Synthesis of 1,3-dialkylurea from ethylene carbonate and amine using calcium oxide

Article abstract of DOI:10.1016/j.molcata.2004.12.014

Several basic metal oxide catalysts were tested for the synthesis of 1,3-disubstituted urea from ethylene carbonate (EC) and amine. Among the catalysts used, CaO has been found to be an excellent recyclable catalyst for the reaction. It has been suggested that strongly basic property of CaO results in its high activity. Disubstituted ureas are obtained from propylamine and butylamine with high yields at 100°C. Slightly higher reaction temperatures are necessary for obtaining good yields from amines having larger molecular weights and urea is not produced from dibutylamine as a secondary amine. Propylene carbonate can be used instead of EC for the reaction. A reaction mechanism was proposed, which involves reaction between EC and amine giving a carbamate followed by catalytic reaction between the carbamate and amine, yielding 1,3-disubstituted urea. It is suggested that the latter reaction is the rate-determining step. On the basis of this reaction mechanism, the synthesis of unsymmetric urea was also examined. 2-Hydroxyethyl butylcarbamate is selectively produced from EC with butylamine in the absence of the catalyst at a low temperature and reacts with benzylamine producing 1-butyl-3-benzylurea along with symmetric dialkyl ureas.

Full text of DOI:10.1016/j.molcata.2004.12.014

Journal of Molecular Catalysis A: Chemical 230 (2005) 43–48
Synthesis of 1,3-dialkylurea from ethylene carbonate and amine
using calcium oxide
Shin-ichiro Fujita∗, Bhalchandra M. Bhanage, Hiroshi Kanamaru, Masahiko Arai
Division of Materials Science and Engineering, Graduate School of Engineering, Hokkaido University, Sapporo 060-8628, Japan
Received 25 October 2004; received in revised form 14 December 2004; accepted 14 December 2004
Available online 12 January 2005
Abstract
Several basic metal oxide catalysts were tested for the synthesis of 1,3-disubstituted urea from ethylene carbonate (EC) and amine. Among
the catalysts used, CaO has been found to be an excellent recyclable catalyst for the reaction. It has been suggested that strongly basic property
of CaO results in its high activity. Disubstituted ureas are obtained from propylamine and butylamine with high yields at 100 ◦C. Slightly
higher reaction temperatures are necessary for obtaining good yields from amines having larger molecular weights and urea is not produced
from dibutylamine as a secondary amine. Propylene carbonate can be used instead of EC for the reaction. A reaction mechanism was proposed,
which involves reaction between EC and amine giving a carbamate followed by catalytic reaction between the carbamate and amine, yielding
1,3-disubstituted urea. It is suggested that the latter reaction is the rate-determining step. On the basis of this reaction mechanism, the synthesis
of unsymmetric urea was also examined. 2-Hydroxyethyl butylcarbamate is selectively produced from EC with butylamine in the absence of
the catalyst at a low temperature and reacts with benzylamine producing 1-butyl-3-benzylurea along with symmetric dialkyl ureas.
© 2004 Elsevier B.V. All rights reserved.
Keywords: Solid base catalyst; Calcium oxide; Cyclic carbonate; Dialkyl urea; Carbamate
1. Introduction
via phosgenation [7], reductive carbonylation [8–13] or ox-
idative carbonylation [14–20]; however, these reactions are
not eco-friendly due to risks associated with the use of the
poisonous compounds of phosgene and carbon monoxide
and/or a potentially explosive mixture of carbon monoxide
and oxygen. The reactions of amine with bis(4-nitrophenyl)
carbonate [21], diethyl carbonate [22,23] and dimethyl car-
bonate [23–27] produce corresponding 1-substituted car-
bamates. These compounds can further react with amines
producing corresponding 1,3-disubstituted ureas [21,28,29].
However, these carbonates are produced via similar haz-
ardous routes of phosgenation or oxidative carbonylation
[21,30–32]. Reactions of carbon dioxide with amines also
produce disubstituted ureas [33–38]. These reactions are at-
tractive, but expensive dehydrating reagents such as carbodi-
imides and organophosphites are indispensable for getting
high yields [33–36]. A few catalyst systems that do not re-
quire any dehydrating reagents have been reported [37,38];
however, the reaction rates are not so fast.
