Isosorbide

Isosorbide is a bicyclic chemical compound from the group of diols and the oxygen-containing heterocycles, containing two fused furan rings. The starting material for isosorbide is D-sorbitol, which is obtained by catalytic hydrogenation of D-glucose, which is in turn produced by hydrolysis of starch. Isosorbide is discussed as a plant-based platform chemical from which biodegradable derivatives of various functionality can be obtained. Isosorbide is a bicyclic chemical compound from the group of diols and the oxygen-containing heterocycles, containing two fused furan rings. The starting material for isosorbide is D-sorbitol, which is obtained by catalytic hydrogenation of D-glucose, which is in turn produced by hydrolysis of starch. Isosorbide is discussed as a plant-based platform chemical from which biodegradable derivatives of various functionality can be obtained. Isosorbide is currently of great scientific and technical interest as a monomer building block for biopolymeric polycarbonates, polyesters, polyurethanes and epoxides. Hydrogenation of glucose gives sorbitol. Isosorbide is obtained by acid-catalyzed dehydration of D-sorbitol which yields the monocyclic furanoid sorbitan, which in turn forms by further dehydration the bicyclic furofuran derivative isosorbide. The reaction gives about 70 to 80% isosorbide in addition to 30 to 20% of undesirable by-products which have to be removed costly by distillation, recrystallization from alcohols, recrystallization from the melt, by a combination of these methods or by deposition from the vapor phase. A high purity product (> 99.8%) is essential for the use of a monomer when uncoloured, high molecular weight polymers shall be obtained. Isosorbide is a white, crystalline, highly hydrophilic solid. The two secondary hydroxy groups in the V-shaped bicyclic system possess different orientations leading to different chemical reactivities. This allows a selective monoderivatization of isosorbide. The hydroxy group in 5-position is endo oriented and forms a hydrogen bond with the oxygen atom in the adjacent furan ring. This makes the hydroxy group in 5-position more nucleophilic and more reactive than the exo oriented hydroxy group in 2-position; however, it is more shielded from the attack of sterically demanding reactants. With an LD50 value of 25.8 g·kg−1 (rat, oral), isosorbide is similarly nontoxic as D-glucose (also with an LD50 of 25.8 g·kg−1, rat, oral) and is classified by the Food and Drug Administration FDA as GRAS ('generally recognized as safe'). Because of its pronounced hygroscopicity, isosorbide is used as a humectant and in medicine as an osmotic diuretic (for the treatment of hydrocephalus) and acute angle-closure glaucoma. The two secondary hydroxy groups make isosorbide a versatile platform chemical accessible from renewable resources. As a diol, isosorbide can be mono- or biderivatized using the standard methods of organic chemistry, such as nitration, esterification, etherification, tosylation, etc., and converted into compounds with interesting properties or into monomeric units for novel polymers. By nitration of isosorbide with concentrated nitric acid, 2,5-isosorbide dinitrate (ISDN) can be obtained. 2,5-isosorbide dinitrate is suitable (just like its major metabolite 5-isosorbide mononitrate, ISMN) for the treatment of angina pectoris due to its vasodilator effect.