Tetrapropylammonium Perruthenate (TPAP)
Tetrapropylammonium perruthenate, TPAP, is a readily soluble, nonvolatile, air stable oxidant for alcohols. The commercial available reagent can be used in catalytic amounts in the presence of a stoichiometric oxidant, operates at room temperature and is devoid of obnoxious or explosive side products. Suitable co-oxidants are hydroperoxides or N-methylmorpholine N-oxide (NMO), which seems to be the most effective. In oxidations of primary alcohols, TPAP/NMO gives aldehydes rather than carboxylic acids in nonaqueous solutions in the presence of molecular sieves. The presence of water fosters an equilibrium concentration of the aldehyde hydrate, which can undergo further oxidation to the carboxylic acid. (Review: S. Ley, J. Norman, W. P. Griffith, S. P. Marsden, Synthesis, 1994, 639. Abstract)
Tetrapropylammonium perruthenate enables oxidations of a wide range of molecules including examples of both double oxidations and selective oxidations. Mechanistic studies and general experimental procedures are reported. In addition several interesting developments in the chemistry of this reagent are outlined: heteroatom oxidation, cleavage reactions and use in sequential reaction processes.
S. B. Ley, J. Norman, W. P. Griffith, S. P. Marsden, Synthesis, 1994, 639-666.
In a simple, mild, and highly effective method for the direct conversion of primary alcohols to carboxylic acids, TPAP serves as the catalyst, and NMO • H2O plays a dual role, acting as the co-oxidant and as a reagent for aldehyde hydrate stabilization. This previously unknown stabilizing effect of geminal diols by N-oxides is the key for the efficiency of the overall transformation.
A.-K. C. Schmidt, C. B. W. Stark, Org. Lett., 2011, 13, 4164-4167.
An efficient method for the oxidation of an olefin to the less substituted carbonyl compound is described. This one pot conversion includes hydroboration with borane dimethyl sulfide (BDMS), followed by oxidation of the resulting alkylboranes with tetrapropylammonium perruthenate (TPAP) and NMO.
M. H. Yates, Tetrahedron Lett., 1997, 38, 2813-2816.