Lactones

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Different lactones, from left to right: β-, γ-, δ- and ε-lactone
The macrocyclic lactone erythromycin A is a medicinal substance and is produced by bacteria of the genus Streptomyces . The large lactone ring is shown on the left.

In organic chemistry, lactones are heterocyclic compounds that form an ester bond within the molecule , i. H. an oxygen bridge , contained directly on the same carbon atom of a carbonyl group . They are intramolecular , cyclic esters of hydroxycarboxylic acids .

nomenclature

Greek letters indicate the position or position of the hydroxyl group in the formally underlying hydroxycarboxylic acid relative to the carboxy group . The carbon atom adjacent to the carboxy group is referred to as the α- position , the next as the β-position, and so on.

Lactones are also named by adding the ending -olide to the name of the corresponding hydrocarbon; the position of the C atom involved in the ring closure is given as a number: z. B. Propan-3-olide = β-propiolactone.

Occurrence

Like other fruits, peaches contain lactones with a typical fruit odor.

Lactones are an important group among flavoring substances . In nature, mainly γ- and δ-lactones with unbranched side chains occur, with γ-lactones occurring more frequently in vegetable products and δ-lactones more frequently in animal products. Most naturally occurring lactones have an even number of carbon atoms, but there are also some with odd numbers. Lactones with 8 to 12 carbon atoms are particularly relevant as flavoring substances. Lactones with less than 10 carbon atoms have a fruity curmin- like smell , whereas those with more than 10 carbon atoms have a peach-like smell.

For example, apricots , nectarines and peaches contain a large number of γ-lactones with six to twelve carbon atoms (such as γ-decalactone ) and δ-lactones with eight to twelve carbon atoms (such as δ-decalactone ), which are either coconut-like, fruity- Smell peach-like or fruity-greasy.

An example of the occurrence of lactones in animal products is δ-decalactone , which is found in milk fat . It is an important flavoring for dairy products such as long-life milk , cheese and especially butter , which creates a sweet note.

Manufacturing

While α-lactones, the simplest representative of which is acetolactone , are only known as unstable intermediates and β-lactones (four-membered rings) can only be prepared under special conditions, γ- and δ-lactones (five- and six-membered rings) are easily available stable heterocyclic compounds. γ-lactones are produced by evaporating dilute aqueous solutions of the corresponding γ-hydroxycarboxylic acids. In contrast, α-hydroxycarboxylic acids form oligomers on evaporation and lactides on further heating . If the carboxy group and the hydroxyl group are further apart, the lactones also quickly become unstable. One of the best-known ε-lactones is ε-caprolactone, a lactone from caproic acid . Polyesters can be produced from ε-caprolactone. The copolymerization of ε-caprolactone with lactic acid leads to polyesters that are biodegradable.

Schematic example of lactone formation; the formation of γ-butyrolactone from γ-hydroxybutyric acid by splitting off water :

Lactombildung.png

Another method of producing lactones is the Baeyer-Villiger oxidation . Cyclic ketones are oxidized with peroxycarboxylic acids with ring expansion . The Baeyer-Villiger oxidation of cyclohexanone provides the industrially produced ε- caprolactone in considerable quantities , a starting product for the production of polyesters and polyethers .

Heated or fermented as well as biotransformed castor oil is the source of various lactones.

Examples

See also

Individual evidence

  1. H. Beyer, W. Walter: Textbook of organic chemistry. 20th edition. Hirzel, Stuttgart 1984, p. 264.
  2. Wilfried Schwab & Peter Schreier: Enzymic Formation of Flavor Volatiles from Lipids . In: Tsung Min Kuo & Harold Gardner (Eds.): Lipid Biotechnology . CRC Press, 2002, ISBN 978-0-203-90819-8 , pp. 302-307 ( google.de ).
  3. a b c Wolfgang Legrum: Fragrances, between stench and scent . Occurrence, properties and application of fragrances and their mixtures. Vieweg + Teubner Verlag, Wiesbaden 2011, ISBN 978-3-8348-1245-2 , 5 Flavors in Food, 5.1.3 Lactones, p. 87-88 & 149 , doi : 10.1007 / 978-3-8348-8276-9 ( limited preview in Google Book Search [accessed August 26, 2016]).
  4. Harald Cherdron, Hellmut Ohse, Friedhelm Korte: The polymerization of lactones. Part 1: Homopolymerization of 4-, 6- and 7-membered lactones with cationic initiators , In: The macromolecular chemistry. 56 (1), 1962, pp. 179-186, doi : 10.1002 / macp.1962.020560113 .
  5. Organikum . Wiley-VCH Verlag GmbH, 23rd edition, 2009, ISBN 978-3-527-32292-3 , pp. 683-684.
  6. Otto-Albrecht Neumüller (Ed.): Römpps Chemie-Lexikon. Volume 1: A-Cl. 8th revised and expanded edition. Franckh'sche Verlagshandlung, Stuttgart 1979, ISBN 3-440-04511-0 , p. 586.
  7. Birgit Kamm: Microorganisms in Biorefineries. Springer, 2015, ISBN 978-3-662-45208-0 , p. 277.
  8. ^ Dolf De Rovira, Sr .: Dictionary of Flavors. Second Edition, Wiley-Blackwell, 2008, ISBN 978-0-8138-2135-1 , p. 181.