Patent ID: 7906631

Claim:
A method of producing a rare earth salt of a dialkyl phosphate or a rare earth salt of dioleyl phosphate represented by the following formula (2): M[OPO(OR) 2 ] 3 (2) [in the formula (2), M is a rare earth element and R is an alkyl group having a carbon number of 1 to 18 or oleyl group], characterized in that a rare earth oxide or a rare earth hydroxide is reacted with a dialkyl phosphate or dioleyl phosphate having a purity of not less than 97% and represented by the following formula (1): HOPO(OR) 2 (1) [in the formula (1), R is an alkyl group having a carbon number of 1 to 18 or oleyl group] in a non-polar solvent in the presence of at least one compound selected from a halogenated hydroacid, phosphorous acid and a rare earth halide as a catalyst.