Hydroxamic acid

Hydroxamic acids are a class of chemical compounds that contain a functional group, the grouping -CO- NHOH. They are thus derivatives of carboxylic acids and hydroxylamine. In the functional group of a tautomeric equilibrium exists for hydroxyimine form ( Hydroximsäure ).

Representation

The first representation succeeded in 1869 in the laboratory of Wilhelm Lossen by reaction of ethyl oxalate with hydroxylamine to Oxalohydroxamsäure. A little later, a mixture of mono -, di-and Tribenzoylderivaten the hydroxamic acid via reaction of Hydroxlyamin was obtained with benzoyl chloride. Hydroxamic acids may be generally from carboxylic acid halides, carboxylic acid esters or carboxylic acid by reaction with hydroxylamine, or its hydrochloride obtained. Continue to emerge hydroxamic acids in the acid hydrolysis of primary nitroalkanes intermediate.

Properties

Aromatic hydroxamic acids are relatively stable crystalline solids. Hydroxamic acids are less acidic than the corresponding carboxylic acids ( pKa about 9 ), and are useful as complexing agents for the metal salts, they form, for example, intense red complexes with iron ( III) ions. This reaction is used for the detection of 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 Hydoxamsäure - alkyl esters. Acylations with acid halides provide Acylhydroxamsäuren.

Use

About hydroxamic acid derivatives acyl halides can be reduced to amines. See Lossen rearrangement. Deferoxamine, a natural hydroxamic acid derivative, is used as an antidote to iron poisoning.