Phosphoric acid equilibria

Strong base anion exchangers, 74 395, 411 Strong inversion, in silicon-based semiconductors, 22 239 Strong nitric acid process, materials of construction for, 77 187-188 Strong phosphoric acids, equilibrium composition of, 78 827t Strontianite, 23 317, 321 Strontium (Sr) 23 316-325 chemical properties of, 23 318 economic aspects of, 23 320-321 effect of micro additions on silicon particles in Al-Si alloys, 2 311-312 in ferrites, 77 59... 

Table 5. Equilibrium Composition of the Strong Phosphoric Acids ...

The neutralisation of free phosphoric acid by reaction 15.1 alters the position of equilibrium of equations 15.2, 15.3 and 15.4 towards the right and thereby leads to the deposition of the sparingly soluble secondary phosphates and insoluble tertiary phosphates on the metal surface. 

This reaction shows that the hydrated oxide SiCV-xHjO is acidic, since it reacts with a base-As we mentioned earlier, phosphorus can be found in four different oxidation states. The hydroxides of the +1, +3, and +5 states of phosphorus are hypophosphorous acid, H3P02, phosphorous acid, H3P03, and phosphoric acid, H3P04. Their structures are shown in Figure 20-4. As suggested by their names, these compounds are distinctly acidic, and are of moderate strength. The equilibrium constant for the first ionization of each acid is approximately 10-2 hypophosphorous acid ... 

Sulfurous acid is an equilibrium mixture of two molecules (12a and 12b) in the former, it resembles phosphorous acid, with one of the H atoms attached directly to the S atom. These molecules are also in equilibrium with molecules of S02, each of which is surrounded by a cage of water molecules. The evidence for this equilibrium is that crystals of composition S02-aH20, with x about 7, are obtained when the solution is cooled. Such substances, in which a molecule occupies a cage formed by other molecules, are called clathrates. Methane, carbon dioxide, and the noble gases also form clathrates with water. 

TABLE 1.7. Equilibrium constants for addition or elimination from phosphoric acid esters. ... 

By methods analogous to those used for the tetrahedral intermediates related to carboxylic acid derivatives, Guthrie proceeded from the heat of formation of pentaeth-oxyphosphorane to free energies of the P(OEt) (OH)5 species. °° This allowed the calculation of the equilibrium constants for addition of water or hydroxide to simple alkyl esters of phosphoric acid see Table 1.7. 

According to this scheme, 192 first affords the anion 195 in an initial protonation/ deprotonation equilibrium 195 then undergoes rate-determining unimolecular decomposition to the metaphosphorimidate 197, which reacts fast with water to give the phosphoric acid 197. 

Mixed chalcogen derivatives of phosphinic and phosphoric acids are also known, the most studied being the mixed sulfur-oxygen species. Thiophos-phoric acids exist in two different isomeric forms - the thiono form (18a) and the thiolo form (18b). The equilibria usually sits somewhere in between these two species, being dependent upon the nature of the R substituents, the solvent and in some cases the concentration. Thiophosphinic acids are also able to interconvert between the thiono (19a) and thiolo (19b) tautomers, although the equilibrium position usually sits well on the side of the thiono tautomer.1... 

The former displace the Mn(VII)-Mn(II) equilibrium and lower its reduction potential whilst the phosphoric acid preferentially complexes Fe(III), lowering the reduction potential for Fe(HI)-Fe(II). Hence, the potassium permanganate, having its reduction potential lowered, stoichiometrically oxidizes Fe(IE) without interacting with the chloride ions. 

Deoxy-a-D-ribosyl-l-phosphate 20, a key substrate in the preparation of 2 -deoxynucleosides, was stereoselectively prepared by crystallization-induced asymmetric transformation in the presence of an excess of ortho-phosphoric acid and tri( -butyl)amine under strictly anhydrous conditions (Scheme 2).7 Initial Sn2 displacement of Cl in ot-glycosyl chloride 16 by phosphoric acid resulted in a 1 1 a/p anomeric mixture of 17 and 18 due to the rapid anomerisation of the a-chloride in polar solvents. Under acidic conditions, in the presence of an excess of H3P04, an equilibration between the a and p anomers gradually changed in favour of the thermodynamically more stable a-counterpart. By selective crystallization of the mono tri( -butyl)ammonium salt of the a-phosphate from the mixture, the equilibrium could be shifted towards the desired a-D-ribosyl phosphate 18 (oc/p = 98.5 1.5), which was isolated as bis-cyclohexylammonium salt 19 and deprotected to furnish compound 20. 

The fact that the three equilibrium constants are well separated in phosphoric acid is not relevant. The spreadsheet can deal automatically with any 3-protic acid. Figure 3-20 is the result of replacing the logarithms of the protonation constants in the cells B4 D4 with the values for citric acid (6.4, 4.8, 3.1) ... 

