PURPOSE:To obtain the titled compound in good yield, by reacting an amine compound with dimethyl carbonate in the presence of an alkaline catalyst and thermally decomposing the resultant urethane compound in the presence of a specific metallic compound in a high-boiling solvent. CONSTITUTION:A diamine is reacted with dimethyl carbonate in the presence of an alkaline catalyst consisting of an alkaline (earth) metal alcoholate, especially sodium methylate at 2-50 charging molar ratio of the latter to the former at 30-80 deg.C temperature to provide the corresponding urethane compound, which is then thermally decomposed in the presence of a catalyst of a simple metal selected from Mn, Mo, W and Zn or a compound thereof in a high-boiling solvent (e.g. terphenyl or mixed diphenylbenzene or partially hydrogenated triphenyl) under 1-700Torr reduced pressure to afford the corresponding diisocyanate compound.
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