Preparation of alpha, beta-unsaturated ketones

A process for the preparation of an alpha, beta-unstaturated ketone of the formula I ##STR5## where R.sup.1, R.sup.2 and R.sup.3 are each hydrogen, alkyl, alkenyl of 1 to 12 carbon atoms, cycloalkyl, aryl, aralkyl or alkylaryl, which in turn may be substituted, or R.sup.1 J and R.sup.3 or R.sup.2 and R.sup.3 together with the carbon atoms to which they are bonded may form a cycloalkane or cycloalkene radical, wherein a hydroxy- alkoxy- or carboxyketone of the formula II ##STR6## where R.sup.1, R.sup.2 and R.sup.3 have the above meanings and R.sup.4 is hydrogen, alkyl or carboxyl, is converted in the gas phase at a temperature of from 100.degree. to 500.degree. C. in the presence of an acidic catalyst selected from the group consisting of a zeolite, a phosphate, a metal oxide and phosphoric acid on a carrier.