Formose reaction

Is a mixture of formose sugars, the. By the self- condensation of formaldehyde in basic catalysts (oxides and hydroxides of Ca, Ba, Tl and Pb, but not NaOH ) is produced in the presence of CH- active compounds It is believed that the formose was the key reaction in the development of the primordial soup of first biomolecules and thus forms the basis of the origin of life.

Through them create central biomolecules of metabolism ( glyceraldehyde, pentoses, hexoses ) for the simple C1 - block formaldehyde ( CH2O). The pentoses are the basis of the RNA, the carrier of genetic information in the prebiotic phase of evolution ( Origin of Life ).

The reaction was discovered by Butlerov in 1861 and their complex mechanism was studied over many chemists generations.

Reaction

The whole point of this reaction is the first carbon-carbon bond. Formaldehyde can not respond without catalysis with yourself because an electrophile does not react with another electrophile and formaldehyde, there is only one carbon atom. In a pure, alkaline formalin normally only runs the Cannizzaro reaction, the methanol and formic acid yields ( Fig. 1).

For a carbon-carbon bond is one of the two carbon atoms, at least temporarily reversed. This is done in an elegant way in Formosecyclus ( Fig. 2).

If an alkaline formalin solution with a small amount of α - hydroxy carbonyl compound, such as seeded, for example, glycolaldehyde, an autocatalytic process escalates high within a short time, which directs the reaction in a completely different direction. Through an aldol is formed from glycolaldehyde, glyceraldehyde, which is transferred via the Lobry -de Bruyn - Alberda -van- Ekenstein rearrangement in dihydroxyacetone. This shift of the carbonyl group is essential for the further development of the carbon chain, as a result, the reactivity is reversed. While electrophilic was in the glyceraldehyde C1 and C2 nucleophilic. is electrophilically dihydroxyacetone in C2 or C3 and C1, which formally derives from the previously formaldehyde electrophilic, nucleophilic, so there DSS another aldol addition and thus can take place, a further chain extension. By a further van Ekensteinumlagerung the pattern of reactivity is pushed back again, so that formed by a Retroaldolspaltung two moles of glycol, the flow back into the autocatalytic cycle.

After the first round doubles the Glycolaldehydmenge quadrupled after the second, a thousand-fold after the 10th, after the 20th round of the factor is one million, after 30 in a billion, etc. ( Fig. 3)

The lower sugar glycolaldehyde and glyceraldehyde can turn form C5 or C6 sugars via aldol condensations. Once the sugar has reached the size of 5 or 6 carbon atoms, they can form cyclic hemiacetals and are thus set as the carbonyl largely out of action, so that no higher condensation products are formed, and thus in the nature widespread pentoses and hexoses, the stable end products of the reaction are.

Technically, this reaction can lead to the production of sugars and artificial after the hydrogenolysis for the preparation of glycols ( ethylene glycol, propylene glycol ) can be used.

Selective forms of formose reaction

Vitamin B1 through analog Umpolungskatalysatoren based on Thiazoliumyliden, Triazoliumyliden and Peridiuniumyliden formose may be directed selectively to glycolaldehyde beziehiungsweise dihydroxyacetone.

Technical importance of formose reaction

Given the limited oil reserves and almost unlimited supplies of C1 - sources ( methane hydrates from the deep sea, coal, biogas) research in the field of formose reaction was since the 1990s in the chemical industry intensified, because these are the only selective assembly reactions to C1 basis are and they allow a long-term change of feedstocks.