Key Technologies for Isocyanate Synthesis without the Use of Phosgene

Abstract

A comparative analysis of phosgene-free methods for the synthesis of MDI and TDI was carried out. The most popular method is the thermal decomposition of carbamic acid esters (carbamates), during which isocyanate is formed and alcohol is released. To introduce an isocyanate group into an amino compound, it is advisable to use carbonate, preferably dimethyl carbonate, and urea. These processes are the most studied; easily available reagents and catalysts are used for synthesis. The method of direct conversion of a nitro compound into an isocyanate is of scientific interest, but it has a number of disadvantages, such as harsh synthesis conditions (high pressure and temperature), expensive catalysts, and low selectivity of the isocyanate.