Protonation constants of some N-substituted thiophene-2-carboxamidoximes

The stoichiometric protonation constants of some N-substituted thiophene-2- carboxamidoximes have been determined in 50% ethanol-water mixture (v/v) at ionic strength of 0.1 M NaClO4 and at 25 degrees C A potentiometric titrat ion method was used and calculation was done by using recently developed so ftware. Variations of the protonation constant of these compounds were disc ussed in view of structural effects exerted on amino nitrogen and thiopheny l moiety by the substituents. (C) 1999 Elsevier Science B.V. All rights res erved.