Method for producing enol ethers

A process for the preparation of enol ethers of the formula I

• wherein R1 is an aliphatic, cycloaliphatic, araliphatic, aromatic or heterocyclic radical which may carry further substituents which do not react with acetylenes or allenes, and the radicals R, independently of one another, are hydrogen or aliphatic, cycloaliphatic, araliphatic, aromatic or heterocyclic radicals, which may be bonded to one another to forma ring, and m is 0 or 1, wherein an acetal or ketal of the formula II
• is reacted with an acetylene or allene of the formula III or IV
• where R and R1 have the abovementioned meanings, in the gas phase at a temperature from 50 to 400° C. in the presence of a heterogeneous catalyst selected from the group consisting of a zinc- silicon- and oxygen-containing heterogeneous catalyst and a cadmium- silicon- and oxygen-containing heterogeneous catalyst.