COMPLEX-FORMATION BETWEEN TRIBUTYL-PHOSPHATE AND NITRIC-ACID AND THE HYDRATION OF THE COMPLEXES IN DODECANE

Complex-formation of nitric acid with tributyl phosphate (TBP) and the hydration of the complexes in dodecane were examined from the acid an d water distribution data between the aqueous and organic phases at 29 8 K. The equilibrium constants were determined by analyzing the acid a nd water distribution data as functions of the TBP concentration in th e organic phase, the aqueous acid activity, and the water activity. Th ree complexes (TBP . HNO3, (TBP)(2) . HNO3, and (TBP)(3) . HNO3) were found in the organic phase when the aqueous nitric acid concentration was not higher than 3 mol dm(-3). The hydration numbers for these comp lexes were also obtained. The TBP . HNO3 was chiefly anhydrous, but pa rtially a monohydrate. In contrast, the (TPB)(2) . HNO3 was only a mon ohydrate and (TBP)(3) . HNO3 was only a tetrahydrate. The TBP-HNO3-H2O stoichiometry, by taking account of these complexes in addition to th e TBP hydrates and free nitric acid in the organic phase, applied very well, up to 2 mol dm(-3) (54.6 vol%) TBP in dodecane without any acti vity correction.