Liquid absorbents. If the partial pressure of the water in the gas is greater than the equilibrium partial pressure at the surface of a liquid, condensation will take place as a result of contact between the gas and liquid. Thus, water vapour is frequently removed from a gas by bringing it into contact with concentrated sulphuric acid, phosphoric acid, or glycerol. Concentrated solutions of salts, such as calcium chloride, are also effective. The process may be carried out either in a packed column or in a spray chamber. Regeneration of the liquid is an essential part of the process, and this is usually effected by evaporation. 

Step 1 Write the equation for the dissociation equilibrium of phosphoric acid in water. Then set up an ICE table. 

Similar to that observed for pure phosphoric acid, the transport properties of PBI and phosphoric acid are also dependent on the water activity, i.e., on the degree of condensation (polyphosphate formation) and hydrolysis. There is even indication that these reactions do not necessarily lead to thermodynamic equilibrium, and hydrated orthophosphoric acid may... 

After extraction, the organic solvent, loaded with phosphoric acid, is scrubbed with a phosphoric acid solution in equilibrium with the organic solvent. In this way, coextracted contamination is removed. The scrub liquor is recycled to extraction. 

Enols and enolization feature prominently in some of the basic biochemical pathways (see Chapter 15). Biochemists will be familiar with the terminology enol as part of the name phosphoenolpyruvate, a metabolite of the glycolytic pathway. We shall here consider it in non-ionized form, i.e. phosphoenolpyruvic acid. As we have already noted (see Section 10.1), in the enolization between pyruvic acid and enolpyruvic acid, the equilibrium is likely to favour the keto form pyruvic acid very much. However, in phosphoenolpyruvic acid the enol hydroxyl is esterified with phosphoric acid (see Section 7.13.2), effectively freezing the enol form and preventing tautomerism back to the keto form. 

Kim ST, O Neil JR (1997) Equilibrium and nonequUibrium oxygen isotope effects in synthetic carbonates, Geochim Cosmochim Acta 61 3461-3475 Kim S-T, Mucci A, Taylor BE (2007) Phosphoric acid fractionation factors for calcite and aragonite between 25 and 75°C, Chem Geol 246 135-146... 

The suggestion was that the components on either side of the equilibrium united, without the intervention of water, to form the sucrose-phosphoric acid adduct XX, which decomposed in either direction as shown by the dotted lines. 

Heating phosphoric acid converts it to metaphosphoric acid, HPO3, and pyrophosphoric acid, H4P2O7. If anhydrous phosphoric acid is melted and allowed to stand for several weeks, it partially converts to pyrophosphoric acid, H4P2O7. The equilibrium occurs in liquid phase ... 

The results at 6° between 5° and 90° are represented by (S =18 0 -J-0 4550. The equilibrium conditions in the presence of phosphoric acid have been previously discussed, Fig. 92. 

Nitrosamines (257) are amphoteric their acidic character is shown by their dissolution in alkalis, producing intensely dark-colored liquids from which the starting material may be regenerated by acids.170 Due to their weakly basic properties, they also dissolve in strong sulfuric and phosphoric acid and may be extracted therefrom, at least partially, by ether. In these acidic media, equilibrium mixtures are formed with the corresponding diazonium salt which may be precipitated under suitable conditions (see Section III.H, 1). 3-... 

H3PO4 (phosphoric acid)). The dissociation reactions for each pair are shown where they occur along a pH gradient. The equilibrium or dissociation constant (fCa) and its negative logarithm, the p/Ca, are shown for each reaction. 

Migration of the double bond of terminal alkenes to internal position is favored by the equilibria. Thus 1-butene in the presence of activated clay, silica gel, alumina, or phosphoric acid on pumice may yield equilibrium product mixtures comprised of about 20% 1-butene and 80% 2-butenes.91 The main transformation of branched 1-alkenes under mild conditions is also double-bond migration. For example, 2,4,4-trimethyl-1-pentene is isomerized to the equilibrium mixture92 with 20% 2,4,4-trimethyl-2-pentene when treated with silica gel at 25°C. 

Skeletal isomerization requires higher temperature and stronger acid catalysts than do double-bond migration and cis-trans isomerization. Butylenes, for example, are transformed to isobutylene over supported phosphoric acid catalysts.98 The equilibrium mixture at 300°C contains approximately equal amounts of straight-chain and branched butenes. Similar studies were carried out with pentene isomers.99 Side reactions, however, may become dominant under more severe conditions.100... 

To measure calcium ions, for example, an aliphatic diester of phosphoric acid (R0)2P(0)0 can be used (Fig. 18.5). Concentration equilibrium exists on each side of the wall ... 

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