Potentiometric and polarimetric studies of the reaction of boric acid and tetrahydroxyborate ion with polyhydroxy compounds

Abstract

Values of the association constant, K_n, 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 K_n 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.