Process for producing aliphatically N-substituted maleimides

An improved process for producing maleimides of formula I ##STR10## in which n is one of the numbers 1, 2 or 3, R.sup.1 and R.sup.2 are independently hydrogen or methyl, A is an n-valent aliphatic, cycloaliphatic, aliphatic-cycloaliphatic or aliphatic-aromatic radical having up to 30 carbon atoms by means of the cyclizing dehydration at a temperature range of 40.degree. to 100.degree. C. of a maleamic acid of the formula II ##STR11## in which the acid amide group is attached to aliphatic or cycloaliphatic C atoms in the presence of a low-molecular weight dehydrating carboxylic anhydride in an organic solvent and in the presence of a catalyst wherein the improvement comprises employing an effective amount of a catalyst which is an organic or inorganic compound of a metal selected from the group consisting of Li, Mg, Ni, Co, Cu, Mn, Zn, Sn, Ti, Tl, Fe. Pb, V and La, and

• carrying out the reaction in a sufficient amount of a polar aprotic solvent selected from the group consisting of dimethylformamide, dimethylacetamide, diethylacetamide, tetramethylurea, hexamethyl phosphoric acid triamide, N-methylcaprolactam, N-methylpyrrolidone and mixtures thereof, to give at least a partial solution of the starting materials.