Alternative Reaction Media in Industrial Processes

Electrophilic aromatic substitutions are reactions of great importance for industry and ionic liquids have been used in these reactions as alternative reaction media, mainly with the aim of reducing the environmental impact of these processes. Only few reactivity data, which might be used to quantitatively estimate the effect of the ionic reaction medium on these reactions, have been collected. 

Because of the generally excellent solubility of metal catalysts in RTILs, many of the reactions studied in these media are homogeneously metal catalysed. For example, rhodium catalysed hydroformylation reactions have been studied at length and a wide variety of phosphine ligands used. This particular reaction in RTILs has just been the subject of an extensive review. In most cases, only minimal leaching of the catalyst out of the ionic liquid phase is observed and the catalysts can be very effectively recycled. These efforts are necessary because the industrial aqueous-biphasic process (Chapter 10) only works effectively for smaller olefins and therefore alternative approaches are needed for more hydrophobic, higher-mass olefins. 

The oxidation of alcohols to carbonyl compounds is one of the most fundamental and important processes in the fine chemical industry. The classical methodology is based on the stoichiometric use of heavy metals, notably Cr and Mn (1,2). Alternatively metal-free oxidation, such as the Swern and Pfitzner-Moffat protocols, is based on e.g., dimethylsulfoxide as oxidant in the presence of an activating reagent such as N,N -dicyclohexylcarbodiimide, an acid anhydride or acid halide (3). Although the latter methods avoid the use of heavy metals, they usually involve moisture-sensitive oxidants and environmentally undesirable reaction media, such as chlorinated solvents. The desired oxidation of alcohols only requires the formal transfer of two hydrogen atoms, and therefore the atom economy of these methods is extremely disadvantageous. The current state of the art in alcohol oxidations... 

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