A spectrophotometric study of the protonation processes of some N-[1-(benzimidazol)-1-yl]methylbenzamide derivatives

The protonation of N-[1-(benzimidazol)-1-yl]methylbenzamide derivatives in aqueous acids (H2SO4) media was investigated, using a spectrophotometric method. The investigated compounds have two protonation processes. The first protonation process occurs in weakly acidic aqueous solutions (pH range) and refers to the protonation of the benzimidazole part of the molecule. The second protonation process occurs in concentrated sulfuric acid solutions and refers to protonation of the amide group. The protonation constants of the second process were calculated by the Hammett and Cox-Yates method. The effect of chemical structure on the ionisation constants is discussed. A correlation between the protonation constants and antimicrobial activity was established.