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Monamidophosphoric Acid, NH2PO(OH)2

Monamidophosphoric Acid, NH2PO(OH)2, has been obtained by several reactions, among which are the hydrolysis of diphenyl amidophosphate by means of alkali, thus

NH2PO(OC6H5)2 + 2NaOH = NH2PO(OH)2 + 2C6H5ONa

and the action of nitrous acid on diamidophosphoric acid. The sodium salt (which results in the former method) may be converted into the lead salt, which may then be decomposed by hydrogen sulphide at 0° C. The acid is precipitated from the filtrate by alcohol in the form of tabular or cubic crystals. It is very soluble in water, has a sweetish taste, and is hydrolysed after long standing at room temperature or rapidly in hot solution, into ammonium dihydrogen phosphate, thus

NH2PO(OH)2 + H2O = NH4OPO(OH)2

Ammonium and hydroxylamine salts of this acid furnish interesting examples of isomerism. Thus, ammonium hydrogen amidophosphate, NH2PO(OH)ONH4 (prepared by double decomposition between the silver salt and ammonium sulphide, with subsequent precipitation with alcohol as needle-shaped crystals), is isomeric with hydrazine phosphite, N2H4.H3PO3, while hydroxylamine amidophosphate, NH2PO(OH)(ONH3OH), is isomeric with hydrazine phosphate, N2H4.H3PO4.

The mono- and di-sodium salts and the corresponding potassium salts have also been prepared. The salt NH2PO(OH)(OK) was obtained by hydrolysing diphenylamidophosphate with a boiling solution of KOH, acidifying the cold solution with acetic acid and washing the precipitate with alcohol. It forms rhombohedral crystals which are very soluble in water. The solution is neutral and is gradually hydrolysed on standing. Lithium, silver and lead amidophosphates were precipitated by adding salts of these metals to alkali amidophosphates.
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