Tetra--Propylammonium Perruthenate TPAP Ley Oxidation

As expected, inorganic perruthenates, like sodium perruthenate (NaRu04) or potassium perruthenate (KRu04), are soluble in water and insoluble in apolar organic solvents. On the other hand, the perruthenate ion (Ru04) is unstable in aqueous solution because it produces the oxidation of water according to the following Equation.55 

It is possible to oxidize alcohols using the perruthenate57 or the ruthe-nate10,58 ion in aqueous solution, but because of the instability of these ions in water, the identification of the genuine oxidant is open to discussion.59 

A milestone in the routine employment of perruthenate in the oxidation of alcohols was established with the publication by Griffith, Ley et al. in 1987 on the catalytic use of tetra- -propylammonium perruthenate (TPAP).11 The presence of the tetra- -propylammonium cation renders this compound soluble in apolar media and allows the existence of a high concentration of perruthenate ion in organic solvents. The tetra- -propylammonium perruthenate is easily prepared and can be employed catalytically in CH2CI2 solution in the oxidation of alcohols to ketones and aldehydes, using /V-methyl morpholine A-oxide (NMO) as the secondary oxidant. 

Griffith, Ley et al. also described the tetra-n-butylarmnonium perruthenate (TBAP) since it is more difficult to prepare, its use is not as convenient as the employment of TPAP. 

Oxidations are typically performed at room temperature in CH2C12, using only 5 mol% of TPAP as being quite expensive, in the presence of ca. 1.5 equivalents of NMO. The addition of molecular sieves is often very beneficial, since they remove both the water formed during the reaction and present in NMO, which normally is hydrated. 

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