Electrohydrogenation of 4-amino-5-nitrosodimethyluracil with a foamed nickel cathode

Abstract

The hydrogenation of 4-amino-5-nitrosodimethyluracil as an intermediate of commercially synthesized caffeine is generally carried out using iron powder reduction or Raney nickel catalyst. However, the iron powder results in serious pollution and the Raney nickel catalyst needs an expensive hydrogen supply system operated under severe conditions. A ‘green’ chemical technology using an electrohydrogenation process with a foamed nickel cathode was studied experimentally in a filter-press cell to eliminate the pollution and the unsafe conditions. The results showed that the electrohydrogenation process mainly depended on the pH of the catholyte, the current density and the temperature. All conversions for the pH range 2–8 were over 98%, but the current efficiency gradually decreased with increasing pH. For the current density range 84–420 A m−2 the conversion was over 98%, but the current efficiency decreased with increasing current density. The current efficiency improved with increasing temperature. The results show that to obtain a conversion of over 98% and a current efficiency of nearly 100%, the operating conditions should be pH 3–4, 84–168 A m−2 and 20–30 °C. The conversion and the current efficiency of the electrohydrogenation process were improved by using a foamed nickel cathode with a three-dimensional reticulated structure.