| 摘要 |
The instant invention relates to an improved process for the continuous production of an aliphatic monoisocyanate from the corresponding N-alkyl carbamic acid aryl ester. More particularly, the invention is directed to a process for the continuous production of monoisocyanates corresponding to the formula R-NCO in which R represents an aliphatic hydrocarbon radical containing 1 to 3 carbon atoms comprising thermally decomposing the corresponding N-alkylcarbamic acid aryl esters corresponding to the formula R-NH-CO-O-R' in which R has the meaning above and R' represents a radical of the type obtained by removing the hydroxyl group from a monophenol having a boiling point below 250 DEG C. at normal pressure, and separating the decomposition products by decomposition, further characterized in that (a) a solution of the N-alkylcarbamic acid aryl ester in an organic solvent, which solvent is inert under the reaction conditions and has a boiling point lying at least 20 DEG C. above the boiling point of the monoisocyanate to be formed, is heated to a temperature of from 160 DEG C. to 250 DEG C. at normal pressure or at slightly reduced pressure within the range of 200 to 1013 mbar, thereby resulting in the decomposition of the ester into the corresponding monoisocyanate and the corresponding phenol, as well as the evaporation of the solvent and the decomposition products, and (b) the vapors formed are fed into a distillation column with the monoisocyanate obtained at the head of the column and with the phenol and at least a major portion of the solvent obtained from a side stream or from several side streams. |
