Aerobic oxidation of alcohols to aldehydes (Yeda)
The catalytic oxidation of alcohols using ground state molecular oxygen, O2, as a primary oxidant has attracted many researchers motivated by the apparent ecological advantage that such a transformation would have compared to other methods. The great significance of this synthetic method is that the selective oxidation of alcohols to aldehydes without over-oxidation to carboxylic acids is challenging. Thus, a technique for the selective and specific oxidation with O2 of primary alcohols to aldehydes can be valuable.
High yields of aldehyde product (80-95 mol %)
Fast aerobic oxidation of alcohols.
Highly specific towards primary alcohols.
No need for a base during activation of catalysis.
Synthesis of aldehydes from primary alcohols.
A sandwich type polyoxometalate is used as a ligand to attach a palladium(II) center. This Pd-POM compound is an active catalyst for the fast aerobic oxidation of alcohols. The unique property of this catalyst is its significant preference for the oxidation of primary versus secondary aliphatic alcohols. This is a result of the intrinsically higher probability for oxidation of primary alcohols attenuated by steric factors as borne out by the higher reactivity of for example 1-octanol versus 2-ethyl-1-hexanol. The reaction is highly selective to aldehyde with little formation of carboxylic acid; autooxidation is inhibited. No base is required to activate the alcohol. The fast reactions, where typically lless than 1 hour is needed, appear to be related to the electron-acceptor nature of the polyoxometalate ligand.
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