Synthesis of Isoidide through Epimerization of Isosorbide using Ruthenium on Carbon

• Published in: ChemSusChem 2013-04, Vol.6 (4), p.693-700
• Main Authors: LeNôtre, Jérôme, vanHaveren, Jacco, vanEs, Daan S
• Format: Article
• Language: English
• Subjects: biodegradable polymers; carbohydrates; Carbon - chemistry; Catalysis; catalytic isomerization; chiral building-blocks; coating applications; derivatives; dynamic kinetic resolution; heterogeneous catalysis; isomerization; Isosorbide - chemistry; Nickel - chemistry; polyesters; renewable resources; ruthenium; Ruthenium - chemistry; secondary alcohols; Silicon Dioxide - chemistry; succinic acid; Sugar Alcohols - chemistry
• ISSN: 1864-5631; 1864-564X
• DOI: 10.1002/cssc.201200714

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 (pH 8) at 220 °C, under 40 bar of hydrogen, and using a Ru/C catalyst (5 % Ru) for 2 h 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 360 ppm Ru) and recyclable. High purity isoidide is obtained by high‐vacuum distillation of an equilibrium mixture on a 200 g scale. The high substrate loading (50 wt % in water), high selectivity, and the possibility for substrate reuse makes this procedure highly atom efficient and therefore, highly attractive for industrial use. The thermodynamic scale: Isoidide, the most attractive isohexide isomer for polymer synthesis, is obtained as the major product through the epimerization of isosorbide with a ruthenium‐on‐carbon catalyst under a relatively low pressure of hydrogen. The catalyst can be recycled, and isomannide and the unreacted isosorbide can be reused in further experiments, making this process highly atom efficient.