Cerium dioxide catalyzed synthesis of methyl N-phenylcarbamate from carbon dioxide, aniline and methanol in the presence of n-butyllithium

Article abstract of DOI:10.1016/j.molcata.2015.04.017

Direct synthesis of methyl N-phenylcarbamate (MPC) from carbon dioxide (CO₂), aniline and methanol catalyzed by cerium dioxide (CeO₂) in the presence of n-butyllithium (BuLi) was developed. The catalytic activity of CeO₂ was significantly improved by the addition of BuLi. The conversion of aniline and the yield of MPC were dependent on the amount of CeO₂ and BuLi, reaction conditions including the pressure of CO₂, reaction time and temperature, and 9.4% yield of MPC was obtained under the optimized conditions. The formation pathway of MPC was also investigated in detail by varying reactants based on previously reported investigations, and phenyl isocyanate (PI) was believed to be the intermediate for the synthesis of MPC. A possible reaction pathway for the direct synthesis of MPC from CO₂, aniline and methanol was proposed.

Full text of DOI:10.1016/j.molcata.2015.04.017

Journal of Molecular Catalysis A: Chemical 404 (2015) 92–97
Contents lists available at ScienceDirect
Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Cerium dioxide catalyzed synthesis of methyl N-phenylcarbamate
from carbon dioxide, aniline and methanol in the presence of
n-butyllithium
∗
Guozhi Fan , Shanshan Luo, Tao Fang, Qiang Wu, Guangsen Song, Jianfen Li
School of Chemical and Environmental Engineering, Wuhan Polytechnic University, Wuhan, Hubei 430023, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Direct synthesis of methyl N-phenylcarbamate (MPC) from carbon dioxide (CO ), aniline and methanol
catalyzed by cerium dioxide (CeO2) in the presence of n-butyllithium (BuLi) was developed. The catalytic
2
Received 28 January 2015
Received in revised form 19 April 2015
Accepted 21 April 2015
activity of CeO2 was significantly improved by the addition of BuLi. The conversion of aniline and the yield
of MPC were dependent on the amount of CeO2 and BuLi, reaction conditions including the pressure of
CO2, reaction time and temperature, and 9.4% yield of MPC was obtained under the optimized conditions.
The formation pathway of MPC was also investigated in detail by varying reactants based on previously
reported investigations, and phenyl isocyanate (PI) was believed to be the intermediate for the synthesis
of MPC. A possible reaction pathway for the direct synthesis of MPC from CO2, aniline and methanol was
proposed.
Available online 22 April 2015
Keywords:
Methyl N-phenylcarbamate
Carbon dioxide
Aniline
Methanol
© 2015 Published by Elsevier B.V.
CeO2
1
. Introduction
Organic carbamates, the important raw materials in terms of
hydrogen, alkenes, acetals, epoxides, amines, phenol and
carbon–carbon unsaturated compounds, have been explored
to react with CO2 in the presence of metal catalysts [10–16],
and revealed excellent catalytic performance for the synthesis of
sustainable chemistry [1], are widely applied in the production
of polyurethane foams, elastomers, phenol-formaldehyde resins,
paints, rayons/nylons and pesticides [2]. The alcoholysis of iso-
cyanates and the aminolysis of chloroformates are traditionally
employed for the production of carbamates [3], in which highly
toxic phosgene is generally required. Therefore, corrosive by-
products such as hydrogen chloride and contaminative solution
are inevitable, leading to problems of environmental pollution and
equipment corrosion. Therefore, much attention has recently been
devoted to developing environmentally benign process for the syn-
thesis of carbamates [4].
carbonates as well as urea derivatives from CO [7,17–20].
2
Recently, there has been a focus on the reaction of CO2 with
amines to provide carbamic acid [21], carbamates/cyclic carba-
mates [22] and urea derivatives [23,24]. The direct synthesis of
carbamates from CO , amines and alcohols is one of the most
2
promising fields for the utilization of CO [3,25] since highly toxic
2
phosgene is replaced by non-toxic and non-corrosive CO [26], and
2
water is the sole by-product theoretically. It has been reported that
base catalysts such as cerium dioxide (CeO ), caesium carbonate
2
(Cs CO ) and potassium carbonate (K CO ) are effective catalysts
2
3
2
3
Carbon dioxide (CO ), the chief greenhouse gas resulted from
human activities, causes global warming and climate change more
for the synthesis of cyclic carbamates from CO2 and aminoalco-
hols, methyl benzylcarbamate from CO2 and benzylamine [3,26].
However, few works have been focused on the direct synthesis of
2
and more serious [5]. The concentration of CO in the atmosphere
2
increases at an accelerating rate from decade to decade. Actually,
CO2 is not only a greenhouse gas but also the greatest carbon
resource from a chemical science perspective. The conversion
of CO2 into useful intermediates and chemicals has attracted
extensive interest [6–9]. A number of compounds, including
methyl N-phenylcarbamate (MPC) from CO , aniline and methanol,
and relatively poor results have been reported due to the inertness
of aniline [26,27].
