Halo nitroaromatic Reduction

The selective hydrogenation of halo nitroaromatics is a commonly used transformation in fine chemicals and pharmaceutical syntheses. The challenge is hydrodehalogation, i.e. the loss of the halogen substituent(s) needs to be avoided. Evonik has developed three technologies which provide highly selective catalyst systems.

Copper promoted Platinum Powder Catalysts

CF 105 RA/W 1% Pt + 0.1% Cu
CF 1082 RA/W 1% Pt + 0.1% Cu
CF 105 RA/W 3% Pt + 0.3% Cu

Copper moderates the activity of platinum catalysts so that their selectivity is increased, i.e. hydrodehalogation is suppressed.

Iron promoted Palladium Powder Catalysts

CE 105 R/W 5% Pd + 1% Fe
CE 101 R/W 5% Pd + 0.3% Fe

Iron moderates the activity of palladium catalysts so that their selectivity is increased, i.e. hydrodehalogation is suppressed.

Vanadium promoted Platinum Powder Catalysts

CF 1082 BV/W 1% Pt + 2% V
CF 1082 RV/W 3% Pt + 0.6% V
CF 105 BV/W 1% Pt + 2% V

In addition to their high selectivity in the hydrogenation of halo nitroaromatics, Vanadium promoted Platinum catalysts have an additional feature: they prevent the accumulation of hazardous intermediates which may cause safety problem. This problem may arise with certain substrates, especially aromatic halonitro compounds.

There are several intermediary stages in the catalytic hydrogenation of aromatic nitro compounds to their corresponding aromatic amines. Important among these is the production of nitroso compounds and, in particular, the hydroxylamine intermediate. This intermediate poses a special problem in practice, because under specific conditions it can accumulate in large amounts in reaction solutions. This applies in particular to aromatic nitro compounds, the hydrogenation of which results in relatively stable arylhydroxylamines. This may become a serious problem, especially when carried out in a batch reactor. Arylhydroxylamines can undergo spontaneous decomposition, are known carcinogens, and are responsible for unwanted by-product formation through condensations.

Vanadium-promoted Platinum Powder Catalysts solve this problem. Vanadium affects the mechanism of the nitro group hydrogenation by catalysing the disproportionation of the intermediate arylhydroxylamine. This avoids the intermediary accumulation of the arylhydroxylamines.

Evonik took a licence from Solvias AG to market the technology and to sell the catalysts.

Your benefits:

• No safety problems
• faster reaction rate
• higher selectivity (e.g. no coloured products, no hydrodehalognation i.e. no removal of halogen substituents)
• less health hazards
• less catalyst deactivation
• Licence from Solvias and the right to use the product is already included in the catalyst price; no separate licence negotiation needed.

Vanadium-promoted Platinum Powder Catalysts can also be used in combination with hypophosphoric acid which makes these catalysts even more selective. To learn more click here.