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

Di- or trivalent metal-exchanged silicotungstic acid salts-catalyzed oxidative esterification of benzaldehyde with hydrogen peroxide

Márcio José da Silva, Alana Alves Rodrigues, and Rafael Luíz Temóteo

Chemistry Department, Federal University of Viçosa, Viçosa, Brazil

E-mail: silvamj2003@ufv.br

Received: 10 November 2025  Accepted: 16 February 2026

Abstract:

In this work, a series of metal-exchanged silicotungstic acid salts was synthesized and assessed as catalysts on the oxidative esterification of benzaldehyde with hydrogen peroxide in a one-pot reaction in homogeneous phase. Initially, the three commercial heteropolyacids (H₃PW₁₂O₄₀, H₃PMo₁₂O₄₀, and H₄SiW₁₂O₄₀) were tested at the same concentration of Brønsted acid sites. Since the silicotungstic acid was the most active, their metal salts were prepared and evaluated as catalysts. Among the salts synthesized (M₄(SiW₁₂O₄₀)_x, M^x+ = Al³⁺, Fe³⁺, Cr³⁺, In³⁺, Co²⁺, Cu²⁺, Zn²⁺, Ni²⁺, and Mn²⁺), the Cu₄(SiW₁₂O₄₀)₂ (divalent) and Fe₄(SiW₁₂O₄₀)₃ (trivalent) were the most efficient catalysts toward the formation of the goal product (i.e., benzoate methyl). The highest activity of the catalyst was attributed to the stronger Lewis acid character of Cu²⁺ and Fe³⁺ cations if compared to the other metal cations evaluated. The influence of the main reaction parameters, like catalyst load, temperature, and reactant stoichiometry, was investigated. A probable reaction pathway was proposed based on the acidity measurements and reaction selectivity, where the Lewis and Brønsted acidity sites of the catalyst are responsible by the activating of the substrate (benzaldehyde) and reactant (hydrogen peroxide). The catalyst load and the reactant’s proportion are key aspects to achieve a high benzaldehyde conversion and ester selectivity. The copper(II) silicotungstate was also evaluated in the esterification of other aldehydes and alcohols.

Keywords: Metal silicotungstate catalysts; Hydrogen peroxide; Oxidative esterification; Benzaldehyde

Full paper is available at www.springerlink.com.

DOI: 10.1007/s11696-026-04743-3

Chemical Papers 80 (6) 5981–5995 (2026)