Synthesis of Isoidide through Epimerization of Isosorbide using Ruthenium on Carbon

A highly efficient procedure for obtaining resin-grade isoidide through catalytic epimerization of isosorbide using a ruthenium-on-carbon (Ru/C) catalyst is reported. A comprehensive reaction-parameter variation study involving substrate concentration, catalyst (type of metal, support, and loading), initial pH value, hydrogen pressure, solvent, and reaction temperature demonstrates that superior performance and high selectivity can be achieved. Epimerization of isosorbide in water (pH8) at 220 degrees C, under 40bar of hydrogen, and using a Ru/C catalyst (5% Ru) for 2h results in a thermodynamic equilibrium mixture containing 55% isoidide, 40% isosorbide, and 5% isomannide. In comparison with previously reported nickel-based catalysts, the Ru/C catalyst is advantageous because it is highly active (as low as 360ppm Ru) and recyclable. High purity isoidide is obtained by high-vacuum distillation of an equilibrium mixture on a 200g scale. The high substrate loading (50wt% in water), high selectivity, and the possibility for substrate reuse makes this procedure highly atom efficient and therefore, highly attractive for industrial use.