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polypeptides would probably have little impact on the catalytic aerobic
oxidative decontamination (sulfoxidation) of HD.
18.
OXIDATION OF THIOETHERS OTHER THAN CEES
The majority of this comprehensive study has been concentrated on the
chemistry of CEES oxidation, since it closely resembles one toxic target,
mustard gas. However, the Au-based catalysts reported here are able to
oxidize a variety of thioethers, as well as disulfides. In fact, of the six
organosulfur compounds tested, CEES under optimized catalytic conditions
is actually oxidized at a much lower rate and shows more significant
inhibition than the other substrates. For comparison, when THT was
evaluated, the optimized Au-based catalyst under ambient conditions yields
~27 turnovers in 30 min, while Riley's Ce-based system yields 17.6
turnovers at elevated temperature and pressure over the same time period.
25
Table 3 gives the substrates that were evaluated at similar concentrations, the
induction period associated with each substrate, as well as the initial rates of
oxidation. The thioether oxidations were found to be completely selective in
that only sulfoxide was formed, while the products arising from dimethyl
disulfide oxidation have not yet been characterized (cleavage of S-S bond is
suspected). The thioethers thus far studied can be divided into two groups.
The first group are those that exhibit no visible induction period (Figure 8),
and the second group are those that do exhibit a visible induction period
(Figure 9). Thioethers with higher initial oxidation rates, tend to have
shorter induction periods.
An interesting feature of our Au-based catalysts is the high substrate
selectivity during competitive thioether oxidation (Figure 10). When equal
amounts of two thioethers (0.36 M total thioether concentration), THT and
CEES, are added simultaneously to the
system, the initial
rates of oxidation of the two substrates are
and
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