Using combination of Mn-Co transition metal species with N-hydroxyphthalimide as a catalyst for one-step oxidation of cyclohexane with molecular oxygen in acetic acid at 353 K can give more than 95% selectivity towards oxygenated products with adipic acid as a major product at a high conversion (ca. 78%). A turnover number of 74 for this partial oxidation are also recorded.

A feasibility study into the novel concept of using molecular oxygen to carry out one-step catalytic oxidation of cyclohexane to adipic acid in supercritical carbon dioxide over two types of catalysts, namely Co 2þ =Mn 2þ =NaBr and Ag polyoxometallate, the silver decamolybdodivanadophosphate ðAg 5 PMo 10 V 2 O 40 Þ was carried out. Poor activity and selectivity towards adipic acid were initially noted over the aqueous micellar Co 2þ =Mn 2þ =NaBr catalyst for the cyclohexane oxidation in supercritical carbon dioxide while under comparable conditions, the same catalyst gave a high activity for alkylaromatics oxidation to corresponding acids. It was later found that the adipic acid, being the extremely polar oxidised products, was virtually insoluble in the supercritical phase, which was rapidly degraded to carbon oxides after its prolonged contact with catalyst and O 2 . Thus, the one-step cyclohexane oxidation to adipic acid with good selectivity can only be achieved by modifying the solvent with acetic acid or methanol, which enabled isolation of the acid from further oxidation. On the other hand, Ag 5 PMo 10 V 2 O 40 , in methanol modified supercritical carbon dioxide gave an impressive selectivity for cyclohexane conversion to other oxygenates.