Glucose To Sorbose In A Single Step

Some 100,000 tons of l-ascorbic acid (vitamin C) are produced annually worldwide from d-glucose by way of l-sorbose intermediates. The conversion typically follows a multistep indirect pathway, such as sequential hydrogenation of d-glucose to d-sorbitol in the presence of a nickel-based catalyst followed by selective oxidation of d-sorbitol using microbial enzymes. Caltech chemical engineers Rajamani Gounder and Mark E. Davis have come up with a simpler conversion method. The team reports that d-glucose can be isomerized to l-sorbose stereospecifically in a single step by using an acidic zeolite catalyst (ACS Catal. 2013, DOI: 10.1021/cs400273c). Specifically, the team found that the conversion is mediated by Ti⁴⁺ Lewis acid sites in a titanium-doped zeolite known as Ti-Beta. Zeolites are a family of porous crystalline aluminosilicates that are widely used as catalysts in oil refining and other industrial processes. On the basis of isotope labeling studies, the Caltech group proposes that the Ti-Beta-mediated isomerization proceeds through an intramolecular C5-C1 hydride shift.