Reactions of Phosphates

The chemistry of phosphates as relevant to aquatic systems is discussed as an example of the importance of heterogeneous equilibria in waters. Phosphorus, present as various forms of phosphate, is of central concern to a wide variety of biological and chemical processes in natural waters, wastewater, and water treatment. Phosphate is a nutrient required for the growth of all living protoplasm that,contains approximately 2 percent phosphorus on a dry weight basis. As such, phosphorus can be the 

Several of the more common classes of phosphorus-containing compounds are presented in Table 6-3. In the orthophosphate anion, the P atom is centrally bonded to the oxygen atoms, which are located at the corners of a tetrahedron. The condensed phosphates—the polyphosphates and metaphosphates—are formed by the condensation of two or more orthophosphate groups and have the characteristic P—O—P linkage. While polyphosphates are linear molecules, the metaphosphates are cyclic. 

Typical concentrations of phosphates found in various waters are given in Table 6-4. In fresh raw domestic wastewater the phosphate is distributed approximately as follows orthophosphate, 5 mg/liter as phosphorus, tripolyphosphate, 3 mg/liter as phosphorus, pyrophosphate, 1 mg/liter as phosphorus and organic phosphates 1 mg/liter as phosphorus. Secondary biological treatment, and indeed prolonged contact with the microorganisms in raw sewage, ensures the hydrolysis, ( reversion ) of condensed phosphates to orthophosphate. Tripolyphosphate, for example, hydrolyzes as follows  

Hydrolysis is catalyzed by H. Examination of Fig. 2-8 shows that at 10°C the time for 5 percent hydrolysis of a pyrophosphate solution at pH 4 is about 1 year at pH 7 is many years and at pH 10 is over a century Of course, catalysis of the hydrolysis reaction by enzymes is important in nonsterile natural waters. Wastewater effluent and natural waters contain significant amounts of organically bound phosphate. Indeed, some estimates of the phosphate content of natural waters assign between 30 to 60 percent of the total phosphate to the organically bound category. 

Phosphate solubility equilibrium constants and complexation equilibrium constants are given in Table 6-5. 

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NSP is produced by the reaction of phosphate rock and sulfuric acid. This reaction quickly yields a soHd mass containing monocalcium phosphate monohydrate and gypsum, CaSO 2H20, according to the simplified equation... 

Neiman, R. Sarma, A. C. (1980). Setting and thermal reactions of phosphate investments. Journal of Dental Research, 59, 1478-85. 

A FIA system has been proposed for the CL detection of phosphate based on an enzymatic reaction and the application of a subsequent luminol reaction [41], The system consists of an immobilized pyruvate oxidase column, a mixing chamber for the CL reaction, and a PMT. H202 is generated by the reaction of phosphate and pyruvate oxidase and then reacts with luminol and HRP, producing... 

Takemoto and Miyabe recently found that the iridium complex of pybox L4 catalyzed the reaction to form the branched product with good enantioselectivity (Equation (3)).10 In the presence of CsOHH20, the reaction of phosphate 26 with BnONHBz proceeded smoothly to give the branched product 27 with 92% ee. 

Metal-methoxide reactions of phosphates, phosphorothioates, phosphonates and phosphonothioates. The rate constant data for the (La3 + ( OCH3))2 and 9 Zn2 + ( OCH3)-catalyzed methanolysis of the phosphates and phosphorothioates are given in Tables 9 and 10, respectively, while those for the phosphonates (22a-f)17e and phosphonothioates (23a-e)1 s are given in Tables 11 and 12 along with the corresponding methoxide data. The latter two series data are displayed in... 

Scheme 6 A proposed mechanism for the concerted La + ( OCH3)2-catalyzed methanolysis reaction of phosphate triesters with XAr leaving groups.

Two major methods are utilized for the production of phosphoric acid from phosphate rock. The wet process involves the reaction of phosphate rock with sulfuric acid to produce phosphoric acid and insoluble calcium sulfates. Many of the impurities present in the phosphate rock are. also solubilized and retained in the acid so produced. While they are of no serious disadvantage when the acid is to be used for fertilizer manufacture, their presence makes the product unsuitable for the preparation of phosphatic chemicals. 

There arc two main processes for the industrial production of phosphoric add, H3PO4. from phosphate rock (1) the wet process which involves tlie reaction of phosphate rock with H2SO4 to yield phosphoric acid and insoluble calcium sulfites, Several of the impurities present in the rock dissolve and remain with the product add. These are not important when the add is used for fertilizer manufacture. However, the impurities are deleterious to the manufacture of phosphorus chemicals. For a purer product, (2) the furnace process is used, wherein the phosphate rock is combined with coke and silica, producing elemental phosphorus as previously described. Oxidation of the phosphorus produces P2O5 which, when combined with H2O, yields H3PO4. 

