Peroxide process
The peroxide process is a method for the industrial production of hydrazine.
In this process hydrogen peroxide is used as an oxidant instead of sodium hypochlorite, which is traditionally used to generate hydrazine. The main advantage of the Peroxide process to hydrazine relative to the traditional Raschig process is that it does not coproduce salt. In this respect, the Peroxide process is an example of Green Chemistry. Since many millions of kilograms of hydrazine are produced annually, this method is of both commercial and environmental significance.
In the usual implementation, hydrogen peroxide is used together with acetamide. This mixture does not react with ammonia directly but does so in the presence of methyl ethyl ketone to give the oxaziridine.
Balanced equations for the individual steps are as follows. Imine formation via condensation:
Oxidation of the imine to the oxaziridine:
Condensation of the oxaziridine with a second molecule of ammonia to give the hydrazone:
The hydrazone then condenses with a second equivalent of ketone to give the ketazine:
Typical process conditions are 50 °C and atmospheric pressure, with a feed mix of H2O2:ketone:NH3 in a molar ratio of about 1:2:4. A similar process based on benzophenone has also been described.
The final stage involves hydrolysis of the purified ketazine:
The hydrolysis of the azine is acid-catalyzed, hence the need to isolate the azine from the initial ammonia-containing reaction mixture. It is also endothermic, and so requires an increase in temperature (and pressure) to shift the equilibrium in favour of the desired products: ketone (which is recycled) and hydrazine hydrate. The reaction is carried out by simple distillation of the azeotrope: typical conditions are a pressure of 8 bar and temperatures of 130 °C at the base of the column and 179 °C at the top of the column. The hydrazine hydrate (30–45% aqueous solution) is run off from the base of the column, while the methyl ethyl ketone is distilled off from the top of the column and recycled.
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