Studies on mono- and di-n-butylphosphoric acids—V: The extraction of nitric acid from aqueous solution by di-n-butylphosphoric acid and further results on the distribution of di-n-butylphosphoric acid in aqueous-organic solvent systems

Abstract The distribution of 32 P-labelled di- n -butylphosphoric acid (HDBP) between toluene and aqueous nitric acid has been measured as a function of (i) the concentration of HNO 3 from 0·5–12 M for 0·01, 0·05 and 0·5 M HDBP, and (ii) the concentration of HDBP from 10 −5 -0·5 M for 1, 6 and 10 M HNO 3 . The dimerization constant and monomer distribution coefficient for HDBP in toluene-1 M HNO 3 correspond to log K 2 = 5·09 and log K d = 0·70. The amount of HNO 3 extracted by a 0·5 M solution of HDBP in toluene can be expressed by the relation C HNO 3(org) = 0·051 C HNO 3(unionized, aq) up to 12 M HNO 3 in the aqueous phase; approximately 20 per cent of the uncomplexed HDBP and 40 per cent of the HDBP·HNO 3 complex are hydrated. A third phase forms in the 0·5 M HDBP-kerosene-HNO 3 system at >4 M HNO 3 in the aqueous phase; at 12 M HNO 3 the third phase has the empirical formula HDBP·HNO 3 ·H 2 O.