Synthesis of diphenolic acid from levulinic acid under heterogeneous catalysis with commercial Amberlyst15 resin and sulfonated C5- and C6-hydrochars

Diphenolic acid is assuming today a great importance because it has been found as a promising candidate for bisphenol A replacement. Despite bisphenol A advantages, environmental and health concerns have led to searching for its possible substitutes, finding in diphenolic acid a great potential. The two main DPA isomers, ortho,para-diphenolic acid (o,p’-DPA) and para,para-diphenolic acid (p,p’-DPA), are traditionally synthesized by condensation between two molecules of phenol and one of levulinic acid, in the presence of a Brønsted acid as catalyst. Remarkably, only the p,p’-DPA isomer is industrially attractive, leading to polymers with better mechanical and optical properties. Within the project PRIN 2020 LEVANTE "LEvulinic acid Valorization through Advanced Novel Technologies", the catalytic performances of commercial and ad hoc synthesized acid catalysts have been evaluated, to selectively produce the p,p'-DPA isomer, starting from levulinic acid and phenol. The reaction optimization with the commercial ion exchange resin Amberlyst15 has led to good p,p'-DPA yields, about 45 mol%, an excellent achievement from the perspective of the heterogeneous catalysis approach. Moreover, new ad hoc acid catalysts have been synthesized by sulfonation of xylose- and glucose-derived hydrochars, and tested for the p,p’-DPA synthesis. Maximum p,p'-DPA yield of about 20 mol% have been achieved with such new catalysts, opening the way to the use of much cheaper acid catalysts deriving from biomass, providing new more sustainable opportunities for the chemical industry.