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Determination of pKa values of some novel benzimidazole salts by using a new approach with 1H NMR spectroscopy

Benzimidazoles and their derivatives including imidazole are studied widely because they exist in the structure of natural products and different drugs. pKa values are extremely important for drug discovery and improvement in order to determine pharmacokinetic and pharmacodynamic features such as permeation through biological barriers, interactions with the target area or side effects. Acid–base features (pKa) have great importance not only for physiological characteristics but also for being used as a ligand or changing physico‐chemical features by turning benzimidazoles into salts. Within the scope of this study, a variety of new benzimidazole salts were synthesized, and their characterizations were made by NMR spectroscopy, FTIR spectroscopy and element analysis techniques. The pKa values of synthesized benzimidazole salts were determined by inflection point approach using integration values obtained with 1H NMR spectroscopy and Henderson–Hasselbalch analysis. pKa values of some benzimidazole salts were also determined by potentiometric methods in order to compare those of NMR spectroscopy results. Copyright © 2015 John Wiley & Sons, Ltd.