Platinum Metals Rev., 1966, 10, (3), 90
Isocyanate Preparation with Palladium Chloride
The manufacture of numerous plastics and synthetic surface coatings involves the production on a large scale of several important isocyanates. These are generally produced by treating a primary amine or its salt with phosgene, resulting in the intermediate formation of a carbonyl chloride from which HC1 is eliminated to yield the isocyanate.
Research carried out by E. W. Stern and M. L. Spector of the M. W. Kellogg Company, New Market, New Jersey (J. Org. Chem., 1966, 31, (2), 596), has yielded a new route to isocyanates that is unusual in that it employs palladium chloride as a reactant. In this method, the primary aliphatic or aromatic amine reacts with carbon monoxide in the presence of palladium chloride at, or very slightly above, atmospheric pressure and in the temperature range 65 to 85°C, yielding the isocyanate while the salt is reduced to metallic palladium:
A detailed mechanism of the reaction has not yet been worked out; the in situ formation of phosgene from PdCl2 and the carbon monoxide, however, has been ruled out, since no reduction of the salt to metal occurs in the absence of the amine. It seems possible that both the amine and the carbon monoxide combine with the palladium chloride to form a complex that leads to isocyanate formation on decomposition.