Lactams
Internal
cyclic amides of amino carboxylic acids that contain a —CO—NH— group in the
ring (I). The tautomeric, enol form of lactam is known as lactim (II):
Lactams are classified
as β-, γ-, δ-, ε-, and so forth according to the type of amino carboxylic acids
included in their composition, for example, β-propiolactam (III; melting point,
73°-74°C), γ-butyrolactam (IV; melting point, 24.6°C), and ε-caprolactam (V;
melting point, 68°-69°C):
Lactams are
primarily obtained by the cyclization of amino carboxylic acids or their
derivatives [Y—(CH2)nNH2, where Y = COOH,
COOR, CONH2, CN], as well as by the cyclization of amides of halogen
carboxylic or hydroxycarboxylic acid [X—(CH2)nCONHR,
where X = OH or a halogen]. An important method of obtaining lactam is the
Beckmann rearrangement of cyclic ketoximes, which is used in the industrial
preparation of ε-caprolactam.
Lactams
readily undergo alkylation, acylation, and halogena-tion with retention of the
ring. The lactam ring, however, is opened at the —CO—NH—bond during hydrolysis,
ammonolysis, hydrogenolysis, and polymerization. For example, ε-caprolactam
polymerization yields polycaproamide, from which nylon 6 fiber is made. Many
lactams are biologically active substances (for example, a molecule of
penicillin contains a β-propiolactam residue).
Why The lactam must be cyclic??????
BalasHapusthanks