Ionone or 4-(2,6,6-trimethyl-1-cyclohexen-1-yl)-3-Buten-2-one or cyclocitrylideneacetone or irisone C₁₃H₂₀O is a chemical substance and part of the terpene family. Ionone is a aroma compound. It is a pale yellow liquid with a woody, dry, fruity, raspberry and violet smell. It is a raw material for the production of retinol

Beta ionone (left) has a less pronounced odor than alpha ionone (right).

Organic synthesis

Ionone can be synthesised from citral and acetone with Calcium oxide as a basic heterogeneous catalysis^[1] and serves as an example of an Aldol condensation followed by a rearrangement reaction.

The nucleophilic addition of the carbanion 3 of acetone 1 to the carbonylgroup on citral 4 is base catalysed. The aldol condensation product 5 eliminates water throught the enolate ion 6 to the pseudoionone 7.

The reaction proceeds by acid catalysis where the double bond in 7 opens to form the carbocation 8. A rearrangement reaction of the carbocation follows with ring closure to 9. Finally a hydrogen atom can be abstracted from 9 by a acceptor molecule (Y) to form either 10 (extended conjugated system) or 11.

References

• ^[1] NODA, C., ALT, G. P., WERNECK, R. M. et al. Aldol Condensation of Citral with Acetone on Basic Solid Catalysts. Braz. J. Chem. Eng., June 1998, vol.15, no.2. ISSN 0104-6632. [1] open access publication