Promoters of Catalytically Active Compounds

We will now discuss the effect of metal-containing promoters when added to catalytically active compounds, although it is difficult to compare experimental results generally not obtained under comparable conditions. 

These results indicate that the effect due to these and other promoters reported below should be taken with a certain caution. Moreover, conflicting results might be due to the different experimental procedures adopted (for instance, all the reagents, including carbon monoxide, are introduced into the autoclave at room temperature and the mixture is then heated to the chosen reaction temperature, or carbon monoxide or the nitro compound are introduced only after the system has been heated last but not least, the type of stirring adopted can have a decisive influence on the outcome of the reaction). 

TDI has been obtained from DNT under CO pressure by using PdX and/or RhCb (X = Cl, Br, I), pyridine, and iron and/or manganese molybdates [145], 

It has been reported that one of the most selective catalysts for the carbonylation of DNT is the system PdPy2Cl2/Fe203/V20s (yields of TDI up to 90 % at 260 °C and 200 atm) [152, 153]. However the catalytic ratio DNT/Pd was only ca. 10 for the system in [153] and the reaction reported in [152] is essentially only stoichiometric. 

Iron(III) chloride and Fe203 promote PdCl2 catalysts containing an heterocyclic base and sometimes M0O3 in the carbonylation of DNT and PhN02 to form isocyanates [161]. However, a similar activating effect of the steel reactor walls was also observed. Iron(III) prevented the reduction of 

---