Hydroxylamine-O-sulfonic acid is the inorganic compound with molecular formula H3NO4S that is formed by the sulfonation of hydroxylamine with oleum. It is a white, water-soluble and hygroscopic, solid, commonly represented by the condensed structural formula H2NOSO3H, though it actually exists as a zwitterion and thus is more accurately represented as +H3NOSO3−. It is used as a reagent for the introduction of amine groups, for the conversion of aldehydes into nitriles and alicyclic ketones into lactams, and for the synthesis of variety of nitrogen-containing heterocycles.
HOSA reacts under basic conditions as nucleophile and under neutral and acid conditions as electrophile.
Aminations
It reacts with tertiary amines to trisubstituted hydrazinium salts and with pyridine to the 1-amino pyridinium salt. From 1-aminopyridinium salts the photochemically active 1-N-iminopyridinium ylides are accessible by acylation. The photochemical rearrangement of the obtained 1-N-iminipyridinium ylides leads in high yields to 1H-1,2-diazepines N-amination of 1H-benzotriazole with hydroxylamine-O-sulfonic acid yields a mixture of 1-aminobenzotriazole and 2-aminobenzotriazole. From 1-aminotriazole, benzyne is formed in an almost quantitative yield by oxidation with lead acetate, which rapidly dimerizes to biphenylene in good yields. Electron deficient heterocycles, such as tetrazole, can be N-aminated with hydroxylamine-O-sulfonic acid, while even more electron-deficient compounds, such as 5-nitrotetrazole, react only with stronger aminating agents such as O-tosylhydroxylamine or O- mesitylene sulfonylhydroxylamine to amino compounds, which were investigated as explosives. In the N-amination of the unsubstituted tetrazole, a mixture of 1-amino- and 2-aminotetrazole is obtained. Also sulfur compounds can be aminated with hydroxylamine-O-sulfonic acid to sulfinimines or phosphorus compounds can be aminated to phosphine imides via the intermediate aminotriphenylphosphonium hydrogen sulfate. The reaction of hydroxylamine-O-sulfonic acid with metal salts of sulfinic acids in sodium acetate solution produces primary sulfonamides in very good yields. Diimine can formed in situ from hydroxylamine-O-sulfonic acid respectively hydroxylamine-O-sulfonic acid hydroxylamine sulfate mixtures, which hydrogenates selectively conjugated multiple bonds.
At room temperature and below, hydroxylamine-O-sulfonic acid reacts with ketones and aldehydes as a nucleophile to the corresponding oxime-O-sulfonic acids or their salts. The oxime-O-sulfonic acids of aldehydes react above room temperature upon elimination of sulfuric acid in high yields to nitriles. Aliphatic ketones provide under similar conditions in very high yields oximes, arylalkyl ketones react in a Beckmann rearrangement to amides. When heated to reflux for several hours under acidic conditions alicyclic ketones react to provide lactams in high yields. Under basic conditions in the presence of primary amines, hydroxylamine-O-sulfonic acid forms with aldehydes and ketones diaziridines, which can easily be oxidized to the more stable diazirines. The reaction also provides substituted aziridines from simple aldehydes and ketones with high yield and diastereoselectivity. 1,2-Benzisoxazole is efficiently produced by nucleophilic attack of hydroxylamine-O-sulfonic acid to the carbonyl group of 2-hydroxybenzaldehyde followed by cyclization. 1,2-Benzisoxazole is a structural element in the antipsychotic risperidone and paliperidone, as well as the anticonvulsantzonisamide. In a one-pot reaction, N-arylpyrazolopyrimidines are obtained in good yields from simple 4,6-dichloropyrimidine-5-carboxaldehyde, which can be used as purineanalogs for a wide range of diagnostic and therapeutic applications.
Further reactions
The chemiluminescence of the system luminol/cobalt chloride is dramatically enhanced by the addition of hydroxylamine-O-sulfonic acid.
