate (20.5 g, 0.08 mol) and aluminum nitrate
nonahydrate (15.0 g, 0.04 mol) were dissolved in 100 mL
of deionised and decarbonated water. The pH of the solution
was adjusted to 11.5 by the addition of NaOH (4 M). The
slurry was stirred for 2 h under nitrogen at room temperature
and then was crystallized for 48 h at 80 °C and filtered under
nitrogen and dried under vacuum at 80 °C to get Mg-Al-
220
50
2
-
LECO). The amount of OH was estimated as a balance on
-
2-
-
the assumption that NO
3
, CO
3
, and OH neutralize the
electric charge on the brucite-like layers. TG-DSC (PEAKIN-
ELMER) analysis of Mg-Al-hydrotalcites was performed.
The distillates during reaction and product mixture were
analyzed by gas chromatography (HP 6890) and mass
spectroscopy (HP 5973).
NO
3
-hydrotalcite. Calcined Mg-Al-hydrotalcite was pre-
pared by calcination of Mg-Al-hydrotalcite at 500 °C for
12 h. The particle sizes of Mg-Al-hydrotalcites were 80-
9
0 mesh.
2.3. Typical Procedure of the Synthesis of DPC. The
3 Results and Discussion
reaction was carried out in a 250-mL three-necked round-
bottomed flask equipped with a nitrogen inlet, a thermometer,
and a fractionating column (30 cm in length, 3 cm in
diameter, filled with small glass beads) connected to a liquid
dividing head. In a typical experiment, under nitrogen gas,
3.1. Thermodynamic Analysis. The stoichiometric equa-
tion for the transesterification of DMC with phenol is as
follows:
47.0 g (0.5 mol) phenol, 22.5 g (0.25 mol) DMC, and 0.7 g
Mg-Al-hydrotalcite were added to the flask, with stirring
and slowly increasing temperature. When the temperature
was about 140 °C, the occurrence of reaction was indicated
by the attainment of a temperature 62-63 °C at the top of
the column, which corresponded to the 70:30 boiling
azeotrope of methanol and DMC. This azeotrope was
analyzed by GC once an hour to measure the amount of
MeOH and to determine the extent of reaction. The tem-
perature was kept between 160 and 180 °C. The reaction
mixture was under refluxing condition between 160 and 180
The thermodynamic properties for reactions 5 and 4 were
29-31
calculated on the basis of references
Tables 1 and 2.
and are shown in
As shown in Table 1, at temperatures below 180 °C, the
transesterification reaction 5 is endothermic, and the equi-
librium constant (Keq) increases with increase of temperature.
Above 180 °C, phenol is vaporized, and reaction 5 becomes
exothermic. Between 150 and 250 °C, Keq remains almost
unchanged. Thus, the suitable temperature for reaction 5
should be 150-180 °C. As the reaction 4 is endothermic, a
higher temperature is preferable for this reaction (see Table
°
C. After filtration to recover the catalyst, the reaction
mixture was analyzed by GC-MS.
.4. Analysis. The structures of Mg-Al-hydrotalcites
were characterized by XRD (Rigaku D/MAX-3B). The
2
). The thermodynamic data in Tables 1 and 2 show that
2
the reaction of transesterification of DMC with phenol is
thermodynamically unfavorable even at 250 °C, while the
reaction of O-methylation of phenol with DMC is thermo-
dynamically favorable at room temperature. Thus, to choose
-
2-
absolute contents of intercalated NO
3
and CO
3
in samples
were measured by CHN analysis (CHN-600 Analyzer,
(
(
(
26) Choudary, B. M.; Kantam, M. L.; Reddy, C. V.; Rao, K. K.; Figueras, F.
(29) Sinke, G. C.; Hildenbrand, D. L.; McDonald, R. A.; Kramer, W. R.; Stull,
D. R. J. Phys. Chem. 1958, 62, 1461-1462.
(30) Steele, W. V.; Chirico, R. D.; Knipmeyer, S. E.; Nguyen, A. J. Chem. Eng.
Data 1997, 42, 1008-1020.
(31) Steele, W. V.; Chirico, R. D.; Knipmeyer, S. E.; Nguyen, A.; Smith, N. K.
J. Chem. Eng. Data 1997, 42, 1037-1052.
Green Chem. 1999, 187-189.
