Glyceraldehyde

• Glyceraldehyde
• Glyceronaldehyd
• 2,3- Dihydroxypropanal
• Glyceraldehyde

• 367-47-5
• 56-82-6 [ DL- (±)- glyceraldehyde ]
• 453-17-8 [D- ( )- glyceraldehyde ]

Colorless powder

Fixed

1.46 g · cm -3 (D, L-form)

145 ° C

140-150 ° C ( 1.1 hPa)

• 30 g · L- 1 in water at 18 ° C.
• Well in ethanol, badly in diethyl ether

Template: Infobox chemical / molecular formula search available

Glyceraldehyde is a sweet-tasting chemical compound that forms a crystalline solid in anhydrous condition. It belongs to the group of sugar and within the subgroup of trioses. Because it contains a chiral center, there are two enantiomers. Regarding the molecular construction is the simplest types of simple sugars. The physiological significance of the connection is great since it is a raw material of metabolism, from which the cell is able to make very many other substances. Glyceraldehyde has C3H6O3 with the same molecular formula as the isomeric dihydroxyacetone.

Occurrence and biological significance

Glyceraldehyde and a derivative - glyceraldehyde -3-phosphate - are widespread, there are key substances of cell metabolism. Thus, glyceraldehyde -3-phosphate, an intermediate of glucose metabolic pathways in the cell, of glycolysis (see, glyceraldehyde -3 -phosphate dehydrogenase ), and the Entner- Doudoroff pathway. But also the formation of glucose from pyruvate, gluconeogenesis, proceeds via the intermediate stage of the glyceraldehyde-3- phosphate. In addition represents a molecule of glyceraldehyde -3- phosphate represents the net gain of carbon in CO2 fixation and reduction in the Calvin cycle of photosynthesis, which can be used for the construction of hexoses.

Molecular structure and optical properties

Glyceraldehyde is an optically active compound having a chiral center at the central carbon atom. Depending on the spatial arrangement of the substituents at this chiral center are two compounds whose molecules behave towards each other as mirror images. The two enantiomers are, as usual sugars, usually referred to according to the Fischer projection as D- glyceraldehyde and L- glyceraldehyde. With the Cahn- Ingold-Prelog convention, the terms obtained (S)- glyceraldehyde or (R)- glyceraldehyde. L- glyceraldehyde rotates plane polarized light to the left, D- glyceraldehyde, however, to the right.

Particular historical significance in the stereochemistry

Glyceraldehyde comes in the history of science a special role, since an agreement was concerned that connection, the configuration (ie, the spatial arrangement of the substituents ) of other chiral molecules could be specified.

Without the actual spatial arrangement of the hydroxyl groups to know the glyceraldehyde following has been agreed: The one glyceraldehyde- enantiomer that rotates plane polarized light to the right got the configuration assigned to D (the D stands for dexter, Latin for right). Thus, it was assumed that the hydroxy group in the Fischer projection shows right at the chiral center. (For more information: see Fischer projection ). The glyceraldehyde- enantiomer that rotates light to the left arbitrary linear polarisertes got the configuration L attributed. Would have been the other way round assignment can choose for absolute stereochemistry and the direction of rotation may as well differ from each other (for example,. L-lactic acid rotate linearly polarized light to the right)

With this agreement, the configuration of other chiral molecules could be specified: Man convicted the compound to be tested ( eg, lactic acid ) by chemical reactions in glyceraldehyde, without changing the configuration at the chiral center. Turned the resulting compound linearly polarized light to the left, as it was known that it is by convention to L- glyceraldehyde. It could be concluded that the starting compound had the L-configuration, since the chemical reactions are carried out with retention of configuration (for example, L-lactic acid).

Only after the introduction of the X-ray structure analysis, the actual configuration could be tested experimentally. It was found that the assignment ( levorotatory glyceraldehyde → L configuration, right-handed glyceraldehyde → D configuration ) was coincidentally in agreement with the chosen Fischer projection.

Production

Glyceraldehyde can be conveniently prepared by catalytic reversal of formaldehyde.

In the laboratory it can be just like its isomer dihydroxyacetone by oxidation of glycerol with hydrogen peroxide and a ferrous salt are shown as a catalyst. Dihydroxyacetone and glyceraldehyde can be separated by their different solubilities in water.

Chemical Properties

By a suitable oxidizing agent, the aldehyde group (- CHO) may be oxidized to the carboxyl group (-COOH). Here, the connection goes into glyceric acid.

Glyceraldehyde isomerized base catalysis in the Lobry -de Bruyn - Alberda -van- Ekenstein rearrangement both dihydroxyacetone and from the D-form in the L-form. There is therefore equilibrium reaction between D- and L- glyceraldehyde and the non- chiral dihydroxyacetone. The following figure shows the residual R is the group -CH 2- OH:

Accordingly, glyceraldehyde -3-phosphate to dihydroxyacetone phosphate is in equilibrium. In the cell, the equilibria are catalyzed by specific enzymes.

Proof

The aldehyde group of glyceraldehyde can be detected by the Fehling's test, the Tollensprobe or by the Schiff test.