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Formose reaction
 
 
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The formose reaction, discovered by Aleksandr Butlerov
Aleksandr Butlerov

Aleksandr Mikhailovich Butlerov was a Russia chemist, one of the creators of the theory of chemical structure , the first to incorporate double bonds into structural formulas, the discoverer of formaldehyde, and the discoveror of the formose reaction....
 in 1861, involves the formation of sugars
Sugar

Sugar is a class of edible crystalline substances, mainly sucrose, lactose, and fructose. Human taste buds interpret its flavor as sweet. Sugar as a basic food carbohydrate primarily comes from sugar cane and from sugar beet, but also appears in fruit, honey, sorghum, sugar maple , and in many other sources....
 from formaldehyde
Formaldehyde

Formaldehyde is a chemical compound with the chemical formula H2CO. It is the simplest aldehyde. Formaldehyde exists in several forms aside from H2CO: the cyclic trimer trioxane and the polymer Polyoxymethylene....
. Formose is a contraction of formaldehyde and aldose.

Reaction and mechanism
The reaction is catalyzed by a base
Base (chemistry)

In chemistry, a base is most commonly thought of as an aqueous substance that can accept protons. A base is also often referred to as an alkali if OH- ions are involved....
 and a divalent metal such as calcium hydroxide
Calcium hydroxide

Calcium hydroxide, traditionally called slaked lime, hydrated lime, or pickling lime, is a chemical compound with the chemical formula Calcium2....
. The intermediary steps taking place are aldol reaction
Aldol reaction

The aldol reaction is a carbon-carbon bond formation chemical reaction in organic chemistry. In its usual form, it involves the nucleophilic addition of a ketone enolate to an aldehyde to form a Hydroxy ketone, or "aldol" , a structural unit found in many biomolecule and pharmaceuticals....
s, reverse Aldol reactions, and aldose-ketose isomerizations. Intermediates are glycolaldehyde
Glycolaldehyde

Glycolaldehyde is the smallest possible molecule that contains both an aldehyde group and a hydroxyl. It is the only possible diose, a 2-carbon monosaccharide, although a diose is not strictly a saccharide....
, glyceraldehyde
Glyceraldehyde

Glyceraldehyde is a triose monosaccharide with chemical formula Carbon3Hydrogen6Oxygen3. It is the simplest of all common aldoses....
, dihydroxyacetone
Dihydroxyacetone

Dihydroxyacetone is a simple carbohydrate that is primarily used as an ingredient in sunless tanning products. It is often derived from plant sources such as sugar beets and sugar cane, by the fermentation of glycerin....
, and tetrose
Tetrose

A tetrose is a monosaccharide with 4 carbon atoms. They either have an aldehyde functional group in position 1 or a ketone functional group in position 2 ....
 sugars.






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The formose reaction, discovered by Aleksandr Butlerov
Aleksandr Butlerov

Aleksandr Mikhailovich Butlerov was a Russia chemist, one of the creators of the theory of chemical structure , the first to incorporate double bonds into structural formulas, the discoverer of formaldehyde, and the discoveror of the formose reaction....
 in 1861, involves the formation of sugars
Sugar

Sugar is a class of edible crystalline substances, mainly sucrose, lactose, and fructose. Human taste buds interpret its flavor as sweet. Sugar as a basic food carbohydrate primarily comes from sugar cane and from sugar beet, but also appears in fruit, honey, sorghum, sugar maple , and in many other sources....
 from formaldehyde
Formaldehyde

Formaldehyde is a chemical compound with the chemical formula H2CO. It is the simplest aldehyde. Formaldehyde exists in several forms aside from H2CO: the cyclic trimer trioxane and the polymer Polyoxymethylene....
. Formose is a contraction of formaldehyde and aldose.

