Autocatalytic alkaline hydrolysis of tri-n-butyl phosphate

Abstract

Although the alkaline hydrolysis of tri-n-butyl phosphate, TBP, in homogeneous aqueous solution shows normal second order kinetics, the hydrolysis of a solution with a hydrocarbon diluent by concentrated sodium hydroxide at 388 K shows an induction period followed by an autocatalytic reaction. The reaction starts with two liquid phases, and ends with three, the third phase consisting mainly of sodium di-n-butyl phosphate, NaDBP, together with hydrocarbon, TBP, BuⁿOH, H₂O and NaOH. The autocatalysis arises from the fact that the third phase dissolves appreciable concentrations of both TBP and NaOH, and serves to bring the reactants together, although the second order rate constant for reaction in the third phase is not much greater than it is in water. As hydrolysis proceeds the volume of the third phase increases while the other phases shrink, thus increasing the rate and resulting in autocatalysis.