710 J. CHEM. RESEARCH (S), 1999
J. Chem. Research (S),
1999, 710^711y
A Novel Method for the Synthesis of
Disubstituted Ureas and Thioureas Under
Microwave Irradiaton
Mohammad M. Mojtahedi, Mohammad R. Saidi* and
Mohammad Bolourtchian
aDepartment of Chemistry, Sharif University of Technology, Teheran, I.R. of Iran
bChemistry and Chemical Engineering Research of Iran, Teheran, I.R. of Iran
Several symmetrically disubstituted ureas and thioureas are synthesized by heating of urea or thiourea with aro-
matic amines or phenylhydrazine under environmentally benign conditions without any solvent in a conventional
microwave oven.
The synthesis of substituted ureas and thioureas are import-
ant reactions in organic owing chemistry to their
Table 1 Preparation of disubstituted ureas from aromatic amines
or phenylhydrazine under microwave irradiation
applications in agriculture, medicinal chemistry and chemi-
Yielda
3
cal transformations.1
Although the synthesis of mono-
Entry
Amine
PhNH2
Product
S
t / min
(%)
and di-substituted ureas have been extensively documented
by a variety of methods, many of these have limitations
7
in their general applications.4 Recently the preparation
1
2
3
65
40
90
2.5
1.0
2.0
PhNH
NHPh
of symmetrically substituted ureas and thioureas were
reported by reductive alkylation of aromatic aldehydes,8
from amines and CS2,9 and from aliphatic amines with
acetoacetanilide.10
Microwave irradiation has opened new perspectives in
synthetic organic chemistry, not only in terms of yield
and selectivity, but also ease of the reaction conditions.11
In view of the above, and in conjunction with our recent
work on microwave-assisted reactions under solvent-free
conditions,12 we sought to develop a new method for the
preparation of symmetrically disubstituted ureas and
thioureas under environmentally benign conditions, using
a microwave oven, without any solvent.
S
PhNHNH2
PhNHNH2
PhNHNH
PhNHNH
NHNHPh
NHNHPh
O
Cl
Cl
O
Cl
NH2
NH2
4
5
70
83
4.0
4.0
N
H
N
H
O
O
N
H
N
H
MeO
Br
OMe
Br
MeO
6
7
8
85
40
45
4.0
4.0
5.0
N
H
N
H
NH2
NH2
O
H
N
H
N
O
O
MW,
NHNH2
NH2
Br
O
S
N
H
N
H
2.0 min
N
H
N
H
+
+
H2N
H2N
NH2
NH2
MW,
2.5 min
N
H
N
H
S
Cl
Cl
Cl
NH2
N
H
N
H
O
PhNH2
9
66
2.0
PhNH
NHPh
Scheme 1
a Yields refer to isolated and chromatographically pure products.
All products exhibited spectral data consistent with their structures.
Here, we report a new method for the synthesis of sym-
metrically disubstituted ureas and thioureas from aromatic
amines or phenylhydrazine under microwave irradiation
without any solvent or solid support. The reaction of an
aromatic amine or phenylhydrazine (2 mmol) with urea
or thiourea (1 mmol) in a conventional microwave oven pro-
duced symmetrically disubstituted ureas or thioureas in
good to excellent yields, Scheme 1. The product is formed
by loss of ammonia after 1^10 min (Table 1). Disubstituted
ureas and thioureas were easily recovered by adding water
to the ¢nal reaction mixture, removing the solid product
by ¢ltration, and recrystallizing the product from
ethanol^water. Moreover, in comparison with reported
procedures,9;10 there is no need for the use of any hetero-
geneous catalysts or CS2 in this procedure.
In conclusion, we have shown that direct heating of aro-
matic amines or phenylhydrazine with urea or thiourea
leads to an e¤cient synthesis of symmetric N,N-
disubstituted ureas or thioureas from aromatic amines or
phenylhydrazine.
Experimental
1H NMR spectra were recorded in CDCl3 on a Bruker AC 80
spectrometer, using SiMe4, as internal standard. IR spectra were
obtained on Matt Son 1000 Unicam FTIR spectrophotometer. Mass
spectra were recorded on Fisons 800 Trio instrument.
General Procedure for the Preparation of Disubstituted Ureas.öAn
aromatic amine or phenylhydrazine (2 mmol) was mixed thoroughly
with urea (1 mmol, 0.06 g) in a 5 ml beaker. Then the beaker was
placed in conventional microwave oven until the mixture became
liquid. The time required for each reaction is indicated in Table 1.
To remove the unreacted urea, water (10 mL) was added to the
* To receive any correspondence (e-mail: saidi@ch.sharif.ac.ir).
This is a Short Paper as de¢ned in the Instructions for Authors,
Section 5.0 [see J. Chem. Research (S), 1999, Issue 1]; there is
therefore no corresponding material in J. Chem. Research (M).
Mojtahedi, Mohammad M.
