P. Barczynski et M. Szafran, CONDUCTANCE STUDIES OF ACID-BASE EQUILIBRIA BETWEEN 4-METHOXY-2,6-DIMETHYLYPYRIDINE N-OXIDE AND TRIFLUOROACETIC-ACID IN NITROBENZENE, Journal of the Chemical Society. Faraday transactions, 90(17), 1994, pp. 2489-2495
Citations number
49
Categorie Soggetti
Chemistry Physical","Physics, Atomic, Molecular & Chemical
The conductance behaviour of solutions of the equimolar complex (BHA)
of 4-methoxy-2,6-dimethylpyridine N-oxide (B) with trifluoroacetic aci
d (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 triflu
oroacetic acid. Using the Fuoss and Kraus linear relation F(z)/LAMBDA
= 1/LAMBDA(infinity) + LAMBDACy2/[F(z)(LAMBDA(infinity)2K], several ap
parent values of LAMBDA(infinity) and K were obtained and constants of
the equilibria affecting each other in a common reaction mixture were
calculated: formation constants, K(f) greater-than-or-equal-to 10(9)
(AHB), K1+ = 3.7 (BHBA), K1- = 0.6 (AHAHB); homoconjugation constants,
K(h)+ = 3.31 x 10(4) [(BHB)+], K(h)- = 1.37 x 10(5) [(AHA)-], K(hh)-
= 1.9 [(A)-(HA)2]; and dissociation constants, K(c)+ = 1.21 x 10(-3) [
(BHB)+ + A-], K(d) = 1.36 x 10(-7) (A- + HB+); K(c)- = 3.0 x 10(-2) [(
AHA)- + HB+]. Comparison with our earlier study of mixtures of 2,4,6-t
rimethylpyridine with trifluoroacetic acid shows that in both cases th
e 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 h
ydrogen bond is shown to be the major factor affecting the conductance
of acid-base complexes.