AskDefine | Define lactone

User Contributed Dictionary

English

Noun

  1. A cyclic intramolecular ester derived from a hydroxy acid.

Usage notes

Greek prefixes indicate the ring size e.g. α- 3-membered, β- 4-membered

Extensive Definition

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 :

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 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 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)

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

See also

References & notes

lactone in German: Lactone
lactone in Spanish: Lactona
lactone in French: Lactone
lactone in Italian: Lattoni
lactone in Hebrew: לקטון
lactone in Malay (macrolanguage): Lakton
lactone in Dutch: Lacton
lactone in Japanese: ラクトン
lactone in Polish: Laktony
lactone in Portuguese: Lactona
lactone in Russian: Лактоны
lactone in Finnish: Laktoni
lactone in Swedish: Lakton
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