The chloroform TBP aqueous nitric acid interfacial system: a molecular dynamics investigation

We report MD studies on a chloroform / nitric acid water interface, either neat, or saturated by TBP molecules. Two extreme models are compared, where the acid is either neutral HNO3 or dissociated to NO3- and H3O+. The latter species are found to be "repelled" by the neat interface, while the neutral HNO3 molecules are surface active. When the neat interface is saturated by TBP molecules, the latter form highly disordered arrangements instead of a regular monolayer, and water is dragged to the organic phase as 1:1, 1:2 and 2:2 hydrates of TBP. Simulations with the neutral HNO3 model lead to extraction of acid to the organic phase, hydrogen bonded to the phosphoryl oxygen of TBP, forming HNO3:TBP adducts of 1:1 and 2:1 types. Simulations with the ionic model lead to H3O+:TBP adducts of 1:1, 1:2 and 1:3 types in the organic phase and significant mixing of the chloroform, TBP and water liquids in the interfacial region.