Intramolecular catalysis of the hydrolysis of an acetal by an internally hydrogen-bonded hydroxy group

Abstract

The hydrolysis of 1-methoxymethoxy-8-hydroxynaphthalene in aqueous solution at pH 2–4 is catalysed by the hydronium ion and the value of the catalytic coefficient is similar to that for 1-methoxymethoxynaphthalene. In the range pH 5–10 a pH-independent reaction with solvent is dominant and the rate coefficient for the neutral hydrolysis is estimated to be ca. 40-fold higher for 1-methoxymethoxy-8-hydroxynaphthalene than for 1-methoxymethoxynaphthalene. This is attributed to intramolecular catalysis by the hydrogen-bonded hydroxy group. As bond breakage and charge development occur in the transition state the internal hydrogen bond in the leaving group is strengthened.