Tetrapropylammonium perruthenate explained

Tetrapropylammonium perruthenate (TPAP or TPAPR) is the chemical compound described by the formula N(C₃H₇)₄RuO₄. Sometimes known as the Ley–Griffith reagent, this ruthenium compound is used as a reagent in organic synthesis. This salt consists of the tetrapropylammonium cation and the perruthenate anion, .

Uses

Ruthenium tetroxide is a highly aggressive oxidant, but TPAP, which is its one-electron reduced derivative, is a mild oxidizing agent for the conversion of primary alcohols to aldehydes (the Ley oxidation).^[1] Secondary alcohols are similarly oxidized to ketones. It can also be used to oxidize primary alcohols all the way to the carboxylic acid with a higher catalyst loading, larger amount of the cooxidant, and addition of two equivalents of water. In this situation, the aldehyde reacts with water to form the geminal diol hydrate, which is then oxidized again.^[2]

The oxidation generates water that can be removed by adding molecular sieves. TPAP is expensive, but it can be used in catalytic amounts. The catalytic cycle is maintained by adding a stoichiometric amount of a co-oxidant such as N-methylmorpholine N-oxide^[3] or molecular oxygen.^[4]

TPAP is also used to cleave vicinal diols to form aldehydes.

Notes and References

1. Steven V. . Ley . Steven V. Ley. Joanne . Norman . William P. . Griffith . Stephen P. . Marsden . Tetrapropylammonium perruthenate, Pr₄N⁺RuO₄^-, TPAP: A catalytic oxidant for organic synthesis . . 1994 . 7 . 1994 . 639–666 . 10.1055/s-1994-25538. 95136192 . (review article)
2. Applications of Zr-catalyzed carbomagnesation and Mo-catalyzed macrocyclic ring closing metathesis in asymmetric synthesis. Enantioselective total synthesis of Sch 38516 (Fluvirucin B₁) . Z. . Xu . C. W. . Johannes . A. F. . Houri . D. S. . La . D. A. . Cogan . G. E. . Hofilena . A. H. . Hoveyda . . 1997 . 119 . 43 . 10302–10316 . 10.1021/ja972191k.
3. Preparation and use of tetra-n-butylammonium per-ruthenate (TBAP reagent) and tetra-n-propylammonium per-ruthenate (TPAP reagent) as new catalytic oxidants for alcohols . William P. . Griffith . Steven V. . Ley . Steven V. Ley . Gwynne P. . Whitcombe . Andrew D. . White . . 21 . 1987 . 1625–1627 . 10.1039/C39870001625.
4. Tetra-n-propylammonium perruthenate (TPAP)-catalysed oxidations of alcohols using molecular oxygen as a co-oxidant . Roman . Lenz . Steven V. . Ley . Steven V. Ley . J. Chem. Soc., Perkin Trans. 1. 22 . 1997 . 3291–3292 . 10.1039/A707339I.