Hexametaphosphates

A salt originally called sodium hexametaphosphate, with n believed to be 6, is now thought to contain many much larger anion aggregates. It has the important property that it sequesters , i.e. removes, calcium ions from solution. Hence it is much used as a water-softener. 

Citrate, C20 , cycIohexane-I,2-diaminetetraacetic acid, V,V-dihydroxyethyIgIycine, EDTA, F , glycol, hexametaphosphate, OH , P20 , triethanolamine Citrate, CN , C20 , 2,3-dimercaptopropanol, EDTA, F , NagP30io, oxidation to MnOy, P20 , reduction to Mn(II) with NH2OH HCI or hydrazine, sulfosalicylate, tartrate, triethanolamine, triphosphate, tiron... 

CeUulose phosphate esters are also produced by treatment with sodium hexametaphosphate [14550-21-1] by the pad-dry-cure technique. These treated fabrics have high retention of breakiag and tearing strength (61). The reaction products contain more than 1.6% phosphoms and are iasoluble ia cupriethylenediamine [15243-01 -3] iadicating that some ceUulose cross-linking occurs. However, siace durable-press (DP) levels and wrinkle recovery values are low, it seems reasonable that only limited cross-linking takes place. 

Neutralizing Lotion. The principal active ingredient of cold wave neutralizers is usually an oxidizing agent. The most popular is hydrogen peroxide [7722-84-1J, employed at a concentration of 1—2% it continues to find widespread use. Aqueous solutions of sodium bromate [7789-38-0] at a concentration of 10—20% occasionally are used and are technically preferred over the peroxide formulations because of excellent stabiUty and absence of hair bleaching. Neutralizing powders appear to be on the decline but formulations stiU in use consist of sodium perborate [7632-04-4] combined with hexametaphosphates to improve solubiUty in hard water. 

Some water samples contain phosphoms forms other than phosphate, eg, polyphosphate, hexametaphosphate, and organic phosphates. These forms can be hydrolyzed to phosphate in hot sulfuric acid solution and deterrnined by the preceding method. The more refractory organic phosphates require digestion in a sulfuric acid—ammonium persulfate solution. Ion chromatography can also be used to measure at 2 to 10 ppb (21). 

Amphotericin B. Amphotericin B (3), an important polyene antibiotic, is administered almost exclusively via the intravenous route and is therefore discussed in more detail under the systemic antimycotics. The vaginal tablets contain 50 mg amphotericin B, and 100 mg tetracycline base per tablet (see also Antibiotics, tetracyclines). The tablets for oral use contain 50 mg amphotericin B, 250 mg tetracycline base, and 125 mg sodium hexametaphosphate. A combination ointment contains 1 mg fludrocortisone acetate, 2.5 mg neomycin, 0.25 mg gramicidin, and 1 g plastibase in addition to 30 mg amphotericin B (see also Antibiotics, peptides). 

Glassy phosphates (sodium polymetaphosphate [50813-16-6] sodium hexametaphosphate [10124-56-8J) vary in composition, depending upon the... 

Considerable laboratoiy work has indicated that the use of a dispersant such as sodium hexametaphosphate may assist in the stabihza-tion of the medium more recent data report the beneficial effect of the addition of polymers that reduce media viscosity while simultaneously producing a very low settling rate of the ferrous compound. This should be of great value for difficult separations, but at present no data are available from commercial operations. 

Improved nucleation within the phosphate solution itself can produce smoother coatings without the necessity of recourse to preliminary chemical treatment. This may be accomplished by introducing into the phosphating bath the sparingly soluble phosphates of the alkaline earth metals or condensed phosphates such as sodium hexametaphosphate or sodium tripolyphosphate. Such modified phosphating baths produce smoother coatings than orthodox baths and are very much less sensitive to cleaning procedures. 

Although orthophosphates are themselves passivating, anodic inhibitors (and also cathodic inhibitors, forming a calcium phosphate barrier film), the film strength is weak, even in simple HW systems and they are not used for this purpose. Nevertheless, despite the thermal instability of sodium hexametaphosphate and other polyphosphates, phosphates in general have several important properties that make them useful in boiler plant operations. These properties include ... 

