Hydroxamic acids

Hydroxamic acid (left) in tautomeric equilibrium with the hydroxyimine form (right)

Hydroxamic acids are a class of chemical compounds that contain the grouping -CO-NHOH as a functional group . They are thus derivatives of carboxylic acids and hydroxylamine . In the functional group there is a tautomeric equilibrium with the hydroxyimine form (hydroximic acid).

presentation

The first representation was made in 1869 in Wilhelm Lossen's laboratory by reacting ethyl oxalate with hydroxylamine to form oxalohydroxamic acid. A little later, a mixture of mono-, di- and tribenzoyl derivatives of hydroxamic acid was obtained by reacting hydroxylamine with benzoyl chloride . Hydroxamic acids can in principle be obtained from carboxylic acid halides , carboxylic acid esters or carboxylic acid anhydrides by reaction with hydroxylamine or its hydrochloride. Furthermore, hydroxamic acids are formed as an intermediate product in the acidic hydrolysis of primary nitroalkanes .

properties

Aromatic hydroxamic acids are relatively stable crystalline solids . Hydroxamic acids are weaker (pK acidic than the corresponding carboxylic acids _s  ca. 9) and are suitable as complexing agents for metal salts, they form, for example, intense red complexes with iron (III) ions. This reaction is used to detect aldehydes in the Angeli-Rimini reaction . The acid or base catalyzed hydrolysis of hydroxamic acid derivatives leads to the corresponding carboxylic acids and hydroxylamine derivatives. Alkylation reactions lead to hydroxamic acid alkyl esters. Acylations with acid halides yield acylhydroxamic acids.

use

Carboxylic acid halides can be degraded to amines via hydroxamic acid derivatives , see Lossen degradation . Deferoxamine , a natural hydroxamic acid derivative, is used as an antidote for iron poisoning .

Individual evidence

1. ↑ ^{a b c d} Entry on hydroxamic acids. In: Römpp Online . Georg Thieme Verlag, accessed on June 15, 2014.
2. ^ ^{A b} Ludwig Bauer, Otto Exner: The chemistry of hydroxamic acids and N-hydroxyimides . In: Angewandte Chemie . tape 86 , no. 12 , 1974, p. 419-427 , doi : 10.1002 / anie.19740861202 .
3. ↑ Beyer-Walter, Textbook of Organic Chemistry, 23rd Edition, S. Hirzel Verlag 1998 ISBN 3-7776-0808-4