The technology aims to replicate naturally occurring iron containing enzymes for the oxidation of secondary alcohols, employing the bio-inspired hydro-soluble C-scorpionate tris(pyrazol-1-yl)methane Fe(II) complex [FeCl2{η3-HC(pyrazol-1-yl)3}] as catalyst.
By taking advantage of the application of low power microwave (MW) irradiation, an efficient ketone synthetic method was obtained, leading to higher yields in much shorter times than those achieved by conventional heating.
In order to combine the catalytic properties of [FeCl2{η3-HC(pyrazol-1-yl)3}] with the advantages of heterogeneous systems, the complex was anchored on functionalized (oxidised with nitric acid followed by a treatment with sodium hydroxide) multi-walled carbon nanotubes. This material outstandingly originated 34% and 70% yields of cyclohexanone and acetophenone, respectively, after 1h of MW-assisted oxidation of the corresponding alcohols (cyclohexanol and 1-phenylethanol), with t-butyl hydroperoxide (TBHP). The addition of the 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) radical led to a significant increase of the cyclohexanone yield to 98.3%, while maintaining the selectivity.
This catalysis process produces the same results as other more “aggressive” methods, but with fewer catalyst quantities, less additives, less oxidants and no solvents at all. It also requires less reaction time (just 1 hour) and is easier to prepare.
The catalyst is reusable for several cycles, easy to separate from the reagents and produces fewer by-products. It is more active in the oxidation of aliphatic alcohols, and, while being a heterogeneous catalyst, as selective and active as the homogeneous ones.
Overall, this new method is less expensive, more productive and environmentally greener than conventional ones.
Currently, the lab-scale of the technology might be a limitation to the industry.
Ketones have practical applications such as industrial solvents, as diluents in lacquers, paints and plastics, in the textile industry, in wool and for cleaning. Other uses of ketones are in synthetic fibers, car interiors, additives for plastics, fragrances and cosmetics, pharmaceuticals and synthetic supplements such as vitamins, etc.
This technology is useful for chemical companies, namely ketones producers, and fine chemistry companies, that normally do not use many catalysts.
André Fernandes