NOTE PAA = Polyacrylic acid or sodium salt SHMP = Sodium hexametaphosphate SSMA = Sulfonated styrene maleic anhydride... 

Neutral phosphates such as sodium hexametaphosphate (SHMP)... 

FIG. 13 Langmuir-Blodgett films of dioctadecyldimethylammonium bromide incorporating 6.0-nm-diameter CdS nanoparticles stabilized by 0.2 mM sodium hexametaphosphate. (a) Absorbance spectra for 2, 3, 4, 5, 6, 7, 8, and 13 layers (bottom to top) the inset shows the linearity of the absorbance at 450 nm versus the number of layers, (b) Fluorescence spectra (excitation wavelength = 400 nm) for 2, 3, 4, 6, 8, 13, and 18 layers (bottom to top) the inset shows the emission intensity at 480 nm versus the number of layers. (Reproduced with permission from Ref. 152. Copyright 1994 American Chemical Society.)... 

This is usually prepared by either a base-exchange method using sodium zeolite, by a lime-soda ash process, or by the addition of sodium hexametaphosphate. In addition to the bacteria derived from fhe mains water, additional flora of Bacillus spp. and Staphylococcus aureus may be introduced into systems which use brine for regeneration and from the chemical filter beds which, unless treated, can act as a reservoir for bacteria. 

CdS sols of 5 nm particle size stabilized by 10 M sodium hexametaphosphate show a weak green fluorescence 515 nm) besides the red fluorescence at longer... 

Scale prevention methods include operating at low conversion and chemical pretreatment. Acid injection to convert COs to CO2 is commonly used, but cellulosic membranes require operation at pH 4 to 7 to prevent hydrolysis. Sulfuric acid is commonly used at a dosing of 0.24 mg/L while hydrochloric acid is to be avoided to minimize corrosion. Acid addition will precipitate aluminum hydroxide. Water softening upstream of the RO By using lime and sodium zeolites will precipitate calcium and magnesium hydroxides and entrap some silica. Antisealant compounds such as sodium hexametaphosphate, EDTA, and polymers are also commonly added to encapsulate potential precipitants. Oxidant addition precipitates metal oxides for particle removal (converting soluble ferrous Fe ions to insoluble ferric Fe ions). 

Various polyphosphates are effective sequestering agents under appropriate conditions. The best known of these is sodium hexametaphosphate (10.14), the cyclic hexamer of sodium orthophosphate. Further examples are the cyclic trimer sodium trimetaphosphate (10.15), as well as the dimeric pyrophosphate (10.16), the trimeric tripolyphosphate (10.17) and other linear polyphosphates (10.18). All of these polyanions function by withdrawing the troublesome metal cation into an innocuous and water-soluble complex anion by a process of ion exchange as shown in Scheme 10.7 for sodium hexametaphosphate. Hence these compounds are sometimes referred to as ion-exchange agents. 

The disadvantage of the polyphosphates is that at the temperatures (100 °C or higher) used in many textile processes they can be hydrolysed into simpler phosphates that cannot retain the metal atom in the sequestered form. For example, dicalcium disodium hexametaphosphate hydrolyses on prolonged boiling to yield the insoluble calcium orthophosphate. This is one of the main reasons why polyphosphate sequestrants are used much less extensively than the more versatile and stable aminopolycarboxylates. 

Little more need be said here about the simple ion-exchange reactions such as that between sodium hexametaphosphate and calcium ions (Scheme 10.7). It is useful, however, to consider in more detail those reactions involving chelation (Scheme 10.8). This is a reversible reaction, the equilibrium being dependent on the process pH and the concentrations of the reacting species (Equation 10.2). While chelated complexes are less stable at higher temperatures, this effect can be ignored in practice. The factors involved have been discussed in some considerable detail by Engbers and Dierkes [20,23]. 

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