氨基甲酸酯热分解法制备对氯苯基异氰酸酯

对氨基甲酸酯热分解法制备对氯苯基异氰酸酯(4CPI)的工艺进行了研究。以对氯苯胺和碳酸二甲酯为原料,合成了热分解前体对氯苯基氨基甲酸甲酯(M4CPC);通过核磁共振氢谱、傅里叶变换红外光谱和热重分析对M4CPC的结构和性能进行了表征,确定了适宜的M4CPC热分解温度为150～200℃。常压下对M4CPC热分解溶剂的考察结果表明,高介电常数的有机溶剂对M4CPC的分解比较有利。M4CPC热分解制备4CPI的主要副产物为N,N′-双(4-氯苯基)脲。以低毒的N,N′-二甲基乙酰胺为溶剂,在M4CPC的摩尔分数为10%、催化剂用量为m(Bi2O3)∶m(M4CPC)=0.05、反应温度162～164℃、反应时间1h的优化条件下,M4CPC的转化率为90.4%,4CPI的选择性为66.0%。

Synthesis of 4-Chlorophenyl Isocyanate by Thermal Decomposition of Carbamate

The process for synthesizing of 4-chlorophenyl isocyanate(4CPI) by thermal decomposition of carbamate and using Bi2O3 catalyst was studied. The starting reactant methyl N-(4-chlorophenyl)carbamate(M4CPC) was firstly synthesized from p-chloroaniline and dimethyl carbonate. The structure and properties of M4CPC were investigated by means of 1H NMR,FTIR and TG analysis. From TG results,the appropriate temperatures for thermal decomposition of M4CPC were decided in the range of 150-200 ℃. Under normal pressure,solvents with higher dielectric constants were suitable for the liquid thermal and catalytic decomposition of M4CPC. With low toxic N,N'-dimethylacetamide as solvent,the main byproduct of the thermal decomposition of M4CPC to 4CPI was N,N'-bis(4-chloropheny1)urea. Under optimal reaction conditions:mole fraction of M4CPC 10%,mass ratio of catalyst Bi2O3 to M4CPC 0.05,reaction temperature 162-164 ℃ and reaction time 1 h,conversion of M4CPC is 90.4%,selectivity to 4CPI is 66.0%.