Selective Reduction of C=O in α,β-Unsaturated Carbonyls through Catalytic Hydrogen Transfer Reaction over Mixed Metal Oxides

Abstract

Selective reduction of α,β-unsaturated carbonyls was studied over CoO-ZrO₂ using propan-2-ol as a hydrogen donor and KOH as promoter in a liquid phase reaction. The catalyst used for this synthetically useful transformation showed considerable level of reusability as well as good activity.

Key words

catalytic transfer hydrogenation - mixed metal oxide - α,β-unsaturated carbonyl compounds - liquid phase reaction

References

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23

Catalyst Preparation: The catalyst was prepared by a co-precipitation method. To an aq solution containing ZrOCl₂·8H₂O and CoCl₂·6H₂O mixed in a 9:1 ratio (w/w) was added an aq NH₃ solution under vigorous stirring until pH 10.0 was achieved. Then the co-precipitated hydroxides were washed repeatedly to get neutral filtrate free of the anions precursor materials. The precipitate was then dried in an air oven for 24 h at 383 K and ground below 100 mesh. The hydroxide was then calcined in a muffle furnace at 773 K for 8 h.

24

Catalyst Characterisation: The catalyst was characterized by X-ray diffraction using a Siemens d-500 X-ray diffractometer with CuKα radiation and a Ni filter. FTIR spectra were recorded with a JASCO FTIR spectrophoto-meter by the KBr pellet method. The XRD of the synthesized sample of the CoO-ZrO₂ shows the formation of the cubic phase. BET surface area by N₂ adsorption-desorption method and particle size of the catalyst were also determined. The N₂ adsorption-desorption isotherm of the sample indicated that the sample was mesoporous having a surface area 71 m²g^-1. Optical microscopy photography indicates the presence of uniform particle size, which is found to be 45 µm.

25

Typical Experimental Procedure: The liquid phase reaction was carried out in a 100 mL two-necked round bottom flask equipped with a reflux condenser and a thermometer. In a typical catalytic hydrogen transfer reaction, KOH pellets (20 mmol) were dissolved in propan-2-ol (20 mL) to which the substrate (20 mmol) was added along with 130 mg catalyst, which was then heated at reflux at 356 K for a few hours depending upon the nature of the substrate.

26

For checking the reusability, after the first reaction, the catalyst was recovered by simple filtration, and washed several times with acetone followed by thorough washing with water to remove alkali, and further dried at 373 K for 1 h and then the reaction was repeated for the subsequent cycles.