The investigation and experiments were carried out on purification of butyl phosphoric acid, 2-ethylhexyl phosphoric acid and 2-ethyloctyl phosphoric acid. Chemical properties of alkyl phosphoric acids purified by this method were measured, which were distribution ratio between oragnic and aqueous phases, acid dissociation constant and interfacial tension.
The distribution ratio of mono-esters is much lower than that of the corresponding di-esters. Values of the distribution ratio are 5.2, 49 and 570 for butyl, 2-ethylhexyl and 2-ethyloctyl phosphoric acids, respectively. The mono-esters are fairly strong acids whose dissociation constants are 10-2.1, 10-2.3 and 10-2.3 for butyl, 2-ethylhexyl and 2-ethyloctyl phosphoric acids, respectively. The mono-esters are more surface active comparedwith the corresponding di-esters, except butyl phosphoric acid which has high solubility in an aqueous solution. The interface coverage of mono-esters is calculated from interfacial tension measurements according to Gibbs' equation.
