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Encyclopedia > Lactone

A lactone is a cyclic ester in organic chemistry. It is the condensation product of an alcohol group and a carboxylic acid group in the same molecule. The most stable structure for lactones are the 5-membered lactones (gamma-lactone) and 6-membered lactones (delta-lactone), because of the minimal angle strain in the compounds' structure. Gamma-lactones are so stable that 4-hydroxy acids (R-CH(OH)-(CH2)2-COOH) are unstable in the presence of dilute acids at room temperature, immediately undergoing spontaneous esterification and cyclisation to the lactone. Beta-lactones do exist, but can only be made by special methods. General formula of a carboxylate ester. ... Organic chemistry is a specific discipline within chemistry which involves the scientific study of the structure, properties, composition, reactions, and preparation (by synthesis or by other means) of chemical compounds consisting of primarily carbon and hydrogen, which may contain any number of other elements, including nitrogen, oxygen, halogens as well... A condensation reaction (also known as a dehydration reaction or dehydration synthesis when water is lost) is a chemical reaction in which two molecules or moieties react and become covalently bonded to one another by the concurrent loss of a small molecule, often water, methanol, or a type of hydrogen... Functional group of an alcohol molecule. ... In organic chemistry, functional groups are specific groups of atoms within molecules, that are responsible for the characteristic chemical reactions of those molecules. ... Structure of a carboxylic acid The 3D structure of the carboxyl group A space-filling model of the carboxyl group Carboxylic acids are organic acids characterized by the presence of a carboxyl group, which has the formula -(C=O)-OH, usually written as -COOH. In general, the salts and anions... In chemistry, a molecule is an aggregate of two or more atoms in a definite arrangement held together by chemical bonds [1] [2] [3] [4] [5]. Chemical substances are not infinitely divisible into smaller fractions of the same substance: a molecule is generally considered the smallest particle of a pure...

Contents

Etymology

The name lactone derives from the ring compound called lactide, which is formed from the dehydration of 2-hydroxypropanoic acid (lactic acid) CH3-CH(OH)-COOH. Lactic acid, in turn, derives its name from its original isolation from soured milk (latin: lac, lactis). An internal dehydration within the same molecule of lactic acid would have produced a 3-membered lactone which is unstable. Lactide is the anhydride of lactic acid. ... Lactic acid (IUPAC systematic name: 2-hydroxypropanoic acid), also known as milk acid, is a chemical compound that plays a role in several biochemical processes. ...


Nomenclature

Lactones are named by labelling the carbon atoms in the chain of the lactones' precursor compounds. The first carbon atom after the carbon in the -COOH group on the parent compound is labelled alpha, the second will be labelled beta and so forth. The lactone formed will be named after the carbon atom which is connected to the -OH (hydroxy) group that the -COOH group reacts with, and this will determine the prefix of the lactone. The prefixes also indicate the ring size: beta-lactone (4-membered), gamma-lactone (5-membered), delta-lactone (6-membered ring).


Reactions

The reactions of lactones are similar to those of esters, as explified by gamma-lactone in the following sections:


Hydrolysis

Heating a lactone with a base (sodium hydroxide) will hydrolyse the lactone to its parent compound, the straight chained bifunctional compound. Like straight-chained esters, the hydrolysis-condensation reaction of lactones is a reversible reaction, with an equilibrium. However, the equilibrium constant of the hydrolysis reaction of the lactone is higher than that of the straight-chained ester i.e. the products (hydroxyacids) are favoured in the case of the lactones. This is because although the enthalpies of the hydrolysis of esters and lactones are about the same, the entropy of the hydrolysis of lactones is less than the enthropy of straight-chained esters. Sodium hydroxide (NaOH), also known as lye or caustic soda, is a caustic metallic base. ... Hydrolysis is a chemical reaction or process in which a molecule is split into two parts by reacting with a molecule of water, which has the chemical formula H2O. One of the parts gets an OH- from the water molecule and the other part gets an H+ from the water. ... A reversible reaction is a chemical reaction that may proceed in both the forward and reverse directions. ... Chemical equilibrium is the state in which the concentrations of the reactants and products have no net change over time. ... In chemistry, the equilibrium constant is a quantity characterizing a chemical equilibrium in a chemical reaction which is a useful tool to determine the concentration of various reactants or products in a system where chemical equilibrium occurs. ... In thermodynamics and molecular chemistry, the enthalpy or heat content (denoted as Δ or ΔH, or rarely as χ) is a quotient or description of thermodynamic potential of a system, which can be used to calculate the useful work obtainable from a closed thermodynamic system under constant conditions. ... Ice melting - classic example of entropy increasing[1] described in 1862 by Rudolf Clausius as an increase in the disgregation of the molecules of the body of ice. ...


Reduction

Lactones can be reduced to diols using lithium aluminium hydride in dry ether. The reduction reaction will first break the ester bond of the lactone and then, reduce the carboxylic acid group (-COOH) to the alcohol group (-OH). Gamma-lactones, for instance, will be reduced to butane-1,4-diol, (CH2(OH)-(CH2)2-CH2(OH)


Ammonolysis

Lactones also react with ethanolic ammonia, which will first break the ester bond and then react with the acidic -COOH group, because of the basic properties of ammonia, to form a difunctional group, i.e. alcohol and amide. Gamma-lactones will react to yield CH2(OH)-(CH2)2-CO-NH2.


Examples

Image File history File links Propiolactone. ... Propiolactone, or β-propiolactone, is an organic compound classified as a lactone containing a four-membered ring. ... Image File history File links Download high resolution version (1026x718, 4 KB) Description: Chemical structure of gamma-Butyrolactone. ... gamma-Butyrolactone, also known as GBL, butyrolactone, 1,4-lactone, 4-butyrolactone, 4-hydroxybutyric acid lactone, and gamma-hydroxybutyric acid lactone, is a hygroscopic colorless oily liquid with a weak characteristic odor and medium solubility in water (≥ 10 g / 100 ml). ... Image File history File links Download high-resolution version (1100x686, 39 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Lactone Glucono delta-lactone ... Glucono delta-lactone (GDL) is a naturally occurring food additive used as a sequestrant, an acidifier, or a curing, pickling, or leavening agent. ... For the mathematical constant see: E (mathematical constant). ... Image File history File links Caprolactone. ... Caprolactone is a cyclic ester, known as a lactone, with a ring size of seven. ...

See also


  Results from FactBites:
 
Lactone im Wein-Plus Glossar (258 words)
Lactone spielen unter den flüchtigen Stoffen des Weines eine sehr wichtige Rolle, besonders die g-Lactone.
Lactone entstehen schon in den Trauben oder bei der Gärung, aber auch bei der Flaschen-Reifung, besonders bei Weinen mit Barrique-Ausbau mit Fässern aus Eichenholz.
Eigene Anmerkung zu diesem Stichwort an den Autor senden
397. Glucono-delta-lactone (WHO Food Additives Series 6) (1137 words)
BIOLOGICAL DATA BIOCHEMICAL ASPECTS Glucono-delta-lactone, in an aqueous medium, readily forms an equilibrium mixture of the lactone and gluconic acid.
When three men were given 10 g (167 mg/kg) of glucono-delta- lactone orally as a 10% solution, the amounts recovered in the urine in seven hours represented 7.7-15% of the dose.
Short-term studies Rat Groups of 20 male and 20 female rats were fed gluconic acid (as glucono-delta-lactone) for 26 weeks at levels of 0 and 10 000 ppm in the diet without ill-effects or demonstrable changes in the main organs on microscopic examination (Harper & Gaunt, 1962).
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