2
Three possible paths for the synthesis of MPC from CO , ani-
2
line and methanol could be proposed based on the formation of
carbonate from CO and alcohol as well as the formation of diurea
2
from CO and amine [27–30]. One of them is the synthesis of MPC
2
via the transesterification between N,N-diphenylurea (DPU) and
dimethyl carbonate (DMC); another way is the formation of MPC
∗ Corresponding author. Tel.: +86 2783943957; fax: +86 2783943956.
E-mail addresses: fgzcch@163.com, fgzcch@whpu.edu.cn (G. Fan).
http://dx.doi.org/10.1016/j.molcata.2015.04.017
1
381-1169/© 2015 Published by Elsevier B.V.

G. Fan et al. / Journal of Molecular Catalysis A: Chemical 404 (2015) 92–97
93
Table 1
derived from methanol and DPU; and the last one is the forma-
Synthesis of MPC with various catalysts.
tion of MPC derived from DMC and aniline. In fact, isocyanates are
also believed to be crucial intermediates for the synthesis of carba-
mates in the presence of alcohol [31]. Thus, further investigation is
required to exactly understand the reaction mechanism better and
to develop an effective methodology for the direct synthesis of MPC
Entry
Catalyst
Conv. (%)
Sel. (%)a
Yield (%)
MPC
MA
DMA
1
2
3
4
5
6
7
8
9
ZnCl2
AlCl3
ZnI2
AlBr3
K2CO3
LiOH
CsOH
Li2CO3
Cs2CO3
CeO2
CeO2 + Li2CO3
CeO2 + Cs2CO3
25.1
27.4
26.9
28.7
2.1
3.3
6.7
4.3
5.2
–
–
–
–
–
–
1.5
4.6
3.8
15.5
19.0
18.8
–
–
–
–
–
–
0.1
0.2
0.2
0.9
1.2
1.3
1.3
3.5
0.8
0.9
0.2
0.4
0.7
1.3
1.6
1.5
1.4
1.6
19.0
22.1
23.3
25.6
1.5
1.1
5.4
2.1
2.4
from CO , aniline and methanol. There is no doubt that the key lies
2
in developing an effective catalytic system due to the inertness of
aniline.
The aim of this work is to develop an effective methodology for
the direct synthesis for MPC from CO , aniline and methanol based
2
on the inertness of aniline. The reaction was performed in the pres-
ence of various catalysts including bases and Lewis acids. Additives
10
5.8
6.3
6.9
2.1
1.9
1.9
b
1
1
1
2
such as n-butyllithium (BuLi), sodium borohydride (NaBH ) and
4
b
sieves were added to improve the reaction since small amount of
water is expected to form during the reaction. The amount of cat-
alyst and additive, the molar ratio of methanol to aniline, reaction
Reaction conditions: 1.5 mmol aniline, 0.3 mmol catalyst, 150 mmol methanol,
◦
5
MPa CO2, temperature 170 C, time 12 h.
a
Selectivity to MPC.
conditions including the pressure of CO , reaction time and tem-
2
b
0.3 mmol carbonate was added.
perature were optimized in detail. A possible reaction mechanism
for the synthesis of MPC catalyzed by CeO in the presence of BuLi
was also proposed.
2
involving CO . Thus the synthesis of MPC from CO2 and aniline
2
in the presence of methanol was first investigated with these
simple catalysts. Table 1 illustrates that the formation of methy-
laniline (MA) and dimethylaniline (DMA), but almost no methyl
N-phenylcarbamate (MPC) was observed in the presence of Lewis
acids (entries 1–4), revealing the formation of MA and DMA from
aniline and methanol is possibly easier to proceed than that
between CO2 and aniline. This is in accordance with the work
reported by Zhang et al. [27], in which it was found that the for-
mation of MA and DMA from aniline and methanol even can occur
2
. Experimental
2.1. Reagent
All reagents, including aniline, methanol, biphenyl, methylani-
line (MA), dimethylaniline (DMA), zinc chloride (ZnCl ), zinc iodide
2
(
ZnI ), aluminum chloride (AlCl ), aluminum tribromide (AlBr ),
2
3
3
caesium hydroxide (CsOH), lithium hydroxide (LiOH), lithium car-
bonate (Li CO ), acetonitrile (MeCN), N-methylpyrrolidone (NMP),
BuLi, CeO , NaBH , DPU, DMC, K CO and Cs CO , were of analyt-
ical grade. Aniline was redistilled prior to use and other reagents
were used without further purification, and the purity of CO was
spontaneously while the reaction between aniline and CO cannot
2
2
3
occur in the reaction system involving CO , aniline and methanol
2
2
4
2
3
2
3
under acidic condition. That is, the reaction between CO and ani-
2
line is probably prevented in the presence of methanol although it
can occur in the absence of methanol [36]. Sharp drop in the conver-
sion of aniline appeared in the presence of basic catalysts (entries
2
9
9.99%.
