Hydroiodic acid (or hydriodic acid) is a colorless and aqueous solution of hydrogen iodide (HI). It is a strong acid, which is ionized completely in an aqueous solution. Concentrated solutions of hydroiodic acid are usually 48% to 57% HI.[2]
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| Names | |||
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| IUPAC name Iodane[1] | |||
| Other names Hydronium iodide | |||
| Identifiers | |||
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| Properties | |||
| HI(aq) | |||
| Molar mass | 127.91 g/mol | ||
| 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 | |||
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| Danger | |||
| H314 | |||
| P260, P264, P280, P301+P330+P331, P303+P361+P353, P304+P340, P305+P351+P338, P310, P321, P363, P405, P501 | |||
| 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). | |||
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]
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]