Synthesis of 2-oxazolidinone catalyzed by palladium on charcoal: A novel and highly effective heterogeneous catalytic system for oxidative cyclocarbonylation of β-aminoalcohols and 2-aminophenol

Article abstract of DOI:10.1016/j.jcat.2004.07.019

Oxidative cyclocarbonylation of β-aminoalcohols and 2-aminophenol to synthesize corresponding 2-oxazolidinones catalyzed by a Pd/C-I₂ heterogeneous catalytic system has been developed which gave excellent selectivity and high turnover frequency (TOF) values 15 times larger than the best results previously reported. The catalyst could be reused for five times almost without losing its catalytic activity and selectivity. The effects of promoters, pretreatment, solvents, and reaction conditions have been investigated.

Full text of DOI:10.1016/j.jcat.2004.07.019

Journal of Catalysis 227 (2004) 542–546
www.elsevier.com/locate/jcat
Research Note
Synthesis of 2-oxazolidinone catalyzed by palladium on charcoal: a novel
and highly effective heterogeneous catalytic system for oxidative
cyclocarbonylation of β-aminoalcohols and 2-aminophenol
Fuwei Li, Chungu Xia ∗
State Key Laboratory for Oxo Synthesis and Selective Oxidation, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences and Graduate School
of the Chinese Academy of Sciences, Lanzhou 73000, People’s Republic of China
Received 9 May 2004; revised 12 July 2004; accepted 18 July 2004
Available online 21 August 2004
Abstract
Oxidative cyclocarbonylation of β-aminoalcohols and 2-aminophenol to synthesize corresponding 2-oxazolidinones catalyzed by a Pd/C–
I heterogeneous catalytic system has been developed which gave excellent selectivity and high turnover frequency (TOF) values 15 times
2
larger than the best results previously reported. The catalyst could be reused for five times almost without losing its catalytic activity and
selectivity. The effects of promoters, pretreatment, solvents, and reaction conditions have been investigated.
2004 Elsevier Inc. All rights reserved.
Keywords: Palladium on charcoal; Oxidative cyclocarbonylation; β-Aminoalcohol; 2-Aminophenol; 2-Oxazolidinone; Reuse of the catalyst; TOF
1. Introduction
The intramolecular oxidative cyclocarbonylation of β-
aminoalcohols or its derivatives catalyzed by transition
metal is an attractive and effective way to produce these
heterocyclic compounds (Scheme 1). To our knowledge,
only few reports have been described using this catalytic
process [6]. Although some advancements have been made,
the corresponding catalytic turnover frequency (moles of ox-
azolidinones produced per mole of Pd atoms per hour, TOF)
is still too low, the reaction conditions are stern, and the re-
action time is too long (15 h). The most restricting aspect
of these studies is that they were focused on the homoge-
neous catalytic systems, wherein the expensive palladium
catalysts are difficult to be separated and reused. Until now,
no heterogeneous catalyst systems have been studied in the
direct oxidative cyclocarbonylation of β-aminoalcohols to
synthesize the corresponding 2-oxazolidinones. In view of
the importance and applications of palladium-catalyzed car-
bonylation reactions from industrial as well as academic
viewpoints, it is urgent to find an efficient, inexpensive, and
recyclable catalyst system for this interesting reaction.
Herein, we report a highly efficient oxidative cyclo-
carbonylation process for synthesis of 2-oxazolidinones
2-Oxazolidinones have found extensive applications as
intermediates for fine chemicals, pharmaceuticals, cos-
metics, pesticides, and so on. Especially, the chiral 2-
oxazolidinones have been used as chiral auxiliaries in a wide
range of asymmetric syntheses [1,2]. 2-Oxazolidinones are
usually prepared by phosgenation of the corresponding 1,2-
aminoalcohols with toxic phosgene or its derivatives [3],
which may cause serious environmental pollution and equip-
ment corrosion. Nowadays, as an alternative, the use of
diethyl carbonate as a phosgene substitute is relatively ex-
pensive for commercial application [4]. It should be noted
that dialkyl carbonates are currently produced via similar
hazardous phosgenation routes [5]. Because of environmen-
tal concerns, there is a great demand for finding some highly
efficient and environmentally benign methods in place of
such toxic and dangerous reagents.
