The kinetics and mechanism of the hydrolysis of 2,3-(phenylmethylenedioxy)benzene (Oo′-benzylidenecatechol) and benzaldehyde diphenyl acetal

Abstract

General-acid catalysis has been detected in the hydrolysis of OO′-benzylidenecatechol with a Brønsted α-value of 0·47 for catalysis by carboxylic acids. There is also a relatively fast spontaneous hydrolysis with k(H₂O)/(D₂O)= 1·61 and ΔS‡=–21·1 cal deg^–1 mol^–1 at 75°. The entropy of activation for the hydronium-ion catalysed reaction is –8·78 cal deg^–1 mol^–1 and the isotope effect k(H₃O⁺)/k(D₃O⁺)= 0·92 at 75°. These reactions are thought to proceed via A-S_E2 mechanisms.

The hydrolysis of benzaldehyde diphenyl acetal is much faster than that of benzylidenecatechol and in 20%(w/w) dioxan–water mixtures is also general-acid catalysed with α approximately 1 and k(H₃O⁺)/k(D₃O⁺)= 0·67 at 15°. An A-S_E2 mechanism was also favoured for this reaction.