Bifunctional compounds of the formula ##STR1## where R.sup.1, R.sup.2 and R.sup.3 are each alkyl of 1 to 6 carbon atoms, R.sup.2 and R.sup.3 may furthermore be hydrogen, R.sup.2 is furthermore alkoxy and R.sup.4 is hydrogen, alkyl of 1 to 6 carbon atoms or alkoxy, and a double bond may be present between carbon atoms 2 and 3, are prepared by converting a tetraalkoxyalkane or a dialkoxyalkanoate of the formulae ##STR2## where R.sup.1, R.sup.2, R.sup.3 and R.sup.4 have the above meanings, in the presence of a catalyst, such as a zeolite, in particular one of the pentasil type, and/or a phosphate and/or phosphoric acid on a carrier.