Catalysts for selective aerobic oxidation under ambient conditions - Advances in Catalytic Activation of Dioxygen by Metal Complexes - page 244

Ce(IV) and forms another reactive intermediate which in turn
reacts with to produce 2 molecules of sulfoxide product. According to
this mechanism, the oxygen atom in the sulfoxide should be incorporated
from not Since in our system 100% oxygen-18 incorporation from
was observed, such a radical-chain mechanism can be definitively
ruled out. Additional evidence against this mechanism derives from a
competitive oxidation of different thioethers (see section 18). Au(III)-based
catalysts appear to be highly discriminatory with respect to thioethers when a
combination of thioethers are oxidized together. The high-energy
intermediate, proposed to be generated in the Ce-based systems,
would likely not able to discriminate highly between different thioethers. 25
Finally, another possible mechanism for aerobic sulfoxidation is proposed
by Riley and co-workers for the reaction catalyzed by
This chemistry proceeds at rather high temperatures (>100 °C) and requires
the use of alcohols as solvents. The reactive species in this system is
which is produced as an intermediate in the oxidation of Ru(II) to Ru(IV) by
Thus, the Ru(IV) formed is reduced back to Ru(II) by alcohol, a solvent
molecule. The labelling studies in this system show that no oxygen-18
incorporation from occurs, in direct and total opposition to our
Au(III)-based catalytic system (100% incorporation from Additional
evidence against such a mechanism derives from the stoichiometry itself (eq
1 in our case versus eq 6 in Ru-based system) and selectivity (~100% yield
of CEESO at high CEES conversion, but further sulfoxide oxidation to
sulfone in the Ru system studies.

10. ORIGIN OF OXYGEN IN SULFOXIDE PRODUCT;
ROLE OF IN SULFOXIDATION

The simplest procedure for sulfoxide synthesis is thioether oxidation by
and acids are efficient catalysts for this reaction. 51 In the presence of
protons is a potential intermediate in Au(I) reoxidation by eq 28:

HC1 and are formed during the catalytic process, eq 9, and one of the
reactants, is acidic. Thus CEES could be, at least partly, oxidized
by formed during this process. To assess the role of and to
address the formation of a thioxonium salt intermediate (by establishing the
incorporation of oxygen-18 into CEESO from isotope labeling

studies were done by replacing regular with In addition, CEES

oxidation by in the presence of our Au(III)-catalysts was also assessed.