Potentiometric and polarimetric studies of the reaction of boric acid and tetrahydroxyborate ion with polyhydroxy compounds
Abstract
Values of the association constant, Kn, for the reaction of boric acid with sorbitol, mannitol, D-glucose, glycerol and ethylene glycol have been evaluated from a modified Antikainen equation using values of the dissociation constant, K*, obtained by the half-neutralisation method. This procedure gives values of Kn which are easily compared with each other, and which have trends which are compatible with other previously determined values. Measurements of pK* at various temperatures for the complexes of sorbitol and mannitol with boric acid allow estimates to be made of ΔH* and ΔS* for complexation. Polarimetric studies of the sorbitol and mannitol complexes in solution indicate that the tetrahydroxyborate ion, B(OH)–4, is more effectively complexed than boric acid and do not suggest any major differences in complexing ability between sorbitol and mannitol.