Hydroxamic acid

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The general structure of a hydroxamic acid

A hydroxamic acid is a class of organic compounds bearing the functional group RC(O)N(OH)R', with R and R' as organic residues and CO as a carbonyl group. They are amides (RC(O)NHR') wherein the NH center has an OH substitution. They are often used as metal chelators.

Synthesis and reactions[edit]

Hydroxamic acids are usually prepared from either esters or acid chlorides by a reaction with hydroxylamine salts. For the synthesis of benzohydroxamic acid, the overall equation is:[1]


Hydroxamic acids can also be synthesized from aldehydes via the Angeli-Rimini reaction.

A well-known hydroxamic acid reaction is the Lossen rearrangement.

Coordination chemistry and biochemistry[edit]

In the area of coordination chemistry, hydroxamic acids are excellent ligands.[2] They deprotonate to give hydroxamates, which bind to metals ions as bidentate ligands. So high is the affinity of hydroxamates for ferric ions that nature has evolved families of hydroxamic acids to function as iron-binding compounds (siderophores) in bacteria. They dissolve insoluble iron(III) compounds. The resulting complexes are transported into the cell, where the iron is extracted and utilized metabolically.[3]

Ligands derived from hydroxamic acid and thiohydroxamic acid also form strong complexes with lead(II).[4]

Other uses and occurrences[edit]

Hydroxamic acids are used extensively in flotation of rare earth minerals during the concentration and extraction of ores to be subjected to further processing.

Some hydroxamic acids (e.g. vorinostat, belinostat, panobinostat, and trichostatin A) are HDAC inhibitors with anti-cancer properties. Fosmidomycin is a natural hydroxamic acid inhibitor of 1-deoxy-D-xylulose-5-phosphate reductoisomerase (DXP reductoisomerase). Hydroxamic acids have also been investigated for reprocessing of irradiated fuel.


  1. ^ C. R. Hauser and W. B. Renfrow, Jr "Benzohydroxamic Acid" Org. Synth. 1939, volume 19, p. 15ff.
  2. ^ Agrawal, Y K (1979). "Hydroxamic Acids and Their Metal Complexes". Russian Chemical Reviews. 48 (10): 948–963. doi:10.1070/RC1979v048n10ABEH002422.
  3. ^ Miller, Marvin J. (November 1989). "Syntheses and Therapeutic Potential of Hydroxamic Acid Based Siderophores and Analogues". Chemical Reviews. 89 (7): 1563–1579. doi:10.1021/cr00097a011.
  4. ^ Farkas, Etelka; Buglyó, Péter (2017). "Chapter 8. Lead(II) Complexes of Amino Acids, Peptides, and Other Related Ligands of Biological Interest". In Astrid, S.; Helmut, S.; Sigel, R. K. O. Lead: Its Effects on Environment and Health. Metal Ions in Life Sciences. 17. de Gruyter. pp. 201–240. doi:10.1515/9783110434330-008. ISBN 9783110434330. PMID 28731301.

Further reading[edit]