Efficient synthesis of 2-oxazolidinone from epoxides and carbamates with binary MgFe oxides as a magnetic solid base catalyst

Article abstract of DOI:10.1016/j.catcom.2012.08.006

Magnetic binary MgFe oxides were prepared by co-precipitation method, characterized and tested in the synthesis of 2-oxazolidinones from epoxides and carbamates. The catalytic results showed that the catalyst with Mg/Fe molar ratio of 1 and calcined at 400°C exhibited superior catalytic activity. The catalyst could be magnetically separated, recycled and reused for five runs without noticeable deactivation. Under the optimized conditions, various 2-oxazolidinones derivatives were successfully synthesized with good to excellent isolated yields.

Full text of DOI:10.1016/j.catcom.2012.08.006

Catalysis Communications 28 (2012) 13–17
Contents lists available at SciVerse ScienceDirect
Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short Communication
Efficient synthesis of 2-oxazolidinone from epoxides and carbamates with binary
Mg\Fe oxides as a magnetic solid base catalyst
Jianpeng Shang a,b, Shimin Liu a,b, Liujin Lu a, Xiangyuan Ma a, Yude He a, Youquan Deng a,
⁎
a
Centre for Green Chemistry and Catalysis, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou, 730000, China
b
Graduate School of the Chinese Academy of Sciences, Beijing, 100039, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 2 June 2012
Received in revised form 7 August 2012
Accepted 8 August 2012
Available online 21 August 2012
Magnetic binary Mg\Fe oxides were prepared by co-precipitation method, characterized and tested in the
synthesis of 2-oxazolidinones from epoxides and carbamates. The catalytic results showed that the catalyst
with Mg/Fe molar ratio of 1 and calcined at 400 °C exhibited superior catalytic activity. The catalyst could
be magnetically separated, recycled and reused for five runs without noticeable deactivation. Under the
optimized conditions, various 2-oxazolidinones derivatives were successfully synthesized with good to
excellent isolated yields.
Keywords:
2-oxazolidinone
Epoxide
© 2012 Elsevier B.V. All rights reserved.
Carbamate
Solid base
Magnetic oxides
1. Introduction
route for 2-oxazolidinones synthesis is the reaction between epoxy
compounds and carbamates, and then intramolecular cyclization to
2-oxazolidinones are important compounds in both fine chemicals
and synthetic organic chemistry, which are widely applied in the syn-
thesis of pharmaceuticals, pesticides, cosmetics, and so on [1–3].
Since the 2-oxazolidinones preparation generally uses highly toxic
phosgene [4], and therefore involves environmental and safety prob-
lems, much efforts have been made to explore environmentally
benign methods for 2-oxazolidinones synthesis. Several non-phosgene
routes for 2-oxazolidinones synthesis have been developed: (1) oxidative
carbonylation of β-aminoalcohols with CO/O2, (2) carbonylation of
β-aminoalcohols by dialkyl carbonate, (3) cycloaddition of CO2 with
β-aminoalcohols or aziridines. Although the oxidative carbonylation of
β-aminoalcohols catalyzed by transition metal is an efficient way to
produce 2-oxazolidinones [5–9], such route is not eco-friendly due to
the potential explosion hazards and poisonous CO. As an alternative,
dialkyl carbonates were used for the synthesis of 2-oxazolidinones
[10–13]. It should be noted that dialkyl carbonates are mainly produced
by phosgenation or oxidative carbonylation routes [14,15]. Under these
circumstances, the direct synthesis of 2-oxazolidiones from CO2 and
β-aminoalcohols [16–18] or aziridines [19–22] is preferable from envi-
ronmental and economical viewpoints, however, some stoichiometrically
consumed dehydrating reagents and high pressure or high temperature
are required in most of these works.
give the expected 2-oxazolidinones [24–26], Scheme 1. Till now, several
homogenous base catalysts have been reported, such as tertiary amines,
potassium hydroxide and betaines [24,27,28]. However, the separation
and recovery problems of those catalysts are still maintained and
accordingly limit their practical application. Therefore, the develop-
ment of an effective and stable heterogeneous base catalyst is highly
desirable.