27) Watanabe, Y.; Tatsumi, T. Microporous Mesoporous Mater. 1998, 22, 399-
4
07.
28) Armarego, W. L. F.; Perrin, D. D. Purification of Laboratory Chemicals;
Butterworth-Heinemann: Oxford, 1996; p 299.
Vol. 8, No. 3, 2004 / Organic Process Research & Development
•
373

Table 3. Catalytic activity of Mg-Al-hydrotalcitea
DMC DPC MPC anisole transesterification
Table 5. Effect of atom ratio of Mg-Al on the yield of
DPCa
b
catalysts conv./% yield/% yield/% yield/% selectivity /%
DMC
DPC
MPC anisole transesterification
Mg:Al conv./% yield/% yield/% yield/%
selectivity/%
Mg-Al-HT 31.9
14.7
1.2
1.4
11.6
5.2
4.8
5.6
0.9
2.3
0.3
82.4
87.7
72.9
95.5
MoO
3
/SiO
2
7.3
8.5
6.6
1
2
3
4
:1
:1
:1
:1
21.1
31.9
39.5
35.6
40.2
26.1
9.6
14.7
12.9
12.2
12.8
9.9
3.8
11.6
3.6
7.0
4.9
7.7
5.6
23.0
16.4
22.5
10.9
63.5
82.4
41.8
53.9
44.0
58.2
TiO /SiO
2
2
Sm
2
O
3
2.7
3.6
a
Reaction conditions: phenol 47.0 g, DMC 22.5 g, catalyst 0.7 g, 160-180
5:1
:1
°
C, 10 h. The particle sizes for solid catalysts are 80-90 mesh. b Transesteri-
fication selectivity: (DPC yield + MPC yield)
6
5.3
×
100%.
DMC conversion
a
Reaction conditions: phenol 47.0 g, DMC 22.5 g, catalyst 0.7 g, 160-180
C, 10 h.
°
Table 4. Catalytic activities of solid basesa
DMC
DPC
MPC
anisole transesterification
c
catalysts
conv./% yield/% yield/% yield/%
selectivity /%
Mg-Al-HT
calcined
31.9
15.0
14.7
7.5
11.6
1.3
5.6
6.2
82.4
58.7
Mg-Al-HT
MgO-Al2O3
MgO-Al2O3
MgO
b
c
2.9
2.2
3.3
0.9
1.2
0.6
1.2
0.5
0.3
0.1
0.4
0.2
1.4
1.5
1.7
0.2
51.7
31.8
48.5
77.8
R-Al2O3
a
Reaction conditions: phenol 47.0 g, DMC 22.5 g, catalyst 0.7 g, 160-180
b
°
2
C, 10 h. MgO and R-Al
2 3
O were physically mixed according to n(Mg):n(Al) )
:1. c MgO and R-Al
were physically mixed then calcined at 500 °C in air.
2 3
O
suitable catalysts and to design an efficient reaction process
are the keys to increasing the yield and selectivity of the
transesterification products DPC and MPC.
Figure 1. Effect of molar ratio of Mg to Al. Preparation
conditions of Mg-Al-hydrotalcites: under nitrogen atmosphere,
pH of the solution 11.5, crystallization time 48 h at 80 °C.
Spectra a, b, c, d, e, f are corresponding to n(Mg)/n(Al) )1, 2, 3,
3
.2. The Catalytic Activity of Mg-Al-hydrotalcite. Fu
17
3 2
and Ono reported that MoO /SiO was an efficient catalyst
4, 5, 6, respectively.
for the transesterification of DMC with phenol to MPC and
the disproportionation of MPC to DPC and DMC in an
presence of coordinatively unsaturated O2- ions acting as
autoclave. Kim and Lee18 found that supported TiO
was
2
Lewis basic sites in calcined hydrotalcite may be responsible
also an active and selective catalyst for the transesterification
of DMC with phenol to MPC in an autoclave. The catalytic
activity of Mg-Al-hydrotalcite is compared to catalytic
activities of these heterogeneous catalysts in a refluxing
batchwise reactor. The results are shown in Table 3.
As seen in Table 3, Mg-Al-hydrotalcite is a much more
active heterogeneous catalyst for the transesterification of
32
for their activities.
3
.3. The Effect of Atom Ratio of Mg to Al in
Hydrotalcite. The different atom ratio of Mg-Al in hydro-
talcite is related with the catalytic activity of Mg-Al in
hydrotalcite. The effect of this ratio on the transesterification
of DMC with phenol is given in Table 5.
