Lactams

General structure of β-, γ-, δ- and ε-lactams (from left to right).

Cyclic dipeptides (2,5-diketopiperazines) made from glycine and L - alanine (left) and cyclodi- L -prolyl (right) made from two L - proline molecules. The two lactam bonds ( cis peptide bonds) are marked blue in each of the two cyclic peptides .

Lactams ( singular : the lactam ; synonym : intramolecular amide , artificial word from lactone and amide) is called cyclic organic chemical compounds having an amide bond in the ring.

In nomenclature , names of lactams are prefixed with Greek letters , which indicate how many carbon atoms there are in the ring besides the carbonyl carbon . They also indicate the original stability of the carboxy to the amino group in the corresponding aminocarboxylic acid. For example, B. a δ-lactam four carbon atoms, the carbonyl carbon and the nitrogen, so that a six-membered ring is present; in the starting aminocarboxylic acid , the amino group is δ to the carboxy group. However, only γ- and δ-lactams are halfway stable. But they too are split into the corresponding aminocarboxylic acids by alkalis and acids when heated . If the distance between the amino and carboxy groups is even greater , the lactams become less stable and, in the presence of a little water, split into ω-amino acids, which easily condense to form macromolecules .

properties

Lactams with a suitable substitution patterns are subject to lactam lactim - tautomerism . Example:

Manufacturing

Example of lactam formation from γ-aminobutyric acid ( GABA ) to γ-butyrolactam :

In a similar manner, other lactams are usually produced from ω-aminocarboxylic acids by ring closure with elimination of water. Lactams can also be synthesized from open-chain amides with at least one carbon-carbon double bond at both ends of the molecule by ring-closing metathesis.

β-lactams can be produced with the Kinugasa reaction or from imines and ketenes by the so-called Staudinger synthesis .

ε-caprolactam can be produced from the oxime of cyclohexanone via the acid- catalyzed Beckmann rearrangement . Over 2 million t of ε-caprolactam are produced annually.

use

ε-caprolactam forms chain-like macromolecules , which are known as plastic under the name polyamide and are produced on an industrial scale. Thiolactams are made from lactams by reaction with Lawesson's reagent or phosphorus pentasulfide .

Examples

• β-lactam antibiotics
• Beckmann rearrangement

See also

• Lactime
• Lactones
• Lactols

Individual evidence

1. ↑ Martin Watzke, Knut Schulz, Katharina Johannes, Pascal Ulrich and Jürgen Martens : First Synthesis of Bi- and Tricyclic α, β, -Unsaturated δ-Oxacaprolactams from Cyclic Imines via Ring-Closing Metathesis , European Journal of Organic Chemistry 2008 , 3859– 3867.
2. ↑ M. Kinugasa, S. Hashimoto: J. Chem. Soc. Chem. Commun. 1972 , 466-467.
3. ^ Hermann Staudinger: On the knowledge of the ketenes. Diphenylketene . In: Justus Liebig's Annals of Chemistry . tape 356 , no. 1-2 . John Wiley & Sons, Inc., 1907, p. 51-123 , doi : 10.1002 / jlac.19073560106 .
4. ↑ Otto-Albrecht Neumüller (Ed.): Römpps Chemie-Lexikon. Volume 3: H-L. 8th revised and expanded edition. Franckh'sche Verlagshandlung, Stuttgart 1983, ISBN 3-440-04513-7 , p. 2304.
5. ↑ A. Kleemann, J. Martens, K. Drauz: Synthesis of proline from glutamic acid , Chem.-Ztg. 105 ( 1981 ) 266.