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Green Chemistry
PAPER
An unprecedented use for glycerol: chemoselective
reducing agent for sulfoxides†
Cite this: DOI: 10.1039/c3gc36908k
Nuria García, Patricia García-García, Manuel A. Fernández-Rodríguez, Daniel García,
María R. Pedrosa, Francisco J. Arnáiz and Roberto Sanz*
A new application for glycerol that expands its possibilities beyond a green solvent and a precursor of
value-added products has been demonstrated. Simple, easily available, and environmentally friendly dioxo-
molybdenum(VI) complexes are highly efficient catalysts for the chemoselective sulfoxide deoxygenation
with this biomass-derived chemical feedstock. Both refined glycerol and crude glycerin can be used, thus
expanding the potential application of this reaction. Subsequent transformation of glycerol during this
reductive process has also been investigated.
Received 12th June 2012,
Accepted 5th February 2013
DOI: 10.1039/c3gc36908k
to the corresponding sulfides is an important organic reaction
as this functionality can be cleanly cleaved from the target
Introduction
The increasing demand for biodiesel production has caused, in molecule once its presence is no longer required. So, several
recent years, a continuous growth in the production of glycerol, methodologies have been described to achieve this transform-
generated as a by-product of this process, leading to an over- ation,13 which also has biological relevance for avoiding oxi-
supply of this renewable chemical that could be considered an dative damage of cells.14 However, the development of new
important biorefinery feedstock.1 Therefore, the efficient trans- green protocols for the reduction of sulfoxides bearing
formation of glycerol into valuable chemicals has attracted additional functionalities remains an important challenge.15
much attention from both academia and industry.2 Due to its
In the last few years we have been involved in the develop-
multifunctional structure, glycerol opens the door to the prep- ment of new synthetic methodologies including reactions cata-
aration of a large number of chemicals through different path- lyzed by easily available and environmentally friendly
ways such as oxidation,3 reduction,4 dehydration,5 dioxomolybdenum(VI) complexes16 for the reduction of oxyge-
esterification,6 etherification,7 or reforming to syngas.8 In nated compounds such as sulfoxides,17 nitroaromatics,18 and
addition, glycerol has also found use as a sustainable solvent N-oxides.19 Looking for new and cleaner reagents that could
for green chemistry,9 although some problems associated with act as oxygen acceptors in Mo-catalyzed processes,20 we have
its high viscosity and the presence of potentially reactive recently reported the use of pinacol (2,3-dimethyl-2,3-butane-
hydroxyl groups should be considered. However, the use of diol) as a reducing agent for the reduction of sulfoxides and
glycerol as a reagent for promoting organic transformations is nitroarenes.21 Herein, we report the successful application of
considerably less developed, except for the synthesis of glycerol- glycerol as a reagent for the dioxomolybdenum(VI)-catalyzed
based acetals that are valuable chemical intermediates,10 and chemoselective deoxygenation of sulfoxides.
the metal-catalyzed transfer hydrogenation reaction from gly-
cerol to unsaturated compounds,11 which also can be con-
sidered an environmentally friendly route to glycerol oxidation.
So, the development of new applications, as well as the expan-
sion of existing ones, for glycerol as a low-cost raw material con-
Results and discussion
Establishment of reaction conditions
stitutes an important goal in modern chemistry.
On the other hand, taking into account the significant role
played by sulfoxides in asymmetric synthesis,12 their reduction
Based on our previous experience for the deoxygenation of
sulfoxides with phosphites17 and pinacol,21 we selected bis
(p-tolyl)sulfoxide as a model substrate and MoO2Cl2(dmf)2 as
a catalyst for testing the possibility of using glycerol as an
oxygen acceptor (Table 1).22
Gratifyingly, we observed complete conversion of the sulf-
oxide and high isolated yields of the corresponding sulfide in
different solvents with 5 mol% of the dioxomolybdenum
complex and only 4 equiv. of glycerol at 170 °C (entries 1–4).23
Departamento de Química, Facultad de Ciencias, Universidad de Burgos, Pza. Misael
Bañuelos s/n, 09001-Burgos, Spain. E-mail: rsd@ubu.es; Fax: (+34)947258831
†Electronic supplementary information (ESI) available: NMR spectra of the
products and experimental details for the recycling study. See DOI:
10.1039/c3gc36908k
This journal is © The Royal Society of Chemistry 2013
Green Chem.