Kinetics of the alkaline hydrolysis of 1,8-bis(trifluoroacetylamino)naphthalene to 1-amino-8-trifluoroacetylaminonaphthalene in 70%, 80% and 90%(v/v) Me2SO–H2O

Abstract

The kinetics of the hydrolysis of 1,8-bis(trifluoroacetylamino)naphthalene to 1-amino-8-trifluoroacetylaminonaphthalene have been studied in 70%, 80% and 90%(v/v) Me₂SO–H₂O in the presence of hydroxide ion. Under these conditions the product of the reaction is present as the amide anion and does not undergo further reaction. Approximate values of pK₁ 5.7 and pK₂ 15.9 have been measured in 70%(v/v) Me₂SO–H₂O for dissociation of the amide protons of 1,8-bis(trifluoroacetylamino)naphthalene. The hydrolysis involves reaction of the amide monoanion because negligible concentrations of the undissociated amide are present and the dianion is unreactive. The dependence of the first-order rate coefficient (k_obs) on [OH^–] in 70% and 80%(v/v) Me₂SO–H₂O is fitted by the expression k_obs=(k₀+k₁[OH^–]+k₂[OH^–]²)/(1 +K″[OH^–]) where K″ is the equilibrium constant for proton removal by hydroxide ion from the monoanion of 1,8-bis(trifluoroacetylamino)naphthalene to give the dianion. The magnitude of k₀ in 70%(v/v) Me₂SO–H₂O suggests that the attack of water on the amide carbonyl at the 1-position is assisted by intramolecular catalysis involving the amide anion at the 8-position. The data in 90%(v/v) Me₂SO–H₂O are fitted by the expression k_obs=(k₂/K″)[OH^–]. Under these conditions the amide is practically fully dissociated into the dianion and the k₀ and k₁[OH^–] terms are negligibly small in comparison with the k₂[OH^–]² term.