It was reported that the amount of basicity on hydrotalcite-
type materials increased with decreasing concentration of Al
3 2 2 2 2 3
DMC with phenol than MoO /SiO , TiO /SiO , and Sm O .
The double-layered hydroxide structure in Mg-Al-hydro-
talcite which makes it easy to abstract hydrogen of phenol
to form phenoxide seems to be responsible for the higher
catalytic activity for the transesterification of DMC with
33
in the brucite-like layers. For 1:1 and 6:1 Mg-Al-
hydrotalcites, although they have higher selectivities for
transesterification, the transesterification yield is lowest (see
Figure 1). This shows that the highest or lowest basicity for
Mg-Al-hydrotalcite is not favorable for the transesterifica-
tion of DMC with phenol. Mg-Al-hydrotalcite with a 2:1
atom ratio of Mg to Al has the highest catalytic activity,
while Mg-Al-hydrotalcites with 3:1 to 5:1 Mg/Al catalyze
O-methylation of phenol with DMC more favorably. These
results indicate that Mg-Al-hydrotalcite with moderate
basicity performs good catalytic activity for the transesteri-
fication of DMC with phenol. The XRD pattern for 2:1 Mg-
Al-hydrotalcites consists of sharp and symmetrical peaks,
being characteristic of a layered structure and similar to the
phenol. For MoO
3 2 2 3
, TiO , and Sm O , a phenol molecule
dissociatively absorbs to coordinate to the surface molyb-
17
denum, titanium, or samarium to be activated. This process
makes it difficult to abstract hydrogen of phenol to form
phenoxide.
Under the same reaction conditions, calcined Mg-Al-
2 3 2 3
HT, MgO-Al O , MgO and R-Al O were tested as catalysts
in the reaction of DMC with phenol. The results are given
in Table 4.
The strong Bronsted basic sites (hydroxyl groups) in
double layers of Mg-Al-HT27 lead to the high catalytic
activity for transesterification of DMC with phenol. The
calcined Mg-Al-hydrotalcite is a Mg-Al mixed oxide. The
(32) Di Cosimo, J. I.; Diez, V. K.; Xu, M.; Iglesia, E.; Apestegu ´ı a, C. R. J.
Catal. 1998, 178, 499-510.
(33) Cavani, F.; Trifiro, F. A.; Vaccari, A. Catal. Today 1991, 11, 173-175.
374
•
Vol. 8, No. 3, 2004 / Organic Process Research & Development

Table 6. Effect of molar ratio of phenol to DMCa
DMC DPC MPC anisole transesterification
Table 7. Effect of reaction time on transesterificationa
DMC
DPC
MPC anisole transesterification
n(phenol):n(DMC) conv./% yield/% yield/% yield/% selectivity/%
time/h conv./% yield/% yield/% yield/%
selectivity/%
1
1
2
3
4
:2
:1
:1
:1
:1
3.8
20.0
31.9
26.1
13.6
0.5
6.1
14.7
10.8
6.1
1.7
6.4
11.6
9.5
1.6
7.5
5.6
5.8
3.2
57.9
62.5
82.4
77.8
76.5
7
0
21.8
31.9
33.2
32.7
9.2
14.7
17.2
13.5
7.8
11.6
7.5
4.8
5.6
8.5
78.0
82.4
74.4
54.1
1
1
1
2
b
6
4.2
15.0
4.3
a
Reaction conditions: phenol 47.0 g, DMC 22.5 g, 2:1 Mg-Al-hydrotalcite
a
Reaction conditions: 2:1 Mg-Al-hydrotalcite 0.7 g, 160-180 °C, 10 h.
b
0
.7 g, 160-180 °C. Reaction temperature 160-190 °C.
The total amounts of DMC and phenol are constant.
n(DMC) ) 4:1] may cause a higher acidity in the reaction
mixture, which is unfavorable for the transesterification. The
excess of DMC leads to vaporisation of DMC easily from
XRD pattern of 1.8:1 Mg-Al-hydrotalcite reported in the
literature.
2
7
3.4. The Effect of Temperature. As the reaction of
1
60 to 180 °C. The vapor-phase reaction of DMC with
transesterification of DMC with phenol is thermodynamically
unfavorable and endothermic, it should proceed at high
temperature to increase the yields for DPC and MPC.
