Chromate-mediated, oxidation

Chromium-mediated oxidation of benzylic methylene groups to the corresponding oxo derivatives has also been reported [4], Tri-n-butylstannyl chromate appears to be the best co-oxidant and a trace of 4-toluenesulphonic acid also aids the oxidation. 

Chromate-mediated percarbonate oxidation of primary and secondary alcohols and of benzylic methylene groups... 

The oxidation of alcohols by sodium percarbonate is also promoted by the addition of molybdenyl acetoacetate [5] and yields are comparable with those obtained by the chromate mediated reactions. 

Chromate ester (Section 12.12A) An intermediate in the chromium-mediated oxidation of an alcohol having the general structure R-0-Cr03H. 

The catalytic process is also achieved in the Pd(0)/Cr(II)-mediated coupling of organic halides with aldehydes (Scheme 33) [74], Oxidative addition of a vinyl or aryl halide to a Pd(0) species, followed by transmetallation with a chromium salt and subsequent addition of the resulting organo chromate to an aldehyde, leads to the alcohol 54. The presence of an oxophile [Li(I) salts or MesSiCl] allows the cleavage of the Cr(III) - 0 bond to liberate Cr(III), which is reduced to active Cr(II) on the electrode surface. 

Still, these coatings are far from ideal and are not yet sufficiently stable for technical application. Their reoxidation is strongly hindered, necessitating a relatively high overpotential of several hundreds of millivolts and their stability is insufficient, with chromium bleeding out as chromate. Yet the results obtained by the method that allows fixing with an easily applicable method a soluble redox mediator to an oxidic anode is encouraging. The an-... 

This activity is particularly useful for degradation of strongly hazardous substances or recalcitrant pollutants that are difficult to remove in chemical or biochemical processes. In this respect any pathway leading to abatement of chromate(VI) pollution arouses interest. One such pathway seems to be created by cooperation between iron and chromium photocatalytic cycles, which were reported as effective in conversion of chromate(VI) into Crm species [20-23,97]. A synergistic photoreduction of CrVI and Cu11 mediated by Ti02 [98], or photocatalytic reduction of Crvl and oxidation of organic matter by environmental polyoxometallates as photocatalysts [99], may constitute alternative possibilities. 

The chromate conversion coating process is aided by fluoride, which prevents rapid passivation of the A1 surface, thus allowing Cr " to Cr " reduction and is also aided by ferricyanide, which functions as a mediator between A1 oxidation and chromate reduction and accelerates the redox reaction. ... 

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