Condensation of aldehydes with ketones by multiphase reaction

A process for preparing an α,β-unsaturated ketone of the formula I

• where R1 and R2 each independently represent a branched or unbranched, saturated or unsaturated aliphatic or cycloaliphatic-aliphatic hydrocarbon radical of 1 to 20, carbon atoms or a saturated or unsaturated cycloaliphatic hydrocarbon radical of 5 to 12 carbon atoms which may contain alkyl groups as substituents, or an endoalkylene group or an araliphatic hydrocarbon radical of 7 to 15 carbon atoms, or an aromatic hydrocarbon radical, R3 represents hydrogen or an aliphatic hydrocarbon radical of 1 to 10 carbon atoms, wherein R1 and R3 may combine with the two adjacent carbon atoms to form members of a common alicyclic ring and wherein in R1, R2 and R3 one or more methylene groups which are not α-disposed relative to a carbonyl group may be substituted by an oxygen or sulfur atom, which process comprises reacting an aldehyde of the formula II with a ketone of the formula III, where R1, R2 and R3 are each as defined above, in the liquid phase in a tubular reactor
• wherein the catalyst is present in the continuous phase and at least one reactant is present in a dispersed phase and a loading factor B of the tubular reactor is not less than 0.8.