Lactone 299675 226003491 2008-07-16T12:00:31Z Cvf-ps 3836647 /* Nomenclature */ +pic of different types [[Image:Propiolactone.png|120px|thumb|right|&beta;-propiolactone, formed from [[beta-Hydroxypropionic acid|&beta;-hydroxypropionic acid]]]]A '''lactone''' is a cyclic [[ester]] in [[organic chemistry]] <ref>''March's Advanced Organic Chemistry: Reactions, Mechanisms, and Structure'' Michael B. Smith, Jerry March Wiley-Interscience, 5th edition, 2001, ISBN 0-471-58589-0 </ref>. It is the [[condensation reaction|condensation]] product of an [[alcohol]] [[functional group|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, in the presence of dilute acids at room temperature, 4-hydroxy acids (R-CH(OH)-(CH<sub>2</sub>)<sub>2</sub>-COOH) immediately undergo spontaneous esterification and cyclisation to the lactone. Beta-lactones do exist, but can only be made by special methods. ==Etymology== The name lactone derives from the ring compound called [[lactide]], which is formed from the dehydration of 2-hydroxypropanoic acid ([[lactic acid]]) CH<sub>3</sub>-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== [[Image:Lactone Types.png|thumb|right|200px|Different lactones: α, β, γ and δ types]] 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]] trees, and impart [[flavor]] to [[whisky]]. ==Synthesis== Many methods in [[ester]] synthesis can also be applied to that of lactones. In one industrial synthesis of [[oxandrolone]] the key lactone-forming step is an [[organic reduction]] - [[esterification]] <ref>''Development of a Commercial Process to Produce Oxandrolone'' John E. Cabaj, David Kairys, and Thomas R. Benson Org. Process Res. Dev.; '''2007'''; 11(3) pp 378 - 388; (Article) {{DOI|10.1021/op060231b}}</ref> <ref>The complete reaction sequence is [[bromination]] to a [[haloketone]] (not displayed), [[elimination reaction]] with [[lithium chloride]] to an [[enone]], [[organic oxidation]] by [[osmiumtetroxide]] and [[lead tetraacetate]] with ring-opening and finally reduction of the [[aldehyde]] to the [[alcohol]] with [[sodium borohydride]] and intramolecular lactone formation</ref>: :[[Image:OxandrolonesSynthesis.png|400px|Oxandrolone Synthesis]] In '''halolactonization''', an [[alkene]] is attacked by a [[halogen]] via [[electrophilic addition]] with the cationic intermediate captured intramolecularly by an adjacent [[carboxylic acid]] (See also [[iodolactamization]]), for example in this iodolactonization <ref>[[Organic Syntheses]], Coll. Vol. 7, p.164 (1990); Vol. 64, p.175 ('''1986''') [http://orgsynth.org/orgsyn/pdfs/CV7P0164.pdf Article link].</ref>: :[[Image:Iodolactonization.png|350px|iodolactonization]] ==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]]) 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 [[chemical equilibrium|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 [[enthalpy|enthalpies]] of the hydrolysis of esters and lactones are about the same, the [[entropy]] 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, (CH<sub>2</sub>(OH)-(CH<sub>2</sub>)<sub>2</sub>-CH<sub>2</sub>(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 CH<sub>2</sub>(OH)-(CH<sub>2</sub>)<sub>2</sub>-CO-NH<sub>2</sub>. == Examples == <gallery> Image:Propiolactone.png|<center>[[propiolactone|β-propiolactone]]</center> Image:GBL_chemical_structure.png|<center>[[gamma-butyrolactone|γ-butyrolactone]] (GBL)</center> Image:Glucono-delta-lactone-2D-skeletal.png|<center>[[glucono delta-lactone|<small>D</small>-glucono-δ-lactone]] ([[E number|E575]])</center> Image:Caprolactone.png|<center>[[Caprolactone|ε-caprolactone]]</center> </gallery> == See also == * [[Lactam]], a cyclic [[amide]] * [[Lactim]], a cyclic [[imide]] ==References & notes== {{reflist}} [[Category:Lactones]] [[Category:Carboxylate esters]] [[Category:Oxygen heterocycles]] [[de:Lactone]] [[es:Lactona]] [[fr:Lactone]] [[it:Lattoni]] [[he:לקטון]] [[ms:Lakton]] [[nl:Lacton]] [[ja:ラクトン]] [[pl:Laktony]] [[pt:Lactona]] [[ru:Лактон]] [[fi:Laktoni]] [[sv:Lakton]] [[zh:内酯]]