Epimerization of isosorbide catalyzed by homogeneous ruthenium-phosphine complexes: A new step towards an industrial process

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 h at 170 degrees 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.

Automated summary

The study presents an efficient process for obtaining isoidide by catalytic epimerization of isosorbide using HRu(CO)Cl(PPh3)(3)/Xantphos (1/1) as the organometallic catalyst without hydrogen. The reaction can be carried out in tert-amyl alcohol, without solvent, or in a biphasic system with toluene, showing potential for industrial application. The process demonstrates good activity and stability under different solvent conditions.