*
Corresponding author. Fax: +86 931 827 7088.
E-mail address: cgxia@ns.lzb.ac.cn (C. Xia).
0021-9517/$ – see front matter
doi:10.1016/j.jcat.2004.07.019
2004 Elsevier Inc. All rights reserved.

F. Li, C. Xia / Journal of Catalysis 227 (2004) 542–546
543
Table 1
Oxidative cyclocarbonylation of ethanolamine (1a) to 2-oxazolindinone
a
(2a): effect of iodide promoters
Pd/C
promoters
Scheme 1.
+ CO/O
→
2
(1a)
(2a)
from various aliphatic β-aminoalcohols and 2-aminophenol
catalyzed by the Pd/C–I2 catalytic system with excellent
turnover frequency under mild conditions. The catalyst
could be easily separated from the reactant and significant
loss of catalytic activity and selectivity was not found even
after recycling five times.
−1
)
Entry
Promoter
Conversion (%)
Selectivity (%)
TOF (h
b
1
–
I
43
–
100
100
99
98
98
76
57
–
245
–
c
2
2
3
4
5
6
7
8
I
2
99
99
99
99
98
96
990
990
980
970
960
730
NaI
CuI
C H I
4
9
LiI
KI
2. Experimental
a
Reaction conditions: Pd/C 0.01 mmol; ethanolamine 10 mmol; pro-
◦
The catalyst, consisting of 10% Pd/C, was purchased
from Fluka; aminoalcohols and solvents were freshly dis-
tilled and used. Carbon monoxide and oxygen with a pu-
rity of 99.99% were commercially available. Other reagents
were of analytical grade and were used as received.
moter 0.036 mmol; temperature 100 C, solvent (DME) 8 ml; P
1.0 MPa; P 0.25 MPa; time 1 h.
CO
O
2
b
Only Pd/C was used.
Only I was used.
c
2
All oxidative cyclocarbonylation experiments were car-
ried out in a 100-ml autoclave equipped with magnetic stir-
ring and automatic temperature control. In a typical ex-
periment, known quantities of β-aminoalcohols (10 mmol),
catalyst: 10% Pd/C (0.01 mmol), I2 (0.036 mmol), and sol-
vent (DME, 8 ml) were charged into the reactor. Then the
autoclave was pressurized with carbon monoxide and oxy-
gen to a total pressure of 1.25 MPa (CO 1.0 MPa and O2
0.25 MPa). The autoclave was placed in oil bath preheated at
100 ◦C, and the whole reaction mixture was stirred for only
1 h. After the reaction, the autoclave was cooled, excess gas
was purged, and the reaction mixture was filtered. The cat-
alyst could be directly reused for the next run without any
treatment and the promoters should be freshly added before
the new carbonylation. Qualitative analyses were conducted
with a HP 6890/5973GC-MS and quantitative analyses were
carried out over a HP 5890 GC.
is observed. Another experiment using only I2 in the absence
of Pd/C catalyst gave no conversion of 1a (Table 1, entry 2).
These results suggested that neither Pd/C nor I2 could act
as an efficient catalyst for oxidative cyclocarbonylation of
ethanolamine. It was shown that promoters containing iodide
were absolutely necessary in this oxidative cyclocarbony-
lation catalyst system. Therefore, the effects of a variety
of iodide-containing promoters, particularly I2, NaI, C4H9I,
CuI, LiI, and KI were studied. The data in Table 1 showed
that all the employed iodide compounds besides KI were
very efficient promoters. Furthermore, the selectivities of 2a
were all excellent (> 96%).
Catalyst pretreatment can play an important role in the
activity and selectivity of catalytic reactions and it is neces-
sary to learn the intrinsic activity of catalyst from the pre-
treatment information. Therefore, some experiments were
conducted to investigate the effect of pretreatment of Pd/C
catalyst with CO, O2, and aminoalcohol. In these experi-
ments, the catalyst system with solvent was pretreated with
CO, O2, or aminoalcohol individually and then the oxida-
tive cyclocarbonylation was carried out. The results are pre-
sented in Table 2 along with the conditions of pretreatment.
