Transition Metal-Substituted Potassium Silicotungstate Salts as Catalysts for Oxidation of Terpene Alcohols with Hydroge
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Transition Metal‑Substituted Potassium Silicotungstate Salts as Catalysts for Oxidation of Terpene Alcohols with Hydrogen Peroxide Marcio Jose da Silva1 · Pedro Henrique da Silva Andrade1 · Vinicius Fernando Coelho Sampaio1 Received: 4 March 2020 / Accepted: 30 October 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract In this work, the catalytic activity of the transition metal-substituted potassium silicotungstate salts (i.e. K 8-nSiMn+W11O39 n+ 2+ 2+ 2+ 2+ 3+ (M = Cu , Co , Ni , Zn and Fe ) was investigated on the oxidation reactions of the terpene alcohols with H2O2 aqueous solution. The metal-substituted silicotungstate salts were easily synthesized in one-pot reactions of the precursor metal solutions (i.e. Na2WO4, Na2SiO3 and MCln) with KCl added in stoichiometric amount; after this precipitation step, the solid heteropoly salts were filtered and dried in an oven. This procedure of synthesis avoids multi-step processes that starts from the pristine heteropolyacid. The substituted metal heteropoly salts were characterized by infrared spectroscopy, measurements of the specific surface area (BET) and porosimetry by isotherms of adsorption/desorption of N 2, X-rays diffraction, thermal analyses, dispersive X-rays spectroscopy, scanning electronic microscopy. The acidity strength was estimated by potentiometric titration with n-butylamine. All the salts were evaluated as catalysts in terpenic alcohols oxidation reactions with H2O2. The K5SiFeW11O39 was the most active and selective catalyst toward oxidation products. The impacts of the main reaction variables such as catalyst concentration, temperature, oxidant load, and nature of the terpene substrate were assessed. The highest activity of the K5SiFeW11O39 catalyst was assigned to the highest Lewis acidity.
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10562-020-03449-9) contains supplementary material, which is available to authorized users. * Marcio Jose da Silva [email protected] 1
Chemistry Department, Federal University of Viçosa, Viçosa, Minas Gerais State 36570‑000, Brazil
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Graphic Abstract
Keywords Heteropoly acids · Oxidation · Heterogeneous catalysis · Green chemistry · Alcohols
1 Introduction Monoterpenes are renewable and abundant raw material whose oxygenate derivatives are attractive feedstock for a wide gamma of synthetical applications, which are of interest for flavoring, food, pharmaceutical, and agrochemical industries [1, 2]. The oxidation products obtained from terpenic alcohols have still organoleptic properties that are highly valuable for the fragrance and perfume industries [3, 4]. Among the various oxidation reactions, those involving primary and secondary terpene alcohols remains a relevant synthetic methodology to afford either epoxides, aldehydes, or ketones [5–8]. The pharmaceutical industry faces challenges in relation to the development of oxidative processes due to e
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