Solvent-free selective oxidation of alcohols with tert -butyl hydroperoxide catalyzed by palladium(II) isatin Schiff bas
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Solvent‑free selective oxidation of alcohols with tert‑butyl hydroperoxide catalyzed by palladium(II) isatin Schiff base complex supported into three‑dimensional mesoporous silica KIT‑6 Davoud Mousavi1 · Mehdi Hatefi Ardakani1 · Samira Saeednia1 · Mohammad Sabet1 Received: 1 June 2020 / Accepted: 31 October 2020 © Springer Nature B.V. 2020
Abstract In this work, the catalytic activity of a palladium(II) isatin Schiff base complex immobilized into mesoporous silica KIT-6 (Pd-isatin Schiff base@KIT-6) was studied for the oxidation of different alcohols with tert-butyl hydroperoxide (TBHP, 70% aqueous solution) as an oxidant under solvent-free conditions. To find the suitable reaction conditions, the effect of essential factors including the solvent, temperature, catalyst amount and kind of oxidant on the oxidation of benzyl alcohol was explored. The results showed that in this catalytic system, the corresponding aldehydes and ketones were obtained with high to excellent yields at 50 °C without the formation of carboxylic acids as by-products. The catalyst was easily recovered by simple filtration and reused in five subsequent reaction cycles without any significant loss in the catalytic activity. Moreover, the comparison of the Fourier transform infrared (FT-IR) spectrum, X-ray diffraction (XRD) pattern, scanning and transmission electron microscopy (SEM and TEM) images of the used catalyst with a fresh one showed that the structure of the Pd-isatin Schiff base@KIT-6 catalyst remained intact after five times of reuse. Keywords Palladium · Isatin · Schiff base · KIT-6 · Alcohol oxidation · Solvent-free
* Mehdi Hatefi Ardakani [email protected]; [email protected] 1
Department of Chemistry, Faculty of Science, Vali-E-Asr University of Rafsanjan, Rafsanjan 77188‑97111, Iran
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Introduction The products of the oxidation of alcohols like aldehydes and ketones are widely used for organic synthesis of fine chemicals in laboratories and chemical industries [1]. Aldehydes and ketones exist in many biologically active molecules and functional intermediates for the pharmaceuticals, agricultural chemicals, drugs and fine chemicals [2–4]. The most common procedures for the oxidation of alcohols may use some toxic, unsafe, unstable and expensive reagents such as persulfate and chromate which are not environmentally friendly and economically justified [5, 6]. Therefore, the development of environmentally friendly catalytic systems for the oxidation of alcohols with high activity and selectivity has been considered by researchers. Recently, Guðmundsson et al. reported the first Fe(II) catalyzed biomimetic aerobic oxidation of alcohols along with an electron-rich quinone and an oxygen-activating Co(salen)-type complex as electron transfer mediators (ETMs). These electron transfer mediators are part of what is called the electron transport chain (ETC), where O 2 is typically used as the terminal oxidant and lead to a low energy pathway via stepwise electron transfer [7]. Azom
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