Hydroiodic acid

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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
3D model (JSmol)
EC Number
  • 233-109-9
RTECS number
  • MW3760000
Molar mass 127.91
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
Corrosive (C)
R-phrases (outdated) R34
S-phrases (outdated) (S1/2), S26, S45
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

Hydroiodic acid (or hydriodic acid) is a highly acidic aqueous solution of hydrogen iodide (H I) (concentrated solution usually 48 - 57% HI). It is the second strongest hydrohalic acid, after hydroastatic acid. Hydroiodic acid is a commonly used chemical reagent and is one of the strong acids that ionize completely in an aqueous solution.


Hydroiodic acid readily reacts with oxygen in air, contributing to the deep colours associated with old samples;

4 HI + O2 → 2 H
+ 2 I2
HI + I2 → HI3[citation needed]

Like other hydrogen halides, hydroiodic acid will perform addition reactions with unsaturated hydrocarbons such as alkenes. It can also be used as a reducing agent, for example in the reduction of aromatic nitro compounds to anilines.[2]

Cativa process[edit]

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.[3][4]

The catalytic cycle of the Cativa process

Illicit uses[edit]

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).[5]


  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. ^ 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.
  3. ^ Jones, J. H. (2000). "The Cativa Process for the Manufacture of Acetic Acid" (PDF). Platinum Metals Rev. 44 (3): 94–105.
  4. ^ 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.
  5. ^ Skinner, Harry F. "Methamphetamine Synthesis via HI/Red Phosphorus Reduction of Ephedrine". Forensic Science International, 48 128-134 (1990)

External links[edit]