Patent Watch

June 29, 2009 [Repeated from 2/9/09]

Manufacture isocyanates without using phosgene. A phosgene-free route to aromatic isocyanates is being developed by Repsol. Phosgene is an extremely toxic material, but it is still used as the key raw material for making two very important classes of industrial polymers: polycarbonates and polyurethanes. In the case of polycarbonates, new technologies that have been commercialized over the past 10 years eliminate the need to use phosgene. However, despite intensive research, commercially viable routes to the large-volume isocyanates, methylene diphenylene diisocyanate (MDI) and toluene diisocyanate (TDI), have remained elusive, although nonphosgene routes to smaller-volume aliphatic isocyanates have been developed.

F. L. Serrano Fernández and co-inventors disclose a one-pot catalytic process for making aromatic isocyanates—including TDI—without phosgene. The synthesis is based the use of an immobilized Schiff base type of ligand catalyst that facilitates the oxidative carbonylation of aromatic amines to the corresponding isocyanates. The patent gives the following example.

A stirred autoclave is charged with 10 g of 2,4-toluenediamine, 7.6 g of [Co-tert-butyl-Salen]/silica catalyst, 1.7 g of NaI, and 484 g of 2,2,2-trifluoroethanol (TFE). The autoclave is pressurized with 19:1 v/v CO/O₂. The temperature is raised to 120 °C, and the pressure is adjusted to 40 bar. The reaction is maintained at these conditions for 3 h with stirring. After 3 h, the reactor is cooled and depressurized, and 97.8 g of 1,2-dichlorobenzene is added. The temperature is increased to 180 °C under atmospheric pressure. The TFE vapors are separated and condensed, and TDI is separated from the remaining liquid and purified to 99.9%. The overall yield of TDI is 69.8%. (Repsol YPF S.A. [Madrid]. Eur. Patent 1870398, Dec. 12, 2008; Jeffrey S. Plotkin)

View patent information from CAS.

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