To suppress change in quality of a carbamate in a molten or solution state and to stably store and transport the ester by adding a specific compound as a stabilizer to the ester.
(A) A carbamate in a molten or solution state is mixed with (B) one or more stabilizers selected from an aromatic sulfone compound of the formula (Ar is an aromatic nucleus such as benzene or naphthalene; X is a lower alkyl or amino; Y is a hydroxyl group or amino, etc.; (n) is an integer of 0-3), a sulfide and a phosphorous acid triester. Sulfanylamide, p-toluenesulfonic acid, tris(2-ethylhexyl) phosphite, etc., may be cited as the component B. The amount of the component B added is 0.0001-10wt.%, preferably 0.001-1wt.% based on the component A. Since change in quality of the carbamate is suppressed by the method, the yield when producing an isocyanate by a thermal decomposition reaction is also improved to reduce products in side reactions.
OKAWA TAKASHI
DOTANI MASAHARU
UENO SHUICHI
