Catalytic oxidations of alcohols - Advances in Catalytic Activation of Dioxygen by Metal Complexes - page 149

reported 88 the selective oxidation of alcohols with 70% aq. using
or as the catalyst and methyltrioctyl-
ammonium chloride (Aliquat 336) as a phase transfer agent in a biphasic
(dichloroethane-water) system.
More recently, Noyori and coworkers 89,90 have achieved substantial
improvements in the sodium tungstate-based, biphasic system by employing
a phase transfer agent containing a lipophilic cation and bisulfate as the
anion, e.g. This afforded a highly active catalytic
system for the oxidation of alcohols using 1.1 equivalents of 30% aq.
in a solvent-free system. For example, 1-phenylethanol was converted to
acetophenone with turnover numbers up to 180,000. As with all Mo- and W-
based systems, the Noyori system shows a marked preference for secondary
alcohols, e.g. Reaction 25.
Unsaturated alcohols generally undergo selective oxidation of the
alcohol moiety (Reactions 26 and 27) but when an allylic alcohol contained
a reactive trisubstituted double bond selective epoxidation of the double
bond was observed (Reaction 28).