Nitro-functionalized imidazolium salts as acidic catalysts for cellulose degradation in ionic liquids

Nitro-functionalized imidazolium salts were applied as acidic catalysts for the degradation of cellulose into 5-hydroxymethylfurfural (HMF). The catalytic systems based on [NO₂HMIm][X] (X = TsO, Cl, NTf₂, CF₃CO₂), dissolved in [BMIm][Cl], were capable of producing HMF, glucose, fructose, formic acid, and levulinic acid as products of cellulose degradation at 130 °C. In particular, HMF was obtained in up to 17% yield using 10.8 mol% of [NO₂HMIm][TsO], representing one of the most active protic imidazolium salts reported in the literature for the transformation of cellulose under relatively mild conditions. Indeed, this work presents cost-effective and easily synthesized nitro-functionalized imidazolium salts as efficient catalysts for biomass conversion, offering a sustainable alternative to conventional SO₃H-based imidazolium ILs. Therefore, the strategy of modifying the acidity of a protic imidazolium salt by incorporating a nitro group in the imidazolium ring was successfully achieved, as observed in the degradation of cellulose, and can be extended to other acid-catalyzed reactions of biomass-derived compounds.