Sodium phosphates

from Wikipedia, the free encyclopedia

In summary, the sodium salts of (monomeric) phosphoric acid H 3 PO 4 , the metaphosphoric acids (HPO 3 ) n and polyphosphoric acids H n + 2 P n O 3n + 1 are used as sodium phosphates .

The sodium orthophosphates of the monomeric (ortho) phosphoric acid are divided into

They are approved as food additives in the European Union under the common number E 339 .

In the case of sodium isopolyphosphates, a distinction is made between tetrasodium diphosphate and pentasodium triphosphate .

The condensation of the sodium dihydrogen phosphate results in higher molecular sodium phosphates, which are also known as condensed phosphates and can be divided into cyclic representatives ( sodium metaphosphates with rings of size three to ten) and chain-like types (sodium polyphosphates). A large number of terms such as fused or calcined phosphates are used for the latter in particular.

Important high- molecular sodium phosphates are the crystalline water-insoluble Maddrell's salt , (NaPO 3 ) x with x> 1000 according to the British chemist Robert Maddrell , which can be obtained from sodium dihydrogen phosphate at 200-300 ° C. At about 600 ° C, this changes into the cyclic sodium trimetaphosphate Na 3 (PO 3 ) 3 , which melts at 620 ° C. The quenched, glassy melt is, depending on the reaction conditions, the water-soluble Graham's salt (NaPO 3 ) 40-50 (according to Thomas Graham ) or a glassy product with the composition (NaPO 3 ) 10-20 . The misleading name sodium hexametaphosphate is still used in some cases for both products . This designation is wrong because the latter is usually a mixture of substances. The so-called Kurrol's salt , (NaPO 3 ) n with n ≈ 5000 according to the Estonian chemist Julius Kurrol , is also created from the 600 ° C melt of Maddrell's salt if it is left at around 500 ° C for a short time.

Individual evidence

  1. ↑ a b entry on sodium phosphates. In: Römpp Online . Georg Thieme Verlag, accessed on February 11, 2019.
  2. ^ Robert A. Lewis: Hawley's Condensed Chemical Dictionary . John Wiley & Sons, 2016, ISBN 978-1-119-26784-3 , pp. 1245 ( limited preview in Google Book search).
  3. ↑ a b Alexander Senning: Elsevier's Dictionary of Chemoetymology The Whys and Whences of Chemical Nomenclature and Terminology . Elsevier, 2006, ISBN 978-0-08-048881-3 , pp. 239 ( limited preview in Google Book search).
  4. ↑ Entry on Condensed Phosphates. In: Römpp Online . Georg Thieme Verlag, accessed on February 11, 2019.
  5. ↑ Thomas E. Furia: CRC Handbook of Food Additives, Second Edition . CRC Press, 1973, ISBN 978-0-8493-0542-9 , pp. 630 ( limited preview in Google Book search).
  6. ^ AF Holleman, Egon Wiberg, Nils Wiberg: Inorganic Chemistry . Academic Press, 2001, ISBN 978-0-12-352651-9 , pp. 730 ( limited preview in Google Book search).