Systems for the separation of phosphoric esters by solvent distribution.

The isolation and purification of phosphoric esters are usually accomplished by the fractional precipitation of their metallic salts. This method has been extremely useful and has led to the isolation of a large number of biologically important phosphorus compounds. However, some types of compounds are merely separated by this procedure into groups from which the individual members cannot be readily isolated. The application of solvent extraction, particularly of the Craig countercurrent distribution type (l), appeared to be a desirable approach to this problem. However, the failure of most of the phosphoric esters of biological importance to be distributed to any appreciable extent between an aqueous phase and an organic solvent seemed to preclude the application of this principle, unless a way could be found to increase the solubility of these compounds in the organic solvent phase. A similar difficulty had been experienced in the attempt to apply solvent distribution to the separation and purification of the streptomycins, basic compounds with a large carbohydrate moiety which rendered them insoluble in non-polar liquids. This obstacle was overcome by Plaut and McCormack (2) who successfully separated and determined streptomycin types with a solvent pair which contained amyl alcohol and stearic acid in one phase and aqueous buffer in the other. By analogy it seemed possible to increase the solubility of phosphoric esters (acidic substances) in organic solvents by the inclusion of a long chain fatty amine in the system.