Reaction and mechanism


The reaction is catalyzed by a base
Base (chemistry)

In chemistry, a base is most commonly thought of as an aqueous substance that can accept protons. A base is also often referred to as an alkali if OH- ions are involved....
 and a divalent metal such as calcium hydroxide
Calcium hydroxide

Calcium hydroxide, traditionally called slaked lime, hydrated lime, or pickling lime, is a chemical compound with the chemical formula Calcium2....
. The intermediary steps taking place are aldol reaction
Aldol reaction

The aldol reaction is a carbon-carbon bond formation chemical reaction in organic chemistry. In its usual form, it involves the nucleophilic addition of a ketone enolate to an aldehyde to form a Hydroxy ketone, or "aldol" , a structural unit found in many biomolecule and pharmaceuticals....
s, reverse Aldol reactions, and aldose-ketose isomerizations. Intermediates are glycolaldehyde
Glycolaldehyde

Glycolaldehyde is the smallest possible molecule that contains both an aldehyde group and a hydroxyl. It is the only possible diose, a 2-carbon monosaccharide, although a diose is not strictly a saccharide....
, glyceraldehyde
Glyceraldehyde

Glyceraldehyde is a triose monosaccharide with chemical formula Carbon3Hydrogen6Oxygen3. It is the simplest of all common aldoses....
, dihydroxyacetone
Dihydroxyacetone

Dihydroxyacetone is a simple carbohydrate that is primarily used as an ingredient in sunless tanning products. It is often derived from plant sources such as sugar beets and sugar cane, by the fermentation of glycerin....
, and tetrose
Tetrose

A tetrose is a monosaccharide with 4 carbon atoms. They either have an aldehyde functional group in position 1 or a ketone functional group in position 2 ....
 sugars. In 1959, Breslow
Ronald Breslow

Ronald C. D. Breslow is an American chemist. He is currently University Professor at Columbia University, where he is based in the Department of Chemistry and affiliated with the Departments of Biological Sciences and Pharmacology; he has also been on the faculty of its Department of Chemical Engineering....
 proposed a mechanism for the reaction, consisting of the following steps:

The reaction begins with two formaldehyde molecules condensing to make glycolaldehyde 1 which further reacts in an aldol reaction with another equivalent of formaldehyde to make glyceraldehyde 2. An aldose-ketose isomerization of 2 forms dihydroxyketone 3 which can react with 2 to form ribulose
Ribulose

Ribulose is a ketopentose — a monosaccharide containing five carbon atoms, and including a ketone functional group. It has chemical formula 5105....
 4, and through another isomerization ribose
Ribose

Ribose, primarily occurring as D-ribose, is an organic compound that occurs widely in nature. It is an aldopentose, that is a monosaccharide containing five carbon atoms that, in its acyclic form, has an aldehyde functional group at one end....
 5. Molecule 3 also can react with formaldehyde to produce tetrulose 6 and then aldoltetrose 7. Intermediate 7 can split into 2 in a retro-aldol reaction.

Significance


The formose reaction is of importance to the question of the origin of life as it is a path from simple formaldehyde to complex sugars like ribose
Ribose

Ribose, primarily occurring as D-ribose, is an organic compound that occurs widely in nature. It is an aldopentose, that is a monosaccharide containing five carbon atoms that, in its acyclic form, has an aldehyde functional group at one end....
 and from there to RNA
RNA

Ribonucleic acid is a type of molecule that consists of a long chain of nucleotide units. Each nucleotide consists of a nucleobase, a ribose sugar, and a phosphate....
. In one experiment simulating early Earth conditions, pentoses formed from mixtures of formaldehyde, glyceraldehyde, and borate
Borate

Borates in chemistry are chemical compounds containing boron oxoanions, with boron in oxidation state +3. The simplest borate ion is the trigonal planar, BO33-, although many others are known....
 minerals such as colemanite
Colemanite

Colemanite is a borate mineral found in evaporite Deposition of alkaline lacustrine environments. Colemanite is a secondary mineral that forms by alteration of borax and ulexite....
 Ca2B6O115H2O or kernite
Kernite

Kernite, also known as rasorite is a hydrated sodium borate hydroxide mineral with formula Na2B4O62?3H2O....
 Na2B4O7. Adding to the interest in the formose reaction is the fact that both formaldehyde
Formaldehyde

Formaldehyde is a chemical compound with the chemical formula H2CO. It is the simplest aldehyde. Formaldehyde exists in several forms aside from H2CO: the cyclic trimer trioxane and the polymer Polyoxymethylene....
 and glycolaldehyde
Glycolaldehyde

Glycolaldehyde is the smallest possible molecule that contains both an aldehyde group and a hydroxyl. It is the only possible diose, a 2-carbon monosaccharide, although a diose is not strictly a saccharide....
 have been observed spectroscopically in outer space
Outer space

Outer space comprises the relatively empty regions of the universe outside the atmospheres of celestial bodies. Outer space is used to distinguish it from airspace and terrestrial locations....
.