Catalysis by palladium salts XIII. The reductive carbonylation of nitroaromatic compounds to isocyanates with PdII and Pd0 complexes as homogeneous catalysts

Article abstract of DOI:10.1016/0022-328X(91)80175-J

A study has been made of the reductive carbonylation of 2,4-dinitrotoluene (2,4-DNT) to 2,4-diisocyanotoluene (2,4-TDI) with catalysis either by , in the presence of FeO3 and MoO3 or of Fe(MoO4)3 as cocatalysts, or by Pd⁰ complexes without cocatalysts.In the case of catalytic systems based upon the reaction can be carried out at about 200 deg C and under 200 atm of CO to produce 2,4-TDI with high conversions and acceptable selectivities.With Pd⁰ complexes as catalysts good conversions can be achieved at much lower temperatures (100-120 deg C) but with a low selectivity when a higher pressure of CO is used (300 atm or more).An investigation of the reductive cabonylation of nitrobenzene to phenylisocyanate as a model system, together with a study of the thermal stability of in the presence of CO, has provided evidence that the actual active catalyst could be a reduced (probably zerovalent) form of palladium stabilised by the nitroaromatic substrate or by some of the products formed from it as ligands.