Method for separating reaction product from imide compound catalyst represented by Formula (1) or derivative thereof in reaction mixture obtained by reaction in presence of imide compound catalyst: ##STR1##

wherein R¹ and R² are each, for example, a hydrogen atom or an alkyl group, where R¹ and R² may be combined to form a double bond, an aromatic ring, or a non-aromatic ring, and X is an oxygen atom or a hydroxyl group. The method includes an extraction process using two organic solvents separable from each other to thereby separate the reaction product into one organic solvent layer and the imide compound catalyst component into the other organic solvent layer. The disclosed method efficiently and simply separates the reaction product from the catalyst component.