Fluorides, oxidation-reduction behavior

The separation of Pu by co-precipita ion usually takes advantage of the aforementioned oxidation and reduction cycles to effect purification. The procedure may be illustrated with the carrying of Pu(III) and Pu(IV) and the non-carrying of Pu(VI) on LaFg. Only those elements with co-precipitation and oxidation-reduction behavior very similar to that of Pu interfere. The oxidation-reduction cycle may be repeated as many times as needed to get any desired degree of purity. The use of LaFg precipitation is also a valuable group separation and volume reduction step, since not very many elements have acid-insoluble fluorides. 

In contrast to the cathodic reduction of organic tellurium compounds, few studies on their anodic oxidation have been performed. No paper has reported on the electrolytic reactions of fluorinated tellurides up to date, which is probably due to the difficulty of the preparation of the partially fluorinated tellurides as starting material. Quite recently, Fuchigami et al. have investigated the anodic behavior of 2,2,2-trifluoroethyl and difluoroethyl phenyl tellurides (8 and 9) [54]. The telluride 8 does not undergo an anodic a-substitution, which is totally different to the eases of the corresponding sulfide and selenide. Even in the presence of fluoride ions, the anodic methoxylation does not take place at all. Instead, a selective difluorination occurs at the tellurium atom effectively to provide the hypervalent tellurium derivative in good yield as shown in Scheme 6.12. 

The photodegradation rate dependence on phenol concentration in the TiOi/F system shows a plateau in the 3 X IO " M to 3 X 10 M range, whereas for naked TiO2, a maximum is reached around 2 X 10 M of phenol followed by a decrease. This behavior is rationalized by the possibility of reductive back reactions of intermediates formed after the first oxidation step. The presence of fluoride could limit the occurrence of this detrimental effect, reducing the interaction of the formed intermediates with the surface. Moreover, also the change of the oxidation pathway changes the amount of the products. 

Km, but it is too fast to observe at higher concentrations. The T e 1 center has been considered for some time as the initial point at which electrons from substrate enter the laccase molecule 94, 95). In the absence of oxygen, the reduction of the Type 3 Cu-pair is unimolecular at high substrate concentration and is very slow k = 1—2 sec-i). Type 3 reduction is also independent of the nature and concentration of substrate and of enzyme [62, 90, 95). It has been proposed that this slow reduction results from an internal oxidation of Type 1 Cu2+ by Type 3 Cu [90, 95). Fluoride ion strongly inhibits the reduction of Type 3 Cu ( =0.008 sec i) (95), but does not change the qualitative behavior of the reaction. The important fact is that whether fluoride is present or absent the reduction as observed by transient kinetics occurs much too slowly to be a viable step in the catalytic action (62, 90, 94). 

If low impurity levels are required, the method of preparing the fluoride for the electrolytic method is not as critical as for the Ca reduction method - at least with respect to the O content of CeFs. In the electrolytic method Ce02 or Ce203 is added to the fluoride flux, and it is the oxide which is reduced to the metal. For the Ca reduction method the O content of the fluoride is quite critical since any oxide present in the fluoride will end up in the metal. Furthermore, as noted by Carlson et al. (1960) the fluoride flux may serve to extract some of the impurities. These authors found that the levels of C, N, O, F, Mg and Ni in a Y-Mg alloy are reduced by extraction with a fused salt. Similarly, in the electrolytic preparation one might expect that the long contact time of the metal with the fluoride flux may decrease the level of some impurities in the metal. This behavior of the fluoride flux, however, may lead to difficulties if the flux is contaminated from the previous runs, since continued use would saturate the flux with certain impurities, and they would no longer be extracted, and even might be introduced into the next metal sample. 

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