Iron salicylate catalyzes oxidative esterification of biomass-derived aldehydes

Abstract

The production of specialty chemicals from lignocellulosic biomass can be increased by valuing underutilized biomass products using sustainable methods. The present work reports the activity of the biomass-derived iron(III) salicylate as a biocompatible and recyclable catalyst for the oxidative esterification of multi-functional aldehydes obtained as products from biomass processing. Esters were obtained in the presence of methyl, ethyl, i-propyl, and amyl alcohols as solvents, at room temperature and with H2O2 as a green oxidant. The catalytic system is selective for the esterification of 2- and 4-hydroxybenzaldehydes, namely salicylaldehyde, o-vanillin and vanillin; as well as of furfural and benzaldehyde, while esters of 9-formylanthracene and (E)-cinnamaldehyde were obtained concomitantly with products of hydroxylation of the polyaromatic ring to ethyl 10-hydroxyanthracene-9-carboxylate (η 46%), and of double bond oxidative cleavage of cinnamaldehyde to ethyl benzoate (η 27%), respectively. The ester products have applications as fragrances, flavors, photo- or bioactive compounds, or as intermediates for synthesis. The results were benchmarked against other Fe(III)–based catalysts, such as Fe(III) porphyrins ([Fe(TSPP)Cl] and [Fe(TMPyP)Cl]) and iron oxide nanoparticles. These studies confirmed the higher performance of Fe(III) salicylate. Graphical Abstract