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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,*
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 which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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MDPI and ACS Style

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.

AMA Style

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(4):94-103.

Chicago/Turabian Style

Kaczmarczyk, Ewa; Puszko, Aniela; Lorenc, Jadwiga; Chmurzynski, Lech. 1999. "A Study of Acid-Base Equilibria in Acetonitrile Systems of 2-Halo(Cl,Br,I)-4-nitropicoline(3,5,6) N-oxides." Molecules 4, no. 4: 94-103.



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