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Lactone
 
 
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A lactone is a cyclic ester
Ester

An ester is an often Aroma compound organic chemistry or partially organic compound formed by the reaction between an acid and an alcohol or aromatic alcohol with the elimination of water....
 in organic chemistry
Organic chemistry

Organic chemistry is a discipline within chemistry which involves the science study of the structure, properties, composition, chemical reaction, and preparation of chemical compounds that contain carbon....
 . It is the condensation
Condensation reaction

A condensation reaction is a chemical reaction in which two molecules or moieties combine to form one single molecule, together with the loss of a small molecule....
 product of an alcohol
Alcohol

In chemistry, an alcohol is any organic compound in which a hydroxyl Functional group is bound to a carbon atom of an alkyl or substituted alkyl group....
 group
Functional group

In organic chemistry, functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules....
 and a carboxylic acid
Carboxylic acid

Carboxylic acids are organic acids characterized by the presence of a carboxyl group, which has the Chemical formula -COH, usually written -COOH or -CO2H....
 group in the same molecule
Molecule

In chemistry, a molecule is defined as a sufficiently stable, electric charge neutral group of at least two atoms in a definite arrangement held together by very strong chemical bonds....
. 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.






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Propiolactone
A lactone is a cyclic ester
Ester

An ester is an often Aroma compound organic chemistry or partially organic compound formed by the reaction between an acid and an alcohol or aromatic alcohol with the elimination of water....
 in organic chemistry
Organic chemistry

Organic chemistry is a discipline within chemistry which involves the science study of the structure, properties, composition, chemical reaction, and preparation of chemical compounds that contain carbon....
 . It is the condensation
Condensation reaction

A condensation reaction is a chemical reaction in which two molecules or moieties combine to form one single molecule, together with the loss of a small molecule....
 product of an alcohol
Alcohol

In chemistry, an alcohol is any organic compound in which a hydroxyl Functional group is bound to a carbon atom of an alkyl or substituted alkyl group....
 group
Functional group

In organic chemistry, functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules....
 and a carboxylic acid
Carboxylic acid

Carboxylic acids are organic acids characterized by the presence of a carboxyl group, which has the Chemical formula -COH, usually written -COOH or -CO2H....
 group in the same molecule
Molecule

In chemistry, a molecule is defined as a sufficiently stable, electric charge neutral group of at least two atoms in a definite arrangement held together by very strong chemical bonds....
. 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, in the presence of dilute acids at room temperature, 4-hydroxy acids (R-CH(OH)-(CH2)2-COOH) immediately undergo spontaneous esterification and cyclisation to the lactone. Beta-lactones do exist, but can only be made by special methods.

A recent study has isolated beta-lactones from bromination of 2,3-dimethylmaleate and/or 2,3-dimethylfumarate disodium salts, under ambient and aqueous conditions. The carboxylate groups of the maleate and fumarate moieties exhibit neighbouring group effects and alpha-lactones are proposed in the detailed mechanism.

Etymology

The name lactone derives from the ring compound called lactide
Lactide

Lactide is the cyclic di-ester of lactic acid, i.e., 2-hydroxypropionic acid. Lactic acid can not form a lactone as other hydroxy acids do because the hydroxy group is too close to the carboxylic group....
, which is formed from the dehydration of 2-hydroxypropanoic acid (lactic acid
Lactic acid

Lactic acid , also known as milk acid, is a chemical compound that plays a role in several biochemistry processes. It was first isolated in 1780 by a Swedish chemist, Carl Wilhelm Scheele, and is a carboxylic acid with a chemical formula of C3H6O3....
) 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.

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).

Natural sources


Lactones (specifically 3-methyl-4-octanolide) are found in oak
Oak

The term oak can be used as part of the common name of any of about 400 species of trees and shrubs in the genus Quercus , which are listed in the List of Quercus species, and some related genera, notably Lithocarpus....
 trees as well as many other plants, and impart flavour to whisky
Whisky

Whisky or whiskey refers to a broad category of Distilled beverages that are distilled from Fermentation grain Mashing and aged in wooden casks ....
.

