Perruthenate and Ruthenate Ions

Polymer supported sodium ruthenate is able to catalyze the oxidation of alcohols with iodosobenzene or tetrabutylammonium periodate in CH2CI2.8 It is not clear whether the primary oxidant is ruthenate or perruthenate. 

In fact, equilibria between ruthenium ions in different oxidation states in aqueous solution add complexity to the mechanistic analysis of these oxidations. Thus, Burke and Healy presented mechanistic evidences9 suggesting that putative oxidations of alcohols with ruthenate ion are in fact produced by perruthenate originated by dismutation of ruthenate. 

An aqueous solution of soditun ruthenate is able to oxidize cyclohexanol. These reaction conditions are hardly appropriate for routine employment in the laboratory because of the high price of Na2Ru04 that is used stoichiometrically and of the need to perform the reaction in aqueous 1M NaOH in order to avoid the dismutation of sodium ruthenate. Some mechanistic studies suggest that the real oxidant could be perruthenate,9 present in very small amounts and in equilibrium with ruthenate regardless of 

The perruthenate ion can be made soluble in organic solvents by using the t c t r a - / z - p r o p y 1 a mm 011 i um contraanion, that is by employing tetra-w-propylammonium perruthenate (TPAP) (50). 

Griffith, Ley et al.n discovered that, in variance with the instability and complex behaviour of perruthenate and ruthenate ions in aqueous solution, TPAP in organic media is quite stable and behaves as a very good oxidant for alcohols. Normally, it is employed in catalytic quantities in dry CH2CI2 with addition of TV-methylmorpholine /V-oxide (NMO) as the secondary oxidant. Catalytic TPAP in the presence of NMO is able to oxidize alcohols to adehydes and ketones under very mild conditions in substrates adorned by complex functionalities, and it has become one of the routine oxidants for alcohols in most Synthetic Organic Chemistry laboratories. 

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