Hydrogenation of nitro compounds with supported platinum catalyst in supercritical carbon dioxide

Hydrogenation of a series of substituted nitro compounds such as 2-,3-,4-nitroanisole, 2-,3-,4-nitrotoluene, 2,4-dinitrobenzene and 2,4-dinitrotoluene has been studied in supercritical carbon dioxide, scCO2 (two phases), and ethanol (three phases) with a 5 wt.% carbon supported platinum catalyst. The solubility of these compounds in scCO2 has also been examined in the presence and absence of hydrogen. The solubility of those nitro compounds increases with increasing CO2 pressure but decreases with the presence of hydrogen. The solubility is in the order of nitrotoluene > nitroanisole > dinitrotoluene, dinitrobenzene. Although the total conversion obtained with hydrogenation in scCO2 is similar to that in ethanol, the selectivity to amino products is higher in the former reaction medium, indicating that scCO2 is an ideal medium for the production of amino compounds with hydrogenation of nitro substrates using conventional supported metal catalysts.