Process for producing .alpha.,.beta.-unsaturated aldehydes

A process for producing a compound of the formula (II):

• ##STR16## wherein R.sup.1 and R.sup.2 are each hydrogen or a straight-chain or branched alkyl group having 1 to 6 carbon atoms, R.sup.3 is hydrogen or an unsubstituted or substituted hydrocarbon group having 1 to 20 carbon atoms, and n is an integer of 1 to 10, which comprises:
• reacting a compound of the formula (IV):
• ##STR17## wherein X is halogen and the other symbols are as defined above, with hexamethylenetetramine in a solvent selected from water, an organic solvent or a combination thereof, wherein the organic solvent is selected from the group consisting of halogenated hydrocarbons, ethers, esters, amides and alcohols, to give a compound of the formula (I):
• ##STR18## wherein each symbol is as defined above and a compound of the formula (II):
• ##STR19## wherein each symbol is as defined above;
• followed by, if necessary, adding water or organic solvent as defined above to the reaction mixture, and then separating the resultant mixture into aqueous and organic layers, and
• i) subjecting the resultant compound of the formula (I) in the aqueous layer to hydrolysis in the presence of an organic solvent homogenously immiscible with water wherein the organic solvent is selected from the group consisting of halogenated hydrocarbons, ethers and esters, while
• ii) reacting the resultant compound of the formula (II) in the organic solvent as defined above with sodium hydrogensulfite to give a compound of the formula (III):
• ##STR20## wherein each symbol is as defined above, and iii) reacting the resultant compound of the formula (III) with formaldehyde in water and an organic solvent homogenously immiscible with water and the organic solvent as defined above.