5
–10), and the total yield of by-products significantly decreased
compared to that obtained in the presence of Lewis acids. Instead,
.9% yield of MPC was given by using CeO2 as the catalyst (entry
10), suggesting base catalysts prevents the reaction between ani-
line and methanol but are favorable for the formation of MPC. The
results in Table 1 also show that the yield of MPC was relatively poor
using carbonate as catalyst alone (entries 8 and 9), but the catalytic
2.2. Catalytic test
0
General procedure for the synthesis of MPC from CO , ani-
2
line and methanol is as following: 1.5 mmol aniline, 150 mmol
methanol and 0.3 mmol CeO2 were charged into a 50 ml stainless
steel autoclave. The autoclave was sealed and flushed with 2 MPa
CO2 three times to wash out the air in it. CO2 was then pressed
to 5 MPa and introduced into the autoclave using a high-pressure
pump. The mixture was further heated to the desired reaction
temperature while stirring. The autoclave was cooled to room tem-
perature after 12 h, and the pressure in the autoclave was gradually
released. Then the mixture was centrifuged after the addition of
performance of CeO2 was enhanced by the addition of (Li CO3 or
2
Cs CO3 entries 11,12). So it is reasonable to conclude that Li CO3
2
2
or Cs CO3 plays the role of co-catalyst. No formation of MPC was
2
observed using LiOH as the catalyst (entry 6) though it can be eas-
ily converted into Li CO3 in the presence of CO , which might be
2
2
ascribed to water is also produced from LiOH and CO [37]. The for-
2
1
0 mL methanol.
mation of water is unfavorable for the synthesis of MPC from CO2,
aniline and methanol since it is believed to be a reversible reaction,
in which water is the sole by-product theoretically [27].
To determine the conversion of aniline, the yield and the selec-
tivity towards MPC, the product in the liquid mixture obtained
after the reaction was analyzed quantitatively by GC with a HP-5
capillary column (30 m × 0.32 mm × 0.25 ␮m, 5% phenyl methyl-
siloxane) and FID detector using biphenyl as internal standard. The
yield of MPC was calculated based on the charged aniline. The for-
mation of MPC was also identified qualitatively by GC–MS equipped
with a HP-5 capillary column and EI source.
3.2. Investigation on the catalytic system
It has been demonstrated that the synthesis of urea deriva-
tives from CO2 and amine proceeds well in MeCN and
N-methylpyrrolidone (NMP) [22,35]. However, it can be seen from
Table 2 that no MPC was detected with the addition of MeCN
and NMP. Generally, sieve is employed as the dehydrating agent
in the reactions involving the formation of water as by-product
to improve activity [38]. The results in Table 2 show that almost
no improvement in the yield of MPC was observed with the addi-
tion of sieve (entries 4,5). Surprisingly, the yield and the selectivity
towards MPC were obviously improved by the addition of BuLi,
in which 3.8% yield and 48.7% selectivity were obtained (entry 6)
3
. Results and discussion
3
.1. Screening of catalyst
Various catalysts such as Lewis acids including ZnCl , ZnI ,
2
2
AlCl , AlBr [32,33], CsOH [28], CeO [26,30,34], K CO and Cs CO
3
3
2
2
3
2
3
[
35] reveal outstanding catalytic performance for the reactions

9
4
G. Fan et al. / Journal of Molecular Catalysis A: Chemical 404 (2015) 92–97
Table 2
Synthesis of MPC with various additives and amounts of catalyst.
since it is a strong alkaline compound. The reaction between CO2
and aniline may be prevented with larger amount of BuLi because
of the weak basicity of aniline.
Entry
Additive
Conv. (%)
Sel. (%)
Yield (%)
1
2
3
4
5
6
7
–
5.8
1.1
13.1
6.3
6.6
7.8
11.6
3.7
2.4
6.3
6.7
15.5
–
–
0.9
–
MeCN (6 ml)
NMP (1.5 ml)
3A sieve (1.5 g)
4A sieve (1.5 g)
BuLi (0.5 mmol)
NaBH4 (0.5 mmol)
BuLi (0.5 mmol)
–
Trace
0.8
1.1
3.8
1.6
–
0.4
1.0
3.0
6.4
7.3
5.4
3
.3. Optimization of reaction condition
12.7
16.7
48.7
13.8
–
16.7
15.9
44.8
52.4
51.8
54.0
Table 3 reveals the influence of reaction variables including the
pressure of CO , reaction temperature and time. The conversion of
aniline, the yield and the selectivity towards MPC were improved
with an enhancement in the pressure of CO below 5 MPa, and the
maximum yield of 7.3% and selectivity of 51.8% were obtained at
5 MPa (entry 3), respectively. In this work, CO2 was charged into the
autoclave before heating the reaction mixture to expected temper-
ature to retard the side reaction between aniline and methanol.
