Imidazole protonation constants were determined potentiometrically, using a (H+)-glass electrode, in LiCl, NaCl, KCl, CaCl2, MgCl2, tetramethylammonium (Me4N-) iodide and chloride, Et4N-, Pr4N- and Bu4N-iodides. Salt effects were tentatively explained by assuming that complexes [H(Im)X]o (Im = imidazole, X−=Cl− or I−), [M(Im)]2+ (M2+=Mg2+ or Ca2+) and [A(Im)]+ (A+ = tetraalkylammonium cation) were formed in solution. Calcium(II)-selective electrode measurements confirmed our hypothesis about the formation of the Ca2+-imidazole complex. The reliability of the complex formation model is discussed on the basis of its self consistency and in light of previous results.

Salt Effects on the Protonation of Imidazole in Aqueous Solution at Different Ionic Strengths: A Tentative Explanation by a Complex Formation Model.

DE ROBERTIS, Alessandro;DE STEFANO, Concetta;SAMMARTANO, Silvio
1989

Abstract

Imidazole protonation constants were determined potentiometrically, using a (H+)-glass electrode, in LiCl, NaCl, KCl, CaCl2, MgCl2, tetramethylammonium (Me4N-) iodide and chloride, Et4N-, Pr4N- and Bu4N-iodides. Salt effects were tentatively explained by assuming that complexes [H(Im)X]o (Im = imidazole, X−=Cl− or I−), [M(Im)]2+ (M2+=Mg2+ or Ca2+) and [A(Im)]+ (A+ = tetraalkylammonium cation) were formed in solution. Calcium(II)-selective electrode measurements confirmed our hypothesis about the formation of the Ca2+-imidazole complex. The reliability of the complex formation model is discussed on the basis of its self consistency and in light of previous results.
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11570/2174679
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