carbohydrate chemistry Carbohydrate chemistry is a subdiscipline of chemistry primarily concerned with the detection, synthesis, structure, and function of carbohydrates. Due to the general structure of carbohydrates, their synthesis is often preoccupied with the selec ...

, the Lobry de Bruyn–Van Ekenstein transformation also known as the Lobry de Bruyn–Alberda van Ekenstein transformation is the base or acid

catalyzed Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recycl ...

transformation of an aldose into the ketose isomer or vice versa, with a tautomeric

enediol In organic chemistry, alkenols (shortened to enols) are a type of reactive structure or intermediate in organic chemistry that is represented as an alkene (olefin) with a hydroxyl group attached to one end of the alkene double bond (). The ter ...

reaction intermediate In chemistry, a reaction intermediate or an intermediate is a molecular entity that is formed from the reactants (or preceding intermediates) but is consumed in further reactions in stepwise chemical reactions that contain multiple elementary ...

. Ketoses may be transformed into 3-ketoses, etcetera. The enediol is also an intermediate for the

epimerization In stereochemistry, an epimer is one of a pair of diastereomers. The two epimers have opposite configuration at only one stereogenic center out of at least two. All other stereogenic centers in the molecules are the same in each. Epimerization i ...

of an

aldose An aldose is a monosaccharide (a simple sugar) with a carbon backbone chain with a carbonyl group on the endmost carbon atom, making it an aldehyde, and hydroxyl groups connected to all the other carbon atoms. Aldoses can be distinguished from ket ...

ketose A ketose is a monosaccharide containing one ketone group per molecule. The simplest ketose is dihydroxyacetone, which has only three carbon atoms. It is the only ketose with no optical activity. All monosaccharide ketoses are reducing sugars, be ...

. Momcilo Miljkovi
''Carbohydrates: Synthesis, Mechanisms, and Stereoelectronic Effects''
2009 (Google books) The reactions are usually base catalyzed, but can also take place under acid or neutral conditions. A typical

rearrangement reaction In organic chemistry, a rearrangement reaction is a broad class of organic reactions where the carbon skeleton of a molecule is rearranged to give a structural isomer of the original molecule. Often a substituent moves from one atom to another at ...

is that between the aldose

glyceraldehyde Glyceraldehyde (glyceral) is a triose monosaccharide with chemical formula C3 H6 O3. It is the simplest of all common aldoses. It is a sweet, colorless, crystalline solid that is an intermediate compound in carbohydrate metabolism. The word ...

and the ketose

dihydroxyacetone Dihydroxyacetone (; DHA), also known as glycerone, is a simple saccharide (a triose) with formula . DHA is primarily used as an ingredient in sunless tanning products. It is often derived from plant sources such as sugar beets and sugar cane ...

in a

chemical equilibrium In a chemical reaction, chemical equilibrium is the state in which both the reactants and products are present in concentrations which have no further tendency to change with time, so that there is no observable change in the properties of the ...

. The Lobry de Bruyn–Van Ekenstein transformation is relevant for the industrial production of certain

s and was discovered in 1885 by Cornelis Adriaan Lobry van Troostenburg de Bruyn and Willem Alberda van Ekenstein.

Aldose-ketose transformation

The following scheme describes the interconversion between an aldose and a ketose, where R is any organic residue. The equilibrium or the ''reactant to product ratio'' depends on

concentration In chemistry, concentration is the abundance of a constituent divided by the total volume of a mixture. Several types of mathematical description can be distinguished: '' mass concentration'', '' molar concentration'', '' number concentration'' ...

solvent A solvent (s) (from the Latin '' solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid. Water is a solvent for ...

, pH and

temperature Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer. Thermometers are calibrated in various temperature scales that historically have relied on ...

. At equilibrium the aldose and ketose form a mixture which in the case of the glyceraldehyde and dihydroxyacetone is also called glycerose. A related reaction is the alpha-ketol rearrangement.

Epimerization

The carbon atom at which the initial

deprotonation Deprotonation (or dehydronation) is the removal (transfer) of a proton (or hydron, or hydrogen cation), (H+) from a Brønsted–Lowry acid in an acid–base reaction.Henry Jakubowski, Biochemistry Online Chapter 2A3, https://employees.csbsju. ...

takes place is a

stereocenter In stereochemistry, a stereocenter of a molecule is an atom (center), axis or plane that is the focus of stereoisomerism; that is, when having at least three different groups bound to the stereocenter, interchanging any two different groups cr ...

. If, for example, D-

glucose Glucose is a simple sugar with the molecular formula . Glucose is overall the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, usi ...

(an Aldose) rearranges to D-

fructose Fructose, or fruit sugar, is a ketonic simple sugar found in many plants, where it is often bonded to glucose to form the disaccharide sucrose. It is one of the three dietary monosaccharides, along with glucose and galactose, that are absorb ...

, the ketose, the stereochemical configuration is lost in the

enol In organic chemistry, alkenols (shortened to enols) are a type of reactive structure or intermediate in organic chemistry that is represented as an alkene (olefin) with a hydroxyl group attached to one end of the alkene double bond (). The te ...

form. In the chemical reaction the enol can be protonated from two faces, resulting in the backformation of glucose or the formation of the

epimer In stereochemistry, an epimer is one of a pair of diastereomers. The two epimers have opposite configuration at only one stereogenic center out of at least two. All other stereogenic centers in the molecules are the same in each. Epimerization is ...

D-mannose Mannose is a sugar monomer of the aldohexose series of carbohydrates. It is a C-2 epimer of glucose. Mannose is important in human metabolism, especially in the glycosylation of certain proteins. Several congenital disorders of glycosylation are ...

. The final product is a mix of D-glucose, D-fructose and D-mannose.

References

{{DEFAULTSORT:Lobry de Bruyn-Van Ekenstein transformation Carbohydrate chemistry Rearrangement reactions Name reactions