Thus the pressure in the autoclave increased with an enhance-
2
a
8
9
b
0c
2
1
1
1
1
1
–
1
2
3
4
BuLi (0.25 mmol)
BuLi (0.75 mmol)
BuLi (1 mmol)
BuLi (1.25 mmol)
12.2
14.1
10.0
Reaction conditions: aniline 1.5 mmol, CeO2 0.3 mmol, methanol 150 mmol, CO2
MPa, temperature 170 C, time 12 h.
a
◦
5
ment in the reaction temperature and finally kept around 8.2 MPa,
closing to the critical pressure of pure CO , at 170 C with an orig-
No CeO2 was employed.
.2 mmol CeO2 was employed.
.4 mmol CeO2 was employed.
◦
b
2
0
0
c
inal pressure of 5 MPa. The variation of density around the critical
point generally causes a change in chemical or physical equilibrium,
and thus affects the rate and the selectivity of reactions [40]. The
unique properties appearing near the critical point are probably
responsible for the positive effect observed at an original pressure
of 5 MPa. Similar results with a maximum selectivity at a pres-
though no MPC was observed in the presence of BuLi alone (entry
). It is believed that the synthesis of MPC from CO , aniline and
methanol is a reversible reaction [27], which thus could be corre-
spondingly promoted to shift to the right due to the consumption
of by-product via the severe reaction between water and BuLi. In
addition, LiOH is produced via the violent reaction of BuLi with
water [39], and LiOH could be further converted to Li CO since
the reaction between LiOH and CO proceeds easily [37]. As shown
in Table 1, the catalytic performance of CeO was improved by the
addition of Li CO (Table 1, entry 11), which might play the role
of co-catalyst in the present catalytic system. The improvement in
the yield of MPC by the addition of BuLi can be ascribed to two fac-
tors. One is the consumption of by-product water; and the other
is Li CO derived from BuLi plays the role of co-catalyst. Thus, we
speculate that BuLi is not only as a dehydrating agent but also as a
promoter.
8
2
sure near the critical point of CO were reported elsewhere [32,41].
2
The temperature dependence on the synthesis of MPC reveals that
the conversion of aniline monotonously increased with improv-
ing temperature, and the yield of MPC was also notably enhanced
till the temperature increased to 170 C (entries 3, 5–7). A further
increase in the temperature then led to a loss in the yield and
the selectivity (entry 8), so it is reasonable to conclude that the
reversible reaction for the synthesis of MPC from CO , aniline and
methanol possibly reaches equilibrium around 170 C, resulting in
the loss in the yield and the selectivity with further increase in
temperature.
Table 3 also indicates that the synthesis of MPC was significantly
dependent on the reaction time (entries 3, 9–12). The conver-
sion of aniline was observed to obviously increase till the reaction
time increased to 12 h, and an improvement in the selectivity was
observed in the range from 6 to 10 h but then almost kept constant
with further increasing in the reaction time. Correspondingly, the
yield of MPC increased with prolonging the reaction time in the
range from 6 to 12 h while almost no change once the reaction time
beyond 12 h. The evident improvement in the selectivity towards
MPC with increasing the reaction time below 10 h reveals that the
reaction between aniline and methanol is possibly easier to pro-
ceed at the earlier stage. So the reaction was heating to the expected
2
3
◦
2
2
2
3
2
◦
2
3
The results in Table 2 also show that the yield of MPC was depen-
dent on the amount of CeO and BuLi while the selectivity towards
MPC almost kept constant in the presence/absence of BuLi. The
yield of MPC slightly increased with increasing the amount of CeO2
while the selectivity almost kept constant (entries 1, 9, 10). Both
the conversion of aniline and the yield of MPC were enhanced by
increasing the amount of BuLi (entries 6, 10–13), achieving maxi-
mum values by using 1 mmol BuLi. 14.1% conversion of aniline and
2
7
.3% yield of MPC were obtained, respectively (entry 13). The con-
version and the yield were then observed to decrease with a further
increase in the amount of BuLi (entry 14). The basicity of the reac-
tion system increases with enhancement in the amount of BuLi
temperature after the charging CO to diminish side reaction.
2
Table 3
Influence of the reaction conditions on the synthesis of MPC.
Table 4
Molar ratio of methanol to aniline corresponding to the synthesis of MPC.
