二苯甲烷二异氰酸酯清洁合成过程研究Ⅱ.二苯甲烷二氨基甲酸甲酯催化合成及其分解

STUDY OF CLEAN SYNTHESIS PROCESS FOR METHYLENE DIPHENYL DIISOCYNATE Ⅱ.Catalytic Synthesis and Cleavage of Methylene Diphenyl Dicarbamate

针对苯氨基甲酸甲酯 (MPC)和甲醛 (HCHO)缩合合成二苯甲烷二氨基甲酸甲酯 (MDC) ,然后分解制备二苯甲烷二异氰酸酯 (MDI)的反应 ,考察了不同催化剂的催化性能及反应工艺条件的影响。在 MPC缩合反应中 ,盐酸既作为催化剂又作为溶剂 ,且母液循环使用两次时 ,MDC的收率为 78.4 %;若以 Zn Cl2 为催化剂、硝基苯为溶剂时 ,MDC的收率为 87.4 %;若以笔者开发的固载化 Zn Cl2 /AC作为催化剂 ,其单位摩尔 Zn Cl2 的 MDC收率远高于液体 Zn Cl2 催化剂。以混合溶剂溶解 MDC后 ,进行液相分解得到 MDI,锌及其有机盐对该反应有较高的催化活性 ,当以锌粉为催化剂时 ,MDI收率为 87.3 %

Methylene diphenyl diisocyanate (MDI) was prepared by the cleavage of methylene diphenyl dicarbamate (MDC), which was synthesized by the condensation of methyl phenylcarbamate (MPC) and formaldehyde. As for the condensation reaction, hydrochloride acid was used both as solvent for MPC and as catalyst, and MDC yield was 78.4% under recycling the reaction solution twice. The MDC yield was 87.4% while liquid ZnCl 2 was employed as the catalyst and nitro benzene as the solvent. Supported catalyst ZnCl 2/AC was developed and the MDC yield per mole ZnCl 2 was higher than that over liquid ZnCl 2 catalyst. As for the cleavage reaction, MDC was first dissolved in mixed solvents then added into the reactor to undergo the thermolysis reaction. Zinc and its organic salts have higher catalytic activity for the cleavage reaction. MDI yield was 87 3% when zinc powder was used as the catalyst.