Ruthenium tetroxide oxidation mechanism

The alcohol oxidations discussed above involve as a key step the oxidative dehydrogenation of the alcohol to form low-valent hydridoruthenium intermediates. On the other hand, high-valent oxoruthenium species are also able to dehydrogenate alcohols via an oxometal mechanism (see Figure 5.6). It has long been known that ruthenium tetroxide, generated by reaction of ruthenium dioxide with periodate, smoothly oxidizes a variety of alcohols to the corresponding carbonyl compounds [47]. 

The rates of hydrolysis of monomeric ruthenium(n) chloride complexes which are generated electrochemically have been reported and are much more rapid than those observed for the corresponding ruthenium(m) species. It is suggested that Ru chloride complexes may exist as unstable intermediates when the ruthenium(iii) species are reduced. Ruthenium(n) dimethyl sulphoxide complexes have been shown to be the products of refluxing the hydrated ruthenium(iii) chloride with DMSO. The use of ruthenium tetroxide as an oxidant has also been described. In the oxidation of tetrahydrofuran in aqueous perchloric acid, an inverse hydrogen-ion dependence is observed, the proposed mechanism involving hydride abstraction with recombination to yield an ester. A scheme consistent with isotope-labelling data may be represented as... 

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