Determination of the stability constants of nitritoborate lon by means of an NOx-selective electrode and of boric acid complexes of acetate and phthalate by pH measurement

Abstract

The complex between boric acid and nitrite was studied by means of an NO_x-selective gas-sensing membrane electrode and the stability constant found to be log β=–0.49 ± 0.02 at 25 °C. Interaction between boric acid and both acetate and phthalate ions was also observed and stability constants for the complexes of boric acid with acetate, phthalate and hydrogenphthalate were determined from pH measurements at 25°C to be (log β)–0.43 ± 0.03, –0.07 ± 0.02 and ≈–1, respectively. These measurements enable a revised linear free-energy relationship for boric acid complexes with univalent ions to be calculated. Excluding the less reliable result for hydrogenphthalate, the relationship may be expressed by log β=–(2.15 ± 0.58)+(0.45 ± 0.05) pK_a over a range of seven ligands, with a correlation coefficient of 0.97.