It was seen that treatment of Pd/C with all the reactants had
almost no effect on the catalytic activity and selectivity. If
there were some effects obtained in the pretreatment cata-
lyst system, the more or less similar results would probably
appear in the fresh catalyst system. It was because that they
reacted under the same reaction conditions and it was un-
sure which reactant would first act on the catalyst. Though
a detailed mechanism for pretreatment effects has not been
studied here, the reported data showed that there was no need
to conduct catalyst pretreatment with reactants; therefore, all
further experiments were carried out without any pretreat-
ment.
3. Results and discussion
Iodine compounds (e.g., iodine, sodium iodide) have been
employed in recent years as promoters for a number of
reactions. It should be noted that a heterogeneous iodide-
promoted oxidative carbonylation of amines to carbamate
esters or diphenylureas has been described by Fukuoka and
co-workers and Chaudhari and co-workers [7]. During the
investigation of our catalyst system, the effects of promoters
were examined under the typical reaction conditions (Ta-
ble 1). Initially, the comparison experiments of oxidative car-
bonylation of ethanolamine (1a) were carried out using Pd/C
as catalyst with and without promoter, I2 (Table 1, entries 1
and 3). It was observed that in the absence of I2, only 43%
conversion and 57% selectivity of 2-oxazolidinone were ob-
tained, while with I2, quantitive conversion of ethanolamine

544
F. Li, C. Xia / Journal of Catalysis 227 (2004) 542–546
Table 2
a
Effect of CO, O , and ethanolamine pretreatment on activity of a 10% Pd/C–I catalyst system
2
2
Pretreatment
Pretreatment conditions
Duration (min)
Conversion
(%)
Selectivity
(%)
◦
Temperature ( C)
Pretreatment (MPa)
Fresh catalyst
CO
Pretreatment O
–
–
–
2
2
2
100
100
98
99
99
98
98
60
60
60
100
100
100
2
Pretreatment ethanolamine (under N )
2
99
a
◦
Pretreated catalyst reaction conditions: Pd/C 0.01 mmol; ethanolamine 10 mmol; promoter 0.036 mmol; temperature 100 C; P 1.0 MPa; P 0.25 MPa;
CO
O
2
DME 8 ml; time 1 h.
Table 3
Table 4
Oxidative cyclocarbonylation of ethanolamine (1a) to 2-oxazolindinone
(2a): effects of different solvents on the reaction
Oxidative cyclocarbonylation of ethanolamine (1a) to 2-oxazolindinone
(2a): effects of various reaction conditions
a
−1
Entry
Temperature
( C)
P
Conversion
(%)
Selectivity
(%)
TOF
Entry
Solvent
Conversion (%)
Selectivity (%)
TOF (h
)
CO/O
2
◦
(MPa)
1
2
3
4
5
6
DME
DMF
DMSO
100
100
100
58
52
40
99
100
98
96
96
990
1000
980
557
499
1
2
3
100
80
60
100
100
120
100
100
120
1.0/0.25
1.0/0.25
1.0/0.25
1.0/0.25
2.0/0.5
2.0/0.5
2.0/0.5
2.0/0.5
2.0/0.5
100
54
43
100
52
72
58
81
98
99
98
96
99
99
100
100
100
98
990
530
413
CH OH
3
b
C H OH
4
990
2
5
c
THF
100
400
5
1030
1440
1160
1620
1921
c
6
7
Reaction conditions: Pd/C 0.01 mmol; ethanolamine 10 mmol; promoter
d
◦
0.036 mmol; temperature 100 C; P
8 ml; time 1 h.
1.0 MPa; P 0.25 MPa; solvent
O
2
CO
e
8
e
9
a
Reaction conditions: Pd/C 0.01 mmol; ethanolamine 10 mmol; I
2
Reaction solvents play a key role in the activity and selec-
tivity of catalysts during the catalytic reactions. The effects
of different solvents on the reaction were also investigated
at 100 ◦C, 1.25 MPa with Pd/C–I2 as the catalytic system.
The results are presented in Table 3. High catalytic activities
were obtained when DME acted as the reaction media. How-
ever, when other polar solvents (methanol, ethanol) were
used in the reaction, the catalyst showed comparatively poor
catalytic activity. This phenomenon was the same as that re-
ported by Gabriele and co-workers, which explained it as
follows: the polarity of is higher in CH3OH than in DME
and it is well established that the basicity of amines is sig-
nificantly reduced in low-polar aprotic solvents with respect
to polar protic solvents [6c,6d,8]. That is, the high polarity
is disadvantageous to the oxidative carbonylation. However,
when the more polar DMF and DMSO act as the solvents,
as high as 1000 TOF was obtained with absolute conversion
of substrate. Therefore, the protic/aprotic nature of the sol-
vent alone is not enough to explain the observed change in
activity of the catalyst.
