Metaphosphoric acids

The increased proportion of long-chain polyphosphoric acids obtained with high concentrations of P2O5 is accompanied by increased viscosities and a transition through oily and wax-like stages to glass-like products above about 90% P2O5. The older literature describes many such amorphous mixtures as metaphosphoric acid . 

One method of producing metaphosphoric acid is from the ortho acid and urea  

Metaphosphoric acid, H P 03 (P2O5 H2O, with P2O5 = 88.7%), represents an infinite chain and in theory is the limiting member of the simple linear polyphosphoric acid series. The exact meta composition is achieved only with cyclic acids, which have not been isolated although many well-defined salts are known (Section 5.4). Acids with P2O5 88.7% are not easily isolated, even as mixtures, and represent tetrahedra in arranganents more complex than simple chains or rings. Ultraphosphates are probably present (Section 5.4). 

All condensed oxyacids will hydrolyse to orthophosphoric acid in dilute solution, but the rate is very dependent upon temperature and can be affected by impurities. At 25°C, the formation of ortho acid from condensed species may take days or months, whereas at lOOX hydrolysis may be complete in a few minutes. 

In dilute solutions, there is one strongly acidic H atom for each PO4 unit in the polyphosphate chain. There is also a relatively weakly ionised H atom associated with each end of the chain, since in practice it has a finite length and the add composition is correctly represented as H +2P 03 ,.i, which is polyphosphoric acid. 

---

HPO3 metaphosphoric acid H2S103 metasilicic acid... 

In acidic solution, the degradation results in the formation of furfural, furfuryl alcohol, 2-furoic acid, 3-hydroxyfurfural, furoin, 2-methyl-3,8-dihydroxychroman, ethylglyoxal, and several condensation products (36). Many metals, especially copper, cataly2e the oxidation of L-ascorbic acid. Oxalic acid and copper form a chelate complex which prevents the ascorbic acid-copper-complex formation and therefore oxalic acid inhibits effectively the oxidation of L-ascorbic acid. L-Ascorbic acid can also be stabilized with metaphosphoric acid, amino acids, 8-hydroxyquinoline, glycols, sugars, and trichloracetic acid (38). Another catalytic reaction which accounts for loss of L-ascorbic acid occurs with enzymes, eg, L-ascorbic acid oxidase, a copper protein-containing enzyme. 

A mixture of 85% orthophosphoric acid (4 parts) and metaphosphoric acid (1 part)... 

Meta-phosphorsiure, /. metaphosphoric acid -saure, /. meta acid, metasomatisch, a. metasomatic. meta-stabil, a. metastable, -st dig, a. in the meta position. 

One hour after addition of the tetracycline, the clear reaction solution was poured into 1,500 ml of chloroform. A yellow product separated and was collected on a coarse sintered glass filter and air dried. The tetracycline-metaphosphoric acid complex weighed about 10 grams, contained 7.34% of phosphorus and had a bioassay of 634 gammas per milligram. Solubility in water is 750 mg/ml. 

Metaphosphoric acid may also be used it hydrolyses in warm acid solution forming phosphoric(V) acid. Thus bismuth may be precipitated as bismuth phosphate in a dense, crystalline form. 

Mercury(II) chloranilate 700 Mercury(II) nitrate standard soln. of, 359 Mercury/mercury( II )-EDTA electrode (mercury electrode) 586 potentiometric titration of metallic ions with EDTA and, 588 prepn. of, 587 Mercury thiocyanate 700 Metaphosphoric acid in homogeneous precipitation, 426 Metal apparatus 93 Metal ion buffer 53... 

Monofluorophosphoric acid is available by treatment of metaphosphoric acid with anhydrous HF (75) ... 

Thus it has so far proved possible to isolate stable derivatives of monomeric metaphosphoric acid and of metathio- and metaselenophosphoric acid, which, understandably, generally bear tert-butyl and/or trimethylsilyl substituents u. Specifically, we know aminobisiminophosphoranes (3, Z = NR2, X = Y = NR)2,3,4), aminoiminothio (or seleno)phosphoranes (5, Z = NR2, X = NR, Y = S or Se)5), and aminoiminomethylenephosphoranes (1, R = NR2, X = NR)6>. Conspicuously, no stable phosphorus(V) three-coordinate compounds have been synthesized with oxygen as divalent ligand. 

The fact that salts or other derivatives of monomeric metaphosphoric acid HP03 hitherto resisted isolation is generally attributed to the fast reaction of nucleophiles... 

Esters of monomeric metaphosphoric acid like 147 are just as unisolable as metaphos-phoric acid itself or its anion. All the metaphosphoric esters described in the previous literature1011 are probably actually mixtures of oligomeric metaphosphoric esters, or well defined compounds such as cyclic trimetaphosphate. 

A further indication of formation of monomeric metaphosphoric esters or monomeric metaphosphoric acid itself by gas phase fragmentation comes from the behavior of 3-oxo-2-butyl phosphates in the mass spectrometer 1U). 

Thus, for example, 157 decomposes thermally (ca. 200 °C) into acetoin and monomeric metaphosphoric acid (158) both fragments appear in the mass spectrum. 

Bergstrom et al. [63] used HPLC for determination of penicillamine in body fluids. Proteins were precipitated from plasma and hemolyzed blood with trichloroacetic acid and metaphosphoric acid, respectively, and, after centrifugation, the supernatant solution was injected into the HPLC system via a 20-pL loop valve. Urine samples were directly injected after dilution with 0.4 M citric acid. Two columns (5 cm x 0.41 cm and 30 cm x 0.41 cm) packed with Zipax SCX (30 pm) were used as the guard and analytical columns, respectively. The mobile phase (2.5 mL/min) was deoxygenated 0.03 M citric acid-0.01 M Na2HP04 buffer, and use was made of an electrochemical detector equipped with a three-electrode thin-layer cell. The method was selective and sensitive for mercapto-compounds. Recoveries of penicillamine averaged 101% from plasma and 107% from urine, with coefficients of variation equal to 3.68 and 4.25%, respectively. The limits of detection for penicillamine were 0.5 pm and 3 pm in plasma and in urine, respectively. This method is selective and sensitive for sulfhydryl compounds. 

The P3093 ion (known as the trimetaphosphate ion) and (S03)3, a trimer of S03, also have this structure. The trimetaphosphate ion can be considered as the anion of the acid H3P309 (trimetaphos-phoric acid), a trimeric form of HP03 (metaphosphoric acid). Note that this acid is formally related to H5P3O10, tripolyphosphoric acid, by the reaction... 

Removal of another molecule of water would result in HP03, which is metaphosphoric acid. Viewed in a different way, the phosphoric acids can be considered in terms of the ratio of water to P205, the empirical formula for P4O10. If the ratio of H20 to P205 is 5 1, the reaction can be shown as... 

HP03/ which is known as metaphosphoric acid, and it is a strong acid. We can view the formation of ff4P207 (known as diphosphoric acid or pyrophosphoric acid) as arising from the addition of P205 to ff3P04 or the removal of a molecule of water from two molecules of H3P04. The first process can be shown as... 

Synonyms metaphosphoric acid glacial phosphoric acid. Long chain linear or cyclic metaphosphoric acids of formula (HP03)n are also called poly-metaphosporic acids. 

Metaphosphoric acid is used in making oxyphosphate dental cement. It also is used as an analytical reagent. 

Metaphosphoric acid also is obtained from partial hydration of phosphorus pentoxide by dissolving it in cold water. 

---