Sodium hexametaphosphate

SHMP is used as a sequestrant and has applications within a wide variety of industries, including as a food additive in which it is used under the E number E452i. Sodium carbonate is sometimes added to SHMP to raise the pH to 8.0–8.6, which produces a number of SHMP products used for water softening and detergents.

A significant use for sodium hexametaphosphate is as a deflocculant in the production of clay-based ceramic particles.The Role Of Sodium Hexametaphosphate In The Dissolution Process Of Kaolinite And KaolinF. Andreola; E.Castellini; T.Manfredini; M.Romagnoli. Journal of the European Ceramic Society, Volume 24, Number 7, June 2004.Impact Of Dispersants On The Mechanical Strength Development Of Alumina-Spinel Self-Flowing Refractory Castables. Sasan Otroj, Mohammad Reza Nilforushan, Arash Daghighi, Reza Marzban. Ceramics – Silikáty 54 (3) 284–289 (2010)Effect Of Adding Sodium Hexametaphosphate Liquefier On Basic Properties Of Calcium Phosphate Cements. S. Hesaraki; A. Zamanian; F. Moztarzadeh. Journal of Biomedical Materials Research Part A. Vol. 88A, No. 2, 2009Study Of Clay’s Mineralogy Effect On Rheological Behavior Of Ceramic Suspensions Using An Experimental Design. Afef Jmal Ayadi; Julien Soro; Amel Kamoun; Samir Baklouti. International Journal of Recent Research and Applied Studies 14 (2). February 2013. It is also used as a dispersing agent to break down clay and other soil types for soil texture assessment.ASTM D422 – 63(2007) Standard Test Method for Particle-Size Analysis of Soils.

It is used as an active ingredient in toothpastes as an anti-staining and tartar prevention ingredient.{{cite web |url=http://www.crestprohealth.com/pro-health-faq/ |title=Crest Pro-Health Frequently Asked Questions |access-date=2012-11-20 |archive-date=2012-11-19 |archive-url=https://web.archive.org/web/20121119051133/http://www.crestprohealth.com/pro-health-faq/ |url-status=dead }}

As a food additive, SHMP is used as an emulsifier. Artificial maple syrup, canned milk, cheese powders and dips, imitation cheese, whipped topping, packaged egg whites, roast beef, fish fillets, fruit jelly, frozen desserts, salad dressing, herring, breakfast cereal, ice cream, beer, and bottled drinks, among other foods, can contain SHMP.{{cite web | url=http://www.befoodsmart.com/ingredients/sodium-hexametaphosphate.php | title=Ingredient Results - Sodium Hexametaphosphate}}{{cite web | url=https://www.fda.gov/food/ingredientspackaginglabeling/foodadditivesingredients/ucm091048.htm | title=Food Additives & Ingredients - Food Additive Status List| website=Food and Drug Administration| date=26 August 2021}}{{cite web | url=http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/cfrsearch.cfm?fr=173.310 | title=CFR - Code of Federal Regulations Title 21}}

SHMP is used in Diamond Crystal brand Bright & Soft Salt Pellets for water softeners in a concentration of 0.03%. It is the only additive other than sodium chloride.

SHMP is prepared by heating monosodium orthophosphate to generate sodium acid pyrophosphate:

:{{chem2|2 NaH2PO4 -> Na2H2P2O7 + H2O}}

Subsequently, the pyrophosphate is heated to give the corresponding sodium hexametaphosphate:

:{{chem2|3 Na2H2P2O7 -> (NaPO3)6 + 3 H2O}}

followed by rapid cooling.

SHMP hydrolyzes in aqueous solution, particularly under acidic conditions and/or heat, to sodium trimetaphosphate and sodium orthophosphate.{{cite book|last1=Van Wazer|first1=John|title=Phosphorus and its Compounds|date=1958|publisher=Interscience Publishers|location=New York|url=http://catalog.hathitrust.org/Record/010058734|access-date=7 April 2015}}

