Catalytic esterification reactions of model lignin phenols towards hydrophobicity

Two lignin model compounds, eugenol (Eu) or 2-methoxy-4-propylphenol (MPP), were esterified with a protonating acetic acid (AcA), H2SO4 catalyst and water. Initial product analysis showed a high related number of the unspecific process spe-cies of Eu reactions. Therefore, research was continued only with MPP. Temperature, equivalent MPP/AA molar ratio and quantified H2SO4 mass amount were varied, reactants were monitored, and it was determined that the functionalisation’s best conditions were 130 °C, indicated total contained MPP/AA 1:3 and 1 mol% rate-increasing H2SO4. Yields exceed 15 mol%. Other H+ donors, HCl or p-toluene-sulfonic acid, were used, but resulted in lower yields (2 mol% or less). Afterwards, MPP esterification was attempted with five bio-based molecules, but only levulinic acid produced a measurable ester value (4 mol%). Two enzymes, lipase from Rhyzopus oryzae or immobilized lipase B from Candida antarctica, were also applied, not forming products. A micro-kinetic system representation was developed, based on a proposed elementary mechanism, which revealed the comparable activation energy of MPP substitution, catalysed by H2SO4. Barrier (24 kJ mol–1) was less than that with H-beta (zeolite) (39 kJ mol–1), while higher than that with AmberLite XAD 16 (resin) (10 kJ mol–1).