Ayse E. Puetuen, G. Bereket, E. Keskin
1995
Citations
0
Influential Citations
16
Citations
Journal
Journal of Chemical & Engineering Data
Abstract
The acidity constants of 16 2-substituted 5-nitrobenzimidazole derivatives were determined in dimethyl sulfoxide, 60% (v/v) isopropyl alcohol+40% (v/v) water, and 60% (v/v) dimethyl sulfoxide+40% (v/v) water by the potentiometric method. Tetrabutylammonium hydroxide was used as the titrant for the measurements done in dimethyl sulfoxide as a solvent, and aqueous KOH was used for the measurements done in mixtures. The pK a values were obtained from the half-neutralization potentials which were obtained from an analysis of the potentiometric titrations. The order of the acidic strengths obtained depends on the alkyl, aryl, and heterocyclic substituents on 5-nitrobenzimidazole. The acidic strengths of the alkyl-substituted 5-nitrobenzimidazoles in each solvent were in the following order: 2-(trifluoromethyl)>2-(difluorochloromethyl)>2-(chloromethyl)>3-nitrobenzimidazole> 2-methyl > 2-(hydroxymethyl)-5-nitrobenzimidazole. The acidic strengths of the aryl-substituted 5-nitrobenzimidazoles in each solvent were in the following order: 2-(4'-chlorophenyl)> 2-(2'-chlorophenyl)>2-(3'-chlorophenyl) >2-(2'-hydrophenyl)>2-phenyl>5-nitrobenzimidazole>2-(4'-methophenyl)> 5-nitrobenzimidazole. The increasing acidic strengths of the heterocyclic-group-substituted 5-nitrobenzimidazoles for three solvent systems were in the order 2-(2'-thienyl)>2-(2'-pyridyl)> 2-(3'-pyridyl)>2-(2'-furyl)>5-nitrobenzimidazole