ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

One-pot synthesis of benzaldehyde derivatives in PdCl₂-catalyzed reactions with H₂O₂ in alcoholic solutions

Márcio J. da Silva, Giovanna R. N. da Silva, Vinícius F. C. Sampaio, Castelo B. Vilanculo, Sergio A. Fernandes, and Milena G. Teixeira

Chemistry Department, Federal University of Viçosa, Campus Universitário, Viçosa, Brazil

E-mail: silvamj2003@ufv.br

Received: 11 October 2019  Accepted: 28 October 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, PdCl₂ (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

Full paper is available at www.springerlink.com.

DOI: 10.1007/s11696-020-01408-7

Chemical Papers 75 (4) 1545–1554 (2021)