Sodium hexametaphosphate is the alkali salt of one of the series of polymetaphosphoric acids (acids formed by the polymerization of phosphate groups).{{cite journal |last1=Mehrotra |first1=R.C. |title=Synthesis and properties of simple and complex polymetaphosphate glasses of alkali metals |journal=Pure and Applied Chemistry |date=1975 |volume=44 |issue=2 |pages=201–220 |doi=10.1351/pac197544020201 |url=https://www.degruyter.com/document/doi/10.1351/pac197544020201/html?lang=en}} Hexametaphosphoric acid was first made in 1825 by the German chemist Johann Frederich Philipp Engelhart (1797-1853).Stanley, Michael (November 1979) [https://oro.open.ac.uk/57012/8/473676_2.pdf "The Chemical Work of Thomas Graham"] Ph.D. thesis (The Open University, Milton Keynes, England, UK), p. 151. For his doctoral thesis, Engelhart intended to determine whether iron was responsible for the red color of blood. In order to purify his blood samples, Engelhart had found that he could coagulate the blood serum's albumin (dissolved proteins) by treating the blood with phosphoric acid. This contradicted the findings of the famous Swedish chemist Jöns Jacob Berzelius, who had stated that phosphoric acid did not coagulate water-soluble proteins such as egg white.Engelhart, Johann Friedrich (1825) [https://books.google.com/books?id=ajlSAAAAcAAJ&pg=PA40 "Commentatio de vera materiae sanguini purpureum colorem impertientis natura"] [Commentary on the true nature of the substance of blood which imparts its purple color] Ph.D. thesis (University of Göttingen, Göttingen, Germany),(in Latin), pp. 40-42.

• Review, in English, of Engelhart's Ph.D. thesis: {{cite journal |last1=Engelhart |first1=Johannis Friderici |title=Commentatio de vera materiae sanguini purpureum colorem impertientis natura […] |journal=Edinburgh Medical and Surgical Journal |date=1827 |volume=27 |pages=95–102 |url=https://babel.hathitrust.org/cgi/pt?id=mdp.39015011935882&seq=110}} See.p. 98. Berzelius and Engelhart collaborated with the intention of resolving the contradiction; they concluded that Engelhart had produced a new form of phosphoric acid simply by burning phosphorus in air and then dissolving the resulting substance in water.{{cite journal |last1=Berzelius |title=Sonderbare Verhalten der Phosphorsäure zur Eiweiss |journal=Annalen der Physik und Chemie |date=1827 |volume=9 |pages=631–632 |url=https://babel.hathitrust.org/cgi/pt?id=umn.31951d00316717p&seq=657 |series=2nd series |trans-title=Strange behavior of phosphoric acid toward egg white |language=German}}
• Reprinted in French: {{cite journal |last1=Berzelius |title=Manière singulière dont se comporte l'acide phosophorique avec l'Albumine |journal=Annales de Chimie et de Physique |date=1827 |volume=36 |pages=110–111 |url=https://archive.org/details/s3id13208050/page/110/mode/2up |trans-title=Singular way in which phosphoric acid behaves with albumin |language=French}} However they did not determine the new acid's composition. That analysis was accomplished in 1833 by the Scottish chemist Thomas Graham, who named the sodium salt of the new acid "metaphosphate of soda".{{cite journal |last1=Graham |first1=Thomas |title=Researches on the arseniates, phosphates, and modifications of phosphoric acid |journal=Philosophical Transactions of the Royal Society of London |date=1833 |pages=253–284 |url=https://books.google.com/books?id=KshofG09bW4C&pg=PA277}} See p. 277.
• Reprinted in German: {{cite journal |last1=Graham |first1=Thomas |title=Untersuchungen über die arsensauren und phosphorsauren Salze, so wie über die Abänderungen der Phosphorsäure |journal=Annalen der Physik und Chemie |date=1834 |volume=32 |issue=3 |pages=33–76 |url=https://babel.hathitrust.org/cgi/pt?id=umn.31951d00316737j&seq=47 |series=2nd series |doi=10.1002/andp.18341080302 |bibcode=1834AnP...108...33G |trans-title=Investigations of the salts of arsenic and phosphoric acid, as well as of the modifications of phosphoric acid |language=German}} Graham's findings were confirmed by the German chemists Justus von Liebig and Theodor Fleitmann.{{cite journal |last1=Liebig |first1=Justus |title=Ueber die Constitution der organischen Säuren |journal=Annalen der Pharmacie |date=April 1838 |volume=26 |issue=2 |pages=113–189 |doi=10.1002/jlac.18380260202 |url=https://babel.hathitrust.org/cgi/pt?id=pst.000067446544&seq=489 |trans-title=On the composition of organic acids |language=German}} See p. 142.
• Reprinted in French: {{cite journal |last1=Liebig |first1=J. |title=Sur la constitution des acides organiques |journal=Annales de Chimie |date=1838 |volume=68 |pages=5–93 |url=https://babel.hathitrust.org/cgi/pt?id=nyp.33433062741818&seq=45 |series=2nd series |trans-title=On the composition of organic acids |language=French}} See p. 39.
• See also: Stanley (1979) p. 186ff, footnote 162. In 1849 Fleitmann coined the name "hexametaphosphoric acid".{{cite journal |last1=Fleitmann |first1=Th. |title=Ueber die verschiedenen Metaphosphorsäuren und zwei neue Säuren derselben Verbindungsproportion |journal=Annalen der Physik und Chemie |date=1849 |volume=78 |pages=233–260, 338–366 |url=https://babel.hathitrust.org/cgi/pt?id=umn.31951d00321228n;view=1up;seq=251 |series=2nd series |trans-title=On various metaphosphoric acids and two new acids of the same compound proportion |language=de}} On p. 239, Fleitmann coined the name Hexametaphosphorsäure (hexametaphosphoric acid).{{cite journal |last1=Griffith |first1=E.J. |last2=Buxton |first2=R.L. |title=The preparation and properties of the twelve-membered ring hexametaphosphate anion |journal=Inorganic Chemistry |date=1965 |volume=4 |issue=4 |pages=549–551 |doi=10.1021/ic50026a023}} ; see p. 549.

