Alkali metal polyphosphates, effect

Adenosine 5 -phosphate, 20-22 Adenosine triphosphate, 9,lQf Alkali metal polyphosphates, effect of... 

Partial replacement of cations when using excess of alkali phosphate was at first interpreted by supposing that the cations were in part bound as a complex with the polyphosphates. This led to incorrect conclusions regarding the molecular size of polyphosphates, which persist even now in the designation of Graham s salt as hexametaphosphate. The correct interpretation of these very complicated relationships stems from the discovery that in dilute solutions of polyphosphates even salts of the alkali metal ions are only partially dissociated—up to a maximum of 30-40% 260, 280, 282, 288, 333). The degree of dissociation a for alkali polyphosphates depends on many factors. Thus, for example, the effective degree of... 

The effect of cations on the rate of hydrolysis of cycio-tri- and cvc/o-tetra-phosphates has also been studied.260 Alkali metal cations retarded the hydrolysis of both cyclo-phosphates in acidic solution but accelerated the reaction in basic solution. The catalytic activity followed the sequence Li+ > Na+> K+. Mg11, Ca11 and Ni11 retarded the hydrolysis of the cyclo-phosphates in the pH range 1.0-2.0 or 1.0-2.7, but accelerated the reaction at pH>3. Catalysis by Cu11 is observed above pH 2, while Alni has a marked catalytic effect at pH 1 and 2. A variety of other papers have appeared dealing with metal ion-promoted hydrolysis of polyphosphates.261-264 However, the mechanistic details of these reactions remain unclear and the catalytically active complexes remain undefined. 

Phosphorus has an even wider range of oxoacid chemistry, and a commensurately wide range of phosphates, phosphites, polyphosphates, hypophosphites, and so on of the alkali metals are preparable. Sodium and potassium are the most common cations used, largely because of their availability and low cost. The cation often has little effect on the properties and applications, which are covered in Phosphates Solid-state Chemistry. Most form a variety of crystalline hydrates, which have been well covered in previous treatments and need not be repeated here. Trae to form, lithium is the exception, forming no stable hydrates with phosphorus oxoanions. 

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