Useful novel ketene O,O-acetals of the formula I ##STR1## where R.sup.1 is a tertiary alkyl radical of 4 to 6 carbon atoms or unsubstituted or halogen-substituted phenyl, R.sup.2 is hydrogen and R.sup.3 and R.sup.4 independently of one another are each phenyl which is unsubstituted or substituted by halogen, alkoxy, alkyl, phenyl, phenoxy, cyano, nitro or trifluoromethyl, their preparation and their use for the preparation of ketene O,N-acetals.