Comparatively Speaking: Esters vs. Lactones

By: Anthony J. O'Lenick, Jr., Siltech LLC and Mark Garrison, Avon

Posted: January 27, 2009

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Lactones are also esters, but in lactones the ester forms a ring structure. Thus, the acid and alcohol groups are part of the same molecule. When a lactone hydrolyzes, only one molecule forms, which contains both functional groups, as shown in Figure 3. Lactones are classified as alpha, beta, gamma and delta based on the position of the OH group relative to the acid group, as shown in Figure 4.

Most lactones are gamma or delta, having five or six membered rings. These lactones are more stable than the lower members of the series because they have minimal ring strain. Lactones in the cosmetic and personal care industry are not nearly as common as the conventional esters described earlier. Considering the starting materials required for each, this makes sense. There exists a large variety of alcohols and carboxylic acids available to synthesize esters, and they are relatively inexpensive. However, starting materials for lactones are hydroxy acids, which are not nearly as abundant or inexpensive. So it is not surprising that there are not an abundance of lactones available for use as cosmetic emollients.

As with volatile esters, some lactones are used as flavors and fragrances. For example, gamma undecalactone has a peach aroma while gamma nonalactone smells like coconut (see Figure 5). Outside of the personal care industry are some interesting natural compounds that are lactones. For example, nepetalactone is the active constituent in catnip. Artemesinin, a complex structure, is a sesquiterpene lactone, which is used to treat malaria.

To summarize, esters and lactones contain the same functional group but lactones are in a ring structure. Esters are quite common in the personal care industry, useful as emollients and solubilizers. Lactones are much less common in personal care/cosmetics, but there are many interesting and useful natural compounds that are lactones. Volatile members of both groups find use as flavor and fragrance components.

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