33, 308; New. J. Chem., 1996, 20, issue dedicated to the ‘Environmen-
tally Benign Chemistry and Chemical Technology’; R. A. Sheldon,
Chem. Ind. (London), 1997, 12.
DPU synthesis was demonstrated by extending the reaction to
different aromatic amines 1 and recovering the products 3 with
good yields and excellent selectivities (entries h–l).
A representative procedure for the preparation of DPUs is as
follows: a flask containing a mixture of the selected aromatic
amine 1 (10 mmol) and zeolite HSZ-360 (0.5 g) was placed in
a hot oil bath (180 °C) and 2 (0.8 g, 0.8 ml, 6 mmol) was added
dropwise during 1 min. The mixture was efficiently stirred at the
same temperature for 5 h.13 After cooling to room temp. the
slurry was washed with boiling MeOH containing 5% water (2
3 100 ml). After filtration the product was recovered from the
solution by addition of more water and cooling.14 Alternatively,
hot DMSO could be successfully utilized under the same
conditions.
The formation of compounds 3 could be attributed to the
initial production of acetoacetanilides and their subsequent
reaction with a second molecule of aromatic amine to give
DPUs and acetone. This hypothesis was in part confirmed by
quantitative production of diphenylurea by heating a 1:1
mixture of acetoacetanilide and aniline in the presence of zeolite
HSZ-360. We then estimated the catalyst activity on reuse. Our
results confirmed that the activity of HSZ-360 recovered by
filtration, washed with acetone and reactivated by heating at
500 °C for 8 h was the same for 5 runs.
In conclusion the above reported method of utilizing 2 as
carboxylating agent, zeolite HSZ-360 as solid catalyst and
avoiding the use of any solvent, represents an innovative
phosgene-free route for the selective synthesis of symmetric
diphenylureas.
Thanks are due to the Ministero dell’Universita` e della
Ricerca Scientifica e Tecnologica (MURST), Italy, and the
Consiglio Nazionale delle Ricerche (CNR), Italy, for financial
support. The authors are also grateful to the Centro Interfacolta`
Misure (C.I.M.) for the use of NMR and mass spectrometry
instruments and to Mr Pier Antonio Bonaldi for technical
assistance.
3 T. P. Vishnyakova, I. A. Golubeva and E. V. Glebova, Russ. Chem. Rev.
(Engl. Transl.), 1985, 54, 249.
4 J. March, Advanced Organic Chemistry, Wiley, New York, 1985,
p. 370; H.-J. Kno¨lker, T. Braxmeier and G. Schlechtingen, Angew.
Chem., Int. Ed. Engl., 1995, 34, 2497.
5 P. Majer and R. S. Randad, J. Org. Chem., 1994, 59, 1937.
6 T. M. Flyes, T. D. James, A. Pryhitka and M. Zojsji, J. Org. Chem.,
1993, 58, 7456; M. Lamothe, M. Perez, V. Colovray-Gotteland and
S. Halazy, Synlett, 1996, 507.
7 L. E. Overman, G. F. Taylor, C. B. Petty and P. J. Jessup, J. Org. Chem.,
1978, 43, 2164.
8 W. Werner, Tetrahedron, 1969, 25, 255; W. Werner, Tetrahedron,
1971, 27, 1755.
9 Zeolite HSZ-360 is a commercial (Tosoh Corp.) acid faujasitic-type
catalyst with 13.9 SiO2–Al2O3 molar ratio, pore size 7.4 Å, surface area
500 ± 10 m2 g21 (determined in our laboratory by the BET method:
S. Brunauer, P. H. Emmett and E. Teller, J. Am. Chem. Soc., 1938, 60,
309), acidity 0.51 mequiv. H+ g21 [determined in our laboratory by
temperature programmed desorption of ammonia gas (NH3-TPD):
P. Berteau and B. Delmon, Catal. Today, 1989, 5, 121] and with the
following chemical composition (wt% dry basis): SiO2 89.0, Al2O3
10.9, Na2O 0.06.
10 Zeolite HSZ-330 is a commercial (Tosoh Corp.) acid faujasitic-type
catalyst with 5.9 SiO2–Al2O3 molar ratio, pore size 7.4 Å, surface area
460 ± 10 m2 g21 (determined in our laboratory by the BET method),
acidity 1.59 mequiv. H+ g21 [determined in our laboratory by
temperature programmed desorption of ammonia gas (NH3-TPD)] and
with the following chemical composition (wt% dry basis): SiO2 86.1,
Al2O3 13.7, Na2O 0.19.
11 KSF is a commercial (Fluka) montmorillonite with surface area 15 ± 10
m2 g21, acidity 0.85 mequiv. H+ g21 [determined in our laboratory by
temperature programmed desorption of ammonia gas (NH3-TPD)] and
with the following chemical composition (average value): SiO2
(54.0%), Al2O3 (17.0%), Fe2O3 (5.2%), CaO (1.5%), MgO (2.5%),
Na2O (0.4%), K2O (1.5%); K10 is a commercial (Fluka) montmor-
illonite with surface area 200 ± 10 m2 g21, acidity 0.70 mequiv. H+ g21
[determined in our laboratory by temperature programmed desorption of
ammonia gas (NH3-TPD)] and with the following chemical composition
(average value): SiO2 (73.0%), Al2O3 (14.0%), Fe2O3 (2.7%), CaO
(0.2%), MgO (1.1%), Na2O (0.6%), K2O (1.9%).
Notes and References
† E-mail: sartori@ipruniv.cce.unipr.it
12 See for example: R. A. Sheldon, Chem. Ind. (London), 1992, 903;
R. A. Sheldon, J. Mol. Catal., A, 1996, 107, 75; D. C. Dittmer, Chem.
Ind. (London), 1997, 779.
13 By carrying out the reaction for longer times the same value of yield
( ~ 70%) was observed.
14 A. F. M. Iqbal, Helv. Chim. Acta, 1976, 59, 655. 3g: pale brown solid,
mp 237–238 °C (lit., 236–238 °C); 3h: pale brown solid, mp
237–283.5 °C (lit., 239 °C); 3i: pale brown solid, mp 218–220 °C (lit.,
219–220 °C); 3j: pale brown solid, mp 263–264 °C (lit., 263–265 °C);
3k: pale brown solid, mp 283–284.5 °C (lit., 284 °C).
1 I. E. Maxwell, J. Inclusion Phenom., 1986, 4, 1; W. F. Holderich,
M. Hesse and F. Naumann, Angew. Chem., Int. Ed. Engl., 1988, 27, 226;
H. Van Bekkum, Recl. Trav. Chim. Pays-Bas, 1989, 108, 283;
M. Balogh and P. Laszlo, Organic Chemistry using Clays, Springer
Verlag, New York, 1993; A. Cornelius and P. Laszlo, Synlett, 1994,
155; J. H. Clark, S. R. Cullen, S. J. Barlow and T. W. Bastock, J. Chem.
Soc., Perkin Trans. 2, 1994, 1117; A. Corma, Chem. Rev., 1995, 95, 559;
J. H. Clark and J. Macquarrie, Chem. Soc. Rev., 1996, 303; G. Eder-
Mirth and J. A. Lercher, Recl. Trav. Chim. Pays-Bas, 1996, 115, 157;
W. F. Holderich, Comprehensive Supramolecular Chemistry, ed. G.
Alberti and T. Bein, Pergamon, Oxford, 1996, vol. 7, pp. 671–692;
G. W. Kabalka and R. M. Pagni, Tetrahedron, 1997, 53, 7999.
Received in Liverpool, UK, 6th November 1997; 7/08019K
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Chem. Commun., 1998