◦
Entry
CO2 (MPa)
Temp. ( C)
Time (h)
Conv. (%)
Sel. (%)
Yield (%)
Entry
Methanol/aniline (mol. ratio)
Conv. (%)
Sel. (%)
Yield (%)
1
2
3
4
5
6
7
8
9
3
4
5
6
5
5
5
5
5
5
5
5
170
170
170
170
140
150
160
180
170
170
170
170
12
12
12
12
12
12
12
12
6
0.8
9.4
14.1
11.4
0.8
2.9
9.6
15.9
6.4
7.4
25.0
38.3
51.8
44.7
50.0
48.3
53.1
33.3
20.2
33.8
47.1
52.1
0.2
3.6
7.3
5.1
0.4
1.4
5.1
5.3
1.3
2.5
4.9
7.2
1
2
3
4
5
6
7
100
110
130
150
160
170
180
–
14.1
14.9
16.7
16.8
17.3
17.8
21.4
–
51.8
51.3
49.7
55.9
54.3
53.9
31.3
56.0
–
7.3
7.6
8.3
9.4
9.4
9.6
6.7
1.8
0.8
a
8
b
10
11
12
8
10
14
9
–
4.5
10.4
13.8
Reaction conditions: aniline 1.5 mmol, CeO2 0.3 mmol, CO2 5 MPa, BuLi 0.5 mmol,
◦
temperature 170 C, time 12 h.
a
Reaction conditions: aniline 1.5 mmol, CeO2 0.3 mmol, methanol 150 mmol, BuLi
mmol.
Ref. [26].
Ref. [42].
b
1

G. Fan et al. / Journal of Molecular Catalysis A: Chemical 404 (2015) 92–97
95
3.5. Investigation on the synthetic pathway for MPC
Several pathways for the synthesis of MPC from CO , aniline
2
and methanol might be proposed based on the reported procedures
27–31]. Herein, reactions with various reactants were further car-
[
ried out to reveal possible pathway. The results in Table 5 reveal
that no objective product was observed in the presence of aniline
and DMC (entry 1). It is not in accordance with the work reported
by Honda et al. [26], in which DMC was believed to be an intermedi-
ate for the synthesis of methyl benzylcarbamate from benzylamine
Scheme 1. Plausible pathway for the synthesis of MPC from CO2, aniline and
methanol.
and CO in the presence of methanol. Unexpectedly, the formation
2
of MA and DMA was observed with increasing the molar ratio of
aniline to DMC (entries 2 and 3).
Synthesis of MPC from DMC and DPU was further investigated.
The results in Table 5 reveal that the yield of MPC was improved by
increasing the amount of DMC (entries 4 and 5), and 19.4% yield of
MPC was obtained with a 4:1 molar ratio of DMC to DPU. However,
the yield of MPC dramatically decreased with a further increase in
the amount of DMC, only 8.3% yield of MPC was obtained with a
3
.4. Influence of the amount of methanol
Synthesis of MPC was further investigated by varying the molar
ratio of aniline to methanol. Table 4 reveals that both the conver-
sion of aniline and the yield of MPC were improved with increasing
the amount of methanol (entries 1–4). Yield of 9.4% was obtained
with 150 molar ratio of methanol to aniline. Then no obvious
change in the yield of MPC was observed until the molar ratio
was elevated up to 180 (entries 5–7). Drop in the yield and the
selectivity towards MPC was observed although the conversion
of aniline increased monotonously with a further increase in the
amount of methanol (entry 7), revealing larger excessive amount of
methanol is probably more favorable for the side reaction between
methanol and aniline. The results in Table 4 reveal that the required
amount of methanol to obtain acceptable reaction rate is far more
than that based on the stoichiometry, in which only one molar
ratio of methanol to aniline is essential (as shown in Scheme 1),
indicating methanol might also take the role of solvent besides
reactant.
1
00:1 molar ration of DMC to DPU (entry 6). These results reveal
that a moderate excessive amount of DMC is beneficial to the reac-
tion while larger amount of DMC is not, which may be due to drop
in the concentration of catalyst and DPU in the latter. Table 5 illus-
trates that 4.7% yield of MPC was given even in the absence of
catalyst (entry 7), revealing the reaction between DMC and DPU
proceeds easily.
Relatively higher yield of MPC was obtained by using DPU and
methanol as raw materials whether in the presence of or absence
of catalyst (entries 8 and 9), 91.2% and 87.5% yield of MPC were
achieved, respectively. It is believed that the synthesis of MPC from
DPU and methanol is accompanied by the formation of aniline [27],
which can further react with methanol and thus give by-products
including MA and DMA. Therefore, 0.5% and 9.5% yield of MA was
observed in the presence of and absence of catalyst (entries 8 and
9
), respectively, revealing the presence of catalyst favors the main
As mentioned earlier, few works have been focused on the direct
synthesis of carbamate from aniline due to its inertness, and the
comparison of the results was given in Table 4 (entries 8 and 9).
