Preparation process of N-substituted maleimides

In a process for the preparation of N-substituted maleimide by heat-dehydrating N-substituted maleamic acid in a solvent mixture containing an organic solvent capable of forming water azeotrope and an organic aprotic polar solvent and simultaneously conducting a dehydrating imidization reaction under azeotropic distillation of the reaction generated water, the improvement which comprises conducting the dehydrating imidization in the absence of a Broensted acid having a pKa of 3 or less and in the presence as reaction catalyst of a catalytically effective amount of a zinc salt of the maleamic acid, metallic zinc or a zinc compound which forms a zinc salt of the maleamic acid in the reaction system.