Since magnetic materials have emerged as efficient supports for
catalysts and can facilitate their separation from the reaction media
using an external magnetic field [29,30], herein, we report the prepa-
ration binary Mg\Fe oxides as highly effective and recoverable mag-
netic solid base catalyst for the synthesis of 2-oxazolidinone from
epoxides and carbamates.
2. Experimental
2.1. Catalysts preparation
A mixture of given amount of Mg(NO3)2·6H2O and Fe(SO4)2·7H2O
in designated ratios was dissolved into 100 mL distilled water under
stirring. Subsequently, 40 mmol Na2C2O4 was dissolved into 100 mL
water at 80 °C and then was added dropwise into the former solution.
The resulting precipitate then was aged for 2 h, filtrated, washed, and
calcined in static air for 2 h. The obtained solids were denoted as
xMgFe-T, where x represents the Mg/Fe molar ratio, and T is the calcina-
tion temperature.
Since epoxy compounds are known to produce ring-opened addi-
tion products with nucleophilic reagents [23], another phosgene-free
⁎ Corresponding author. Fax: +86 931 4968116.
E-mail address: ydeng@licp.cas.cn (Y. Deng).
1566-7367/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.catcom.2012.08.006

14
J. Shang et al. / Catalysis Communications 28 (2012) 13–17
Scheme 1. Synthesis of 2-oxazolidinones from alkyl carbamate and epoxide.
composition with different Mg content, which was confirmed with
2.2. Catalysts characterization
the results of XRD as discussed blow.
XRD patterns of MgO, Fe2O3, MgFe2O4 standards and binary
Mg\Fe oxides are shown in Fig. 1. The results showed that the char-
acteristic diffraction peaks of Fe2O3 (JCPDS 24–0072) were observed
for all the samples and confirmed the Fe2O3 formation. For the
0.5MgFe-400, the peaks at 30.1, 35.5, 43.1 and 62.6° were also
existed, which could be well indexed to spinel MgFe2O4 (JCPDS
17–0464). Compared to the 0.5MgFe-400, the diffraction peaks at 43
and 63° were also observed for MgFe-400 and 2MgFe-400, which
could be ascribed to the (200) and (220) planes of MgO (JCPDS
87–0653), and the intensity of such diffraction peaks become signifi-
cantly stronger in samples with higher Mg content. Therefore, the
formation of additional crystalline MgO phase in MgFe-400 and
2MgFe-400 suggested that such materials could be used as solid
base catalyst. Moreover, all the diffraction lines become slightly
stronger and sharper after calcined at higher temperature, suggested
that the higher calcinations temperature promoted the crystallization
of the catalyst. Compared to the MgFe-500, however, the intensities
of diffraction peaks of the MgO and Fe2O3 in MgFe-600 were much
lower than that of MgFe-500, suggesting that the higher calcinations
temperature favored the formation of spinel MgFe2O4 from MgO
and Fe2O3.
The influence of the calcination temperature on the chemical
states of the binary Mg\Fe oxides is shown in Fig. 2. The binding
energy of Mg 2p and Fe 2p3/2 varied slightly around 49.4 0.1 and
710.9 0.2 eV, respectively, suggesting that the chemical states of
Mg and Fe species on the catalyst surface were mainly Mg2+ and
Fe3+ (Fig. 2a and b). As shown in Fig. 2c, two O 1s peaks could
be well resolved with their binding energy at 529.9 and 531.6 eV,
which should be assigned to oxygen of oxide and hydroxyl groups,
respectively [31]. Moreover, the ratio of hydroxyl and oxide groups
was decreased with the calcination temperature elevated from 400
to 600 °C. Since the surface of the MgO is easily hydroxylated duo
to dissociative chemsorption water when it was exposed to the air,
it can be conjectured that the content of the MgO phase in binary
The BET surface areas, pore volumes and average pore diameters of
catalysts were obtained with physisorption of N2 using a Micromeritics
ASAP 2010.
