Oxidation of geraniol to geranial
Geraniol, the terpene alcohol of rose and palmarosa oils, has a primary allylic alcohol. Activated manganese dioxide oxidizes it selectively to the aldehyde, geranial (citral A), which has a strong lemon odour and is an intermediate in the industrial synthesis of vitamin A and the ionones.
The reaction is carried out in dichloromethane at room temperature with an excess of solid MnO2, which is removed by filtration. The oxidant does not touch saturated alcohols or double bonds and retains the E geometry of the conjugated double bond.