18-Molybdic acid-2-phosphates

By analogy with the 18-molybdic acid-2-phosphates, these compounds should probably be classified as salts of an 18-molybdic-2-arsenic acid H6[(As04)s(Mo309)6 aq.]. 

In 1826 J. J. Berzelius found that acidification of solutions containing both molybdate and phosphate produced a yellow crystalline precipitate. This was the first example of a heteropolyanion and it actually contains the phos-phomolybdate ion, [PMoi204o] , which can be used in the quantitative estimation of phosphate. Since its discovery a host of other heteropolyanions have been prepared, mostly with molybdenum and tungsten but with more than 50 different heteroatoms, which include many non-metals and most transition metals — often in more than one oxidation state. Unless the heteroatom contributes to the colour, the heteropoly-molybdates and -tungstates are generally of varying shades of yellow. The free acids and the salts of small cations are extremely soluble in water but the salts of large cations such as Cs, Ba" and Pb" are usually insoluble. The solid salts are noticeably more stable thermally than are the salts of isopolyanions. Heteropoly compounds have been applied extensively as catalysts in the petrochemicals industry, as precipitants for numerous dyes with which they form lakes and, in the case of the Mo compounds, as flame retardants. 

Cambella and Antia [385] determined phosphonates in seawater by fractionation of the total phosphorus. The seawater sample was divided into two aliquots. The first was analysed for total phosphorus by the nitrate oxidation method capable of breaking down phosphonates, phosphate esters, nucleotides, and polyphosphates. The second aliquot was added to a suspension of bacterial (Escherichia coli) alkaline phosphatase enzyme, incubated for 2h at 37 °C and subjected to hot acid hydrolysis for 1 h. The resultant hot acid-enzyme sample was assayed for molybdate reactive phosphate which was estimated as the sum of enzyme hydrolysable phosphate and acid hydrolysable... 

Mild acidification of molybdate-phosphate solutions yielded the colorless [P2Mos023]"6 anion, isolated as the sodium salt48,49 The heteropoly acid containing pentavalent antimony, H3[SbMo12O40] 48 H20, was reported to have been prepared by refluxing M/20 molybdic acid with M/75 potassium pyroantimonates°), however, more work is necessary to elucidate to exact nature of molybdenum heteropoly compounds containing antimony. 

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. 

K8. Kuttner, T., and Cohen, H. R., Microcolorimetric studies. I. A molybdic acid, stannous chloride reagent. The microestimation of phosphate and calciiun in pus, plasma, and spinal fluid. J. Biol. Chem. 76, 517-531 (1927). 

Alumina catalysts activated by additions of dehydrogenating catalysts, e.g., nickel oxide, copper oxide or sulfide, zinc oxide or sulfide, cobalt selenide, zinc phosphate, cadmium tungstate, mixtures of the oxides of zinc and tungsten, of cadmium and molybdenum, etc., are claimed to be superior in the formation of acetaldehyde from mixtures of steam and acetylene at 350° to 400° C.l-la Zinc oxide catalysts may be activated in a similar way by the addition of small amounts of molybdates or molybdic acid, and are effective at 300° to 350° C.121b... 

By analogy to the 12-molybdic acid-1-phosphates, which they very closely resemble, all compoxmds of this class should be classified as salts of a 12-molybdic-l-arsenic acid Hs [ASO4(Mo3O9) 4 ... 

Beryllium has very little tendency to form acid salts and only an acid oxalate, an acid molybdate, an acid phosphate, an acid arsenate and four acid selenites have place in chemical literature. The first has been shown to be a simple mixture of the normal oxalate and oxalic acid, and tlie molybdate and selenites were little more than the residues left on evaporating the constituents with little of detail in their study. The phosphate was non-crystalline. These salts need confirmation although from the well known tendencies of phosphoric acid, the existence of an acid phosphate would seem as probable as any acid salt of beryllium. 

Mild steel (ferritic) OH NO 3, CNNH HjO, moist CO / COj - gas CO 3 /HC03, molybdates, salts from acetic acid, phosphates, saturated H2O vapour, acid SO 4 , SO4" + H2S. ... 

Molybdenum tungsten hydroxide oxide phosphate, compd. with ethyl 2-(6-ethylamino)-3-(ethylimino)-2,7-dimethyl-3H-xanthen-9-yl) benzoate. See Pigment red 81 Molybdenum white. See Calcium-zinc-molybdenum complex Zinc molybdate Molybdic acid, ammonium salt, tetrahydrate. 

The sample is first ashed and dissolved in hydrochloric acid the phosphate can then be determined titri-metrically or colorimetrically. The most widely accepted method is a colorimetric method using Mission s reagent, which is based on the reaction between the acidified sample solution and an acid reagent containing molybdic acid and vanadic acid, to produce the stable orange-yellow vanadomolybdo-phosphoric acid. 

Soluble silicates also react with molybdic acid under the above conditions forming a soluble silicomolybdic acid. This product, in its turn, reacts with benzidine similarly to the phosphoric acid compound, thus impairing the decisive nature of the test for phosphate. 

Procedure. One drop of the test solution is spotted on filter paper and dried. The paper is then dipped into or sprayed with a 1 % solution of methyl violet. After about 30 seconds, the paper is sprayed with a solution at 12 g of ammonium molybdate in 150 ml of water acidified with 35 ml of 10 N hydrochloric acid. Phosphates give a blue spot. 

Phosphorus an indirect ultraviolet method Phosphate, as complex with vanadic and molybdic acids differentially at 390 m/i... 

If a white precipitate floccnlates when the acid solntion is diluted, dissolve about 2 g of the original sample in 50 ml of cone. HCl and filter. DUnte the resultant filtrate to 100 ml, boU for 30 minutes, and add 5 ml of 5% sodium molybdate solution and 5 ml of amino solution while hot Reheat to a boil and cool. A resultant bine color indicates the seale is ealeium acid phosphate. 

In the competitive system, we can propose that both molybdate and phosphate ions could be adsorbed in neighboring sites. This would imply that adsorbed molybdates impede the polymerization of adsorbed phosphate and phosphates would produce the same effect on molybdates. The latter may explain the highest surface dispersion of both P and Mo observed for the coimpregnated sample. Since polymerization of phosphorus as well as molybdenum was favoured by high contents of these elements, we could suggest that interactions between neighboring molybdate and phosphate adsorbed species may occur causing the formation of Mo-P heteropoly compounds after calcination. One may speculate that acidity produced for the latter compounds should be different from that produced by phosphates on alumina. 

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