Triacetic acid lactone (TAL; 4-hydroxy-6-methyl-2-pyrone) is an

organic compound Some chemical authorities define an organic compound as a chemical compound that contains a carbon–hydrogen or carbon–carbon bond; others consider an organic compound to be any chemical compound that contains carbon. For example, carbon-co ...

derived enzymatically from

glucose Glucose is a sugar with the Chemical formula#Molecular formula, molecular formula , which is often abbreviated as Glc. It is overall the most abundant monosaccharide, a subcategory of carbohydrates. It is mainly made by plants and most algae d ...

. It is a light yellow solid that is soluble in organic solvents.

Structure

Triacetic acid lactone consists of two main

tautomer In chemistry, tautomers () are structural isomers (constitutional isomers) of chemical compounds that readily interconvert. The chemical reaction interconverting the two is called tautomerization. This conversion commonly results from the reloca ...

s. :

The tautomer on the left, featuring a 4-hydroxy group, the C4 carbon, is dominant. Triacetic acid lactone is classified as a 2-pyrone compound owing to the ketone group on the C2 carbon in its dominant form.

Synthesis

Triacetic acid lactone is synthesized either from

dehydroacetic acid Dehydroacetic acid is an organic compound which has several industrial applications. The compound is classified as a pyrone derivative. It presents as an odorless, colorless to white crystalline powder, almost insoluble in water and moderately so ...

, another

2-pyrone 2-Pyrone (α-pyrone or pyran-2-one) is an Saturated and unsaturated compounds, unsaturated cyclic chemical compound with the molecule, molecular formula C5H4O2. It is isomeric with 4-pyrone. 2-Pyrone is used in organic synthesis as a building blo ...

derivative, or from

by enzymatic catalysis. In its original synthesis, triacetic acid lactone was obtained by treatment of dehydroacetic acid with

sulfuric acid Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid (English in the Commonwealth of Nations, Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen, ...

at 135 °C. Dehydroacetic acid undergoes ring-opening and hydration to form "tetracetic acid". Upon cooling, triacetic acid reverts to a lactone ring similar to the dehydroacetic acid structure, and the triacetic acid lactone is recovered by crystallization in cold water. : Collie

Biosynthesis

The microbial synthesis of triacetic acid lactone requires the enzyme 2-pyrone synthase (2-PS). This enzyme has been examined in two hosts Escherichia coli and Saccharomyces cerevisiae. The Saccharomyces cerevisiae host being used during the synthesis produces a higher yield (70%) compared with the Escherichia coli host, which produces a yield of 40% of triacetic acid lactone. This enzyme catalyzes the synthesis of triacetic acid lactone from

acetyl-CoA Acetyl-CoA (acetyl coenzyme A) is a molecule that participates in many biochemical reactions in protein, carbohydrate and lipid metabolism. Its main function is to deliver the acetyl group to the citric acid cycle (Krebs cycle) to be oxidation, o ...

via two subsequent condensations with

malonyl-CoA Malonyl-CoA is a coenzyme A derivative of malonic acid. Biosynthesis Malonyl-CoA cannot cross membranes and there is no known malonyl-CoA import mechanism. The biosynthesis therefore takes place locally: * cytosol: Malonyl-CoA is formed by c ...

. This produces an intermediate of 3,5-diketohexanoate thioester, which undergoes ring closure to produce triacetic acid lactone.

Reactivity

The lactone is a versatile intermediate in

organic synthesis Organic synthesis is a branch of chemical synthesis concerned with the construction of organic compounds. Organic compounds are molecules consisting of combinations of covalently-linked hydrogen, carbon, oxygen, and nitrogen atoms. Within the gen ...

. Substantial negative charge accumulates on the C3 carbon, rendering it nucleophilic, but the C5 carbon is inert. It has also been described as a platform chemical, meaning that it could be the precursor to other fine chemicals. The lactone undergoes

decarboxylation Decarboxylation is a chemical reaction that removes a carboxyl group and releases carbon dioxide (CO2). Usually, decarboxylation refers to a reaction of carboxylic acids, removing a carbon atom from a carbon chain. The reverse process, which is ...

acetylacetone Acetylacetone is an organic compound with the chemical formula . It is classified as a 1,3-diketone. It exists in equilibrium with a tautomer . The mixture is a colorless liquid. These tautomers interconvert so rapidly under most conditions that ...

. It is also a precursor to

sorbic acid Sorbic acid, or 2,4-hexadienoic acid, is a natural organic compound used as a food preservative. It has the chemical formula and the structure . It is a colourless solid that is slightly soluble in water and sublimes readily. It was first iso ...

, dienoic acid, and hexenoic acid. Dienoic acid is used to inhibit the growth of various molds and hexenoic acid is used as a flavoring agent. Acetylacetone is used for metal extraction and plating and as a food additive.{{cite journal , doi = 10.1039/C2GC35343A , title = Triacetic acid lactone as a potential biorenewable platform chemical , year = 2012 , last1 = Chia , first1 = Mei , last2 = Schwartz , first2 = Thomas J. , last3 = Shanks , first3 = Brent H. , last4 = Dumesic , first4 = James A. , journal = Green Chemistry , volume = 14 , issue = 7 , pages = 1850

References

2-Pyrones Hydroxyarenes

Structure

Synthesis

Biosynthesis

Reactivity

See also

References