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

General-acid catalysis has been detected in the hydrolysis of OO-benzylidenecatechol with a Brønsted -value of 0·47 for catalysis by carboxylic acids. There is also a relatively fast spontaneous hydrolysis with k(H2O)/(D2O)= 1·61 and S=–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-SE2 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 approximately 1 and k(H3O+)/k(D3O+)= 0·67 at 15°. An A-SE2 mechanism was also favoured for this reaction