It can be seen from Table 4 that the yield of MPC obtained in this
work was higher than those reported in the literatures, in which
reaction. It can also be seen from Table 5 that the yield of MPC
changed in a small range from 78.4 to 91.2% with various catalysts
(entries 8–13), indicating catalysts show insignificant effect on the
synthesis of MPC from DPU and methanol. However, larger num-
ber of by-products such as MA and DMA were observed with Lewis
acids as the catalysts (entries 10–13). This could be ascribed to the
1
.8% (0.09 mmol MPC obtained from 5 mmol aniline) [26] and 0.8%
[
42] yield of MPC have been attained.
Table 5
a
Investigation on the possible synthetic pathway for the synthesis of MPC.
Entry
Catalyst
Amount (mmol)
Aniline
Yield (%)
DMC
Methanol
DPU
PI
MPC
MA
–
5.4
22.4
–
–
0.4
–
0.5
9.5
2.8
5.9
8.0
4.9
–
DMA
1
2
3
4
5
6
7
8
9
CeO2
CeO2
CeO2
CeO2
CeO2
CeO2
–
1.5
15
75
–
–
–
–
–
–
–
–
–
–
–
–
–
1.5
1.5
1.5
1.5
6
150
6
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
150
150
150
150
150
150
150
150
150
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
0.2
–
0.1
–
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
–
19.4
8.3
4.7
91.2
87.5
85.3
83.7
81.6
78.4
100
100
–
–
CeO2
–
Trace
–
1
1
1
1
1
1
1
1
1
0
1
2
3
4
5
6
7
8
ZnCl2
AlBr3
ZnI2
AlCl3
CeO2
–
CeO2
CeO2
–
0.1
1.0
0.6
0.4
–
–
–
–
–
–
1.5
1.5
–
–
–
–
–
–
–
–
–
b
b
b
1.5
1.5
Tracec
–
–
–
–
◦
Reaction conditions: catalyst 0.3 mmol, temperature 170 C, time 12 h, 4 MPa N2 was introduced.
a
All the yields were based on the charged reactant with smaller amount.
b
5
MPa CO2 was introduced, BuLi 1 mmol.
c
The amount of PI formed from CO2 and aniline.

9
6
G. Fan et al. / Journal of Molecular Catalysis A: Chemical 404 (2015) 92–97
Fig. 2. Mass spectrum of PI from CO2 and aniline.
and DMA were detected but a small amount of N-butyl aniline was
observed besides MPC. It is believed that N-butyl aniline resulted
from the side reaction between BuLi and aniline, thus lowering the
selectivity towards MPC listed in Tables 1–4. No DMC, DPU and PI,
which have been supposed to be intermediates for the formation
of carbamate from CO , amine and alcohol [3,26,31], were detected
2
by GC–MS analysis. It is not inconsistent with the work reported by
Ion et al. [3], in which possible intermediates such as diurea and
isocyanate were detected.
Although CO2 is a relatively inert molecule, it easily combines
with amines to afford the corresponding carbamic acids [43,44], but
the further transformation of carbamic acids into ureas normally
requires quite drastic conditions. It has indeed been demonstrated
that the base-catalyzed formation of urea from amine is ineffec-
tive [35]. On the contrary, the formation of the corresponding
isocyanate is easily obtained by the thermal dehydration of unsta-
ble carbamic acid [3]. The results in Table 5 revealed that PI could be
Fig. 1. Mass spectra of (a) MPC and (b) N-butyl aniline from CO2, aniline and
methanol.
produced from CO and aniline in the absence of methanol (entry
2
1
7), and the formation of PI from CO and aniline was further con-
2
weak basicity of aniline, which possibly makes the reaction of ani-
line with methanol easier to proceed than that between aniline and
CO2 in the presence of acid, which is accordance with the results
given in Table 1.
Isocyanate, which could be interconverted into diurea, was
believed to be intermediate for the synthesis of carbamates from
CO2 and amine in the presence alcohol [3,31]. Thus the synthesis
of MPC was also performed in the system including phenyl iso-
cyanate (PI) and methanol. The observation of almost 100% yield of
MPC even without the addition of catalyst (entry 15) reveals that
PI can be converted to MPC easily.
firmed by GC–MS analysis (Fig. 2). Moreover, the results in Table 5
clearly reveal that the formation of MPC from PI and methanol is
relatively easy to proceed, in which 100% yield of MPC was obtained
(Table 5, entries 14 and 15). So it is reasonable to speculate that PI
was the intermediate and could be converted into MPC instanta-
neously in the presence of methanol. As a result, PI was detected in
the mixture collected from CO2 and aniline but not in the mixture
from CO2, aniline and methanol.