X-ray diffraction (XRD) was measured on a Siemens D/max-RB
powder X-ray diffractometer. Diffraction patterns were recorded
with Cu Kα radiation (40 mA, 40 kV) over a 2θ range of 15 to 85°.
X-ray photoelectron spectroscopy (XPS) analysis was performed
with a VG ESCALAB210 instrument. Mg Kα radiation at an energy
scale calibrated versus adventitious C1s peak at 285.00 eV was used.
The surface acid–base properties of the catalysts were measured
by temperature programmed desorption of CO2 and carried out on
TPD flow system equipped with an MS detector (DM300, AMETEK,
USA). The quantitative analysis for CO2 desorption is calculated
based on the integration of the corresponding TPD traces.
2.3. Catalytic testing
All reactions were carried out in a 90 mL stainless steel autoclave
with a glass tube inside and magnetic stirring. In a typical test,
10 mmol propylene oxide (PO) (0.58 g), 15 mmol ethyl carbamate
(EC) (1.33 g) and 58 mg binary Mg\Fe oxides catalyst were added
in the reactor. The reaction mixture were heated up to 140 °C for
8–12 h. After the reaction was completed, the catalyst was recovered
using an external magnetic field. The qualitative and quantitative
analyses of the liquid mixture were conducted with GC-MS (Agilent
6890/5973) and GC (Agilent 7890) equipped with a FID detector.
3. Results and discussion
3.1. Catalysts characterization
The physical properties of the binary Mg\Fe oxides are summa-
rized in Table 1. The BET surface area and porous volumes decreased
monotonically from 156.1 to 23.1 m2/g and 0.54 to 0.15 cm3/g,
respectively, while the average pores diameter was increased mono-
tonically from 9.4 to 24.4 nm, with the decreasing of the Mg content
and the increasing of calcination temperature from 400 to 600 °C. All
those suggested that both the Mg content and the calcination temper-
atures have a strong impact on the texture of the binary Mg\Fe
oxides. Moreover, the sintering effect, especially when the catalyst
calcined at higher temperature (500 or 600 °C), may resulted in the
decreasing of the BET surface area. As to the variation of the BET sur-
face area with the Mg content, it might be duo to the different bulk
Table 1
Physicochemical properties of the binary Mg\Fe oxides.
Entry
Catalysts
SBET
dp
(nm)
vp
Total
basic sites (μmol/g)
a
b
(m2/g)
(cm3/g)
1
2
3
4
5
2MgFe-400
MgFe-400
0.5MgFe-400
MgFe-500
MgFe-600
156.1
90.4
87.5
61.8
23.1
9.4
13.6
14.3
16.1
24.4
0.54
0.45
0.41
0.32
0.15
249
205
93
113
52
a
Average pore size.
Average pore volume.
Fig. 1. XRD patterns of MgFe2O4 (JCPDS 17–0464), Fe2O3 (JCPDS 24–0072), MgO
(JCPDS 87–0653), 0.5MgFe-400, MgFe-400, 2MgFe-400, MgFe-500 and MgFe-600.
b

J. Shang et al. / Catalysis Communications 28 (2012) 13–17
15
Fig. 3. TPD-CO2 profiles of 2MgFe-400, MgFe-400, 0.5MgFe-400, MgFe-500 and MgFe-600.
