HYDROXYLAMINE or HYDROXY-AMMONIA, a compound prepared in 1865 by W. C. Lossen by the reduction of ethyl nitrate with tin and hydrochloric acid. In 187o E. Ludwig and T. H. Hein obtained it by passing nitric oxide through a series of bottles containing tin and hydrochloric acid, to which a small quantity of platinum tetrachloride had been added, pouring off the liquid after reaction had ceased, precipitating the tin with sulphuretted hydrogen, evaporating the liquid to dryness, and extracting hydroxylamine hydrochloride with absolute alcohol. E. Divers obtained it by mixing cold saturated solutions containing one molecular proportion of sodium nitrite, and two molecular proportions of acid sodium sulphite, and then adding a saturated solution of potassium chloride to the mixture. After standing for 24 hours potassium hydroxylamine disulphonate, crystallized out. This was boiled for some hours with water and the solution cooled, when potassium sulphate separated first, and then hydroxylamine sulphate. The method used for the commer cial preparation of this salt is similar to the foregoing. Pure anhydrous hydroxylamine was first obtained by C. A. Lobry de Bruyn from the hydrochloride by dissolving it in absolute methyl alcohol and then adding sodium methylate. The precipitated sodium chloride is filtered, and the solution of hydroxylamine distilled in order to remove methyl alcohol, and finally fraction ated under reduced pressure. It is better prepared by distilling the phosphate in a vacuum, The free base is a colourless, odourless, crystalline solid, melting at 33° C, and boiling at 58° C (under a pressure of 2 2mm.) . It deliquesces and oxidizes on exposure, inflames in dry chlorine and is reduced to ammonia by zinc dust. Its aqueous solution is strongly alkaline, and with acids it forms well-defined stable salts. It is a strong reducing agent, giving a precipitate of cuprous oxide from alkaline copper solutions at ordinary temperature convert ing mercuric chloride to mercurous chloride, and precipitating metallic silver from solutions of silver salts. With aldehydes and ketones it forms oximes (q.v.). W. R. Dunstan (1899) found that the addition of methyl iodide to a methyl alcohol solution of hydroxylamine resulted in the formation of trimethylamine oxide, Many substituted hydroxylamines are known, substitution (3 a taking place either in the a or / position (NH_.•OH). f nylhydroxylamine, is obtained in the reduction of nitrobenzene in neutral solution (e.g., by the action of zinc dust upon nitrobenzene suspended in ammonium chloride solution at about io° C). It also appears as an intermediate product in the electrolytic reduction of nitrobenzene in sulphuric acid solution. By gentle oxidation it yields nitrosobenzene. By the action of ammonia and amyl nitrite upon it in ethereal solution, one obtains "cupferron," the ammonium salt of nitrosophenylhydroxylamine, which finds extensive application in quantita tive analysis.
Substituted hydroxylamines are also obtained by oxidizing primary amines by Caro's acid Dihydroxyammonia, a hydrated form of the hypothetical "nitroxyl," N.OH, has not been isolated, but its existence in solution has been demon strated by A. Angeli, Sopra alcuni composti ossigenati dell'azoto Under certain conditions hydroxylamine may act as an oxidizing agent ; thus in alkaline suspension it oxidizes ferrous hydroxide to ferric hydroxide, and it oxidizes solutions of ferrous salts in am moniacal tartrate solution to ferric salts. It therefore seems probable that it possesses alternative structures—NH2•OH in acid solution or when acting as a reducing agent, and NH;,O in alkaline solution (F. Haber) . Although many methods have been sug gested for the estimation of hydroxylamine, most of them depend on very careful adjustment of the acidity of the solution. That of F. Raschig, however, is less sensitive to conditions and is the most trustworthy; the hydroxylamine solution is boiled with a considerable excess of ferric sulphate in sulphuric acid, and the ferrous salt thus formed by reduction is titrated with potassium per manganate. See A. D. Mitchell, bourn. Chem. Soc. (1926).