Scheme 1 shows a plausible pathway for the direct synthesis
of MPC from CO2, aniline and methanol using CeO2 as the catalyst
in the presence of BuLi based on the above-mentioned results and
previous investigations [3,43]. It is proposed that phenylcarbamic
acid 1 forms first via the reaction of CO2 with aniline, then unstable
1 undergoes a thermal dehydration to give the corresponding inter-
mediate PI 2 [3]. Finally, 2 further reacts with methanol to produce
MPC. CeO2 plays the role of catalyst in the formation of carbamic
acid 1 since the reaction of PI with methanol even can proceed well
without the addition of catalyst (Table 5, entry 15) and unstable
1 could be converted into 2 easily [3]. The water produced from
the thermal dehydration of 1 could be expected to react with BuLi,
promoting the reaction to the right and deriving Li2CO3 which may
participate in the catalysis, as shown in Table 1.
It can be concluded from Table 5 that the formation of MPC
possibly undergoes three paths. One is from DMC and DPU, the
other is from methanol and DPU, and the third one is from PI and
methanol. The results in Table 5 also reveal that no DMC and DPU
were detected in the presence of CO /methanol and CO /aniline
2
2
(
entries 16,17), respectively. However, a small amount of PI was
observed via the reaction between CO and aniline in the presence
2
of CeO2 (entry 17). Therefore, it is reasonable to propose the last
one is the most possible favorite way for the synthesis of MPC from
CO . No PI was detected without the addition of CeO indicated that
2
2
catalyst is essential for the reaction of CO and aniline (entry 18).
2
The liquid product catalyzed by CeO2 in the presence of BuLi
was detected by GC–MS analysis to further understand the reac-
4. Conclusions
tion mechanism for the synthesis of MPC from CO , aniline and
2
methanol. The formation of MPC was confirmed by GC–MS analy-
sis, and the mass spectra were presented in Fig. 1. Almost no MA
The direct synthesis of MPC from CO , aniline and methanol cat-
2
alyzed by CeO was investigated. The catalytic activity of CeO was
2
2

G. Fan et al. / Journal of Molecular Catalysis A: Chemical 404 (2015) 92–97
[12] Z.F. Zhang, Y. Xie, W.L. Li, S.Q. Hu, J.L. Song, T. Jiang, B.X. Han, Angew. Chem.
97
significantly enhanced by the addition of BuLi. It is believed that
Int. Ed. 47 (2008) 127–1129.
BuLi was not only a dehydrating agent but also a promoter. The con-
version of aniline, the yield and the selectivity towards MPC were
[
[
13] A. Correa, R. Martin, J. Am. Chem. Soc. 131 (2009) 15974–15975.
14] T. Iijima, T. Yamaguchi, J. Mol. Catal. A: Chem. 295 (2008) 52–56.
evidently dependent on the amount of CeO and BuLi, the pressure
[15] T. Iijima, T. Yamaguchi, Appl. Catal. A: Gen. 345 (2008) 12–17.
2
[
16] H. Kawanami, A. Sasaki, K. Matsui, Y. Ikushima, Chem. Commun (2003)
96–897.
17] F. Barzagli, F. Mani, M. Peruzzini, Green Chem. 13 (2011) 1267–1274.
of CO2 as well as the reaction conditions including reaction time
and temperature. Yield of 9.4% and selectivity of 55.9% towards MPC
were achieved under the optimized conditions. A possible mecha-
8
[
[18] J. Sun, S.I. Fujita, F. Zhao, M. Arai, Appl. Catal. A: Gen. 287 (2005) 221–226.
[19] B.M. Bhanage, S. Fujita, Y. Ikushima, M. Arai, Green Chem. 5 (2003) 340–342.
20] Y.P. Patil, P.J. Tambade, N.S. Nandurkar, B.M. Bhanage, Catal. Commun. 9
2008) 2068–2072.
nism for the synthesis of MPC from CO , aniline and methanol was
2
[
proposed based on the investigation on the synthetic pathway of
MPC with different reactants, in which PI was found to be the most
possible intermediate. Phenylcarbamic acid was supposed to form
(
[21] Y. Kayaki, T. Suzuki, T. Ikariya, Chem. Asian J. 3 (2008) 1865–1870.
[22] M. Tamura, M. Honda, K. Noro, Y. Nakagawa, K. Tomishige, J. Catal. 305 (2013)
191–203.
first via the reaction of aniline and CO , and then convert into the
2
[
[
23] J.C. Anderson, R.B. Moreno, Org. Biomol. Chem. 10 (2012) 1334–1338.
24] F. Shi, Y.Q. Deng, T. SiMa, J.J. Peng, Y.L. Gu, B.T. Qiao, Angew. Chem. Int. Ed. 42
(2003) 3257–3260.
crucial intermediate PI, which could further react with methanol
to produce MPC.
[
[
25] T. Sakakura, J.C. Choi, H. Yasuda, Chem. Rev. 107 (2007) 2365–2387.
26] M. Honda, S. Sonehara, H. Yasuda, O. Nakagawa, K. Tomishige, Green Chem.
Acknowledgments
1
3 (2011) 3406–3413.