In conventional base-catalyzed organic syntheses, homo-
geneous catalysts such as alkali alkoxide and organic amine
are used. However, they have drawbacks in catalyst–product
separation, regeneration, etc. Solid base catalysts are inex-
pensive and are more easily separable and recyclable than
the homogeneous catalysts [1–5]. Hence, the use of solid
base catalysts is desirable from the viewpoints of economy
and green chemistry and is gaining much attention. However,
little effort has been given to the study of solid base catalysts
in contrast to extensive study of solid acid catalysts [1–5].
1,3-Disubstituted ureas have found extensive applications
such as dyes, antioxidants, corrosion inhibitor, and interme-
diates for the preparation of pharmaceuticals and agricul-
tural chemicals [6]. They can be synthesized from amines
∗
Corresponding author. Tel.: +81 11 706 6596; fax: +81 11 706 7556.
E-mail address: sfuji@proc-ms.eng.hokudai.ac.jp (S.-i. Fujita).
1381-1169/$ – see front matter © 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2004.12.014

44
S.-i. Fujita et al. / Journal of Molecular Catalysis A: Chemical 230 (2005) 43–48
in acetone and its composition was determined by gas chro-
matography. In catalyst recycling runs, the product was dis-
solved in DMF. Then, the catalyst was separated by filtration,
washed with acetone, dried under vacuum, and used for the
next run.
Scheme 1. Synthesis of 1,3-disubstituted urea from ethylene carbonate and
amine.
Synthesis of unsymmetric urea was also investigated. Af-
ter 40 mmol of EC and 40 mmol of butylamine (amine 1) were
charged in the rector, the reactor was heated to 70 ◦C and kept
for 2 h. After the reaction, the reactor was cooled to room
temperature, to the reaction mixture were added 40 mmol of
benzylamine (amine 2) and 0.5 g of CaO, and then the mix-
ture was heated to 125 ◦C and kept for 3 h. After the reaction,
the resulting reaction mixture was treated as described above
using acetone as a solvent. In a reverse manner, experiments
using benzylamine as amine 1 and butylamine as amine 2
were also conducted.
Basic properties of the catalysts were measured by tem-
perature programmed desorption (TPD) of adsorbed CO2 us-
ing a conventional flow reactor. After a stream of 20 vol.%
CO2–He mixture was passed over 0.25 g of the catalyst
at room temperature for 20 min, gases in the reactor were
flushed with a helium stream. Then, the temperature was
ramped at a heating rate of 10 K/min to 800 ◦C. The efflu-
ent from the reactor was analyzed by gas chromatography or
mass spectrometry.
Another way to synthesize 1,3-disubstituted urea is the re-
action of amine and ethylene carbonate (EC) in the presence
of base catalysts (Scheme 1). This reaction could be an EC
based carbon dioxide fixation to important chemicals, since
EC is synthesized in a large amount via the reaction of ethy-
lene oxide and carbon dioxide. In a recent preliminary paper,
we have first reported that calcium oxide is a good solid cat-
alyst for the syntheses of disubstituted ureas from EC and
primary amines [39]. Good yields are obtained with CaO un-
der mild conditions and these values are comparable to those
obtained with homogeneous base catalysts such as sodium
methoxide and trialkyl amines [40]. In the present paper, a
detailed study is reported.
2. Experimental
Catalysts of CaO, ZnO, ZrO2 and MgO were used. CaO,
ZnO and ZrO2 were prepared by decomposition of calcium
hydroxide at 550 ◦C for 4 h, hydroxy zinc carbonate at 350 ◦C
for 4 h and zirconium oxynitrate at 500 ◦C for 3 h, respec-
tively. MgO was a commercially available reagent and used
without any pretreatments. BET surface areas of CaO, ZnO,
ZrO2 and MgO thus obtained were 13, 49, 49 and 14 m2/g,
respectively. As a control, a homogeneous base catalyst of
sodium methoxide was also used for the reaction. The cal-
cined catalyst samples were kept in a desiccator using glass
bottles filled with argon gas.
The reaction was performed in a 50 mL stainless steel au-
toclave equipped with a mechanical agitator. After 40 mmol
of ethylene carbonate, 80 mmol of amine (propylamine, buty-
lamine, hexylamine, cyclohexylamine, benzylamine, aniline)
and 0.5 g of the catalyst were charged into the reactor, the re-
actor was heated to the desired reaction temperatures and
kept for 1 or 3 h. After the reaction, the reactor was cooled
to room temperature and the reaction mixture was dispersed
in 50 mL of a solvent, which was water for the experiments
with propylamine and butylamine, ethanol for that with cy-
clohexylamine and acetone for those with the other amines.
