Acid-base equilibria of substituted pyridine N-oxides in methanol |
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Authors: | Lech Chmurzyński |
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Institution: | (1) Institute of Chemistry, University of Gdansk, Sobieskiego 18, 80952 Gdansk, Poland;(2) Present address: School of Medicine, University of Maryland, Department of Surgery, Tinnitus Research Laboratory, 10 S. Pine St., MSTF Building, Room 434F, 21201-1192 Baltimore, MD |
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Abstract: | Acid dissociation constants in methanol for eight substituted pyridine N-oxides having a wide range of acid-base properties, quinoline N-oxide (bi-cyclic amine N-oxide) and pyridine (heterocyclic amine)] have been determined using the potentiometric titration method. A linear correlation between ourmethanol data and aqueous pK
a
values from the literature has been found. As in polar aprotic solvents cationic homoconjugation phenomenon has been found to be present for sufficiently basic N-oxides. The tendency of substituted pyridine N-oxides towards cationic homoconjugation in methanol is weaker than in polar aprotic solvents and increases with increasing basicity of N-oxides. It has also been found that, in contrast to polar aprotic solvents, the cationic homoconjugation phenomenon in methanol is much more pronounced for heterocyclic amines than their N-oxides. |
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Keywords: | Acid dissociation cationic homoconjugation equilibrium constants substituted pyridine N-oxides methanol |
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