27] L.L. Zhang, S.J. Yao, H.L. An, X.Q. Zhao, Y.J. Wang, Nat. Gas Chem. Ind. 38 (2013)
2–46 (in Chinese).
28] P. Munshi, D.J. Heldebrant, E.P. McKoon, P.A. Kelly, C. Tai, P.G. Jessop,
Tetrahedron Lett. 44 (2003) 2725–2727.
[
[
4
This work was supported by the Scientific Research Project from
Hubei Provincial Department of Education (No. D20141704).
[
[
29] Z.H. Fu, O. Yoshio, J. Mol. Catal. A: Chem. 91 (1994) 399–405.
30] W.K. Kang, J. Yao, G.Y. Wang, C.W. Hu, X.P. Jing, J. Mol. Catal. A: Chem. 17
References
(
2003) 136–139.
[
[
31] M. Abla, J.C. Choi, T. Sakakura, Chem. Commun. (2001) 2238–2239.
32] G.Z. Fan, H.T. Zhao, Z.X. Duan, T. Fang, M.H. Wan, L.N. He, Catal. Sci. Technol. 1
[
[
1] P. Adams, F.A. Baron, Chem. Rev. 65 (1965) 567–602.
2] R. Srivastava, M.D. Manju, D. Srinivas, P. Ratnasamy, Catal. Lett. 97 (2004)
(
2011) 1138–1141.
33] G.Z. Fan, Z.G. Wang, B. Zou, M. Wang, Fuel Process. Technol. 92 (2011)
052–1055.
34] Y. Yoshida, Y. Arai, S. Kado, K. Kunimori, K. Tomishige, Catal. Today 115 (2006)
5–101.
4
1–47.
3] A. Ion, C. Van Doorslaer, V. Parvulescu, P. Jacobs, D. De Vos, Green Chem. 10
2008) 111–116.
[
[
[
1
(
[
[
4] D. Chaturvedi, A. Kumar, S. Ray, Tetrahedron Lett. 44 (2003) 7637–7639.
5] H. Arakawa, M.J.N. Aresta, M.A. Armor, E.J. Barteau, A. Beckman, J.E. Bell, C.
Bercaw, X.A. Creutz, O.E. Dinjus, D.A. Dixon, K. Domen, D.L. DuBois, J. Eckert, E.
Fujita, O.D.H. Gibson, W.A. Goddard, D.W. Goodman, J. Keller, G.J. Kubas, H.H.
Kung, J.E. Lyons, L.E. Manzer, T.J. Marks, K. Morokuma, K.M. Nicholas, R.
Periana, L. Que, J. Rostrup-Nielson, W.M.H. Sachtler, L.D. Schmidt, A. Sen, G.A.
Somorjai, P.C. Stair, B.R. Stults, W. Tumas, Chem. Rev. 101 (2001) 953–996.
6] G. Centi, S. Perathoner, Catal. Today 148 (2009) 191–205.
9
[
[
[
[
[
[
[
35] A. Ion, V. Parvulescu, P. Jacobs, D. De Vos, Green Chem. 9 (2007) 158–161.
36] S.J. Yao, X.Q. Zhao, H.L. An, Y.J. Wang, CIESC J. 6 (2012) 812–818 (in Chinese).
37] D.A. Boryta, A.J. Maas, Ind. Eng. Chem. Process Des. Dev. 10 (1971) 489–494.
38] G.Z. Fan, T. Li, G.X. Li, Appl. Organomet. Chem. 20 (2006) 656–662.
39] L.X. Zhou, Mod. Chem. Ind. 27 (2007) 500–503 (in Chinese).
40] M. Chatterjee, Y. Ikushima, F. Zhao, New J. Chem. 27 (2003) 510–513.
41] F.Y. Zhao, R. Zhang, M. Chatterjee, M. Ikushima, M. Arai, Adv. Synth. Catal. 346
[
[
[
[
7] S.N. Riduan, Y. Zhang, Dalton Trans. 39 (2010) 3347–3357.
8] I. Omae, Catal. Today 115 (2006) 33–52.
9] T. Sakakura, K. Kohno, Chem. Commun. (2009) 1312–1330.
(
2004) 661–668.
[
42] X.Q. Zhao, S.J. Yao, H.L. An, Y.J. Wang, CN Patent, 2012/10261742 A, (in
Chinese).
[
[
10] J. Sun, S. Fujita, F. Zhao, M. Hasegawa, M. Arai, J. Catal. 230 (2005) 398–405.
11] Z.F. Zhang, S.Q. Hu, J.L. Song, W.J. Li, G.Y. Yang, B.X. Han, ChemSusChem 2
[
[
43] E.M. Hampe, D.M. Rudkevich, Tetrahedron 59 (2003) 9619–9625.
44] K.J. Butcher, Synlett (1994) 825–826.
(
2009) 234–238.