Mg\Fe oxides with different calcinations temperature or ratios of
Mg and Fe, entries 2–6. Among the catalysts calcined at different tem-
perature, entries 2–4, the PO conversions were decreased with the
catalysts calciantion temperature elevated from 400 to 600 °C and
the MgFe-400 exhibited superior catalytic activity with 97% PO con-
version. Furthermore, the binary Mg\Fe oxides with different molar
ratios of Mg and Fe calcined at 400 °C were also tested, entries 2
and 5–6. The conversions of PO were greatly improved and increased
with increasing the ratio of Mg and Fe, reaches its maximum 97% at
Mg/Fe molar ratio of 1:1. With further increasing the ratio of Mg
and Fe to 2, the conversion of PO remained almost constant. That is,
the catalyst with Mg/Fe molar ratio of 1:1 and calcined at 400 °C
was the most active catalyst for 2-oxazolidinone synthesis. According
to the quantitative results of TPD-CO2, it could be found that the cat-
alytic activity sequence is correlated to amounts of the basic site
of the catalysts, which indicate that the catalytic activity is mostly
determined by their relative basic strength. Furthermore, the larger
amount of basic sites and the removal of carbonate from MgO surface
at high temperature (>400 °C) could be the major reasons for the
higher catalytic activity for MgFe-400. Moreover, the catalyst was
recycled through simple magnetic separation, and washed with
ethyl acetate and dried at 100 °C to remove the adsorbed organic
Fig. 2. XPS spectra of (a) Mg 2p, (b)Fe 2p and (c) O 1s spectra of MgFe-400, MgFe-500
and MgFe-600.
Mg\Fe oxide was decreased when it was calcined at higher temper-
ature and the higher calcinations temperature was favorable to
convert MgO to MgFe2O4, which is consistent with the results of XRD.
Fig. 3 shows the TPD-CO2 profiles over various binary Mg\Fe
oxides. Generally, broadened CO2 desorption peaks in the tempera-
ture region of 50–350 °C were observed over all the tested samples,
which were derived from the weak and medium strength basic sites.
Other CO2 desorption peaks appeared above 400 °C in 2MgFe-400 and
MgFe-400 samples, which was attributed to strong strength basic sites
by isolated O2- in MgO. From the quantitative results of TPD-CO2
(Table 1), it can be seen that the total basic sites decreased from 249
to 93 μmol/g with decreasing the ratio of Mg and Fe from 2 to 0.5,
respectively, suggesting that the basic site mainly derived from the
MgO phase in the binary Mg\Fe oxides. Moreover, the total basic
sites sharply decreased from 205 to 52 μmol/g with the calcination tem-
perature elevated from 400 to 600 °C, which most probably because of
the relative lower surface area of MgFe-500 and MgFe-600 than that of
MgFe-400.
Table 2
Results of 5-methyl-2-oxazolidinone synthesis from EC and PO over different catalysts a
.
b
Entry
Catalysts
Conv./%
Sel./%
Yield/%
1
2
3
4
5
6
7
8
9
None
10
97
81
52
75
98
93
42
23
98
97
99
99
98
98
99
98
98
98
99
8
95
77
48
73
95
93
40
22
97
MgFe-400
MgFe-500
MgFe-600
0.5MgFe-400
2MgFe-400
Used MgFe-400
MgFe-400
MgFe-400
MgFe-400
c
d
e
f
10
a
3.2. Catalytic testing
Reaction conditions: PO, 10 mmol; EC, 15 mmol; catalysts, 58 mg (10 wt.%);
reaction temperature, 140 °C; reaction time, 8 h. Conversions and selectivities were
determined by gas chromatography.
The reaction of EC and PO for 5-methyl-2-oxazolidinone synthesis
was investigated over various catalysts, Table 2. In the blank test
(entry 1), the PO conversion was only 10%, suggested that catalyst
was essential for such reaction proceeded successfully. The moderate
to good PO conversions of 52-98% were achieved over the binary
b
Isolated yield based on the charged PO.
Catalyst reused for five times.
Reaction conducted at 120 °C.
11.6 mg MgFe-400 (2 wt.%).
c
d
e
f
87 mg MgFe-400 (15 wt.%).

16
J. Shang et al. / Catalysis Communications 28 (2012) 13–17
Table 3
which was formed duo to nucleophilic ring-opening of PO at the
methyl substitute site.
a
Scope and limitation of MgFe-400 for catalytic syntheses various 2-oxazolidinones
.
3.3. Scope of the catalysts
The scope of the MgFe-400 catalyst in 2-oxazolidinones synthesis
with different alkyl carbamates and epoxides was further investigated,
Table 3. Firstly, the corresponding 2-oxazolidinones were successfully
synthesized with different alkyl carbamates and PO over MgFe-400,
entries 1–3, suggested that the substituent on the oxygen atom of
alkyl carbamate has little influence on such reaction. Then, various
epoxides with different functional groups were further investigated.
