Kiyoshi Kudo, Futoshi Ikoma, Sadayuki Mori, Koichi Komatsu and Nobuyuki Sugita
In the presence of caesium carbonate, the direct reaction of CO2 (110 atm) with CO (50 atm) resulted in reductive capture of CO2 to give caesium oxalate in good yield (90.1%) at high temperature (380 °C). The reaction is characteristic of caesium carbonate. When lithium, sodium, potassium and rubidium carbonates were used, oxalate was scarcely produced. The effects of the reaction variables, such as the pressures of CO2 and CO, and the reaction temperature, were examined to optimize the process. From the results of mechanistic studies including a separately examined two-step reaction, 13C-labelling experiments and IR spectroscopic studies of the intermediates, it was concluded that the reaction proceeds through a nucleophilic addition of CO upon the carbonyl carbon of CO2 which is activated by the complexation to caesium carbonate.