Oxidation reactions in CO2:: Academic exercise or future green processes?

Conducting oxidation reactions using CO2 as the solvent is a promising strategy for creation of greener chemical processes that are also economical, as CO2 and water are probably the only solvents that can be used in oxidation reactions without the formation of any solvent byproducts. However, it must be noted that the promise of CO2-based oxidation still dwarfs the actual realization of CO2-based oxidation processes. Nevertheless, there is extensive literature on the use of CO2 as the solvent for the oxidation of cyclohexane (adipic acid synthesis), cumene oxidation (phenol synthesis), and epoxidation (propylene oxide synthesis). In all of these studies, knowledge of the phase behavior is crucial toward understanding the effects of pressure and temperature on reaction outcomes. To date, much of the research in this field has involved simply using CO2- as a "drop-in" replacement for a conventional organic solvent; it will be interesting in the future to see if the use of CO2 can be combined with innovations in catalyst and reactor design to create truly green oxidation processes where the use of CO2 is not merely tolerated but truly supports process and chemistry innovation.