By 1956, chromatographic analysis of hydrolysates of Graham's salt (sodium polyphosphate) indicated the presence of cyclic anions containing more than four phosphate groups;{{cite journal |last1=Van Wazer |first1=J. R. |last2=Kroupa |first2=E. Karl |title=Existence of ring phosphates higher than tetrametaphosphate |journal=Journal of the American Chemical Society |date=1956 |volume=78 |issue=8 |page=1772 |doi=10.1021/ja01589a086|bibcode=1956JAChS..78Q1772V }} these findings were confirmed in 1961.(Thilo & Schülke, 1963a), p. 1175. In 1963, the German chemists Erich Thilo and Ulrich Schülke succeeded in preparing sodium hexametaphosphate by heating anhydrous sodium trimetaphosphate.See:

• {{cite journal |last1=Thilo |first1=E. |last2=Schülke |first2=U. |title=Darstellung des echten Natrium-hexametaphosphates Na₆[P₆O₁₈] |journal=Angewandte Chemie |date=1963a |volume=75 |issue=23 |pages=1175–1176 |trans-title=Preparation of true sodium hexametaphosphate Na₆[P₆O₁₈] |language=de |doi=10.1002/ange.19630752305|bibcode=1963AngCh..75.1175T }}
• {{cite journal |last1=Thilo |first1=E. |last2=Schülke |first2=U. |title=Preparation of true sodium hexametaphosphate Na₆[P₆O₁₈] |journal=Angewandte Chemie International Edition |date=1963b |volume=2 |issue=12 |page=742 |doi=10.1002/anie.196307421}}

Sodium phosphates are recognized to have low acute oral toxicity. SHMP concentrations not exceeding 10,000 mg/L or mg/kg are considered protective levels by the EFSA and US FDA. Extreme concentrations of this salt may cause acute side effects from excessive blood serum concentrations of sodium, such as: “irregular pulse, bradycardia, and hypocalcemia."{{Ullmann |doi=10.1002/14356007.a19_465.pub3|title=Phosphoric Acid and Phosphates|year=2008|last1=Schrödter|first1=Klaus|last2=Bettermann|first2=Gerhard|last3=Staffel|first3=Thomas|last4=Wahl|first4=Friedrich|last5=Klein|first5=Thomas|last6=Hofmann|first6=Thomas|isbn=978-3527306732}}

{{Reflist}}

• [https://web.archive.org/web/20080602175604/http://www.ohsah.bc.ca/index.php?section_id=393 Occupational Health and Safety Agency for Healthcare in British Columbia]
• [https://www.fishersci.com/store/msds?partNumber=S333500&productDescription=SODIUM+METAPHOSPHAT+PURIF+500G&vendorId=VN00033897&countryCode=US&language=en Material Safety Data Sheet]

{{Glass science}}

Category:Sodium compounds

Category:Metaphosphates

Category:Water treatment

Category:Photographic chemicals

Category:Glass compositions

Category:Twelve-membered rings

Category:Cyclic phosphates