A significant drawback associated with using CO/O2 as
the reagent in organic synthesis is the potential dangers oper-
ating at high reaction temperatures and pressures. Thus, we
were gratified to discover that our catalyst system could op-
erate at low reaction pressures and temperatures. The quan-
titative transformation of reactant could also be obtained un-
der considerable mild reaction conditions (Table 4, entry 1).
Decreasing the temperature below the optimal level (100 ◦C)
resulted in a dramatic decrease in catalytic activity (Table 4,
entries 2 and 3), which indicated that the catalyst system was
sensitive to the reaction temperature. Besides, the mol ratio
of I2 the Pd/C catalyst was also examined. In comparison
0.036 mmol; solvent (DME) 8 ml; time 1 h.
b
Only 0.018 mmol I was added.
2
c
d
e
The mol ratio of 1a/catalyst = 2000.
The mol ratio of 1a/catalyst = 2000, I , 0.05 mmol.
2
The mol ratio of 1a/catalyst = 2000, I , 0.036 mmol, the reaction sol-
2
vent is DMF.
with the results of Gabriele and co-workers, which need a
large excess of promoter (10 or more mole KI per mole of
PdI2) to obtain the optimal catalyst efficiency, the reaction
could be effectively performed using only 1.8 eq of I2 with
respect to Pd/C catalyst under the same conditions (Table 4,
entry 4) [6d]. When the quantity of ethanolamine was in-
creased to 20 mmol, i.e., the mole ratio of substrate/catalyst
is 2000, only 52% yield of 2-oxazolidinone was obtained un-
der the same reaction conditions (Table 4, entry 5). Neither
increasing the quantity of promoter nor improving the reac-
tion temperature could enhance the yield of product greatly.
However, if the solvent was replaced with DMF, the yield
of 2-oxazolidinone was accordingly increased to 81%, and
almost quantitative transformation of 1a was achieved with
the reaction temperature increasing to 120 ◦C (Table 4, en-
try 9). It is important to note that the reaction TOF value
obtained in our catalytic system is 15 times larger than the
highest result previously reported (TOF = 128 h−1).
In addition to the high activity and selectivity, the Pd/C–I2
catalytic system also showed good stability. After the com-
pletion of the oxidative cyclocarbonylation of ethanolamine,
the catalyst was recovered and recycled for the next reac-
tion with the fresh promoter added under the same reaction
condition; any significant loss of catalytic activity and selec-
tivity were not found even after being reused for five times.

F. Li, C. Xia / Journal of Catalysis 227 (2004) 542–546
545
Table 5
Table 6
Oxidative cyclocarbonylation of different β-aminoalcohols (1b–1f) to syn-
Oxidative carbonylation of 2-aminophenol (1g) to produce 2-benzoxazoli-
none (2g)
a
thesize corresponding 2-oxazolidinone (2b–2f) using the Pd/C–I catalytic
2
a
system
Pd/C
promoters
Sub.
R
R
Conversion
(%)
Selectivity
(%)
TOF
(h
1
2
+ CO/O
→
2
−1
)
(1g)
(2g)
1b
1c
1d
H
CH
CH CH
(CH ) CH
CH
H
H
H
H
100
99
99
98
96
100
99
98
98
98
1000
980
970
960
941
3
Sub.
Solvent
Promoter
Conversion (%)
Selectivity (%)
TOF
3
1g
1g
1g
DME
DMF
DMF
NaI
NaI
60
64
100
96
97
100
576
621
1000
3
2
b
1e
3 2
c
1f
(CH ) CH
I
2
3 2
a
a
Reaction conditions: the mol ratio of substrates/catalyst = 1000; pro-
Reaction conditions: the mol ratio of 1g/Pd/C = 1000; promoter
◦
◦
moter (I ) 0.036 mmol; temperature 100 C; P
(DME) 8 ml; time 1 h.
b
= 1.0/0.25; solvent
0.036 mmol; temperature 100 C; P
1 h.
