DOI: 10.1002/cctc.201500805
Full Papers
Highly Selective Cycloalkane Oxidation in Water with
Ruthenium Nanoparticles
Audrey Denicourt-Nowicki,*[a, b] Anastasia Lebedeva,[a, b] ClØment Bellini,[a, b] and
Alain Roucoux*[a, b]
Ruthenium(0) nanospecies, with small sizes of approximately
1.75 nm, proved to be active, selective, and retrievable nanoca-
talysts for the oxidation of various cycloalkanes in neat water,
using tert-butylhydroperoxide as an oxidant and at room tem-
perature. Relevant conversions and selectivities (up to 97%)
were achieved towards the major formation of the ketone
product, which constitutes a high-value-added intermediate
for polymer or fine chemistry. The lifetime of the catalyst has
been checked over several runs, with no significant loss of ac-
tivity and selectivity. Kinetic and mechanistic investigations
proved that radical species are involved in the oxidation pro-
cess. A literature comparison showed the relevance and the
usefulness of the present ruthenium nanocatalytic system in
a benign reaction context.
Introduction
The selective oxidation of saturated hydrocarbons constitutes
an outstanding value-creating synthetic strategy, ranging from
the production of fine chemicals to the replacement of current
petrochemical feedstocks by less expensive and more readily
available alkanes.[1–3] The ensued oxygenated molecules could
be used as building blocks in various branches of the chemical
industry, ranging from polymer synthesis to medicinal chemis-
try.[4] In particular, cyclohexane oxidation remains a large-
scaled industrial process, producing approximately 106 ton per
year of cyclohexanone and cyclohexanol, also known as K-A
oil,[5] which are mostly used in the manufacture of nylon-6 and
nylon-6,6.[6] However, this process is among the least efficient
industrial chemical processes, owing to the difficulty in control-
ling the selectivity toward the target products.[7] In the present
cobalt-catalyzed industrial process, a very low conversion of
less than 5% is preferentially required to achieve a 80% selec-
tivity to K-A oil and to avoid the deep oxidation into over-oxi-
dized by-products.[8,9] Therefore, in recent years, many research
efforts have been devoted towards the search of alternative
and more environment-friendly methodologies to achieve
a high conversion in cyclohexane oxidation, while maintaining
selectivity and reducing energy consumption.[10–13]
potentially advanced catalysts owing to their outstanding in-
trinsic properties.[14–16] Besides their potential recovery poten-
tialities, they could provide relevant catalytic activities owing
to a high number of surface-exposed metal atoms and en-
hanced selectivities owing to a good shape control during the
synthesis.[17–19] As a consequence, metallic nanospecies have
found great applications in various catalytic reactions, such as
hydrogenation, carbonÀcarbon coupling or oxidation reac-
tions.[20,21] Over the last decade, fewer nanocatalysts,[22–25] such
as Fe and/or Co nanostructured catalysts, supported gold
nanoparticles or Au–Pd alloys, have been reported for the se-
lective cyclohexane oxidation, but still suffer from low conver-
sions and/or recyclability owing to metal leaching.
Herein, we report the use of ruthenium(0) nanospecies as
catalysts in the liquid-phase oxidation of various cycloalkanes
into the high-value-added ketone/alcohol products under mild
conditions, in neat water as a suitable industrial green solvent
(Scheme 1).[26] The tert-butylhydroperoxide (t-BHP) has been
In that context, nanoheterogeneous catalysis could consti-
tute a pertinent approach in the quest towards more sustaina-
ble processes for these oxidation transformations. In fact,
nanometer-sized particles have been intensively pursued as
Scheme 1. Ru-catalyzed oxidation of various cycloalkanes in neat water.
chosen as an oxidant because it has emerged as a suitable oxi-
dant for cyclohexane oxidation, possessing higher solubility
than H2O2 or molecular oxygen.[27] After optimization of the re-
action conditions, kinetic and mechanistic investigations have
been performed.
[a] Dr. A. Denicourt-Nowicki, A. Lebedeva, C. Bellini, Prof. A. Roucoux
Ecole Nationale SupØrieure de Chimie de Rennes
CNRS, UMR 6226
11 AllØe de Beaulieu
CS 50837, 35 708 Rennes Cedex 7 (France)
[b] Dr. A. Denicourt-Nowicki, A. Lebedeva, C. Bellini, Prof. A. Roucoux
UniversitØ EuropØenne de Bretagne (France)
ChemCatChem 2016, 8, 357 – 362
357
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim