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Hydroiodic acid

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Aqueous solution of hydrogen iodide
Hydroiodic acid
Space-filling model of hydrogen iodide
Space-filling model of hydrogen iodide
Space-filling model of water
Space-filling model of water
The iodide anion
The iodide anion
Space-filling model of the hydronium cation
Space-filling model of the hydronium cation
Names
Other names
  • Aqueous hydrogen iodide
  • Hydriodic acid
  • Hydrogen iodide, hydrous
  • Hydronium iodide
Identifiers
CAS Number
3D model (JSmol)
ChEBI
ChemSpider
EC Number
  • 233-109-9
PubChem CID
RTECS number
  • MW3760000
UNII
InChI
  • InChI=1S/BrH/h1HKey: CPELXLSAUQHCOX-UHFFFAOYSA-N
  • InChI=1/BrH/h1HKey: CPELXLSAUQHCOX-UHFFFAOYAZ
SMILES
  • .
Properties
Chemical formula HI(aq)
Molar mass 127.912 g·mol (HI)
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
Solubility in water Aqueous solution
Acidity (pKa) −9.3 (HI)
Hazards
GHS labelling:
Pictograms GHS05: Corrosive
Signal word Danger
Hazard statements H314
Precautionary statements P260, P264, P280, P301+P330+P331, P303+P361+P353, P304+P340, P305+P351+P338, P310, P321, P363, P405, P501
NFPA 704 (fire diamond)
NFPA 704 four-colored diamondHealth 3: Short exposure could cause serious temporary or residual injury. E.g. chlorine gasFlammability 0: Will not burn. E.g. waterInstability 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazard ACID: Acid
3 0 0ACID
Flash point Non-flammable
Related compounds
Other anions
Related compounds Hydrogen iodide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C , 100 kPa). Infobox references
Chemical compound

Hydroiodic acid (or hydriodic acid) is a colorless liquid. It is an aqueous solution of hydrogen iodide with the chemical formula HI(aq). It is a strong acid, in which hydrogen iodide is ionized completely in an aqueous solution. Concentrated aqueous solutions of hydrogen iodide are usually 48% to 57% HI by mass.

An oxidized solution of hydriodic acid.

Preparation

Main article: Hydrogen iodide § Synthesis

Reactions

Hydroiodic acid reacts with oxygen in air to give iodine:

4 HI(aq) + O2 → 2 H2O + 2 I2

Like 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.

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.

The catalytic cycle of the Cativa process
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).

References

  1. Perrin, D. D., ed. (1982) . Ionisation Constants of Inorganic Acids and Bases in Aqueous Solution. IUPAC Chemical Data (2nd ed.). Oxford: Pergamon (published 1984). Entry 32. ISBN 0-08-029214-3. LCCN 82-16524.
  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. ISBN 978-3527306732.
  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.

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