The Non-phosgene Approach To Synthesize MDI

The approaches to synthesize methylene diphenyl diisocyanate (MDI) are explored with dimethylcarbonate, which is a kind of "Green Chemicals"as a substitute for phosgene, and aniline as raw materialsin the paper. The process to separate methyl phenylcarbamate (MPC) and to synthesize MDI is alsopresented. MPC is synthesized through ester ammonolysis with dimethyl carbonate and aniline. Compared withother non-phosgene approaches such as amino oxidizing carbonylation and nitro-reductive carbonylation,mild reacting conditions, far less harmful reacting materials, cheap and easily obtained highly activecatalysts, by-product methanol usable to produce dimethyl carbonate, products easy to separate are alladvantages of this approach apart from avoiding the disadvantages of phosgene method. Throughorthogonal experiments, the optimized technology is as follows: the molar ratio of dim ethylcarbonate andaniline 5:1, reacting temperature 180℃, reacting time 4 hours, the molar ratio of Zinc acetate and aniline0.008:1. The best yield is 90.6% (the mole fracition of aniline is the basic parameter). The process to synthesize methylene diphenyl dimethylcarbamate (MDC) is studied, with MPC andformaldehyde as the synthesizing material, hydrochloric acid as catalyst. The optimized technology throughorthogonal experiments is followed: molar ratio of MPC and formaldehyde is 4:1, reacting temperature 80℃, reacting time 4 hours, the density of hydrochloric acid 18%, the best yield of MDC is 64.2% ( the molefracition of MPC is the basic parameter). The process to obtain MDI through decomposing MDC is in research. After selecting four solventsand two catalysts, the primary technology to produce MDI is as follows: pentadecane as solvent, P2O5catalyst, 1 hour reaction under 280℃, the yield of MDI is 68.3%( the mole fracition of MDC is the basicparameter). Testing the structures of the products with IR-8400S Fourier Infro-red Spectrograph and DRX300Nuclear Resonnance Spectrograph, their substances are proved to be true.