A variety of investigations have been carried out on metal ion-catalyzed reactions of phosphate derivatives. However, the mechanistic details are in many cases unclear. 

Marcus RA (1999) Electron transfer past and future. In Jortner J, Bixon M (eds) Electron transfer -from isolated molecules to biomolecules, part 1. Wiley, New York, pp 1-6 Martin RF, Anderson RF (1998) Pulse radiolysis studies indicate that electron transfer is involved in radioprotection by Floechst 33342 and methylproamine. Int J Radiat Oncol Biol Phys42 827-831 Maruthamuthu P (1980) Absolute rate constants for the reactions of sulfate, phosphate and hydroxyl radicals with monomers. Macromol Chem Rapid Commun 1 23-25 Maruthamuthu P, Neta P (1977) Reactions of phosphate radicals with organic compounds. J Phys Chem 81 1622-1625... 

A review dealing with the metal-directed reactions of phosphates. 

Simple additions of such labile aquo ions as Mg, Ca, Zn and Mn "1", which are of importance in enzymic phosphoryl transfer, have resulted in only very modest catalytic effects for reactions of phosphate species (3). The much more effective t Com unit possesses the special advantage that it remains intact for long periods, while trans/cis isomerization and substitution in the fifth and sixth coordination sites proceed at moderately rapid and generally convenient rates. These characteristics make it particularly suitable for use in model studies (4). 

Silica is present in the mineral as an impurity, and it reacts with hydrofluoric acid to yield silicon tetrafluoride, which can be converted to fluorosifi-cic acid, an important source of fluorine. More than half of the phosphoric acid that is produced by the reaction of phosphates with sulfuric acid is converted directly to sodium or ammonium phosphates to be used as fertilizer thus, purity is not a concern. 

Many other organic phosphates exist in nature, but their bonding is not of the anhydride type and their hydrolysis does not result in the release of large amounts of energy. Many such compounds are phosphate esters, whose formation may be envisioned to involve a reaction of phosphate with an alcohol ... 

The neutralization reaction of the above equation is conducted in one or more strongly agitated reaction vessels, whether in a gypsum or in a hemihydrate mode. The system is highly exothermic and the slurry is maintained at 80-85°C for dihydrate processing, 95-100°C for hemihydrate, by evaporative or air cooling. During the reaction of phosphate rock with sulfuric acid, fluorine is evolved and must be scrubbed from the vent gas. 

Reactions of phosphates, etc., proceeding by attack at carbon rather than phosphorus, are noted in Section 8.2.3, pp. 170-1. 

The elimination of phosphate is analogous to elimination reactions of phosphate esters of 3-hydroxy aldehydes and ketones, and of 3-hydroxy esters (Reactions 11 and l2) 8- it is also analogous to the postulated con-... 

Trie Reaction of Phosphate Esters with Nucleophiles 454... 

Heintz, Robert A., see Dunbar, Kim R. Helton, Matthew E., see Kirk, Martin L. Hendry, Philip, and Sargeson, Alan M., Metal Ion Promoted Reactions of Phosphate Derivatives 38 201... 

Metal ion promoted reactions are important-Zn +-catalyses of hydrolysis of a range of organic substrates, for example, phosphate and carboxylate esters and Schiff bases, have recently been reviewed, as has their relevance to biological catalysis, particularly of reactions of phosphates. ... 

Reaction of phosphate with calcite surfaces appears likely in hard water areas, but low adsorption capacity and slow kinetics of the phosphate-calcite reaction under natural conditions probably prevent calcite mediated phosphorus mineralization from becoming a greater phosphorus sink than binding to the amorphous iron oxides. 

Table 10.4 Standard Gibbs energies in kJ mol of reaction for chemical hydrolysis reactions of phosphates at 298.15 K and zero ionic strength in alphabetical order...

It has been proposed by de Duve (see Further Reading) that primordial acetyl phosphate originates by reaction of acetyl-thioester with phosphate ions. According to the Iron-Sulfur World theory, phosphorylation energy may also result from a transfer of the redox energy of CO/H2S in the presence of amino acids (5), which received its first support by phosphate catalysis of peptide formation (16). Subsequently it was supported by the discovery of a formation of aminoacyl phosphate in reaction of phosphate with aminoacyl N-carboxyanhydride (21) ... 

While apatite and other calcium-based and substituted solid phases of phosphate minerals precipitated in the primary formation of cmstal sediments, secondary reactions of phosphate with... 

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