Phosphorous acid

Phosphorous acid (or phosphonic acid) is the compound described by the formula H3PO3. This acid is diprotic (readily ionizes two protons), not triprotic as might be suggested by this formula. Phosphorous acid is an intermediate in the preparation of other phosphorus compounds. Organic derivatives of phosphorous acid, compounds with the formula RPO3H2, are called phosphonic acids.

"Phosphonic acid" redirects here. For the compound class, see phosphonate.
Not to be confused with Phosphoric acid or Phosphorus oxoacid.
Phosphorous acid
Names
IUPAC name
Phosphonic acid
Systematic IUPAC name
Phosphorous acid
Other names
Dihydroxyphosphine oxide

Dihydroxy(oxo)-λ5-phosphane
Dihydroxy-λ5-phosphanone
Orthophosphorous acid
Oxo-λ5-phosphanediol
Oxo-λ5-phosphonous acid

Metaphosphoroic acid
Identifiers
3D model (JSmol)
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.033.682
EC Number
  • 237-066-7
1619
KEGG
RTECS number
  • SZ6400000
UNII
UN number 2834
  • InChI=1S/H3O3P/c1-4(2)3/h4H,(H2,1,2,3) Y
    Key: ABLZXFCXXLZCGV-UHFFFAOYSA-N Y
  • InChI=1/H3O3P/c1-4(2)3/h4H,(H2,1,2,3)
    Key: ABLZXFCXXLZCGV-UHFFFAOYAF
  • OP(=O)O
  • OP(O)O
Properties
H3PO3
Molar mass 81.99 g/mol
Appearance white solid
deliquescent
Density 1.651 g/cm3 (21 °C)
Melting point 73.6 °C (164.5 °F; 346.8 K)
Boiling point 200 °C (392 °F; 473 K) (decomposes)
310 g/100 mL
Solubility soluble in ethanol
Acidity (pKa) 1.1, 6.7
−42.5·10−6 cm3/mol
Structure
pseudo-tetrahedral
Hazards
Occupational safety and health (OHS/OSH):
Main hazards
 skin irritant
GHS labelling:
Danger
H302, H314
P260, P264, P270, P280, P301+P312, P301+P330+P331, P303+P361+P353, P304+P340, P305+P351+P338, P310, P321, P330, P363, P405, P501
NFPA 704 (fire diamond)
3
0
1
Safety data sheet (SDS) Sigma-Aldrich
Related compounds
Related compounds
 H3PO4 (i.e., PO(OH)3)
H3PO2 (i.e., H2PO(OH))
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YN ?)
Infobox references
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