One-pot synthesis of benzaldehyde derivatives in PdCl 2 -catalyzed reactions with H 2 O 2 in alcoholic solutions
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ORIGINAL PAPER
One‑pot synthesis of benzaldehyde derivatives in PdCl2‑catalyzed reactions with H2O2 in alcoholic solutions Márcio J. da Silva1 · Giovanna R. N. da Silva1 · Vinícius F. C. Sampaio1 · Castelo B. Vilanculo2 · Sergio A. Fernandes1 · Milena G. Teixeira1 Received: 11 October 2019 / Accepted: 28 October 2020 © Institute of Chemistry, Slovak Academy of Sciences 2020
Abstract Abstract The activity of the palladium salt catalysts was investigated on the benzaldehyde reactions with H2O2. The PdCl2 salt was the most efficient catalyst for the formation of the goal products. In CH3OH, benzaldehyde was selectively oxidized to benzoic acid and posteriorly esterified to methyl benzoate. In this process, the reaction of the PdCl2 catalyst with aqueous H2O2 provided H + ions, which also promoted the esterification and acetalization reactions. The oxidant load played a key role in the selectivity controlling; while a large excess (9:1) gave benzoic acid (90%), with a lower ratio (3:1), acid and ester were formed with selectivity of 58 and 35%, respectively. With H2O2 at an equimolar ratio, the Pd(0) reduced the benzaldehyde to benzyl alcohol (30%). In absence of the oxidant, P dCl2 (2.5 mol %) condensated benzaldehyde and alcohol to acetal (90%). Therefore, PdCl2 directly catalyzed the oxidation and reduction reactions, and participated in acid-catalyzed reactions (i.e., condensation and esterification), generating H+ ions, demonstrating to be a highly versatile catalyst. An adequate adjusting of reaction conditions allowed to control the reaction selectivity toward the desired products (i.e., benzoic acid or ester benzyl, acetal, or benzyl alcohol). Graphic Abstract
Keywords Homogeneous catalysis · Chemoselectivity · Oxidations · Reductions · Reaction mechanisms · Coordination chemistry
Introduction Electronic supplementary material The online version of this article (https://doi.org/10.1007/s11696-020-01408-7) contains supplementary material, which is available to authorized users. * Márcio J. da Silva [email protected] Extended author information available on the last page of the article
The production of benzoic acid and their esters have gathered a lot of attention, due to extensive use of these products as raw material aiming the industrial production of fibbers, cosmetics, plasticizers, dyestuffs (Ilyas and Sadiq 2009; Chumbhale et al. 2005). Benzoic acid has been industrially produced through toluene oxidation in liquid or vapor phase
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at high temperatures, in a one-pot process that consumes environmentally unfriendly oxidants, which are expensive and generates residues at stoichiometric amounts; in addition, in these processes, low yields have been reached (Dash et al. 2009; Sedelmeier et al. 2010; Yuan et al. 2011; Mukhopadhyay and Datta 2008). For these reasons, environmentally benign routes for the benzaldehyde oxidation using clean oxidants have gradually replaced the stoichiometric oxidation processes (Coronel et al. 2019). Undoubtedl
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