Experimentally, the transesterification reaction initiates at 160
phenol is favorable for producing anisole by O-methylation
36
of phenol with DMC.
3
.6. Effect of Reaction Time on Transesterification.
Because the transesterification of DMC with phenol is
reversible and the reaction rate is slow, the effect of reaction
time on it was studied. The results are given in Table 7.
The data indicate that after 10 h, the conversion of DMC
does not change very much, but the yields of DPC, MPC,
and anisole do change. After 10 h, the temperature reached
approximately 180 °C, and the disproportionation of MPC
to DMC and DPC over Mg-Al-hydrotalcite caused the
increase in the yield of DPC and the decrease in the yield of
MPC, from 10 to 12 h. After 12 h, the temperature increased
further, DMC and phenol were vaporized, the vapour-phase
reaction of DMC with phenol increased the O-methylation
°
C, as indicated by the presence of MPC and DPC in the
flask, DMC and methanol at the top of distillation column.
The temperature was gradually increased from 160 to 180
°
slowly removed from the reaction system. The removal of
methanol out of reaction system could shift the reaction to
the direction of MPC and DPC. The reaction was also
performed under refluxing conditions between 160 and 180
C in about 10 h. During this period, methanol was very
°
C due to the existence of excess amount of phenol. Under
refluxing conditions, Mg-Al-HT activates phenol to form
the active intermediate (PhO ) which nucleophilically attacks
the carbonyl group in DMC to produce methylphenyl
-
36
reaction, and subsequently the yield of anisole increased.
-
carbonate (MPC). Another PhO continuously reacts with
The decarboxylation of MPC and DPC at higher temperatures
also led to decreases in the yields of MPC and DPC.
Therefore, the best reaction time for the transesterification
of DMC with phenol over Mg-Al-hydrotalcite is from 10
to 12 h.
MPC to produce DPC. Fukuda and McIver34 found that the
reaction at the carbonyl group was enhanced by the presence
of solvent. DMC is both reagent and solvent under refluxing
35
conditions in this reaction. Memoli et al. also thought that
the transesterification of DMC with phenol prevailed over
the O-methylation of phenol with DMC under refluxing
conditions. Therefore, the suitable temperature range for the
transesterification of DMC with phenol is 160-180 °C,
which is in agreement with the thermodynamic analysis
4
. Conclusions
For the transesterification of DMC with phenol, Mg-
Al-hydrotalcites were found effective as catalysts. When the
reaction was carried out between 140 and180 °C, with a
molar ratio of phenol to DMC of 2:1, a reaction time 10 h,
the yield and selectivity for transesterification reaction were
(150-180 °C).
3.5. The Effect of Molar Ratio of DMC to Phenol on
the Synthesis of DPC. The effect of molar ratio of phenol
to DMC on the transesterification of DMC with phenol is
shown in Table 6.
26.3 and 82.4%, respectively, over 2:1 Mg-Al-hydrotalcite.
Mg-Al-hydrotalcites are cheap, easy to prepare, and separate
from the products, and they are also reusable; thus, they have
great potential in the application of transesterification reac-
tions.
When the molar ratio of phenol to DMC is 2:1 and 3:1,
the yields and selectivities of DPC and MPC are higher, but
the former is highest. Although the molar ratio 2:1 of phenol
to DMC is stoichiometric according to eq 5, the amount of
phenol is slightly in excess compared with the amount of
DMC due to the discharge of a little amount of DMC from
the flask with methanol during reaction. This result shows
that a little excess amount of phenol can enhance the
transesterification. In addition, the excess of phenol can
decrease the discharge of DMC and keep a high temperature
in the flask. But the large excess of phenol [n(phenol):
Note Added after ASAP Publication: In the version
published on the Internet 4/17/2004, the names of some
authors were inadvertently omitted from a few references.
The final version published 4/23/2004 and the print version
are correct.
Received for review August 28, 2003.
OP0302098
(
(
34) Fukuda, E. K.; McIver, R. T., Jr. J. Am. Chem. Soc. 1979, 10, 2498-2499.
35) Memoli, S.; Selva, M.; Tundo, P. Chemosphere 2001, 43, 115-121.
(36) Tundo, P.; Selva, M. CHEMTECH 1995, 25, 31-35.
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