The protonation of furan- and thiophen-carboxamides

Abstract

The protonation behaviour in aqueous sulphuric acid solution of various furan- and thiophen-carboxamides has been investigated by u.v. spectrophotometry. The pK_BH⁺ values, calculated using the H_A acidity function and the Bunnett–Olsen linear free energy relationship, indicate the lower basicity of furan- and thiophen-2-carboxamides with respect to that of benzamides and of the 3-derivatives. The question of the site of protonation is also discussed.