Hydroiodic acid


Hydroiodic acid (or hydriodic acid) is an aqueous solution of hydrogen iodide (HI). It is a strong acid, one that is ionized completely in an aqueous solution. It is colorless. Concentrated solutions are usually 48% to 57% HI.[2]

Hydroiodic acid
Space-filling model of hydrogen iodide
Space-filling model of water
The iodide anion
Space-filling model of the hydronium cation
IUPAC name
Other names
Hydronium iodide
  • 10034-85-2 checkY
3D model (JSmol)
  • Interactive image
  • CHEBI:43451 checkY
  • 23224 checkY
EC Number
  • 233-109-9
  • 24841
RTECS number
  • MW3760000
  • 694C0EFT9Q ☒N
  • InChI=1S/BrH/h1H checkY
  • InChI=1/BrH/h1H
Molar mass 127.91 g/mol
Appearance colorless liquid
Odor acrid
Density 1.70 g/mL, azeotrope
(57% HI by weight)
Boiling point 127 °C (261 °F; 400 K) 1.03 bar, azeotrope
Aqueous solution
Acidity (pKa) -9.3
GHS labelling:
GHS05: Corrosive
P260, P264, P280, P301+P330+P331, P303+P361+P353, P304+P340, P305+P351+P338, P310, P321, P363, P405, P501
NFPA 704 (fire diamond)
Flash point Non-flammable
Related compounds
Other anions
Hydrofluoric acid
Hydrochloric acid
Hydrobromic acid
Related compounds
Hydrogen iodide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references
An oxidized solution of hydriodic acid.


Hydroiodic acid reacts with oxygen in air to give iodine:

4 HI + O2 → 2 H
+ 2 I2

Like other hydrogen halides, hydroiodic acid adds to alkenes to give alkyl iodides. It can also be used as a reducing agent, for example in the reduction of aromatic nitro compounds to anilines.[3]

Cativa processEdit

The Cativa process is a major end use of hydroiodic acid, which serves as a co-catalyst for the production of acetic acid by the carbonylation of methanol.[4][5]


Illicit usesEdit

Hydroiodic acid is listed as a U.S. Federal DEA List I Chemical, owing to its use as a reducing agent related to the production of methamphetamine from ephedrine or pseudoephedrine (recovered from nasal decongestant pills).[6]

See alsoEdit


  1. ^ Henri A. Favre; Warren H. Powell, eds. (2014). Nomenclature of Organic Chemistry: IUPAC Recommendations and Preferred Names 2013. Cambridge: The Royal Society of Chemistry. p. 131.
  2. ^ Lyday, Phyllis A. (2005). "Iodine and Iodine Compounds". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. pp. 382–390. doi:10.1002/14356007.a14_381.
  3. ^ Kumar, J. S. Dileep; Ho, ManKit M.; Toyokuni, Tatsushi (2001). "Simple and chemoselective reduction of aromatic nitro compounds to aromatic amines: reduction with hydriodic acid revisited". Tetrahedron Letters. 42 (33): 5601–5603. doi:10.1016/s0040-4039(01)01083-8.
  4. ^ Jones, J. H. (2000). "The Cativa Process for the Manufacture of Acetic Acid" (PDF). Platinum Metals Rev. 44 (3): 94–105.
  5. ^ Sunley, G. J.; Watson, D. J. (2000). "High productivity methanol carbonylation catalysis using iridium - The Cativa process for the manufacture of acetic acid". Catalysis Today. 58 (4): 293–307. doi:10.1016/S0920-5861(00)00263-7.
  6. ^ Skinner, Harry F. (1990). "Methamphetamine synthesis via hydriodic acid/Red phosphorus reduction of ephedrine". Forensic Science International. 48 (2): 123–134. doi:10.1016/0379-0738(90)90104-7.

External linksEdit

  • International Chemical Safety Card 1326
  • European Chemicals Bureau