Maddrell’s salt

Maddrell s salt Madelung cyclization Madopa Maduramicin... 

Several crystalline condensed phosphates may also be formed by the dehydration of monosodium phosphate (MSP). Maddrell s salt exists as Form 11 (high temperature MaddreU, NaPO -ll, insoluble metaphosphate-11) and Form 111 (low temperature MaddreU, NaPO -lll, insoluble metaphosphate-111). Both forms are highly polymerized and difficult (slow) to dissolve in water. Mixtures of the two forms are marketed as a dental abrasive for toothpaste formulations containing soluble fluoride. Maddrell s salt is also used with disodium phosphate as a cheese emulsifying aid. 

The complex preparative interrelationships occurring in the sodium polyphosphate system are summarized in Fig. 12.21 (p. 531). Thus anhydrous NaH2p04, when heated to 170" under conditions which allow the escap>e of water vapour, forms the diphosphate Na2H2p207, and further dehydration at 250" yields either Maddrell s salt (closed system) or the cyclic trimetaphosphate (water vapour pressure kept low). Maddrell s salt converts from the low-temperature to the high-lemperaturc form above 300", and above 400" reverts to the cyclic... 

On dehydration of sodium dihydrogen monophosphate in a normal atmosphere it first passes over completely to the acid diphosphate, Na2H2P207, without forming amorphous phases. From this at temperatures above 240°C trimetaphosphate I and Maddrell s salt are formed in proportions which appear to depend in the first place on the water vapor pressure 229). Usually the low-temperature form of Maddrell s salt is the primary prod-... 

Applying the phase rule, it is found that, in the two component system NaP03 + H20, a maximum of four phases is possible at the quadruple points 199,302). In addition to, at the most, two crystalline substances and water vapor, an amorphous glass-like phase is always present. This phase consists of mixtures of polyphosphates, the chain length of which rises with increasing temperature. Only Na2H2P207, Maddrell s salt (h) and trimetaphosphate occur as stable solid phases in addition to NaH2P04. 

In addition, solutions of Graham s salt prove to be identical in their chemical behavior with those of Maddrell s salt (295, 816), the chain-like nature... 

Perhaps the formation of trimetaphosphate and small quantities of tetrametaphosphate from dissolved polyphosphates, which can amount to 70% in presence of Mg++ ions, is an indication of the form in which the anion chains are present in the solution. In any case this formation of trimetaphosphates is not, contrary to what was proposed initially (293, 326), an argument for the assumption that trimetaphosphate rings constitute a structural unit in the polyphosphates. Thus in solutions of Maddrell s salt, the anions of which are known to be linear chains from crystal structure determination (78) (see Section IV,E,2), up to 50% yields of trimeta-... 

Fio. 9. Various chain types in crystalline high-molecular phosphates (a) (LiPCh) low temperature form (b) Rb(P03)x (c) (NaPCb) Maddrell s salt (high temperature form) (d) (NaP().i)x Kurrol s salt. 

Maddrell s salt - pYES, NATURAL] (Vol 8) - [PHOSPHORIC ACID AND PHOSPHATES] (Vol 18)... 

Maddrell s salt 10 maize roots 44 Mannan 105, 151 membrane transport 99 metachomatic granules 53, 54, 62 metaphosphate 3 methylene blue 22, 23 Michaelis constant 78 mitochondria 58, 61, 96, 122, 150 moses 43... 

Sodium metaphosphate, NaPOs.—The metaphosphate is prepared by the interaction of sodium nitrate and phosphoric acid at 330° C.20 It is a white, vitreous mass, almost insoluble in water, and melting21 at 617 2° C. It is sometimes called Maddrell s salt, after its discoverer.22 The semihydrate, NaP03, H20, is formed by heating sodium ammonium hydrogen phosphate at 160° to 170° C., and subsequently raising the temperature to 320° C.23 Tammann24 has proved the existence... 

Maddrell s salt 583 melamine-formaldehyde polymer 578 metaphosphates 581—584, 608, 609, 610... 

Sodium dihydrogen phosphate is converted by way of disodium dihydrogen diphosphate (see above) to the high molecular weight Maddrell s salt (n > 1000) upon heating at temperatures above 250°C. 

Maddrell s salts. (IMP). Insoluble sodium metaphosphate, NaP03-II and NaP03-III. 

Alkali metal and alkaline earth polyphosphates crystallize as short chains, two to six phosphate groups per chain or very long chains with hundreds to thousands of PO3 per chain. All polyphosphates in the alkali metal and alkaline earth systems are amorphous in the intermediate chain lengths. Control of the short chain length polyphosphates, both crystalline or amorphous, is a function of R, the M2O-P2O5 ratio. The control of the chain lengths of very long crystalline polyphosphates as Maddrell s salt, Kurrol s salt, and calcium phosphate fibers is not well understood. 

Maddrell s salt, which are interpreted as showing that kinetic effects are responsible for difficulties in converting the cyclic trimer into the linear polymeric forms. The potassium polyphosphate samples (Kurrol s salt) obtained from the fusion of potassium sulphate and phosphoric acid have chains terminated by OSOJ groups, according to i.r. spectra. Kinetic studies show a first-order dependence of polyphosphate concentration in the hydrolysis of Graham s salt to give trimetaphosphate and short-chain species. The vaporization of sodium metaphosphate from a Knudsen cell leads to predominantly monomeric, with some dimeric, species, according to mass-spectrometric data. ... 

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