PURIFICATION OF N-SUBSTITUTED MALEIMIDES

PURPOSE:To provide the subject compound having a high purity in a high yield, by washing a reaction mixture containing an N-substituted maleimide obtained by the reaction of maleic anhydride with an amine with water, a diluted alkali aqueous solution, etc., and subsequently distilling the washed mixture in the coexistence of phosphoric acid series acids. CONSTITUTION:A reaction mixture containing an N-substituted maleimide (e.g., N-phenylmaleimide) obtained by the reaction of maleic anhydride with an aromatic or aliphatic primary amine is washed with one or more kinds selected from diluted alkali aqueous solutions, water and diluted acid aqueous solutions one or more times, preferably first washed with a diluted alkali aqueous solution and, if necessary, subsequently rewashed with water or a diluted acid aqueous solution. The obtained organic layer is distilled in the coexistence of a phosphoric acid series acid (e.g., phosphoric acid, phosphorous acid or phenylphosphonic acid) to provide the subject compound. The compound is useful as a raw material for medicines, agricultural chemicals, dyes or polymers or as an intermediate thereof. The process can be prevent the simultaneous polymerization of the mixture during the distillation and reduce the amount of residues after the distillation.