A process for the preparation of glutaric dialdehyde by the reaction of alkoxy dihydropyrans of the general formula I ##STR1## in which R stands for C.sub.1 to C.sub.20 alkoxy, with water at temperatures ranging from 0.degree. to 150.degree. C. and pressures of from 0.01 to 50 bar in the presence of a which microporous, crystalline aluminum silicate catalyst, e.g. a beta-type zeolite or pentasil catalyst having a pore diameter greater than 5.4 .ANG..
In a process for the continuous preparation of glutaraldehyde by reaction of an alkoxydihydropyran of the formula I ##STR1## where R is C.sub.1 -C.sub.20 -alkyl, with water at from 0.degree. C. to 200.degree. C. and a pressure in the range from 0.01 bar to 16 bar to form glutaraldehyde and the alcohol corresponding to the alkoxy group, water and alkoxydihydropyran are fed continuously to a reaction column and a distillate enriched in the alcohol corresponding to the alkoxy group is taken off at the top of the column and a product enriched in glutaraldehyde is taken off at the bottom. This process makes it possible to prepare glutaraldehyde or C-substituted glutaraldehydes continuously in high purity in a simple manner with a low outlay in terms of apparatus.
