Intramolecular catalysis. Part 5. The intramolecular Cannizzaro reaction of o-phthalaldehyde and [α,α′-2H2]-o-phthalaldehyde

Abstract

o-Phthalaldehyde, as well as the α,α′-dideuterio isomer, has been shown to undergo a Cannizzaro reaction in water containing base, while partially hydrated and ionised. The reaction of the monoanion of the hydrate is intramolecular and of the first order in the monoanion of the hydrate, and either first or zero order in the base. The rate coefficients have been measured at several temperatures and activation parameters evaluated. The kinetic isotope effect, k_H/k_D, for the first and second order processes were found to be ca. 1.9 and 1.8, respectively. The alkaline hydrolysis of the corresponding lactone, phthalide, has also been studied under the same conditions. The evidence for the intramolecular Cannizzaro reaction indicates a mechanistic pathway involving rate-determining hydride transfer from the chain tautomers of both monoanion and dianion of the hydrate.