Process for the preparation of citral

A process for the preparation of citral, comprising cracking prenal diprenyl acetal in the vapor phase in the presence of a heterogeneous acid catalyst, said acid catalyst being selected from a group of catalysts that do not convert more than 30 % of citral to other products when a stream of citral at a flow rate of 4 ml/h is introduced into a reactor containing 1 ml of said catalyst between two 5 ml quartz beds heated to a temperature of 300.degree. C. for one hour in the presence of a stream of nitrogen at a flow rate of 3 l/h, wherein the catalyst is selected from the group consisting of a zeolite, an oxide of a metal selected from columns IIIb to VIb of the periodic table of elements and phosphate, silicate or chromite salts.