In a process for the production of dialkylphosphinic acids, especially branched, dialkylphosphinic acids in high purity via the reaction of an alpha olefin with a hypophosphorous acid or a salt thereof, the improvement comprising conducting the reaction in the presence of a stoichiometric excess of the olefin and isolating and purifying the desired dialkylphosphinic acid product by neutralizing the monoalkylphosphinic acid by-product with an aqueous base; removing the aqueous phase in which the neutralized monoalkylphosphinic acid is preferentially solubilized; acidifying the dialkyl product in the organic phase; and isolating the purified product.
An improved process for production of dialkyldithiophosphinic acid including sulfurizing a purified dialkylphosphinic acid by: reacting a hypophosphorous acid or salt with a stoichiometric excess of an alpha olefin in the presence of a free radical initiator to form a reaction product comprising monoalkylphosphinic acid and dialkylphosphinic acid; adding sufficient aqueous base to the reaction product to i) form the salts of the phosphinic acids, and ii) establish an aqueous phase and an organic phase, wherein a monoalkylphosphinic acid solubilizes into an aqueous phase; separating the organic phase from the aqueous phase; acidifying the organic phase and removing the olefin from the organic phase; isolating the purified dialkylphosphinic acid product; and sulfurizing the purified dialkylphosphinic acid product to form a dialkydithiophosphinic acid. The present invention also provides a process for preparing purified dialkylthiophosphinic chloride, and a process for preparing purified dialkylmonothiophosphinic acids.
