Conductimetric titrations of acids and bases in benzene and dioxane

Abstract

Acid-base tit rations were made conductimetrically in pure benzene and dioxan e with picric, t ri chloroacetic, and camphorsulfoni c acids, together with primary, secondary, and tertiary amines. Although the conductances of the solutions were extremely low, lower by a'factor of 10-8 or more tllan in water, t h e t itrations gave sharp end points which generally ,;ere accurate to 1 percent or better. The unusual , though similar behavior of all titrations involving trichloroacetic or camphorsulfonic acid, where the conductance of t h e salt was enhanced greatly by the presence of free acid, ,,·as interpreted in term of a reaction between salt and acid leading to the formation o f a complex anion , The occasional variations in conductanc with ti me, in one instance suggesting slow attainment of some secondary ionic equilibrium, and the effect upon the t itrati o n c ur ves of the addition of a small amount o(me thYl a lcohol to the solvent are disc ussed .

Investigations of (acid+base) equilibria in systems modelling interactions occurring in biomolecules

“…The polar amphiprotic solvent, methanol, is evidently unfavourable for homoconjugation equilibria, since the homoconjugation constants could not be determined in it for all the compounds studied. This finding is consistent with the literature reports [17,18] that a small quantity of TABLE 1 The determined negative logarithms of the acidity constants, pK a (HA), for acetic acid (AcOH), phenol (PhOH) and pK a (BH + ) protonated bases: imidazole (ImH), 4(5)-methylimidazole (CH 3 ImH) and n-butylamine (n-ButNH 2 ) in five solvents: acetonitrile (AN), propylene carbonate (PC), acetone (AC), methanol (MeOH) and dimethyl sulfoxide (DMSO) at T = 298. amphiprotic solvent added to an aprotic solvent markedly lowers the stability of the homocomplexes being formed. This is caused by a stronger solvation of the BH + ion by paired solvent molecules resulting in restricted access of the base molecules.…”

Potentiometric determination of standard acidity and cationic standard homoconjugation constants of substituted pyridine N-oxide systems in (acetonitrile + methanol)

“…Generally, the observed tendency towards a decrease of the standard homoconjugation constants with increasing content of methanol is consistent with literature reports (12,13) that a small quantity of amphiprotic solvent added to an aprotic solvent markedly lowers the stability of the homocomplexes being formed. This is caused by a stronger solvation of the BH + ion by paired solvent molecules resulting in restricted access of the base molecules.…”

“…(11) Further, based on the results of conductometric measurements, it was found (12,13) that addition of a small quantity of an amphiprotic solvent to an aprotic one results in the lowering of the stability of homocomplexed ions owing to formation of cation-amphiprotic solvent solvates. The purpose of this contribution was to determine acid-base equilibrium constants in systems involving substituted pyridine N-oxides in (acetonitrile + methanol), where the mole fraction of acetonitrile x(CH 3 CN) was varied between 0 and 1, at x = 0.1.…”

Acid-base equilibrium constants for the reaction of tribenzylamine with picric acid and with trinitro-m-cresol in benzene, from spectrophotometric data

“…In titrating acids conductimetrically with aliphatic amines in benzene, Maryott observed unusual inflections in the curves for the titration of trichloroacetic and camphorsulfonic acids that were not present in the curves for the titration of picric acid. The peculiarities were interpreted in terms of a reaction beLween salt and acid, leading to the formation of a complex anion [15]. In all probability, the reaction studied by Weissberger and Fasold was complicated by similar effects.…”