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 - 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
Names
IUPAC name
Iodane[1]
Other names
Hydronium iodide
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
EC Number
  • 233-109-9
RTECS number
  • MW3760000
UNII
Properties
HI(aq)
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
Acidity (pKa) -9.3
Hazards
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R-phrases (outdated) R34
S-phrases (outdated) (S1/2), S26, S45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

Reactions

Hydroiodic acid reacts with oxygen in air to give iodine:

4 HI + O2 → 2 H
2O + 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 process

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]

The catalytic cycle of the Cativa process

Illicit uses

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]

References
  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. "Methamphetamine Synthesis via HI/Red Phosphorus Reduction of Ephedrine". Forensic Science International, 48 128-134 (1990)
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