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Molecules 1999, 4(4), 94-103; doi:10.3390/40400094
Article

A Study of Acid-Base Equilibria in Acetonitrile Systems of 2-Halo(Cl,Br,I)-4-nitropicoline(3,5,6) N-oxides

1, 2, 2 and 1,*
1 Department of General Chemistry, University of Gdansk, Sobieskiego 18, 80-952 Gdansk, Poland 2 Department of Organic Chemistry, School of Economics, Wroclaw, Poland
* Author to whom correspondence should be addressed.
Received: 9 March 1998 / Accepted: 8 March 1999 / Published: 29 March 1999
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Abstract

An attempt has been made to determine potentiometrically (1) acid dissociation constants of cations obtained by protonation of nine trisubstituted pyridine N-oxides, namely 2-halo(Cl, Br and I)-4-nitropicoline N-oxides with the methyl group at positions 3, 5, and 6, as well as (2) the cationic homoconjugation constants of these cationic acids with conjugated N-oxides in acetonitrile. On the basis of the substitution effect, variations of the acid dissociation constants of the trisubstituted pyridine N-oxide cations are discussed. The determined pKa values of the protonated 2-halo-4-nitropicoline N-oxides are compared with the previously determined equilibrium constants of the cationic acids conjugated with the mono- and disubstituted pyridine N-oxides in acetonitrile. Further, based on the pKa values of the protonated 2-halo-4-nitropicoline N-oxides in acetonitrile, supplemented with correlations between pKa’s of the protonated mono- and disubstituted pyridine N-oxides in acetonitrile and water, the pKa's of the acids conjugated with the trisubstituted N-oxides studied in aqueous solutions have been estimated. Moreover, it has been concluded that the cationic homoconjugation constants cannot be determined by potentiometric titration in acetonitrile solutions of the 2-halo-4-nitropicoline N-oxide systems.
Keywords: acidic dissociation; cationic homoconjugation; 2-halogeno(Cl; Br; I)-4-nitro- (3; 5; 6)-picoline N-oxides; potentiometric titration; acetonitrile acidic dissociation; cationic homoconjugation; 2-halogeno(Cl; Br; I)-4-nitro- (3; 5; 6)-picoline N-oxides; potentiometric titration; acetonitrile
This is an open access article distributed under the Creative Commons Attribution License (CC BY 3.0).

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Kaczmarczyk, E.; Puszko, A.; Lorenc, J.; Chmurzynski, L. A Study of Acid-Base Equilibria in Acetonitrile Systems of 2-Halo(Cl,Br,I)-4-nitropicoline(3,5,6) N-oxides. Molecules 1999, 4, 94-103.

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