Then, the resulting mixture wasstirred for1 hat room temper-
ature. The solid formed was filtered off and washed with the
solvent. The product yield was determined from the weight
of the solid by subtracting the catalyst weight. The product
was characterized by gas chromatography, mass spectrome-
try, melting point measurements, and 1H NMR; comparison
with authentic samples was made whenever possible. In sev-
eral runs using butylamine, the reaction was carried out for
several periods of time, the reaction mixture was dissolved
3. Results and discussion
Several metal oxide catalysts were used for the 1,3-
dibutylurea synthesis from ethylene carbonate (EC) and buty-
lamine. Table 1 lists the reaction results obtained with those
catalysts along with that with sodium methoxide. It is seen
that among the catalysts used only CaO is a good catalyst.
1,3-Dibutylurea is obtained in a yield of 49% after the re-
action for 1 h with CaO (entry 1). When the reaction time is
lengthened from 1 to 3 h, the yield increases from 49% to 78%
(entry 2). In contrast to the reaction with CaO, ZnO gives a
very poor yield (entry 3) and MgO and ZrO2 do not produce
the disubstituted urea (entries 4 and 5). Analysis of the aque-
ous phase used for the post-reaction procedures (see Section
Table 1
1,3-Dibutylurea synthesis using various catalystsa
b
Entry
Catalyst
Yield (%)
TOF (h−1
)
1
2
3
4
5
6
a
CaO
49
78
6
0
0
2.2 (109)c
1.2 (58)c
0.4
0
0
CaOd
ZnO
MgO
ZrO2
CH3ONa
79
3.4
Catalyst, 0.5 g; EC, 40 mmol; butylamine, 80 mmol; temperature,
100 ◦C; time, 1 h.
b
Moles of dibutylurea formed per mole of the catalyst per hour.
Calculated using the numbers of surface active sites estimated from TPD
c
of CO2.
d
The reaction was carried out for 3 h.

S.-i. Fujita et al. / Journal of Molecular Catalysis A: Chemical 230 (2005) 43–48
45
Fig. 1. TPD spectra of adsorbed CO2 over (a) CaO; (b) MgO; (c) ZrO2 and
(d) ZnO.
2) showed that, with all of the catalysts listed in Table 1,
all EC disappeared and 2-hydroxyethyl butylcarbamate were
produced. The formation of the carbamate compound will
be discussed later. The turnover frequency (TOF) based on
total mole of CaO is 2.2 h−1 for the experiment of entry 1.
On the other hand, a homogeneous base catalyst of sodium
methoxide gives a TOF of 3.4 h−1 under the same conditions
(entry 6). Thus, the apparent (low estimated) TOF for CaO
is comparable with TOF for an effective homogeneous cat-
alyst, sodium methoxide. The number of surface active sites
of CaO is estimated to be 0.38 mmol/g from temperature pro-
grammed desorption (TPD) of adsorbed CO2 as described be-
low. TOF based on this amount of the surface active sites are
108 and 58 h−1 for entries 1 and 2, respectively. These (true)
TOF values are much higher than that of sodium methoxide.
To elucidate the difference between the catalysts, basic
properties ofthe catalystswere examined by TPD of adsorbed
CO2. The spectra are illustrated in Fig. 1. For CaO, CO2 des-
orption peaks are observed at 585 and 650 ◦C. For ZnO and
MgO, peaks appeared below 500 ◦C. ZrO2 has a trace amount
of CO2 desorption at 580 ◦C. These results suggest that CaO
has a larger amount of strongly basic sites compared with the
other catalysts, resulting in its higher activity observed.
CaO catalysts were prepared from Ca(OH)2 by calcina-
tion at various temperatures and used for the dibutylurea
synthesis. Fig. 2 illustrates the XRD patterns of these cat-
alysts prepared. A part of Ca(OH)2 remains un-decomposed
after the calcination at 450 ◦C. Above 550 ◦C, Ca(OH)2 de-
composes to CaO completely. Table 2 shows the yields of
dibutylurea along with BET surface areas of the CaO cata-
lysts. Although the difference in the yield is not so distinct,
CaO calcined at 550 ◦C gives the highest dibutylurea yield.
