Hydroxamic acid

In organic chemistry, hydroxamic acids are a class of organic compounds having a general formula R−C(=O)−N(−OH)−R' bearing the functional group −C(=O)−N(−OH)−, where R and R' are typically organyl groups (e.g., alkyl or aryl) or hydrogen. They are amides (R−C(=O)−NH−R') wherein the nitrogen atom has a hydroxyl (−OH) substituent. They are often used as metal chelators. Common example of hydroxamic acid is aceto-N-methylhydroxamic acid (H3C−C(=O)−N(−OH)−CH3). Some uncommon examples of hydroxamic acids are formo-N-chlorohydroxamic acid (H−C(=O)−N(−OH)−Cl) and chloroformo-N-methylhydroxamic acid (Cl−C(=O)−N(−OH)−CH3). Hydroxamic acids are usually prepared from either esters or acid chlorides by a reaction with hydroxylamine salts. For example, consider the synthesis of benzohydroxamic acid: Hydroxamic acids can also be synthesized from aldehydes and N-sulfonylhydroxylamine via the Angeli-Rimini reaction, Alternatively, ferric ions convert aldehydic nitrones (or their hydroxylamine precursors) to hydroxamic acids. Care must be taken not to over-oxidize: the resulting hydroxyimide intermediate (RC(=O)N(OH)C(=O)R′) proceeds immediately to nitrous oxide and the deaminated diacid. Much like the conversion of ketones to acyloins, molybdenum oxide diperoxide oxidizes trimethylsilated amides to hydroxamic acids, although yields are only about 50%. In a variation on the Nef reaction, primary nitro compounds kept in an acidic solution (to minimize the nitronate tautomer) hydrolyze to a hydroxamic acid.