Synthesis

Many methods in ester
Ester

An ester is an often Aroma compound organic chemistry or partially organic compound formed by the reaction between an acid and an alcohol or aromatic alcohol with the elimination of water....
 synthesis can also be applied to that of lactones. In one industrial synthesis of oxandrolone
Oxandrolone

Oxandrolone is an anabolic steroid created by Searle Laboratories, now Pfizer under the trademark Anavar, and introduced into the US in 1964....
 the key lactone-forming step is an organic reduction - esterification
Esterification

Esterification is the general name for a chemical reaction in which two reactants form an ester as the product . Esters are common in organic chemistry and biological materials, and often have a characteristic pleasant, fruity odor....
  :

In halolactonization, an alkene
Alkene

In organic chemistry, an alkene, olefin, or olefine is an Saturation chemical compound containing at least one carbon-to-carbon double bond....
 is attacked by a halogen
Halogen

|}The halogens or halogen elements are a chemical series of nonmetal chemical element from Periodic table group International Union of Pure and Applied Chemistry of the periodic table, comprising fluorine, F; chlorine, Cl; bromine, Br; iodine, I; and astatine, At....
 via electrophilic addition
Electrophilic addition

In organic chemistry, an electrophilic addition reaction is an addition reaction where, in a chemical compound, a pi bond is removed by the creation of two new covalent bonds....
 with the cationic intermediate captured intramolecularly by an adjacent carboxylic acid
Carboxylic acid

Carboxylic acids are organic acids characterized by the presence of a carboxyl group, which has the Chemical formula -COH, usually written -COOH or -CO2H....
 (See also iodolactamization), for example in this iodolactonization :

A specific method is called Yamaguchi esterification
Yamaguchi esterification

The Yamaguchi esterification is the chemical reaction of an aliphatic carboxylic acid and 2,4,6-trichlorobenzoyl chloride to form a mixed anhydride which, upon reaction with an alcohol in the presence of stoichiometric amount of DMAP, produces the desired ester....
.

Reactions

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

Hydrolysis

Heating a lactone with a base (sodium hydroxide
Sodium hydroxide

Sodium hydroxide , also known as lye, caustic soda and sodium hydrate, is a caustic metallic Base . Sodium hydroxide forms a strong alkaline solution when dissolved in a solvent such as water, however, only the hydroxide ion is basic....
) 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
Reversible reaction

A reversible reaction is a chemical reaction that results in an chemical equilibrium mixture of reactants and Product . For a reaction involving two reactants and two products this can be expressed symbolically asA and B can react to form C and D or, in the reverse reaction, C and D can react to form A and B....
, with an equilibrium
Chemical equilibrium

In a chemical process, chemical equilibrium is the state in which the Activity or concentrations of the reactants and products have no net change over time....
. However, the equilibrium constant
Equilibrium constant

For a general chemical equilibriumthe equilibrium constant can be defined bywhere is the activity of the chemical species A etc . It is conventional to put the activities of the products in the numerator and those of the reactants in the denominator....
 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
Enthalpy

In thermodynamics and chemistry, the enthalpy is a quotient or description of thermodynamic potential of a system, which can be used to calculate the heat transfer during a quasistatic process taking place in a closed system thermodynamic system under constant pressure....
 of the hydrolysis of esters and lactones are about the same, the entropy
Entropy

In many branches of science, entropy is a measure of the disorder of a system. The concept of entropy is particularly notable as it is applied across physics, information theory and mathematics....
 of the hydrolysis of lactones is less than the entropy of straight-chained esters.

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)

Aminolysis

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.

Michael reaction

Sesquiterpene lactone
Sesquiterpene lactone

Sesquiterpene lactones are a class of chemical found in many plants that can cause allergic reactions and toxicity if overdosed, particularly in grazing livestock ....
s, found in many plants, can react with other molecules via a Michael reaction
Michael reaction

The Michael reaction or Michael addition is the nucleophilic addition of a carbanion to an ?,?-unsaturated carbonyl compound. It belongs to the larger class of conjugate additions....
.

Examples


See also

  • Lactam
    Lactam

    A lactam is a simple aromatic ring amide. Prefixes indicate how many carbon atoms are present in the ring: beta-lactam , ?-lactam , d-lactam ....
    , a cyclic amide
    Amide

    In chemistry, an amide is one of three kinds of compounds:* the organic chemistry functional group characterized by a carbonyl group linked to a nitrogen atom , or a compound that contains this functional group ; or...
  • Lactim
    Lactim

    Lactim is a cyclic carboximidic acid compound characterized by an endocyclic carbon-nitrogen double bond. It is tautomerism with lactam....
    , a cyclic imide
    Imide

    Organic chemistryIn organic chemistry, imide is a functional group consisting of two carbonyl groups bound to nitrogen. Imides are generally prepared directly from ammonia or a primary amine, and either carboxylic acid or acid anhydrides....