Overoxidation resistance limit

Further studies by this group centered on comparisons of the overoxidation resistance limit (ORL) of polypyrrole materials doped with monoanionic borane clusters [B12H11NH3] or dianionic borane [B12H12]2 or carborane [Co(C2B9Hu)2]2-clusters. The monoanionic boron clusters were found to offer the highest stability to the PPy doped materials against overoxidation than any other charged dopant. They were also found to be far superior to the dianionic clusters in their ability to impart an ORL rise.140... 

For the oxidation of alkenes, osmium tetroxide is used either stoichiometrically, when the alkene is precious or only small scale operation is required, or catalytically with a range of secondary oxidants which include metal chlorates, hydrogen peroxide, f-butyl hydroperoxide and N-methylmorpholine A -oxide. The osmium tetroxide//V-methylmorpholine A -oxide combination is probably the most general and effective procedure which is currently available for the syn hydroxylation of alkenes, although tetrasubstituted alkenes may be resistant to oxidation. For hindered alkenes, use of the related oxidant trimethylamine A -oxide in the presence of pyridine appears advantageous. When r-butyl hydroperoxide is used as a cooxidant, problems of overoxidation are avoided which occasionally occur with the catalytic procedures using metal chlorates or hydrogen peroxide. Further, in the presence of tetraethylam-monium hydroxide hydroxylation of tetrasubstituted alkenes is possible, but the alkaline conditions clearly limit the application. 

Finally, it has been found that promotion of palladium by bismuth not only increases the selectivity in aldehyde but also limits the deactivation of the catalysts. Similar results have been published in the past decade on the partial oxidation of alcohols with similar catalytic systems (ref. 13) Various interpretations on the role of bismuth have been suggested among them, resistance of Pd/C against overoxidation and surface orientation of the reactant suppressing the formation and strong adsorption of poisoning intermediates are also problably the main reasons of the improved performances in the oxidation of p-cresol. 

The change of the electronic resistance of PPy as a function of electrode potential in solutions of various compositions is shown in Figure 60. Because of the selected electrode potential limits, onfy a reversible increase/decrease was found no evidence of overoxidation was observed [73]. With a polymer transistor manufactured with a film of PPy as the active material, Ofer et al. [645] found a limited electrode potential window wherein PPy has a high electronic conductivity. 

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