TPAP oxidation solvent

The commonest solvent for TPAP in organic oxidations is CH Clj (DCM), normally in conjunction with 4 A powdered molecular sieves (PMS) to remove water formed during the oxidation. Addition of CH3CN, as in many Ru-catalysed oxidations, makes reactions with TPAP/NMO more effective [59], and occasionally CH3CN is used as the only solvent [159]. Ionic liquids, e.g. [emim](PF )/PMS [479] and [bmim](BF )/PMS [480] have been used with TPAP/NMO. It has also been used in supercritical CO [457]. 

There are few reported oxidations of this type with TPAP in organic solvents, one of the advantages of the reagent being that the alcohol-to-aldehyde oxidation rarely proceeds further. One natural product which did involve such a step is antascomicin B using TPAP/NMO/PMS/CH Cl [85], In aqueous base however [RuO ] is a much more powerful oxidant than TPAP in organic media, perhaps because oxidation of aldehydes to carboxylic acids may proceed via an aldehyde hydrate, the formation of which is inhibited by the molecular sieves used in catalytic TPAP systems. 

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. 

The reaction mixture is filtered through a pad of Celite or silica gel and the resulting solution is concentrated, providing a residue that may need further purification. When the oxidation is performed in the presence of acetonitrile as solvent, as it tends to wash residual TPAP through the Celite or silica pad, it is advisable to evaporate the solvents and add some CH2C12 before the filtering. 

TPAP causes the isomerization of an allylic alcohol into an aldehyde. Best results are obtained using fluorobenzene as solvent, in the absence of a secondary oxidant and in the... 

Related and Modified Reagents. In addition to the standard reagent, a polymer-supported perruthenate (PSP) compound has been described. i Recent work has also examined the doping of organically modified silicas (ormosils) with TPAP via a sol-gel process, 7 which enhances the general versatility and reusability of TPAP catalysts. The use of supercritical carbon dioxide as a solvent has also been investigated. TPAP has also found use as a convenient source of ruthenium in mthenium-catalyzed hypochlorite oxidations. ... 

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