Hydroiodic acid

Hydroiodic acid (or hydriodic acid) is a highly acidic aqueous solution of hydrogen iodide (HI) (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
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
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R-phrases (outdated) R34
S-phrases (outdated) (S1/2), S26, S45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 readily reacts with oxygen in air, contributing to the deep colours associated with old samples;

4 HI + O2 → 2 H
2O + 2 I2
HI + I2 → HI3

Like other halogens, 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

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

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]

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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. 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 CativaTM 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 CativaTM 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)
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