Lobry-de Bruyn-van Ekenstein transformation

The Lobry-de Bruyn-van Ekenstein transformation also known as the Lobry-de Bruyn-van-Alberda-van-Ekenstein transformation is a base catalyzed Aldose-Ketose-Isomerization in carbohydrate chemistry [ANGYAL, S.J.: The Lobry de Bruyn–Alberda van Ekenstein transformation and related reactions, in: Glycoscience: epimerisation, isomerisation and rearrangement reactions of carbohydrates, Vol. 215, (Ed.: STÜTZ, A.E.), Springer-Verlag, Berlin, 2001, 1–14] . A typical rearrangement reaction is that between glyceraldehyde and dihydroxyacetone in a chemical equilibrium.

The reaction is relevant for the industrial production of certain ketoses and was discovered in 1885 by Cornelis Adriaan Lobry van Troostenburg de Bruyn and Willem Alberda van Ekenstein.

Reaction mechanism

The following scheme describes the reaction mechanism where R is any organic residue.

The position of the equilibrium or the reactant to product ratio depends on concentration, solvent,pH value and temperature. At equilibrium the aldose and ketose form a mixture which in the case of the glyceraldehyde and dihydroxyacetone is also called glycerose.

tereochemistry

The carbon atom at which the initial deprotonation takes place is a stereocenter and based on the equilibrium all reaction steps constitute a epimerization. For example, D-Glucose (an Aldose) rearranges to D-Fructose the ketose. The stereochemical configuration is lost in this reaction in the enol form. In the equilibrium the enol can be protonated from two faces resulting in the backformation of glucose and the formation of D-mannose. The final product is a mix of D-glucose, D-fructose and D-mannose.

References