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- Title
Evaluation of the Activity of Potassium Dodecatungstate Salts in Alcohol Oxidation Reactions: Cobalt(II), Cobalt(III), or Silicon(IV) as the Heteroatom.
- Authors
da Silva, Márcio José; da Silva Andrade, Pedro Henrique; Silva, Tiago Almeida; Diniz, Mariana Beatriz Teixeira; Ferreira, Sukarno Olavo; da Silva, Renê Chagas; de Araujo, Eduardo Nery Duarte
- Abstract
Silicotungstic acid potassium salts had the silicon heteroatom substituted by Co(III) or Co(II) cations and were evaluated as catalysts in oxidation reactions of terpenic alcohols with hydrogen peroxide. Borneol was the model molecule selected. All the catalyst salts were characterized by Fourier-transformed infrared, ultraviolet–visible and Raman spectroscopies, thermal analyses, powder X-rays diffraction and cyclic voltammetry analyses, energy dispersive X-ray spectroscopy and scam electronic microscopy (SEM) analyses, potentiometric titration. This set of techniques revealed that salts containing Co(II) or Co(III) as the heteroatom were successfully obtained. The activity of potassium dodecatungstocobaltate(III) (i.e., K5CoIIIW12O40) was compared to other tungsten heteropoly catalysts (i.e., H4SiW12O40, K4SiW12O40, K6CoIIW12O40, Co2SiW12O40) and the precursor CoCl2. Among the various heteropoly compound investigated, the K5CoIIIW12O40 salt was the most active and selective catalyst toward oxidation product (i.e., camphor). Conversion and selectivity higher than 90% were achieved, indicating the high efficiency of this catalyst. The effects of the main reaction parameters such as temperature, the stoichiometry of reactants, type and catalyst load, were investigated. Special attention was given to correlating the structural properties of catalysts with their activity. Based on experimental data, a reaction pathway was proposed. As far as we know, it is the first time that silicotungstic acid-derived salts having heteroatom Co(II) or Co(III) cations, were used as catalysts in oxidation reactions of terpene alcohols. The effect of the oxidation state and position of Co on the activity of silicotungstic acid was evaluated. The H4SiW12O40 had the Si(IV) heteroatom exchanged with Co(II) or Co(III). Their potassium salts were tested in borneol oxidation reactions with H2O2 being the K5CoIIIW12O40 the most active and selective catalyst.
- Subjects
POTASSIUM salts; X-ray powder diffraction; ALCOHOL oxidation; ENERGY dispersive X-ray spectroscopy; TUNGSTEN catalysts; POTENTIOMETRY
- Publication
Catalysis Letters, 2024, Vol 154, Issue 4, p1648
- ISSN
1011-372X
- Publication type
Article
- DOI
10.1007/s10562-023-04441-9