Recent progress in catalytic selective dehydration of sorbitol

Recently, the use of renewable biomasses has attracted much attention from academics and industry. Sorbitol is a useful biomass- derived chemical that can be converted to high-added-value products; it can be conveniently obtained from cellulose via glucose. Isosorbide and 1,4-anhydrosorbitol, which can be produced by dehydration of sorbitol, are potentially important bio-based industrial chemicals. Sorbitol can be transformed into 1,4-anhydrosorbitol and isosorbide through acid-catalyzed selective dehydration. The catalyst acidity is the most important factor in acid-catalyzed dehydration reactions. It has been observed that strong acidity is favorable for producing isosorbide. Various homogeneous and heterogeneous catalysts have been developed for sorbitol dehydration, depending on the desired products. Mineral acids such as sulfuric acid and hydrochloric acid, and metal halides such as SnCl4 and AlCl3 are efficient catalysts for sorbitol dehydration. However, processes using homogeneous acids have drawbacks from environmental and safety perspectives. Moreover, homogenous catalyst separation from the reaction mixture is cumbersome, which may add extra costs to commercial synthesis. Various solid catalysts such as zeolites, metal(IV) phosphates, layered niobium- molybdate, tungstophosphoric acids supported on various metal oxides, metal oxides modified with phosphoric acid, a superhydrophobic mesoporous polymer-based acid catalyst, and resins (amberlyst-15) have recently been tested in the selective dehydration of sorbitol. In addition, high-temperature liquid water has attracted much attention as a promising reaction medium for sorbitol dehydration. Future prospects for catalytic dehydration of sorbitol are summarized.