Phosphomolybdates ammonium salts

Silica gel-based catalytic systems have been described as efficient promoters for a number of organic reactions.28 Illustrative examples include the oxidative cleavage of double bonds catalyzed by silica-supported KM11O4,29 reaction of epoxides with lithium halides to give /i-halohydrins performed on silica gel,30 selective deprotection of terf-butyldimethylsilyl ethers catalyzed by silica gel-supported phosphomolybdic acid (PMA),31 and synthesis of cyclic carbonates from epoxides and carbon dioxide over silica-supported quaternary ammonium salts.32... 

Impregnate drop-reaction paper with a solution of phosphomolybdic acid and then hold it for a short time over ammonia gas to form the yellow, sparingly soluble ammonium salt dry. Place a drop of the test solution on this paper a blue spot appears if tin(II) is present. 

CARCINOGENIC.) In this test use is made of the fact that benzidine, which is unaffected by normal molybdates and by free molybdic acid, is oxidized in acetic acid solution by phosphomolybdic acid or by its insoluble ammonium salt (see reaction 4 above). This reaction is extremely sensitive two coloured products are formed, viz. the blue reduction product of molybdenum compounds ( molybdenum blue ) and the blue oxidation product of benzidine ( benzidine blue ). Moreover, solutions of phosphates which are too dilute to show a visible precipitate with the ammonium molybdate reagent will react with the molybdate reagent and benzidine to give a blue colouration. 

If the ammonium phosphomolybdate concentration is too high, a yellow precipitate is formed. This has often been used deliberately in test procedures, but such methods suffer from tire reproducibility problems often encountered in tests based on precipitation. The environment must be acidic but the presence of nitric acid enhances the risk of ammonium phosphomolybdate precipitation, and hydrochloric acid gives a yellow precipitate of molybdic acid, H2M0O4. The presence of other ammonium salts also raises the risk of an unwanted ammonium phosphomolybdate precipitation provoked by the common ion effect. 

Ammonium phosphofluoridate. See Ammonium monofluorophosphate Ammonium phosphomolybdate CAS 54723-94-3 EINECS/ELINCS 234-714-0 Synonyms Ammonium molybdophosphate Ammonium-12-molybdophosphate Molybdophosphoric acid ammonium salt Phosphomolybdic acid, ammonium salt Classiheation Metal-ates Empin cal H12M012N3O40P Formula (NH4)3PMoi2O40 XH2O or (NH4)3P04 I2M0O3 3H2O... 

Phospho-12-molybdic acid. See Phosphomolybdic acid Phosphomolybdic acid, ammonium salt. See Ammonium phosphomolybdate Phosphonic acid... 

A very accurate and reliable gravimetric method is to precipitate the phosphorus as quinolinium phosphomolybdate, (C9H7N)3PMOi204q in the presence of citric acid. This is done from a boiling acid solution of the sample, to which has been added a reagent solution of quinoline + molybdate -I- citric acid. The quinolinium compound is less soluble and after drying at 250°C has a more constant composition than the ammonium salt. 

Ammonium salts of molybdic acid, phosphomolybdic acid and tungstic acid as well as mixtures of ammonium salts with MoOg or WOg yield blue ignition residues of the lower oxides of molybdenum and tungsten. The latter reoxidize on further heating. 

Benzidine (see page 283), which is unaffected by free molybdic acid and normal molybdates, is oxidized instantly in acetic acid solution by phosphomolybdic acid and even by its insoluble ammonium salt. This oxidation is... 

Phosphomolybdic acid, or P04 plus Mo04 ions, form insoluble phos-phomolybdates in acid solution not only with ammonium salts but also with salts of organic bases. A brown precipitate results with salts of o-diani-... 

Stannous chloride reduces not only molybdates to the colored lower oxides,2 but also reacts with phosphomolybdic acid and its salts. Molyb-denum blue results. It is an important fact, especially for the detection of tin in the presence of antimony salts, that stannous chloride will reduce not only the soluble phosphomolybdic acid as does antimony trichloride (compare page 105), but also the insoluble phosphomolybdates (e.g., the potassium or ammonium salt). Concerning molybdeniun blue see copper test 5, page 210. 

Wilson critically surveyed the present methods of determining P2O5 and has shown that by precipitating as quinoline phosphomolybdate and completing volumetrically, accurate results can be obtained. Calcium, iron, magnesium, alkali metals, citrates and nitrates do not interfere but ammonium salts must be destroyed and a high concentration of sulphuric acid must be avoided. 

Later, however, it was pointed out that soluble silica interferes to an unknown extent and this method has been superseded by a further method of Wilson" in which citric acid is added this forms a complex with molybdic acid of such stability that its reaction with silicic acid is prevented, whereas the reaction with phosphoric acid proceeds normally. Further, in this method it is no longer necessary to destroy ammonium salts before precipitating quinolinium phosphomolybdate. 

Thalictine (60), C37H40N2O6, an amorphous, air-sensitive base, was isolated from Thalictrum thunbergii D.C. as its nitrate salt, mp 226-228°C. The alkaloid shows [a]D -15.8° (CHC13), -12.2° (MeOH), IR 3550 cm"1 (OH), and it gave a positive ammonium phosphomolybdate color test for a cryptophenol. The... 

Tin(II) chloride reduces not only the reactive phosphomolybdic acid but also its relatively unreactive (e.g. ammonium or potassium) salts to molybdenum blue . However, antimony(III) salts do not reduce ammonium phos-phomolybdate Sn2+ may thus be detected in the presence of Sb3+. 

In this method for the determination of phosphorus in solution, phosphorus (in the form of phosphate) combines with acid ammonium molybdate, forming phosphomolybdic acid. Ascorbic acid reduces the phosphomolybdic acid to give a blue-coloured complex. The antimony salt acts as a catalyst, speeding up the formation of the coloured complex. 

Phosphate and other salts may be measured by various titrimetric and colorimetric methods. Phosphate is measured titrimetrically by precipitation of quinoline phosphomolybdate that is collected and dissolved in a small known excess of alkali and then back-titrated with standard acid. A colorimetric method based on the reaction of the phosphate with ammonium molybdate followed by partial reduction to give molybdenum blue has been developed for use in auto-analyzers. 

Insoluble salts, for example, hydrous zirconium phosphate Heteropolyacids, for example, ammonium phosphomolybdate Complex ferrocyanides, for example, sodium copper cyanoferrate (II)... 

If the tin occurs originally in the bivalent condition, the test may be carried out as described, and antimony salts do not interfere. If however, quadrivalent tin is present, it must be reduced to the stannous condition. This can be done by placing 1 or 2 drops of the test solution in a small porcelain crucible, and warming with either a small strip of magnesium ribbon or a tiny piece of zinc, plus a few drops of concentrated hydrochloric acid, until the metal dissolves. A drop of this solution is placed on ammonium phosphomolybdate paper. Any metallic antimony, which is precipitated as a black powder, does not interfere with the test for tin. 

Surprisingly, this effect is also occasioned by nearly neutral ammonium acetate. The yellow suspensions of the water-insoluble ammonium or potassium salts of phosphomolybdic acid are also affected in this way by OH donors. 

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