Homogeneous Zn(II) salts as efficient Lewis acid catalysts for the esterification of levulinic acid with diols

The valorization of renewable feedstocks to produce biochemicals and biofuels is an essential focus of contemporary research, with non-food crop biomass emerging as a cost-effective and environmentally friendly option. Among the chemicals derived from lignocellulosic biomass, levulinic acid (LAH) is a notable chemical platform due to its versatile applications. This study investigates the eco-friendly esterification of levulinic acid with polyols, catalyzed by zinc(II) species under mild, solvent-free conditions. A comprehensive screening of various zinc(II) species was conducted, to identify the most effective catalyst, ultimately selecting zinc triflate for its performance. The esterification scope was extended to three diols: 1,4-butanediol, 1,6-hexanediol, and 1,8-octanediol. These esters can replace fossil-based chemicals in many emerging sectors, as lubricants and as components in energy storage devices. The reaction conditions were fine-tuned to maximize yield and selectivity, using NMR spectroscopy to monitor the formation of mono- and di-esters and assess reaction profiles. Optimization experiments demonstrated that a catalyst loading of 1.0 %mol and a temperature of 120 °C yielded quantitative conversion within convenient reaction time (2–4 h). The findings highlight the efficiency of simple zinc(II) catalysts in producing levulinate esters with high yields and selectivity under sustainable conditions. Therefore, this research contributes to the development of greener processes to produce valuable chemicals and additives from renewable resources.