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The modified method of spectro-pehametric determination of dissociation constants

Michałowski T., Wybraniec S., Ponikvar M.

Chemia Analityczna

2008

Vol. 53, No. 5

737-742

A Potentiometric Study of the Acid Dissociation and Cationic Homoconjugation Equlibria in Substituted Pyridine N-Oxide Systems in Binary Polar Solvents, Acetonitrile-Acetone and Acetonitrile-Dimethyl Sulfoxide

Wróbel R.

Polish Journal of Chemistry

2001

Vol. 75, nr 9

1341-1350

Acid dissociation constants of protonated substituted pyridine N-oxides and cationic homoconjugation constants of these acids with conjugate N-oxides have been determined by potentiometric titration in mixed polar non-aqueous solvents (acetonitrile - acetone and acetonitrile - dimethyl sulfoxide) with increasing (from 0 to 1) mole fraction of acetonitrile. In acetonitrile - dimethyl sulfoxide mixtures, the acid dissociation constants (expressed as pKa) and cationic homoconjugation constants (expressed as log KBHB+) vary non-linearly with increasing mole fraction of acetonitrile. In systems with the least basic N-oxides, local minima of pKa have been observed. In acetonitrile-acetone mixtures, both the pKa and the cationic homoconjugation constant values changed irregularly in the acid-base systems studied and the character of those variations could not be unambiguously determined.