Issue 17, 1994

Conductance studies of acid–base equilibria between 4-methoxy-2,6-dimethylpyridine N-oxide and trifluoroacetic acid in nitrobenzene

Abstract

The conductance behaviour of solutions of the equimolar complex (BHA) of 4-methoxy-2,6-dimethylpyridine N-oxide (B) with trifluoroacetic acid (HA) has been studied over a wide range of concentration (10–5–10–2 mol dm–3) in pure nitrobenzene and with the addition of increasing amounts of free 4-methoxy-2,6-dimethylpyridine N-oxide or free trifluoroacetic acid. Using the Fuoss and Kraus linear relation F(Z)/Λ= 1/ΛCy2/[F(z)(Λ)2K], several apparent values of Λ and K were obtained and constants of the equilibria affecting each other in a common reaction mixture were calculated: formation constants, Kf[gt-or-equal] 109(AHB), K1+= 3.7 (BHBA), Kl= 0.6 (AHAHB); homoconjugation constants, Kh+= 3.31 × 104[(BHB)+], Kh= 1.37 × 105[(AHA)], Khh= 1.9 [(A)(HA)2]; and dissociation constants, kc+= 1.21 × 10–3[(BHB)++ A], Kd= 1.36 × 10–7(A+ HB+); Kc= 3.0 × 10–2[(AHA)+ HB+]. Comparison with our earlier study of mixtures of 2,4,6-trimethylpyridine with trifluoroacetic acid shows that in both cases the stoichiometry of the chemical species is the same but the nature of the hydrogen bonds is different [e.g. in AHB, BHBA and (BHB)+]. The hydrogen bond is shown to be the major factor affecting the conductance of acid–base complexes.

Article information

Article type
Paper

J. Chem. Soc., Faraday Trans., 1994,90, 2489-2495

Conductance studies of acid–base equilibria between 4-methoxy-2,6-dimethylpyridine N-oxide and trifluoroacetic acid in nitrobenzene

P. Barczynski and M. Szafran, J. Chem. Soc., Faraday Trans., 1994, 90, 2489 DOI: 10.1039/FT9949002489

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