Metaphosphates cyclic

Using phosphorus and proton Tl data it was shown that the dipole-dipole mechanism is mainly responsible for relaxation of 31P in orthophosphorous acid. A pH dependence of the 31P relaxation was observed. The maxima in the plot of 31P relaxation times vs. pH were attributed to the presence of the individual ions PO4, HPOJ and H2PO " (Morgan and Van Wazer, 1975). The 31P relaxation in cyclic metaphosphates was shown to be independent of pH but sensitive to the counter-ion used in this study (Glonek et al., 1976). 

Monoesters of phosphoric acid 536, in the presence of DCC, react with alcohols and phenols to give the corresponding phosphoric acid diesters in quantitative yield. This reaction is widely used in nucleic acid chemistry. The first step in this reaction is the formation of the cyclic metaphosphate trimer 537, which serves as an active phosphorylating agent. ... 

In the discussion to follow, the great differences between sodium and potassium condensed phosphate phase systems is highlighted. Where the sodium Kurrol s salt is metastable with respect to the cyclic sodium trimetaphosphate there is no cyclic metaphosphate in the potassium phosphate two component phase system and the Kurrol s salt is the only stable compound in the phase system with K2O-P2O5 ratios near unity. 

The ease of condensation in this reaction decreases with increasing size of the side group, R. This type of condensation reaction is also used for the preparation of cyclic metaborates and cyclic metaphosphates ... 

Poly(phosphoric acid) is the high-molar-mass condensation product of orthophosphoric acid. The corresponding salts are called polyphosphates. The oligomeric, cyclic metaphosphate compounds, as they are called, are often also classified as polyphosphates. 

Quantitative estimation of the compounds of simple mixtures of phosphates, polyphosphates, and polymetaphosphates can be effected without too much difiSculty. Determinations of orthophosphate, pyrophosphate, triphosphate, and so-called hexametaphosphate" are usually made on mixtures of soluble phosphates. Total phosphorus content is also determined by hydrolyzing all other phosphates to orthophosphoric acid. No distinctive analytical methods are, however, available for the direct quantitative determination of the cyclic metaphosphates. 

Two groups of hydrolyzable phosphates may be distinguished the (linear) polyphosphates with chain-like anions and the (cyclic) metaphosphates with ring-shaped anions. 

Should it be required that (linear) polyphosphates and (cyclic) metaphosphates are differentiated or the hydrolytic breakdown of phosphates of higher molecular weight should be observed, separation by thin-layer chromatography is possible. 

Thurn and Krebs Clearfield and Smith Niemeyer and Richter Crystal structure of Hittorf s Violet phosphorus determined Layer structure of a-Zr(HP04>2.H20 estabhshed Cyclic metaphosphates first detected in hving matter... 

Cyclic metaphosphates lack most of the useful properties of long-chain polyphosphates. The metal-complexing power of the lower members is very weak compared to that of the linear polyphosphates. 

The soluble cyclic metaphosphates all undergo cleavage on alkaline hydrolysis to produce, initially, the corresponding linear polyphosphate (5.183), which will then undergo further splitting until eventually only orthophosphate anions are left in solution. Both alkali metal triphosphates and tetraphosphates can nevertheless be isolated by this method, but octametaphosphate is more resistant to hydrolysis. The linear octaphosphate, when it is produced, is quickly split into smaller units before significant amounts can be collected (Figure 5.28). 

Ample proof of metaphosphate ring structure has been given by x-ray structural analyses of crystalline salts. In solution, cyclic metaphosphates can be distinguished from chain polyphosphates in several ways ... 

NMR spectroscopy. Cyclic metaphosphates give rise to only one characteristic P resonance peak. Linear polyphosphates, on the other hand, contain PO4 tetrahedra in two kinds of environment, corresponding to end and chain groups, and consequently give rise to two resonance peaks (Chapter 14.2). 

The lower cyclic metaphosphates (n < 6) also differ from the polyphosphates in the greater solubility of their salts, their inability to form complexes, and their low resistance to alkaline hydrolysis. They generally lack the great usefulness of the straight-chain polyphosphates. 

Derivatives with terminal amino groups probably exist in equilibrium with zwitterion forms (7.59) and (7.266). The hydrolysis of these cyclic bodies is, however, complex and under some conditions the imido groups may be replaced by oxygen to give cyclic metaphosphates and linear polyphosphates before complete hydrolysis to orthophosphate occurs. 

Triphosphates and pyrophosphates can be estimated in the presence of each other and ortho and cyclic metaphosphates, with tris(ethylenediamine) cobalt chloride. At pH = 3.5, this latter reagent will form an insoluble triphosphate complex but not a pyrophosphate complex. Conversely at pH = 6.5, a pyrophosphate but not a triphosphate complex can be precipitated. Under either of these conditions ortho and cyclic metaphosphates will not give precipitates. 

Heating alkali metal or alkaline earth metal dihydrogen phosphates produces polymeric salts (cyclic metaphosphates and linear polyphosphates) and cross-linked polyphosphates (ultraphosphates), depending on temperature and the presence of other ingredients (11,12). This complex group of polymers includes materials with crystalline, glass-like, fibrous, or ceramic properties as well as some with thermoplastic and thermoset characteristics some are useful as binders for metals, ceramics, and dental restorations. Reviews are available on glasses (12,13), crystalline compounds (14), and polyphosphate fibers (15). 

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