Fe(III)-based Eutectic Mixtures as Multi-Task and Reusable Reaction Media for Efficient and Selective Conversion of Alkynes into Carbonyl Compounds

An efficient, simple and general protocol for the selective hydration of terminal alkynes into the corresponding methyl ketones was developed by using a cheap, easy-to-synthesise and sustainable Fe(III)-based eutectic mixture [FeCl3·6H2O/Gly (3:1)] as both promoter and solvent for the hydration reaction, working: i) under mild (45 ºC) and bench type reaction conditions (air); and ii) in the absence of ligands, co-catalysts, co-solvents or toxic, non-abundant and expensive noble transition metals (Au, Ru, Pd). When the final methyl ketones are solid/insoluble in the eutectic mixture, the hydration reaction takes place in 30 minutes and the obtained methyl ketones can be isolated just by simple decantation of the liquid Fe(III)-DES, allowing the direct isolation of the desired ketones without VOC solvents. By using this straightforward and simple isolation protocol, we have been able to recycle our Fe(III)-based eutectic mixture system up to 8 consecutive times. Furthermore, our Fe(III)-eutectic mixture is able to promote the selective and efficient formal oxidation of internal alkynes into 1,2-diketones, being the system recycled up to 3 consecutive times. Preliminary investigations on a possible mechanism for the oxidation of the internal alkynes seems to indicate that it proceeds through the formation of the corresponding methyl ketones and α-chloroketones.