Mesityl oxide is a α,β-unsaturated ketone with the formula CH3C(O)CH=C(CH3)2.

This compound is a colorless, volatile liquid with a honey-like odor.

[3] It is prepared by the aldol condensation of acetone to give diacetone alcohol, which readily dehydrates to give this compound.

[4][5] Phorone and isophorone may be formed under the same conditions.

Isophorone originates via a Michael addition: Phorone is formed by continued aldol condensation: Mesityl oxide is used as a solvent and in the production of methyl isobutyl ketone by hydrogenation:[5] Further hydrogenation gives 4-methyl-2-pentanol (methyl isobutyl carbinol).