Purification of arylene polyphosphate esters

Abstract

Emulsion formation is minimized or prevented and hydrolytic product degradation is suppressed during purification of impure bisphenol-A bis(diphenylphosphate). This is accomplished by forming a hydrocarbon solution of bisphenol-A bis(diphenylphosphate) plus impurities in a solvent comprising at least one aromatic hydrocarbon and at least one paraffinic hydrocarbon. Optionally, but preferably, this solution is washed with water or an aqueous buffer solution. Next, the hydrocarbon solution is washed one or more times with an aqueous alkaline washing solution that has a specific gravity that differs from the specific gravity of the hydrocarbon solution by at least about 0.05 gram per cubic centimeter. After each washing the mixture settles into a purified organic phase and a separate aqueous phase, and these phases are separated from each other. After completing the one or more alkaline washings and separations, the resultant purified organic phase is washed one or more times with water to remove alkaline components from the hydrocarbon solution, and after each such washing the washed mixture is settled into a less alkaline purified organic phase and a separate aqueous phase. These phases are separated, and preferably the purified product is recovered from the organic phase.