Improving Phase Separation for Extractions in the Presence of Insoluble Debris

Patent US 5,628,906 explains how to perform rapid liquid-liquid extractive separations in unfavorable situations where there is insoluble debris in the liquid mixture or where there are emulsifying substances present that under vigorous agitation could create emulsions that separate only slowly.

The creative idea is to mix two solvents that are fairly miscible to form a superior extractant medium and then subsequently add a third component that causes rapid separation of the total combined solvents into two immiscible phases that can be easily separated. In this way, any surface active agents do not have time to move to the interfacial area and reduce the rate of phase separation, the debris that is insoluble does not float at the interface and prevent separation and the rate of transfer of substrates between phases is much enhanced.

The method might be applicable to removing traces of product from a reactor containing insoluble resins by separating the substrates from the surface and interstices of the resin and it could avoid vigorous stirring of the resin slurry that could mechanically damage the resin.

Might it also work in an emulsifier-promoted reaction between a water/acetonitrile solution containing an emulsifier that is reacted with a poorly soluble reagent followed by a phase separation wherein a third solvent that causes phase separation is added? Imagine for example that you are trying to convert cis-cyclooctene into cis-1,2-cyclooctanediol with potassium permanganate reagent.  This would be advantageous because the classical reagent osmium tetroxide is both expensive and toxic.

The problem is that although the substrate is soluble in organic solvents the permanganate salt is not. A mixture of acetonitrile to assist in the solution of substrate and water to get some permanganate into solution could be emulsified with an unreactive emulsifier to bring them pair into intimate contact so they could react. Then addition of a third solvent miscible with acetonitrile but immiscible with water would break the emulsion and cause the separation of two phases despite the presence of the emulsifier. No shaking of the phases together would be required. The potential for a large interfacial layer would be greatly reduced. Because it might also enable the extraction of a water-rich phase with a water-poor phase without first requiring the separation of a precipitate insoluble in both phases, the coproduct, manganese dioxide would be less likely to interfere with phase separation.