= 1.0/0.25; solvent 10 ml; time
2
CO/O
CO/O
2
2
Racemic.
L enantiomer.
c
It was found that the high efficiency of the Pd/C–iodine
promoter catalytic system was applicable to the oxida-
tive carbonylation of other β-aminoalcohols (1b–1f) un-
der the optimal reaction conditions (the molar ratio of
substrates/catalyst = 1000, temperature 100 ◦C, PCO/O
=
2
1.0/0.25, time 1 h). The results are summarized in Ta-
ble 5. As can be seen, the Pd/C–I2 catalyst system showed
excellent catalytic activity to almost all the employed β-
aminoalcohols under the optimal reaction conditions, pro-
viding the corresponding 2-oxazolidinones in high TOF and
selectivity (> 98%).
The high efficiency of accomplishing the reaction under
considerably mild oxidizing conditions has also permitted
the application of this methodology to substrates particularly
sensitive to oxidizing agents. When 2-aminophenol (1g) was
used as the reaction substrate, 60% yield and 96% selectivity
of 2-benzoxazolinone (2g) were obtained using Pd/C–NaI as
the catalyst system and DME as the solvent in 1 h (Table 6).
Based on the results of the effect of solvents, initially, we
considered that the catalytic activity could be enhanced if
the polarity of the reaction solvent were enhanced. Then the
yield of 2g was slightly increased to 64% with DMF as sol-
vent. However, quantitative conversion of 1g was attained
using I2 as the promoter under the same reaction conditions,
which indicated that I2 was the most efficient promoter in
the oxidative cyclocarbonylation of 2-aminophenol (1g) to
2-benzoxazolinone (2g).
Untill now, the mechanism of oxidative carbonylation
of amine was not well understood. However, all possible
mechanisms proposed the assumption that a Pd–carbamoyl
complex (Pd–CONHR) was formed as an intermediate
species [6b,6c,8]. As can be seen from the results initially
obtained, neither Pd/C nor I2 alone could act as an effi-
cient catalyst for the oxidative cyclocarbonylation of β-
aminoalcohols and Pd/C catalyst combined with I2 was
an active catalytic system for this reaction. Based on the
previous reports, a modified mechanism was proposed in
Fig. 1. Active Pd–I species reacted with the NH2 of the
β-aminoalcohols and CO to produce the cabamoyl-type
complexes (I), which further reacted with the OH of the β-
Fig. 1. Proposed mechanism for oxidative cyclocarbonylation of β-
aminoalcohols to 2-oxazolidinones.
aminoalcohols and then produced stoichiometric quantities
of 2-oxazolidinones. However, unlike the studies of Gabriele
and co-workers, which need a large excess of iodide an-
ions to ensure the reoxidation of the deactivated palladium
catalyst, i.e., there are probably more catalytic steps in his
catalytic cycle, then the catalytic activity was decreased ac-
cordingly. On the contrary, there was no reoxidation process
in our catalytic cycle and only 1.8 eq of I2 with respect to
Pd/C catalyst could achieve a high catalytic turnover fre-
quency. Furthermore, promoter, KI, employed in Gabriele
and co-workers’ research was the poorest promoter in our
catalyst system. In addition, activated charcoal of a Pd/C
catalyst would likely stabilize the active sites and favor the
high catalytic activity.
4. Conclusion
In summary, we have found that Pd/C–I2-catalyzed
oxidative cyclocarbonylation of β-aminoalcohols and 2-
aminophenol producing the corresponding 2-oxazolidinones
could be performed with high yields and excellent catalytic
efficiencies under considerably mild condition. The cata-

546
F. Li, C. Xia / Journal of Catalysis 227 (2004) 542–546
lyst could be reused five times without significant loss in
catalytic activity and selectivity. The catalyst system not
only solves the basic problems of catalyst separation and
recovery but also avoids the use of phosphine ligands in
comparison with homogeneous Pd catalyst systems. This
atom-economical methodology represents a valuable and en-
vironmentally benign nonphosgene alternative to the use of
toxic phosgene or expensive diethyl carbonate. These char-
acteristics make Pd/C–I2 an ideal catalyst system for the
synthesis of these very important heterocyclic compounds.
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