Biobased synthesis of butyl levulinate from levulinic acid by using CTAB-based hydrophobic deep eutectic solvent as a catalyst

The present research discusses the utilization of hydrophobic deep eutectic solvents (HDES) as acid catalysts in the green synthesis of n-butyl levulinate (BL) by esterification of levulinic acid (LA) obtained from cellulose. Butyl levulinate is used as a plasticizer, flavor, fragrance, solvent, and fuel additive. The HDES catalysts were synthesized from cetyl trimethyl ammonium bromide (CTAB) as hydrogen bond acceptor (HBA) and carboxylic acids (oxalic, citric, and para-toluenesulfonic acid monohydrate (p-TSAM)) as hydrogen bond donor (HBD). Hydrophobic deep eutectic solvents (HDES) offer the advantage of ease of recovery and recyclability. The most efficient HDES catalyst for the LA conversion was HDES-1 (mole ratio of CTAB:p-TSAM = 1:3). The HDES-1 catalyst was characterized by FTIR and NMR spectroscopy. This catalyst was subjected to optimization studies. Under optimum conditions (393 K, 0.01 g/cm³ catalyst, ratio of levulinic acid to n-butanol (in moles) = 1:5, 400 rpm, 3 h), maximum LA conversion was 88.77%. Without losing activity, the catalyst was used seven times.