The lowest yield with CaO calcined at 450 ◦C could be owing
to its low surface area and/or the incomplete decomposition
of the Ca(OH)2 precursor phase due to the low calcination
Fig. 2. XRD patterns of CaO obtained from Ca(OH)2 by the calcination at
(a) 450 ◦C; (b) 550 ◦C and (c) 650 ◦C for 4 h. (᭹) Ca(OH)2; (ꢀ) CaO; (ꢀ)
CaCO3.
temperature. Uncalcined Ca(OH)2 was found to have no ac-
tivity for the reaction. However, if the decomposition of the
precursor proceeds according to a contracting sphere model,
Ca(OH)2 phase exists only inside of CaO bulk and, hence,
surface of the sample calcined at 450 ◦C is covered with CaO
phase. Thus, it is highly probable that the lowest yield with
this catalyst would result from the lowest BET surface area.
Although Fig. 2 shows the presence of a small amount of
CaCO3, pure CaCO3 has been found to have no activity for
the reaction. Hence, CaCO3 existing in the samples has no
contribution to the activity. On the basis of these results, fur-
ther experiments were conducted with the CaO sample ob-
tained by the calcination at 550 ◦C.
Table 3 shows the influence of the reaction temperature
on the synthesis of dibutylurea. When the reaction tempera-
ture is increased from 100 to 125 ◦C, the yield of dibutylurea
increases from 49% to 86%. However, further raising the re-
action temperature does not cause increase in the yield.
Table 4 represents the results for the reactions of EC with
various amines. It is seen that CaO is also effective for the
synthesis of various disubstituted ureas. Propylamine and
Table 2
Influence of calcination temperature on BET surface area of CaO and its
activity for the 1,3-dibutylurea synthesis
Temperature (◦C)
BET area (m2/g)
Yield (%)
450
550
650
6
13
11
53
78
70
Reaction conditions: CaO, 0.5 g; EC, 40 mmol; butylamine, 80 mmol; tem-
perature, 100 ◦C; time, 3 h.

46
S.-i. Fujita et al. / Journal of Molecular Catalysis A: Chemical 230 (2005) 43–48
Table 3
Table 6
Influence of reaction temperature on the 1,3-dibutylurea synthesis
Recycling of CaO for disubstituted urea synthesisa
Temperature (◦C)
Yield (%)
Entry
Recyling
Amine (reaction temperature)
Butylamine (100 ◦C)
Yield (%)
100
125
150
49
86
83
1
2
3
4
5
6
7
8
9
a
0
1
2b
0
1
0
1
2
3
49
0
50
77
73
55
56
55
54
Hexylamine (125 ◦C)
Benzylamine (150 ◦C)
Reaction conditions: CaO, 0.5 g; EC, 40 mmol; butylamine, 80 mmol; time,
1 h.
Table 4
Synthesis of 1,3-disubstituted ureas from EC with various amines
Entry
Amine
Temperature (◦C)
Yield (%)
CaO, 0.5 g; EC, 40 mmol; amine, 80 mmol; time, 1 h for butylamine and
3 h for the other amines.
1
2
3
4
5
6
7
8
9
Propylamine
Butylamine
100
100
125
125
150
125
150
125
125
68
78
77
35
59
38
55
0a
b
The catalyst was calcined at 550 ◦C for 1 h before the second recycling
Hexylamine
Cyclohexylamine
Cyclohexylamine
Benzylamine
Benzylamine
Dibutylamine
Aniline
run.
re-calcination in air at 550 ◦C for 1 h (entry 3). Fig. 3 illus-
trates XRD patterns of CaO obtained before and after the first
run (recycle 0) and after the re-calcination. It is seen that CaO
is hydrated to Ca(OH)2 after the reaction and Ca(OH)2 pro-
duced is transformed to CaO again by the re-calcination. In
the course of the post-reaction procedures, the reaction mix-
ture containing the catalyst is treated in water (see Section
2). Furthermore, CaO is recyclable without re-calcination for
the syntheses of dihexylurea and dibenzylurea, for which ace-
tone is used instead of water in the course of the post-reaction
procedures (entries 4–9). Hence, it is concluded that the wa-
ter treatment during the post-reaction procedures causes the
catalyst deactivation. However, it is clear that the catalyst de-
activated with water can be regenerated by the calcination. It
is noted that the procedures for the recycle runs were carried
out under ambient atmosphere. Exposing solid base catalysts
to air, even for short periods, sometimes causes their severe
0b
Reaction conditions: CaO, 0.5 g; EC, 40 mmol; amine, 80 mmol; time, 3 h.
