Hydroxylamine

(HONH2) [7803-49-8] H3NO (MW 33.04) (HONH2·HCl) [5470-11-1] ClH4NO (MW 69.50) ((HONH2)3·H3PO4) [20845-01-6] H12N3O7P (MW 197.12) ((HONH2)2·H2SO4) [10039-54-0] H8N2O6S (MW 164.17) (nucleophile in aromatic substitution,63 oxime-,36 hydroxamic acid-,30 pyridine-61 and isoxazole-forming56 reactions; reducing agent;66 in combination with dehydrating agents, used for the conversion of aldehydes to nitriles43) Physical Data: HONH2: hydroscopic white needles or flakes; decomposes rapidly at rt; mp 32.05 °C; bp 56.5 °C/22 mmHg, 70 °C/60 mmHg, 110 °C/760 mmHg. HONH2·HCl: white crystals; mp 151 °C; d 1.67 g cm−3; pKa1 5.97; pKa2 13.7.10 (HONH2)3·H3PO4: mp 169–171 °C. (HONH2)2·H2SO4: mp 170 °C (dec). Solubility: HONH2: decomposes in hot water; sol cold water, methanol; sparingly sol ether, benzene, chloroform, carbon disulfide.2 HONH2·HCl: 83 g/100 mL in cold water; very sol hot water; 4.43 g/100 mL in EtOH; 16.4 g/100 mL in MeOH; insol ether. Form Supplied in: hydroxylamine hydrochloride is widely available and is the most commonly used hydroxylamine salt. Each of the other salts listed above is also commercially available, as are HONH2·HCl-d4 and HONH2·HCl-15N.6 Preparative Methods: hydroxylamine base has been prepared by the action of sodium butoxide on the hydrochloride in butanol.3 The free base can be isolated as a white solid at −30 °C and is stable to storage for several days at −20 °C.4 It can be prepared just prior to use or, more typically, in situ from one of the salts by treatment with hydroxide, alkoxide, carbonate, or amine base (see below). The preparation of hydroxylamine via the electrochemical reduction of nitric acid has been reported.5 Handling, Storage, and Precautions: all of the salts of hydroxylamine are corrosive and hygroscopic. Specific precautions in the literature indicate that the free base is a much more hazardous substance to work with than are the salts.7 HONH2: a moderately toxic, corrosive irritant to the eye, skin, and mucous membranes. Explodes at 130 °C. Explodes in air when heated above 70 °C. May ignite spontaneously in air, or in contact with PCl3 or PCl5. Calcium reacts to give the heat-sensitive explosive bis(hydroxylamide). In the event of a spill, cover with sodium bisulfite and sprinkle with water. HONH2·HCl: harmful if inhaled or swallowed (oral LD50 400–420 mg kg−1; mouse). Not compatible with oxidizing agents. May explode if heated above 115 °C; do not store above 65 °C. A comprehensive review of the biological activity of hydroxylamine and its salts has appeared.2