Sorbitol dehydration in high temperature liquid water

Sorbitol dehydration in high temperature liquid water proceeded at 523–573 K without adding any acid catalysts. Anhydrosorbitols (1,4-anhydrosorbitol (1,4-AHSO), 2,5-anhydrosorbitol (2,5-AHSO) and 1,5-anhydrosorbitol (1,5-AHSO)) were produced by the monomolecular dehydration of sorbitol, and isosorbide was produced by the stepwise dehydration of 1,4-AHSO. The formation rates of 1,4-AHSO and 2,5-AHSO (five-membered cyclic ethers) from sorbitol dehydration were much larger than that of 1,5-AHSO (six-membered cyclic ether), and 1,4-AHSO was the main product of the monomolecular dehydration of sorbitol. The dehydration rate of sorbitol to 1,4-AHSO was faster than that of 1,4-AHSO to isosorbide; therefore, 1,4-AHSO could be obtained as an intermediate product. A kinetic analysis of sorbitol dehydration in high temperature liquid water showed that the maximum yield of 1,4-AHSO from the dehydration of sorbitol increased with decreasing reaction temperature (for example, 80% at 500 K) and that the maximum yield of isosorbide was 57% at 590 K for 1 h. 1,4-AHSO and isosorbide could be produced selectively from sorbitol dehydration in high temperature liquid water by controlling both the reaction temperature and reaction time.