Catalysts for selective aerobic oxidation under ambient conditions - Advances in Catalytic Activation of Dioxygen by Metal Complexes - page 228

Cu(II) concentrations. Co-catalysis by the d-block ions also results in elimination of the
induction period in some cases.

Key words: Amino acids, Catalytic oxidation under ambient conditions, 2-chloroethyl ethyl
sulfide, Co-catalysis by copper, Decontamination, Effect of ligands, Gold complexes, Mustard
gas, Perfluorinated solvents, Solvent effect, Sulfoxide, Thioether

1. INTRODUCTION

The selective reductant-free catalytic oxidation of organic compounds by
has been a major goal in both fundamental and applied chemistry for
years. Nearly all catalysts for oxidations, whether they be
biological or abiological (synthetic/industrial) contain redox-active metal
centers. 1-7 “Selective” generally means that the radical-chain mechanisms

that dominate the ubiquitous oxidations of nearly all organic and
many inorganic materials (autoxidations) aren t operable. While there are a

handful of radical-chain oxidations that proceed with reasonably
high selectivity, it is the nature of the substrate itself in these cases that
ensures high selectivity and not the chemistry (control of the elementary
processes in the mechanism). One of these rare examples is the oxidation
of p -xylene to p -terephthalic acid, one of the largest scale commercial
homogeneous catalytic processes globally. Despite proceeding by a
homolytic mechanism (radical chains and many radical intermediates), the p -
terephthalic acid product is produced in a very high selectivity >99.9%
primarily because its unusual structure makes it quite stable under the
reaction conditions. 8 The DuPont process for aerobic oxidation of
cyclohexane (adipic acid manufacture) is more indicative. While this also
remains a large scale process given its low cost, it proceeds with poor
selectivity. 9 One of the several reasons for the intrinsically low selectivity
(and consequent generically low desirability) of conventional radical-chain
oxidations, is that many oxygen-based and/or radical intermediates in
such processes are capable of reacting simultaneously with the substrate.
Unfortunately the metal centers in such systems, both catalytic and
structural, typically exacerbate the problem by generating additional
nonselective but kinetically potent reactive intermediates via both redox and
electrophilic

'

processes. 10 non-redox Furthermore, the mechanistic

complexity in conventional radical-chain oxidations, including the