PURPOSE: To obtain advantageously the titled compound useful as an intermediate for a coating compound, etc., having high solvent solubility and a low melting point, by bringing a diamine or its mixture into contact with hydrogen in the presence of an organic solvent and a hydrogenation catalyst in a specific range of temperature.
CONSTITUTION: A compound shown by the formulaIor formula II or a mixture of their isomers is brought into contact with hydrogen at 10°C (preferably about room temperature) W150°C in the presence of an organic solvent (e.g., methanol, toluene, ketone, etc.) and a hydrogenation catalyst (preferably Pd catalyst), to give the desired compound shown by the formula III. When the compound shown by the formula III is used instead of common diaminodiphenylmethane, a prepared maleimide has high solvent solubility, is handled easily because of its low melting point, and has improved resin properties. The raw material diamine is a mixture of isomers of p-isopropenylaniline dimers, and advantageously used in the reaction directly.