PURPOSE: To increase the selectivity of unsaturated aldehyde, and to decrease the yield of high-boiling by-products in the preparation of unsaturated aldehyde by the condensation of acetaldehyde, or acetaldehyde and crotonaldehyde, etc., by carrying out the reaction in the presence of hydrocarbons and water.

CONSTITUTION: In the preparation of crotonaldehyde and sorbaldehyde by the condensation of acetaldehyde, acetaldehyde and crotonaldehyde, or acetaldehyde and aldol using an amine and an acid as catalysts, the reaction is carried out in the presence of a hydrocarbon and water. The hydrocarbon is e.g. aliphatic hydrocarbon, aromatic hydrocarbon and their halogen-substituted compound (e.g. hexane, benzene, chloronaphthalene, etc.). The amounts of the hydrocarbon and water to be added to the raw material are 10W100wt%, and 10W100wt%, respectively. The reaction is carried out under N2 stream at 80W200°C for 5W120min.

USE: Intermediate of n-butanol, sorbic acid, etc.