BINDING OF TRIPOLYPHOSPHATE BY ALIPHATIC-AMINES - FORMATION, STABILITY AND CALCULATION PROBLEMS

The complex formation between tripolyphosphate (P3O105-) and protonate d diethylenetriamine (dien), triethylenetetramine (trien), tetraethyle nepentamine (tetren) and pentaethylenehexamine (penten), has been stud ied potentiometrically, in aqueous solution, at 25 degrees C. It has b een found that the species ALH(j) (A = amine, L = P3O105-) are formed, with j = 1...n (n = 6, 7, 8 and 8 for the above amines, respectively) . The stability of these species is quite high [e.g., H(3)A(3+) + L(5) = ALH(3)(2+): logK = 11.1 (A = trien)] and depends strictly on the c harges involved in the formation reaction. The simple linear relations hips logK = 1.75 z(cation) + 0.58 z(anion) can be used for making a qu antitative estimate of the stability of proton-amine-P(3)O10(5-) compl exes. The stability trend is: penten > tetren > trien > dien, and the cationic mixed species are more stable than the anionic ones. The effe ct of ionic medium and of ionic strength has been carefully taken into account and discussed. Relevant calculation problems are met with whe n dealing with mixed ligand systems: simultaneous formation of several species; strong interferences of Na+ (background salt or NaOH) with p olyanions (tripolyphosphate in this work), and of Cl- (HCl) with amine s; use of a non constant ionic medium; a high number of mass balance e quations. These problems are discussed in detail and a new computer pr ogram (STACO, in Quick Basic, MS-DOS) is described.