Proton transfer from amides to hydroxide ion and buffers in 70%(v/v) Me2SO–H2O

Abstract

Dissociation of the amide proton from several substituted 1-benzoylaminonaphthalenes has been studied in 70%(v/v) Me₂SO-H₂O in the presence of buffers and hydroxide ion. The acidity varies over 7 pK units depending on the substituent. 1,8-Bis(benzoylamino)naphthalene and 1,8-bis(4-nitrobenzoylamino)naphthalene are, respectively, 3 and 5.5 pK units more strongly acidic than 1-benzoylaminonaphthalene. The kinetics of the ionisation of 1,8-bis(benzoylamino) naphthalene has been studied in the presence of buffers. Proton removal from the amide by 4-chlorophenolate and 2-bromophenolate ions occurs with rate coefficients of 1.66 × 10⁷ and 0.58 × 10⁷ dm³ mol^–1 s^–1 respectively and, in the reverse direction the values of the rate coefficients for protonation of the amide anion by the phenols are 1.27 × 10⁷ and 2.8 × 10⁷ dm³ mol^–1 s^–1, respectively. The values are lower than those expected for amide ionisation and possible explanations are discussed.