Ammonium phosphate salts, decomposition

When an aq. soln. of trimetaphosphimic acid, or of one of its salts, acidified with one of the stronger mineral acids, is heated or kept for a long time, decomposition occurs—slowly if cold, rapidly if heated. Orthophosphoric acid and ammonia (ammonium phosphate) are the ultimate products of the decomposition. Several intermediate products have been detected in addition to pyrophosphoric acid, what H. N. Stokes calls diimidotriphosphoric acid, and imidodiphosphoric acid have been found, and he represents the different stages of the decomposition ... 

The ordinary salt, secondary ammonium phosphate, (NH4)2HP04, is prepared by concentrating a solution of phosphoric acid with addition of sufficient ammonia to prevent the development of an acidic reaction. It forms monoclinic crystals,8 of density 1-6199 or 1-678.10 It readily loses ammonia, with formation of the primary phosphate, the decomposition being rapid at 166° C.11 Above this temperature the primary phosphate is transformed into pyrophosphate. The aqueous solution of the secondary phosphate has a strongly alkaline reaction, and is decomposed by boiling, with evolution of ammonia and formation of the primary salt. 

The trivalent orthophosphate anion (PO/ ) readily forms double salts, so that the number of reactants available is very large. Studies have included the decompositions of many acid salts, and acid salts may also be generated during decomposition of ammonium salts following the release of ammonia gas. Comparisons between the decomposition behaviour of related compounds (e.g. metal and acid salts) can yield useful mechanistic information. Removal of water often yields pyrophosphates or metaphosphates. Some higher molecular mass substances form glassy phases and these crystallize only with difficulty. The decompositions of ammonium phosphates are considered in Chapter 15. 

The usual method of blowpipe analysis was to direct the flame on to a small portion of the material on a charcoal block. The substance under investigation was often mixed with sodium carbonate, borax, or microcosmic salt (sodium ammonium phosphate). When the material was heated alone or with sodium carbonate, it often yielded decomposition products with a characteristic appearance and borax or microcosmic salt fused to a glass to which the unknown material might impart a characteristic colour. After Wollaston had introduced a method of producing malleable platinum in 1800, a platinum wire was frequently used to support the material in blowpipe analysis, particularly in the production of glassy beads with borax and microcosmic salt. 

From the thermal decomposition of mono- and dihydrazinium phosphates it appears that both salts decompose through the intermediate formation of N2H5HP2O6 leading to metaphosphoric acid. Further, their decomposition patterns follow the corresponding decomposition pattern of ammonium salts. However, hydrazinium phosphate salts are of interest as superior flame retardants because of the hydrophilic nature or hygroscopic property of the hydrazinium ion. This supports dehydration more efficiently and limits the production of hydrocarbon gases, thereby promoting flame retardancy (see Chapter 6, Section 6.2.4). 

H. Schiff claimed to have prepared PO(NH2)3, or phosphoryl triamide, by slowly leading a current of dry ammonia into cold phosphoryl chloride until the mass was quite sat. The ammonium chloride was washed from the product of the action with cold or warm water, and phosphoric triamide remained as a snow-white powder. H. Schiff claimed that the compound is scarcely attacked by boiling water, an aq. soln. of potassium hydroxide, or dil. acids but that it is slowly attacked by cone, acids. When fused with potassium hydroxide, ammonium and potassium phosphates are formed and when heated out of contact with air, ammonia, and phosphoryl nitrile are produced PO(NH2)3=PON-fi2NH3. J. H. Gladstone, A. Mente, and H. N. Stokes failed to confirm the preparation of H. Schiff s triphosphoramide. According to J. H. Gladstone, the third atom of chlorine cannot be replaced by an amido-group at any temp, below that at which further decomposition occurs (300°). The product of the action of ammonia on phosphoryl chloride is a mixture of ammonium salts of amido- and imido-tetra-phosphoric acids. 

A common feature of the decompositions of many ammonium compounds is the identification of the first step in reaction as proton transfer. The consequent accumulation of protons with the residual oxy-anions may be followed by the elimination of water, accompanied by condensation (or continued condensation) of the anions, see chromates and phosphates above, ultimately leading to residual oxide formation. Alternatively the acid may be volatilized, many ammonium salts sublime... 

LAPIS INFERNALIS (7761-88-8) A powerful oxidizer. Forms friction- and shock-sensitive compounds with many materials, including acetylene, anhydrous ammonia (produces compounds that are explosive when dry), 1,3-butadiyne, buten-3-yne, calcium carbide, dicopper acetylide. Contact with hydrogen peroxide causes violent decomposition to oxygen gas. Violent reaction with chlorine trifluoride, metal powders, nitrous acid, phosphonium iodide, red or yellow phosphorus, sulfur. Incompatible with acetylides, acrylonitrile, alcohols, alkalis, ammonium hydroxide, arsenic, arsenites, bromides, carbonates, carbon materials, chlorides, chlorosulfonic acid, cocaine chloride, hypophosphites, iodides, iodoform, magnesium, methyl acetylene, phosphates, phosphine, salts of antimony or iron, sodium salicylate, tannic acid, tartrates, thiocyanates. Attacks chemically active metals and some plastics, rubber, and coatings. 

Conversion of Phenols to Amines. Aniline and some diphenylamine are formed when phenol and NHs solution are heated under pressure in the presence of FeCh, Al(OH)s, or Fe(OH)j. When NH and phenol or ortho-or para-cresols are reacted in the vapor phase over an AljO catalyst, yields of up to 88 per cent of the corresponding amines are obtained. However, these amines are customarily obtained by reducing the parent nitro compound, except in cases where it is difficult to obtain the required nitro isomer. For example, it is considered that the amination of symr xylenol is the best method of preparing sym-xylidine (l-amino-3,5-di-methylbenzene). When sym-xylenol is heated under pressure to 320 C with ammonium chloride, about equal amounts of sj/m-xylidine and sym-dixylylamine (5-imino-bis-l,3-dimethylbenzene) are formed. The ortho-and para-nitrophenols and nitrocresols can be aminat more readily. 2-Nitro-p-cresol [OH(l), N02(2), CHj(4)] and o-nitrophenol have been aminated in aqueous ammonia containing ammonium salts of weak acids to inhibit decomposition. Phosphoric, boric, carbonic, and formic acids were used. In one case it is claimed that 55-65 per cent yields of 2-nitro-p-toluidine (MNPT of commerce) were obtained when 2-nitro-p-cresol, 28 per cent aqueous NHj, and monoammonium phosphate, 1 11.5 0.2 molar ratio, were heated under pressure for 10 hr at 140-150°C and then 5 hr at about 160 C. Earlier workers, employing somewhat similar conditions, claimed excellent yields of MNPT when 1 mole of ammonium formate was used per mole of 2-nitro-p-cresol. ... 

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