Epimerization of Isosorbide Catalyzed by Homogeneous Ruthenium-Phosphine Complexes: a New Step towards an Industrial Process

Abstract An efficient process for obtaining isoidide by catalytic epimerization of isosorbide using HRu(CO)Cl(PPh3)3/Xantphos (1/1) as organometallic catalyst without hydrogen is reported. The epimerization of isosorbide led to a thermodynamic equilibrium mixture containing 37% isosorbide, 57% isoidide and 6% isomannide in 1 hour at 170°C in tert-amyl alcohol. The same proportions were reached by using the catalytic precursor HRu(CO)Cl(PPh3)3 associated with sulfonated phosphines to isomerize isosorbide without solvent. Interestingly, the reaction can be also performed in a biphasic system (isosorbide/toluene) with the same catalytic activity. In this case, the mixture of isohexides was easily separated from toluene catalytic phase. Thus, by adding in each time a new isosorbide layer, nine successive cycles were performed without a loss of the catalytic activity. A scale-up leading to isomerize 1.3 Kg of isosorbide using only 0.2 g of ruthenium was also performed showing the potentiality of this biphasic catalytic system for an industrial application.