| Identification | More | [Name]
Pyrophosphoric acid | [CAS]
2466-09-3 | [Synonyms]
DIPHOSPHORIC ACID
PYROPHOSPHORIC ACID
Pyrophosphoric acid syrupy
PYROPHOSPHORIC ACID, TECH.
PYROPHOSPHORIC ACID, 90+%
Diphosphoric(V) acid | [EINECS(EC#)]
219-574-0 | [Molecular Formula]
H4O7P2 | [MDL Number]
MFCD00011343 | [Molecular Weight]
177.98 | [MOL File]
2466-09-3.mol |
| Chemical Properties | Back Directory | [Appearance]
White to very pale yellow glassy solid | [Melting point ]
61 °C | [density ]
approximate 1.9g/ml (25℃) | [storage temp. ]
-20°C, Hygroscopic | [solubility ]
DMSO (Soluble) | [form ]
white crystals | [pka]
0.99±0.10(Predicted) | [color ]
white crystals, crystalline | [PH]
pKa1= 0.86, pKa2 = 1.76, pKa3 = 5.88, pKa4 = 8.14(25℃) | [Water Solubility ]
709g/100mL H2O (23°C); soluble alcohol, ether [MER06] | [Merck ]
13,8098 | [Stability:]
Hygroscopic, Moisture Sensitive | [InChI]
InChI=1S/H4O7P2/c1-8(2,3)7-9(4,5)6/h(H2,1,2,3)(H2,4,5,6) | [InChIKey]
XPPKVPWEQAFLFU-UHFFFAOYSA-N | [SMILES]
P(OP(O)(=O)O)(O)(O)=O | [Uses]
Catalyst, manufacture of organic phosphate
esters, metal treatment, stabilizer for organic per-
oxides.
| [CAS DataBase Reference]
2466-09-3(CAS DataBase Reference) | [EPA Substance Registry System]
2466-09-3(EPA Substance) |
| Hazard Information | Back Directory | [Chemical Properties]
White to very pale yellow glassy solid | [Definition]
ChEBI: An acyclic phosphorus acid anhydride obtained by condensation of two molecules of phosphoric acid. | [Description]
Pyrophosphoric 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 | [Physical properties]
Colorless 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. |
| Safety Data | Back Directory | [Symbol(GHS) ]
 
GHS05,GHS07 | [Signal word ]
Danger | [Hazard statements ]
H302-H314 | [Precautionary statements ]
P280-P305+P351+P338-P310 | [Hazard Codes ]
C | [Risk Statements ]
R22:Harmful if swallowed.
R34:Causes burns. | [Safety Statements ]
S26:In case of contact with eyes, rinse immediately with plenty of water and seek medical advice .
S36/37/39:Wear suitable protective clothing, gloves and eye/face protection .
S45:In case of accident or if you feel unwell, seek medical advice immediately (show label where possible) . | [RIDADR ]
UN 3260 8/PG 2
| [WGK Germany ]
3
| [RTECS ]
JL6672500
| [F ]
3-9-21 | [HazardClass ]
8 | [PackingGroup ]
III | [HS Code ]
28092000 |
| Questions And Answer | Back Directory | [Preparation]
Pyrophosphoric 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.
| [Reactions]
The 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.
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