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A lactone is a cyclic ester in organic chemistry [1]. 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.


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.


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).


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 - esterfication [2] [3]:

Oxandrolone Synthesis












See also

References & notes


he:לקטון nl:Lactonsv:Lakton