to
aldehyde with TPAP (0.06 eq.) and
N-methylmorpholine N-oxide (1.7 eq.) with molecular sieves in
dichloromethane.
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). 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. 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 or molecular oxygen. TPAP is also used to
cleave vicinal diols to form aldehydes. == References ==