POTENTIOMETRIC TITRATIONS OF SOME 2-SUBSTITUTED 5-NITROBENZIMIDAZOLE DERIVATIVES IN NONAQUEOUS SOLVENT


PUTUN A., BEREKET G., KESKIN E.

JOURNAL OF CHEMICAL AND ENGINEERING DATA, vol.40, no.1, pp.221-224, 1995 (SCI-Expanded) identifier identifier

  • Publication Type: Article / Article
  • Volume: 40 Issue: 1
  • Publication Date: 1995
  • Doi Number: 10.1021/je00017a046
  • Journal Name: JOURNAL OF CHEMICAL AND ENGINEERING DATA
  • Journal Indexes: Science Citation Index Expanded (SCI-EXPANDED), Scopus
  • Page Numbers: pp.221-224
  • Anadolu University Affiliated: No

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'-hydroxyphenyl) > 2-phenyl > 5-nitrobenzimidazole > 2-(4'-methoxyphenyl) > 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.