Tuning Deep Eutectic Solvents for Greener Oxidations: The Role of Solvent Properties in Aldehyde-to-Acid Transformations

Abstract Deep eutectic solvents (DESs) are emerging sustainable alternatives to traditional organic solvents, yet their influence on chemical reactivity remains underexplored. Here, we investigate the oxidation of aldehydes to carboxylic acids using diluted hydrogen peroxide in a diverse set of 20 DESs. We identify a strong correlation between DES pH and reaction efficiency, with optimal yields observed in mildly basic DESs. Surprisingly, even in the presence of excess KOH, DES pH significantly influenced product distribution, highlighting the importance of solvent-intrinsic properties. Urea-based DESs consistently outperformed others, while acidic systems, particularly those based on chlorocholine chloride, favored side reactions. Comprehensive analysis of DES physical properties, including density, viscosity, and polarity, revealed interdependencies that impact reactivity. These findings highlight the need to consider both composition and physicochemical characteristics when selecting DESs for green oxidation processes, offering valuable insights for the rational design of sustainable reaction media.