Hydroxylammonium salts

A solution of 500 g. NEsPO I2H3O is prepared in one liter of hot water. The filtered solution is added to a filtered solution of 273 g. of (NHgOHlCl in 600 ml. of hot water. The mixture is allowed to cool and is suction-filtered. Approximately 200 g. of hydroxylammonium phosphate is obtained. Further hydroiqrlammonium phosphate can be Isolated from the mother liquor by evaporation, givit a total yield of about 90%. 

White salt. Free hydroxylamine forms upon heating. 

Can be prepared in the same manner as hydroxylammonium phosphate by substituting a solution of 312 g. of NasHAsO 7HgO in 300 ml. of HgO for the phosphoric acid. For neutralization a solution of 40 g. of NaOH in 100 ml. of HgO (efficient coolit not necessary) is required. The crystals are washed three times with 150 ml. of water. The yield is 200-210 g. of 95% salt. After purification by recrystallization from an eightfold volume ofwater, the yield of 98% pure salt is about 145 g. Formula weight 241.03. 

Can also be obtained from the stoichiometric quantities of hydroxylammonium chloride, oxalic acid and sodium hydroxide (sufficient for neutralization). A diluted solution of the hydroxylammonium salt (140 g. in 400 ml. of water) is used. All the solid oxalic acid is added at once with vigorous mechanical agitation, and the mixture is neutralized with a solution of 80 g. of NaOH in 200 ml. of HgO. This solution is added in the fastest possible stream of separate drops. The mixture is agitated for 30 minutes, cooled to 15 C, filtered and washed three times with 100 ml. of HgO. Since the salt at this point often contains up to 10% of oxalic acid, it must be recrystallized from eight times its weight of water. The yield is 95 g. the purity is 99%. Formula weight 156.10. 

Tertiary hydroxylammonium phosphate (20 g.) is placed in a 100-ml. distillation flask. Coarse salt, such as that obtained by seedily, is preferably used. The full scale of the thermometer Inserted in the neck of the flask should be above the stopper (stem correction thermometer) the bulb reaches almost to the bottom of the flask. The flask is connected to an aspirator via a receiver. An in-line manometer is essential. The apparatus is evacuated to 13 mm. and heated carefully with an open flame. Some salt dust is readily carried over in the beginning, and this results in con-tamin ion of the product. If the receiver is cooled, the product immediately solidifies, and characteristic, pointed crystals form. The bulk of the material distills over at 13 mm. at a thermometer reading of 135-137°C. The flask is heated intermittently until the 

Yost and Russeel Systematic Inorganic Chemistry, Prentice-Hall, 

Hydroxylammonium salts are reagents usually employed as sources of hydroxylamine for various inorganic and organic reactions. The chloride and sulfate are the better known commercially available salts obtained by the hydrolysis of the nitroparaffins. The phosphate, arsenate,  

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Diazonium sulphides and derivatives, xanthates Hydrazinium salts, oxosalts of nitrogenous bases Hydroxylammonium salts... 

Alternatively, hydroxylammonium salts can be made either (a) by the electrolytic reduction of aqueous nitric acid between amalgamated lead electrodes in the presence of H2SO4/HCI, or (b) by the hydrogenation of nitric oxide in acid solutions over a Pl/charcoal catalyst ... 

The reagents listed above can be applied to the reduction of many other ions in addition to Fe3+, and there are also a number of other substances which can be employed as reducing agents thus for example hydroxylammonium salts are frequently added to solutions to ensure that reagents do not undergo atmospheric oxidation, and as an example of an unusual reducing agent, phosphorous (III) acid may be used to reduce mercury(II) to mercury(I) see Section 10.129. 

Since free NH2OH is unstable it is usual to prepare it in the form of the hydroxylammonium salts, which resemble ammonium salts. A number of methods were proposed but only 5 offer practical methods... 

The crude hydroxylammonium salt may be obtained from the soln by fractional crystallization. Several modifications of the method exist (Ref 3)... 

The addition of small amounts of hydroxylammonium salts increases the yields... 

Difluoramino compounds Fluorodinitromethyl compounds Haloacetylene derivatives Halogen azides High-nitrogen compounds Hydroxylammonium salts Metal acetylides... 

All hydroxylamine syntheses yield hydroxylammonium salts. Free hydroxylamine can be prepared by adding a strong base to the hydroxylammonium salts. Sodium methanolate NaOCHs can be used for this purpose ... 

After the reaction, the solid sodium salt is filtered off and methanol is distilled off under reduced pressure. Hydroxylamine can also be prepared by the ammonolysis of hydroxylammonium salts in liquid ammonia. The ammonium salt precipitates and is filtered off Hydroxylamine is obtained after evaporating the excess ammonia. 

As a hydroxyderivative of ammonia, hydroxylamine is a weak base (pi b = 8.2) and forms hydroxylammonium salts with acids ... 

In contrast to free NH2OH, the hydroxylammonium salts are relatively stable. Dry hydroxylammonium salts disproportionate upon heating to form the ammonium salts and dinitrogen. ... 

The hydroxylammonium salts (pA a = 5.8) are more acidic in aqueous solution than the ammonium salts (pATa = 9.25) because NH2OH is less basic than NH3. NH2OH is a weak acid (pATa = 13.7), only slightly more acidic than water. The hydroxylamides NH20 , of which the sodium, calcium, and zinc salts are known, are very unstable and explosive. 

A related cyclization process has been reported to give the isoindole carboxylic acid derivative as its hydroxylammonium salt when the keto acid 37 is refluxed in aqueous ethanol with two molar equivalents of hydroxyl-amine.58 A plausible pathway is indicated. 

Non-nitrated aromatic compounds can be directly aminated by hydroxyl-amine-O-sulfonic acid (aminyl hydrogen sulfate) or hydroxylammonium salts... 

When sulfuryl amide or imidodisulfamide is heated with strong sodium hydroxide solution, the sodium salt of amidosulfonic acid results. The free acid itself may be prepared in various ways for example, from urea and sulfuric acid, from many adducts of sulfur trioxide and ammonia, from hydroxylammonium salts and sulfur dioxide, or from SO and acetoxime. Amidosulfonic acid, which is colorless and melts at 205° with decomposition, has, as Baumgarten supposed (13), the structure (LXXXVII). 

Sulfamic acid, NH2SO3H, is an ammonoaquosulfuric acid in which one of the hydroxyl groups of sulfuric acid has been replaced by the isosteric amido group. It is prepared commercially by the interaction of fuming sulfuric acid and urea. This method is not readily adaptable to laboratory preparation on a small scale. Consequently, the sulfur dioxide-hydroxylamine reaction is recom-mended.H Sulfamic acid may also be obtained by the action of sulfur dioxide upon certain compounds which yield hydroxylamine such as acetoxime. The recommended procedures are modifications of older processes and involve the use of sulfur dioxide under pressure upon aqueous solutions of hydroxylammonium salts and compounds yielding hydroxylamine. 

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