a
2-Hydroxyethyl butylcarbamate and 2-dibutylamino-ethanol were
formed.
b
2-Phenylamino-ethanol was formed.
butylamine give good yields for the corresponding disub-
stituted ureas at a reaction temperature of 100 ◦C (entries 1
and 2). It is noted that excess amine is not required under
the present reaction conditions. This is more preferable from
the viewpoint of economics. Slightly higher reaction temper-
atures are necessary for obtaining the substituted ureas from
hexylamine, cyclohexylamine and benzylamine with good
yields (entries 3, 5 and 7). However, no substituted urea is
obtained from dibutylamine as a secondary amine (entry 8)
and from aniline. Thus, CaO is usable for the reaction of EC
with primary amines except for aniline.
For the reactions of various amines, propylene carbonate
(PC) was used instead of EC (Table 5). The disubstituted
ureas are obtained from PC and amines with good yields,
which are almost the same as those from EC shown in Table 4.
Thus, PC is also usable for the title reaction.
Recycling use of CaO was examined for the syntheses of
some dialkylureas (Table 6). After being weighed, the prod-
uct was dissolved in DMF. Then, the catalyst was separated
by filtration, washed with acetone, dried under vacuum, and
reused for a subsequent reaction run. When CaO is reused
for dibutylurea synthesis, its activity disappears by recycling
(entries 1 and 2). The urea is not obtained in the first recycling
run. However, the deactivated catalyst can be regenerated by
Table 5
Synthesis of 1,3-disubstituted ureas from PC with various aminesa
Entry
Amine
Temperature (◦C)
Yield (%)
1
2
3
4
a
Butylamine
Hexylamine
Cyclohexylamine
Benzylamine
100
125
150
150
80
52
64
57
Fig. 3. XRD patterns of CaO (a) before and (b) after the reaction run (entry
1 in Table 6), and (c) after recalcination at 550 ◦C for 1 h before the second
recycling. (ꢀ) CaO; (᭹) Ca(OH)2; (ꢀ) CaCO3.
CaO, 0.5 g; PC, 40 mmol; amine, 80 mmol; time, 3 h.

S.-i. Fujita et al. / Journal of Molecular Catalysis A: Chemical 230 (2005) 43–48
47
Fig. 4. Variation of the composition of the reaction mixture. (ꢁ) EC; (᭹)
butylamine; (ꢀ) 2-hydroxyethyl butylcarbamate; (ꢀ) dibutylurea. Reaction
conditions: CaO, 0.5 g; EC, 40 mmol; butylamine, 80 mmol; temperature,
100 ◦C.
Scheme 2. Reaction mechanism for the synthesis of 1,3-disubstituted urea
from EC and amine.
under the conditions for Fig. 4, producing the corresponding
2-hydroxyethyl butylcarbamate quantitatively. Hence, CaO
may catalyze only the second step. Since it has been postu-
lated that metal cation of basic metal oxide has Lewis acidity
[1,3], the carbamate may be activated on this Lewis acidic
sites.
deactivation [1,3]. However, such deactivation was not ob-
served for the present reaction system.
Dibutylurea synthesis was carried out for various periods
of time. Fig. 4 illustrates change in the amounts of the sub-
strates and the products with time. Within a few minutes, all
EC and almost the same amount of butylamine are consumed.
Simultaniously, 2-hydroxyethyl butylcarbamate is produced
along with a small amount of dibutylurea and the amount of
the carbamate formed is almost the same as that of EC con-
sumed. Then, the amounts of both butylurea remaining and
the carbamate slowly decrease with time and that of dibuty-
lurea increases gradually. On the basis of these results, a reac-
tion mechanism for the title reaction has been proposed as il-
lustrated in Scheme 2. EC reacts with one molecule of amine,
being transformed to 2-hydroxyethyl alkylcarbamate. The
carbamate further reacts with another amine molecule, pro-
ducing ethylene glycol and 1,3-dialkylurea. The variations
of the substrates and products amounts with time strongly
suggest that the second reaction of carbamate and amine is
the rate-determining step for dibutylurea formation. Kaupp
et al. [41] reported that methylamine and ethylamine rapidly
react with EC around room temperature without any cat-
alyst, producing corresponding 2-hydroxyethyl alkylcarba-
mates with high yields. Moreover, in a separate run in the ab-
sence of the catalyst, EC completely reacted with butylamine
As shown in Table 4, no substituted urea was ob-
tained from dibutylamine and aniline. The products observed
were 2-hydroxyethyl dibutylcarbamate and 2-dibutylamino-
ethanol for the former amine and 2-(phenylamino)-ethanol
for the latter amine. For the other amines, the formation of
analogous aminoethanol products was not observed. When
EC and dibutylamine were allowed to react at 70 ◦C for 2 h,
about 60% of EC was converted to 2-hydroxyethyl dibutyl-
carbamate. Probably, the steric hindrance of two butyl groups
should result in low reactivity of the carbamate to the amine,
and hence, in the absence of the tetrasubstituted urea for-
mation. In contrast, no reaction occurred between EC and
aniline at 70 ◦C. This would be the reason why diphenylurea
was not obtained from EC and aniline. Probably, the amino-
ethanol compounds should be formed from the reactions of
the amines with ethylene oxide, which can be produced via
the decomposition of remaining EC [42,43].
