Pyrophosphoric acid Property

Melting point:

61 °C

Density 

approximate 1.9g/ml (25℃)

storage temp. 

-20°C, Hygroscopic

solubility 

DMSO (Soluble)

pka

0.99±0.10(Predicted)

form 

white crystals

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

InChIKey

XPPKVPWEQAFLFU-UHFFFAOYSA-N

CAS DataBase Reference

2466-09-3(CAS DataBase Reference)

EPA Substance Registry System

Diphosphoric acid (2466-09-3)

Safety

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

F 

3-9-21

HazardClass 

8

PackingGroup 

III

HS Code 

28092000

Hazard and Precautionary Statements (GHS)

Symbol(GHS)

Signal word

Danger

Hazard statements

H302Harmful if swallowed

H314Causes severe skin burns and eye damage

Precautionary statements

P280Wear protective gloves/protective clothing/eye protection/face protection.

P305+P351+P338IF IN EYES: Rinse cautiously with water for several minutes. Remove contact lenses, if present and easy to do. Continuerinsing.

P310Immediately call a POISON CENTER or doctor/physician.

Pyrophosphoric acid Chemical Properties,Usage,Production

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.

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

Chemical Properties

White to very pale yellow glassy solid

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.

Uses

Pyrophosphoric Acid has been shown to enhance the rate of pyrophosphate hydrolysis by nonenzymatic catlysis and by inorganic pyrophoshatase. Pyrophosphoric Acid can be used for the preparation of vanadyl pyrophosphato methoxide cluster anion. Pyrophosphoric Acid is used in anion binding of inorganic phosphates due to is ability to form complexes.

Uses

Catalyst, manufacture of organic phosphate esters, metal treatment, stabilizer for organic per- oxides.

Preparation

According 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

Definition

ChEBI: An acyclic phosphorus acid anhydride obtained by condensation of two molecules of phosphoric acid.