PURPOSE: In producing an unsaturated cycloacetal by condensing an unsaturated aldehyde with a polyhydric alcohol, to obtain the desired substance in high purity in high yield, by adding a specific substance to be reactive with the unsaturated aldehyde to the reaction mixture, extracting the desired compound with a specified solvent.

CONSTITUTION: In producing an unsaturated cycloacetal by condensing an unsaturated aldehyde with a polyhydric alcohol, after the reaction is over, the third substance (e.g., ammonia, amine, etc.) which will be reacted with the unsaturated aldehyde to give an inert reaction product of the unsaturated aldehyde, but not reacted with the unsaturated cycloacetal is added to the reaction mixture, and only the desired substance is extracted with a solvent (e.g., hexane, etc.) which will dissolve the unsaturated cycloacetal but has no compatibility with the inert reaction product.

EFFECT: Useful for removing irritating smell of the unsaturated aldehyde and eliminating reaction products produced by side reactions.