3D model (JSmol)
|Density||1.70 g/mL, azeotrope
(57% HI by weight)
|Boiling point||127 °C (261 °F; 400 K) 1.03 bar, azeotrope|
|S-phrases (outdated)||(S1/2), S26, S45|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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. Concentrated hydroiodic acid has a pH of less than 0.
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.
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 methamphetamine from pseudoephedrine (recovered from nasal decongestant pills). This reaction is stereospecific, producing only (d)-methamphetamine.
- Jones, J. H. (2000). "The CativaTM Process for the Manufacture of Acetic Acid" (PDF). Platinum Metals Rev. 44 (3): 94–105.
- 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.
- Skinner, Harry F. "Methamphetamine Synthesis via HI/Red Phosphorus Reduction of Ephedrine". Forensic Science International, 48 128-134 (1990)