FORMATION AND STABILITY OF PYROPHOSPHATE COMPLEXES WITH ALIPHATIC-AMINES IN AQUEOUS-SOLUTION

The complex formation between pyrophosphate (P2O74-) and protonated me thylamine, ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine and pentaethylenehexamine, has been studied pot entiometrically, in aqueous solution, at 25 degrees C. It was found th at the species ALH(q) (A = amine, L = P2O74-) are formed with q = 1... n(n = 3, 5, 6, 7, 7 and 8 for the above amines respectively). Mono- an d di-amines form species A(p)LH(q) too. The stability of these species is quite high [e.g. H(4)A(4+) + HL(3-) reversible arrow ALH(5)(+): lo g K = 8.1 (A = pentaethylenehexamine)] and depends strictly on the cha rges involved in the formation reaction. Charges of reactants being eq ual, the stability trend is penten > tetren > trien > dien > en > meta and cationic mixed species are more stable than anionic ones. These r esults are discussed in relation to speciation problems in natural and biological fluids.