Phosphate hydrates, dehydrations

A.K. Sarkar, Hydration/dehydration characteristics of struvite and dittmarite pertaining to magnesium ammonium phosphate cement system, J. Mater. Set, 26 (1991) 2514-2518. 

The trisodium salt is best made by careful dehydration of an equimolar mixture of hydrated disodium hydrogen phosphate and sodium hydrogen phosphite at 180° ... 

J. P. Guthrie, Hydration and Dehydration of Phosphoric Acid Derivatives Free Energies of Formation of the Pentacoordinate Intermediates for Phosphate Ester Hydrolysis and of Monomeric Metaphosphate, J. Am. Chem. Soc. 1977, 99, 3391. 

In electrochemistry, the effect of acidic anions on the electrode interface is important. The interaction of the adsorbed water molecules is relatively weak with perchlorate ions (Cl04 ) and fluoride ions (F ), intermediate with chloride ions (Cl ) and sulfate ions (S04 "), and relatively strong with phosphate ions (P04 ") and bromide ions (Br ). In a series of halogen anions, fluoride ions (F ), which interact weakly with the metal surface, are adsorbed as hydrated ions (H3O F ) chloride and bromide ions (Cl and Br ), which interact strongly with the metal surface, are adsorbed as dehydrated ions (Cl M and Br M). 

Various preparative methods are adopted at nonstoichiometric formulations, incomplete dehydration or using oxide additives to obtain boron phosphate of varying purity for its catalytic applications. The compound also forms hydrates (tri- tetra-, penta-, and hexahydrates) which readily decompose in water to phosphoric acid and boric acid. 

The rate of dehydration of uridine hydrate (and the hydrates of various uridine phosphates) has been reported by Logan and Whitmore,52 at 86°C and a pH of 8.4. The concentration of hydrate was unspecified (it was prepared by photolysis of uridine solution and not isolated), and the fraction of complete recovery was not specified (about 97.5% recovery is shown). The main purpose was to compare the dehydration rates of uridine, various uridine phosphates and polyuri-dylic acid. The uncertainty about the nature of the products formed in the dehydration of irradiated uridylic acid (see below), however, makes interpretation of the observed rates quite difficult. It would be better to measure the rates of formation of a particular product than to rely too heavily on measurements of absorbance change. 

Concerning the membrane itself, phospholipid hydration was characterized in terms of the types of water, bound and bulk, and their exchange rates, as well as direct observation of the intermolecular contacts between the phosphate headgroup and bound water via HRMAS HOESY and between lipids in mixed membranes via HRMAS NOESY.112 Significantly, Zhou and co-workers found little dehydration of the membranes even when rotation rates as high as 9 kHz were used, providing some comfort that the centripetal forces of sample rotation are not changing the structure of the membrane. 

Phosphates. Some hydrated phosphates and phosphatocomplexes are included in Table 49, p. 1180. Hydrated protactinium(V) phosphate, Pa0(H2P04)3-2H20, dehydrates at 250 °C and decomposes to Pa0(P03)3 at 700 °C, then to (Pa0)4(P207)3 at 1000 °C. The structures of these compounds are not known. 

Another system in which ring-formation has been considered to be manifested on polarographic curves is the reduction of pyridoxal (77, 80). The reduction wave of this compound changes with pH and the observed plot is similar to that shown in Fig. 22. This dependence can be explained either by hydration (as for other pyridine carboxaldehydes), or by hemiacetal formation. The same two interpretations can be applied to electronic spectra. A comparison with the behaviour of pyridoxal-5-phosphate can contribute to the solution of this problem. With this ester the formation of the hemiacetal form is impossible and practically no current decrease in acidic solutions can be observed. Hence it can be concluded that the decrease in the limiting current of pyridoxal is due to ring formation. Nevertheless, the possibility of some participation by a dehydration reaction cannot be completely excluded, for it is possible to assume that the introduction of a phosphoric acid residue into position 5 either shifts the equilibrium towards the dehydrated form or increases the rate of dehydration. 

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