Excellent yields of the corresponding 2-oxazolidinones were obtained
with terminal epoxides (entries 4–9), while the disubstituted epoxide,
cyclohexene oxide (entry 10), gave lower activity towards the produc-
tion of the corresponding 2-oxazolidinones, which might be due to the
high hindrance of cyclohexene oxide. However, the selectivity of the
5-substituted-2-oxazolidinones for the styrene oxide (entry 9) was
much lower than that of other epoxides, which might be ascribed to
the conjugative effect derived from the benzene ring, which should
favourably attack at the carbon atom at which phenyl substitute was
connected to afford 4-substituted-2-oxazolidinones [32]. In one word,
various 5-substituted-2-oxazolidinones were preferentially formed
with high selectivities over the basic MgFe-400 catalyst.
Entry Substrates
Major
products
Conv. Sel. (%)
(%)
Yield
(%)
b
Carbamate
1
Epoxide
major minor
98
97
97
98
99
97
2
1
3
94
95
94
2
3
4
5
96
97
100
96
-
90
94
4
6
98
99
1
95
7
8
97
97
98
99
2
1
93
94
4. Conclusions
In conclusion, binary Mg\Fe oxides were prepared by co-
precipitation method and MgFe-400 was found to be effective cata-
lyst for the synthesis 2-oxazolidinones from epoxides and carba-
mates. The total basic sites of the catalysts were considered to play
an important role for the superior catalytic activity. The catalyst
could be easily isolated using external magnetic field and recovered
for several runs without significant loss of catalytic activity. In general,
good to excellent yields of 2-oxazolidinones were obtained with various
alkyl carbamates and epoxides.
9
95
85
76
24
-
92
82
10
100
a
Reaction conditions: epoxides, 5 mmol; alkyl carbamates, 7.5 mmol; catalyst,
10 wt.% based on the mass of charged epoxide; reaction temperature, 140 °C; reaction
time, entries 1–5, 8 h; entries 6–10, 12 h. Conversions and selectivities were deter-
mined by gas chromatography.
b
Isolated yield based on the charged epoxides.
Acknowledgment
This work has been financially supported with the National Natural
Science Foundation of China (No: 20773416).
materials. The catalyst recycling test showed that the PO conversion
of 93% was obtained even after five runs (entry 7), suggesting that
the catalyst could be reused without significantly loss in activity
after the fifth runs. Additionally, the leaching of the Mg and Fe after
the reaction was determined with ICP analyses, and the results
showed that the amount of Mg and Fe leached were 0.002 and
0.007% of the originally charged MgFe-400 catalyst, respectively,
suggested that the catalytic activity should mainly be derived from
the solid MgFe catalyst. Subsequently, the influence of the reaction
temperature on the reaction was further investigated, entry 8. A sig-
nificant increase in PO conversion from 42 to 97% was observed
when the reaction temperature increased from 120 to 140 °C, and
reached the maximum at 140 °C, indicating that such reaction was
relatively sensitive to the temperature and the higher temperature
favors the conversion of PO to 5-methyl-2-oxazolidinone. The effects
of the amount of catalyst charged on the reaction was also investigat-
ed, entry 9 and 10. It can be seen that the PO conversion was in-
creased from 23 to 97% when the amount of catalyst was increased
from 2 to 10 wt.%, however, with further increasing the amount of
catalyst to 15 wt.%, the conversion of the PO showed little changes.
Notably, the 5-methyl-2-oxazolidinone was preferentially formed
with high selectivities in all cases listed in Table 2. The major product
corresponds to the nucleophilic ring opening of the PO at the less sub-
stitute site under basic conditions [23], followed by intramolecular
cyclization to produce the corresponding 5-methyl-2-oxazolidinone.
Moreover, the 4-methyl-2-oxazolidinone as byproduct was observed,
Appendix A. Supplementary data
Supplementary data to this article can be found online at http://
dx.doi.org/10.1016/j.catcom.2012.08.006.
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