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Pyrophosphoric acid

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Pyrophosphoric acid Basic information
Pyrophosphoric acid Chemical Properties
  • Melting point:61 °C
  • Density approximate 1.9g/ml (25℃)
  • pka0.99±0.10(Predicted)
  • form white crystals
  • Water Solubility 709g/100mL H2O (23°C); soluble alcohol, ether [MER06]
  • Merck 13,8098
  • CAS DataBase Reference2466-09-3(CAS DataBase Reference)
  • EPA Substance Registry SystemDiphosphoric acid (2466-09-3)
Safety Information
  • Hazard Codes C
  • Risk Statements 22-34
  • Safety Statements 26-36/37/39-45
  • RIDADR UN 3260 8/PG 2
  • WGK Germany 3
  • RTECS JL6672500
  • 3-9-21
  • HazardClass 8
  • PackingGroup III
  • HS Code 28092000
Pyrophosphoric acid Usage And Synthesis
  • PreparationPyrophosphoric acid may be prepared by heating orthophosphoric acid at 215°C:
    2H3PO4 → H4P2O7 + H2O
    The acid solution in pure form can be obtained by ion exchange, passing an aqueous solution of sodium pyrophosphate, Na4P2O7, through a suitable cation exchange column.
  • ReactionsThe acid has four replacable H+ ions. Its dissociation constants indicate that two H+ ions are strongly acidic while the other two protons are weakly acidic. The first dissociation constant especially is very large:
    H4P2O7 + H2O ↔ H3O+ + H3P2O7¯          Ka1 ~ 10–1
    H3P2O7¯+ H2O ↔ H3O+ + H2P2O72–         Ka2 ~ 1.5x10–2
    PHOSPHORIC ACID, PYRO 701H2P2O72¯ + H2O ↔ H3O+ + HP2O73–      Ka3 ~ 2.7x10–7
    HP2O73¯ + H2O ↔ H3O+ + P2O74¯          Ka4 ~ 2.4x10–10
    Pyrophosphoric acid forms acid salts, such as NaH3P2O7 and Na2H2P2O7.
  • DescriptionPyrophosphoric acid, also known under the name diphosphoric acid, is colorless, odorless, hygroscopic and is soluble in water, diethyl ether and ethyl alcohol. It is produced from phosphoric acid by dehydration. Pyrophosphoric acid slowly hydrolyzes in the presence of water into phosphoric acid.
    H4P2O7 +H2O?2H3PO4
    Upon heating, phosphoric acid loses water, being converted successively, and to some extent concurrently, into the pyro- and meta-acids:
    2H3PO4?H4P2O7 +H2O
    nH3PO4?(HPO3)n + [H2O]n
  • Chemical PropertiesWhite to very pale yellow glassy solid
  • Physical propertiesColorless needles or liquid; hygroscopic. Crystallizes in two anhydrous forms: a metastable form melting at 54.3°C and a second and more stable form melting at 71.5°C; extremely soluble in cold water, reacting very slowly to form phosphoric acid; decomposing much faster in hot water; very soluble in alcohol and ether.
  • UsesCatalyst, manufacture of organic phosphate esters, metal treatment, stabilizer for organic per- oxides.
  • PreparationAccording to early investigators, the pyro-acid is formed as low as 100 °C, and the conversion is complete between 255 and 260 °C. Phosphorous oxychloride reacts with phosphoric acid in the following manner:
    5H3PO4 + POC13?3H4P2O7 + 3HC1
    A mixture of the ortho- and meta-acids may be condensed together to form the pyro-acid by heating on the water bath:
    nH3PO4 +[HPO3]n?[H4P2O7]n
  • DefinitionChEBI: An acyclic phosphorus acid anhydride obtained by condensation of two molecules of phosphoric acid.
Pyrophosphoric acid Preparation Products And Raw materials
Pyrophosphoric acid(2466-09-3)Related Product Information
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