Determination of thermodynamic pK_a values of benzimidazole and benzimidazole derivatives by capillary electrophoresis

Abstract

Thermodynamic pK(a) values for benzimidazole and several substituted benzimidazoles were determined by CE. Electrophoretic mobilities of benzimidazoles were determined by CE at different pH levels and ionic strengths. The dependence of electrophoretic mobilities on pH was used to obtain pK(a) values at different ionic strengths. Extrapolations to zero ionic strength were used to determine the thermodynamic pK(a) values. Using this method the thermodynamic pK(a) values of 15 benzimidazoles were determined and found to range from 4.48 to 7.38. Results from the CE measurements were compared with spectrophotometric measurements which were evaluated at wavelengths where the highest absorbance difference for varying pH was recorded. The two analytical techniques were in good agreement.

Determination of pKa values of benzimidazole derivatives from mobility obtained by capillary electrophoresis

“…The values are respectively for 1 (5.24; 5.21; 5.25) and 2 (4.60; 4.57; 4.67). Good agreement was recently reported with similar molecules [15,16].…”

The separation of nickel(II) from base metal ions using 1-octyl-2-(2′-pyridyl)imidazole as extractant in a highly acidic sulfate medium

“…This suggests that one proton will be tightly held between the pyridyl and the imidazolyl nitrogen in weakly acidic solutions while the second proton is only accommodated in strongly acidic solutions. The pK 1 value is intermediate between that of imidazole (6.95) and pyridine (5.26) (Pettit and Powell, 2007), and is closer to that of benzimidazole (5.49) (Jerez et al, 2009). The relatively weak-to-mild σ-donicity and the good π-acceptor capability of this ligand infer interesting coordination chemistries towards the base metal ions to the effect that there is an apparent discrimination in its interaction with these metals as a function of pH.…”

Determination of acid dissociation constants of triazole fungicides by pressure assisted capillary electrophoresis

“…The determinations of pK a s by CE usually are not limited by the sample contaminants, if they do not interact with analyzed compounds and if they can be electrophoretically separated from them. The CE determinations of pK a s are commonly performed in aqueous solutions at pH range from 2 to 12 [26,27], or in mixed hydro-organic [19] and organic solvents [24]. The determination of pK a of very weak bases (pK a < 2) is complicated by high ionic strength and high electric conductivity of the strongly acidic background electrolytes (BGEs) and very low electroosmotic flow (EOF) at low pH, which significantly prolongs the time for determination of electroosmotic and effective mobilities.…”