Intramolecular catalysis. Part 8. The intramolecular Cannizzaro reaction of naphthalene-1,8-dicarbaldehyde and [α,α′-2H2]naphthalene-1,8-dicarbaldehyde

Abstract

Naphthalene-1,8-dicarbaldehyde monohydrate has been shown to have a bridged (cyclic) structure in solution, as a cis–trans mixture. The hydrated dialdehyde, as well as the α,α′-dideuterio isomer, has been shown to undergo a Cannizzaro reaction in 70%(v/v) dioxane–water. The reaction has been found to be intramolecular and of the second order, i.e. first order in the monoanion of the hydrate and in base. The kinetic isotope effect, k_H/k_D, was found to be ca. 1.7 and the kinetic solvent isotope effect, k_H2O/k_D2O, ca. 0.60. The alkaline hydrolysis of the corresponding lactone of 8-(hydroxymethyl)-1-naphthoic acid (naphthalide) was studied under the same conditions. The lactone can be excluded as an intermediate in the intramolecular Cannizzaro reaction as it cannot be detected directly under conditions where it would be sufficiently long-lived. The evidence for the Cannizzaro reaction indicates a mechanistic pathway involving rate-determining hydride transfer in the chain tautomer of the dianion of the hydrate.