On the basis of the reaction mechanism proposed, it is
suggested that, if one kind of carbamate is produced from
EC and one kind of amine (amine 1) and then further re-
acts with another kind of amine (amine 2), unsymmetric urea
Table 7
Synthesis of unsymmetric disubstituted ureaa
Entry
Amine 1
Amine 2
Product (yield)b
1
2
a
Butylamine
Benzylamine
Benzylamine
Butylamine
1 (35%), 2 (10%), 3 (16%)
1 (11%), 2 (6%), 3 (2%)
EC (40 mmol) was reacted with amine 1 (40 mmol) at 70 ◦C for 2 h and then carbamate formed was reacted with amine 2 (40 mmol) at 125 ◦C for 3 h using
0.5 g of CaO.
b
Based on the amount of EC used.

48
S.-i. Fujita et al. / Journal of Molecular Catalysis A: Chemical 230 (2005) 43–48
would be synthesized. So, the synthesis of unsymmetric di-
alkylurea was examined. When 40 mmol of EC was allowed
to react with 40 mmol of butylamine at 70 ◦C for 2 h in the
absence of the catalyst, 99% of EC was selectively converted
to 2-hydroxyethyl butylcarbamate. After cooling, to this re-
action mixture were added 40 mmol of benzylamine and CaO
and then the mixture was heated to 125 ◦C and kept for 3 h.
As Table 7 shows, 1-butyl-3-benzylurea 1 is formed by these
procedures; however, dibutylurea 2 and dibenzylurea 3 are
also produced (entry 1). Probably, transamination should oc-
cur between the carbamate and benzylamine and/or between
the urea and the amine. In a reverse manner, 2-hydroxyethyl
benzylcarbamate was selectively synthesized from EC and
benzylamine and further allowed to react with butylamine
using CaO (entry 2). In this case, the three kinds of disub-
stituted ureas are also produced, but their yields are lower
than those from butylcarbamate. The conversion of EC for
the reaction with benzylamine was 92%, which is almost the
same as that for the reaction between EC and butylamine; i.e.
the amounts of the carabamates formed are almost the same
in both cases. Hence, the lower yields of the ureas suggest
the lower reactivity of 2-hydroxyethyl benzylcarbamate than
2-hydroxyethyl butylcarbamate. The structure of the alkyl
group attached to the nitrogen atom of carbamate may affect
the reactivity of the carbamate.
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The present paper shows that CaO is an excellent catalyst
for the synthesis of 1,3-dialkyl ureas from EC and monoalkyl
amines. It has been suggested that strongly basic property
of CaO results in its high activity. Slightly higher reaction
temperatures are necessary for obtaining good yields from
amines having larger molecular weights. Propylene carbon-
ate can be used instead of EC for the title reaction. A re-
action mechanism has been proposed, in which a catalytic
reaction of a carbamate and amine is the rate-determining
step of the title reaction. 2-Hydroxyethyl butylcarbamate and
2-hydroxyethyl benzylcarbamate were selectively produced
with high yields from EC with butylamine and benzylamine,
respectively, in the absence of the catalyst at a low temper-
ature. From these carbamates, unsymmetric urea is obtained
along with symmetric ureas. The latter compounds may be
formed via transamination. The structure of the alkyl group
attached to the nitrogen atom of carbamate may affect the
reactivity of the carbamate.
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A part of this work is supported by a Grant-in-Aid for
Scientific Research from Japan Society for the Promotion of
Science. The authors express their sincere thanks to Mr. M.
Takizawa for his help in the catalyst characterization.