Selective Oxidative Carbonylation of Aniline to
Diphenylurea with Ionic Liquids
Eduardo J. Garcia-Suarez
[b, c, d]
Ureas are found commonly in the structures of alarge number
of biologically active compounds.Moreover,ureic derivatives
have awidespectrum of biological activity and have been ap-
plied extensively as agrochemicals, dyes, antioxidants, and
resin precursors and as key intermediates in organic synthesis,
for example, in the production of isocyanates.
In this context,
the oxidative carbonylation of amines to obtain ureas
(Scheme 1) has received much interest over the past 50 years
as an alternative to the traditional phosgenation process.
reactionisperformed in the presenceofametal catalystoror-
ganocatalyst, an oxidizing agentsuch as I
CO pressure. Among transition metals and organocatalysts,
are effective. Usually,anon-nucleophilic sol-
vent is required to avoid the formation of carbamates.
best result reportedtodate in terms of turnover frequency
(TOF) hasbeen achieved with acatalytic systemthat comprises
and 3-butyl-1,2-methylimidazolium iodide as the co-
catalystinthe presence of O
(17 368 h
). However,the reac-
tion was performed under an explosive CO/O
gas mixture that
required extraordinary safety precautions.
The mechanism of the Pd-catalyzed oxidative carbonylation
of amines has been studied by Hiwatarietal.
who used I
the oxidant(Scheme 2). They suggestedthat the reaction pro-
ceeds through aPd
cycle via aPd-carbamoyl intermedi-
ate, in which the active speciesisaPd
reacts with CO and 2equivalents of amine to form aPd-carba-
moyl complex (II)and an ammonium salt. The reaction of an
amine molecule at the carbonyl of the Pd intermediate II pro-
vides the correspondingisocyanate that reacts in situ to form
urea as final product and Pd
species(III)that is reoxidized to
the active Pd
Scheme1.Generalreaction scheme for the oxidative carbonylation of
amines to ureas.
Scheme2.Mechanism proposed by Hiwatari andco-workers for the Pd-cata-
lyzed oxidative carbonylation of amines.
Acatalytic system for the selectiveoxidative carbonylation of
aniline to diphenylurea based on Pd complexes in combination
with imidazolium ionic liquids is presented. Both oxidants, Pd
complexes,and ionic liquidsaffect the activity of the reaction,
and the choice of oxidant determines the selectivityofthe re-
action. Together they allow the reaction to proceed under
comparatively mild conditions without alossofactivity.Exami-
nation of the reactionbyuse of in situ NMR spectroscopy al-
lowed us to observe an intermediate suggestedonly previous-
ly,which supported the proposed mechanism.
[a] Dr.N.Zahrtmann, Prof. C. Claver,Prof. C. Godard
Department of Physical and Inorganic Chemistry
Universitat Rovira IVirgili
C/Marcel.li Domingo s/n, CampusSescelades, 43007 Tarragona (Spain)
[b] Dr.N.Zahrtmann, Prof. A. Riisager,Dr. E. J. Garcia-Suarez
Centre for Catalysis and Sustainable Chemistry
Department of Chemistry,Technical University of Denmark
2800 Kgs. Lyngby (Denmark)
Tecnalia, Energyand Environment Division
Parque Tecnológico de lava
LeonardoDaVinci, 11,01510 MiÇano (Spain)
IKERBASQUE, BasqueFoundationfor Science
Maria Diaz de Haro 3, 48013Bilbao (Spain)
The ORCID identification number(s) for the author(s) of this article can
be found under https://doi.org/10.1002/cctc.201800004.
ChemCatChem 2018, 10,2450 –2457 2018 Wiley-VCH Verlag GmbH &Co. KGaA, Weinheim2450