Incarbohydrate chemistry, theLobry de Bruyn–Van Ekenstein transformation also known as theLobry de Bruyn–Alberda van Ekenstein transformation is thebase or acidcatalyzed transformation of an aldose into the ketose isomer or vice versa, with atautomericenediol asreaction intermediate. Ketoses may be transformed into 3-ketoses, etcetera. The enediol is also an intermediate for theepimerization of analdose orketose.^[1][2]

The reactions are usually base catalyzed, but can also take place under acid or neutral conditions.^[1] A typicalrearrangement reaction is that between the aldoseglyceraldehyde and the ketosedihydroxyacetone in achemical equilibrium.

The Lobry de Bruyn–Van Ekenstein transformation is relevant for the industrial production of certainketoses and was discovered in 1885 byCornelis Adriaan Lobry van Troostenburg de Bruyn andWillem Alberda van Ekenstein.^{[3][4][5][6][7][8]}

The following scheme describes the interconversion between an aldose and a ketose, where R is anyorganic residue.

The equilibrium or thereactant to product ratio depends onconcentration,solvent,pH andtemperature. At equilibrium the aldose and ketose form a mixture which in the case of the glyceraldehyde and dihydroxyacetone is also calledglycerose.

A related reaction is thealpha-ketol rearrangement.

The carbon atom at which the initialdeprotonation takes place is astereocenter. If, for example, D-glucose (an Aldose) rearranges to D-fructose, the ketose, thestereochemical configuration is lost in theenol form. In the chemical reaction the enol can be protonated from two faces, resulting in the backformation of glucose or the formation of theepimerD-mannose. The final product is a mix of D-glucose, D-fructose and D-mannose.

Sugar Chemistry: Explains mutarotation and interconversion of Glucose ↔ Fructose ↔ Mannose.

Food Chemistry: Important in the alkaline degradation of Sugars and Caramelization.

Biological Relevance: Similar enediol intermediates appear in Glycolysis (via Isomerases).

• Carbohydrate chemistry
• Rearrangement reactions
• Name reactions

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