Abstract
A strontium-doped lanthanum cobaltite perovskite material was prepared, and used as a recyclable and effective heterogeneous catalyst for the direct oxidative coupling of alkenes with aromatic aldehydes to produce α,β-unsaturated ketones. The reaction afforded high yields in the presence of di-tert-butylperoxide as oxidant. Single oxides or salts of strontium, lanthanum and cobalt, and the undoped perovskite offered a lower catalytic activity than the strontium-doped perovskite. Benzaldehyde could be replaced by benzyl alcohol, dibenzyl ether, 2-oxo-2-phenylacetaldehyde, 2-bromoacetophenone or (dimethoxymethyl) benzene in the oxidative coupling reaction with alkenes. To our best knowledge, reactions between these starting materials with alkenes are new and unknown in the literature.
Highlights
This article has been edited by the Royal Society of Chemistry, including the commissioning, peer review process and editorial aspects up to the point of acceptance
Energy-dispersive X-ray (EDX) investigation confirmed the presence of La, Sr, Co and O elements in the structure of the perovskite with La : Sr : Co molar ratio of 0.63 : 0.37 : 1.07 being recorded
Since the direct oxidative coupling of benzaldehyde with 1,1-diphenylethylene to produce 1,3,3triphenylprop-2-en-1-one using the strontium-doped lanthanum cobaltite perovskite catalyst progressed in a liquid phase, a vital point that must be studied is whether the α,β-unsaturated ketone product was generated via truly heterogeneous or to some extent homogeneous conditions
Summary
The strontium-doped lanthanum cobaltite perovskite powder was prepared via gelation and calcination approach [49]. The nitrate salts of lanthanum (La(NO3)3.6H2O, 3.90 g, 0.009 mol), strontium (Sr(NO3)2, 1.28 g, 0.006 mol) and cobalt (Co(NO3)2.6H2O, 4.45 g, 0.015 mol) were dissolved in deionized water (100 ml) with vigorous stirring. The resulting mixture was heated at 80°C under continuous stirring for 4 h in a water bath, and the clear pink solution was transformed into a red gel. The red gel was burnt at 140°C overnight in an electric oven to produce soft-ash form. The resulting powder was ball-milled in ethanol media using 5 mm diameter zirconia balls for 12 h at room temperature, and dried overnight in an electric oven at 140°C to achieve the strontium-doped lanthanum cobaltite perovskite (La0.6Sr0.4CoO3, 2.56 g)
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