CONDUCTANCE STUDIES OF ACID-BASE EQUILIBRIA IN 2,4,6-TRIMETHYLPYRIDINIUM TRIFLUOROACETATE IN NITROBENZENE

The conductance behaviour of solutions of 2,4,6-trimethylpyridinium trifluoroacetate (BHA) is presented over a wide range of concentration (10(-5)-10(-2) mol dm-3) in pure nitrobenzene and with addition of increasing amounts of free trifluoroacetic acid or free 2,4,6-trimethylpyridine. Using the Fuoss and Kraus linear relation F(z)/DELTA(c) = 1/DELTA(infinity) + DELTA(c)Cof2/F(z)(DELTA(infinity))2K, several apparent DELTA(infinity)s and Ks were obtained. This and the previous IR studies allowed division of the plot of the conductivity vs. acid-base mole ratio into eight sections. The following equilibrium constants have been evaluated: formation constants, K(f) = 1.3 x 10(7) (BHA); homoconjugation constants, K(h)- = 1.07 x 10(5) [(AHA)-]; K(h)+ = 24.4 [(BHB)+]; and dissociation constants, K(d) = 2.6 x 10(-6) (A- + HB+); K(c)- = 7.4 X 10(-2)[(AHA)- + HB+]; K(c)+ = 5.8 x 10(-5) [(BHB)+ + A-]. The results show that: (a) complex formation is not complete in the stoichiometric mixture; (b) addition of acid or base leads to formation of 2 : 1 and 1 : 2 acid-base complexes and homoconjugated anions or cations, respectively. Species AHAHB and AHA- are more stable than BHBA and BHB+; (c) anions are more mobile than cations.