PURPOSE:To suppress formation of high-boiling by-products and obtain a compound useful as a raw material for polyurethanes or carbamate based agricultural chemicals in good yield with ready separation of the product from a catalyst, by subjecting carbamic acid esters to thermal decomposition reaction in the presence of a catalyst. CONSTITUTION:Carbamic acid esters are subjected to thermal decomposition reaction in the presence of one or two or more catalysts selected from carbides or nitrides of vanadium and chromium family elements of the periodic table. The reaction is carried out in a solvent (e.g. bromonaphthalene) inert to isocyanates without dissolving the catalyst at 100-350 deg.C for several min - several tens of hr to afford the aimed substance. Since the catalyst is insoluble in the reaction solution, separation thereof from the product is readily carried out and the method is particularly advantageous to production of high-boiling isocyanates which are hardly distilled by distillation.
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