Aluminium iodide

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Aluminium iodide
Names
IUPAC name
Aluminium iodide
Other names
Aluminium(III) iodide
Aluminium triiodide
Properties
AlI3 (anhydrous)
AlI3·6 H2O (hexahydrate)
Molar mass 407.695 g/mol (anhydrous)
515.786 g/mol (hexahydrate)
Appearance White solid (anhydrous)
Yellowish (hexahydrate)
Odor Odorless
Density 3.98 g/cm3 (anhydrous)
2.63 g/cm3 (hexahydrate)
Melting point anhydrous
382 °C (720 °F; 655 K) (sublimes)
Boiling point anhydrous
188.28 °C (370.90 °F; 461.43 K)
hexahydrate
185 °C (365 °F; 458 K) (decomposes)
Solubility Soluble in alcohols, carbon disulfide, carbon tetrachloride, diethyl ether, liq. NH3, THF
Solubility in phosphorus trichloride 17 g/100 ml (20 °C)[1]
Solubility in pyridine 0.82 g/100 ml (25 °C)[2]
Solubility in sulfur dioxide 0.23 g/100 ml (0 °C)[3]
Thermochemistry
195.9 J·mol-1·K-1
-302.9 kJ/mol
Hazards
Safety data sheet Sigma-Aldrich (anhydrous)
Flash point Non-flammable
Related compounds
Related compounds
Aluminium chloride
Aluminium bromide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Aluminium iodide is a chemical compound containing aluminium and iodine, with the formula AlI3. It can also be encountered as hexahydrate (AlI3·6H2O).

Properties

Chemical

Anhydrous AlI3 is a strong Lewis acid and will absorb water from the atmosphere to form hexahydrate.

It is employed as a reagent for the scission of certain kinds of C-O and N-O bonds. It cleaves aryl ethers and deoxygenates epoxides.[4]

Physical

Aluminium iodide is a colorless solid, soluble in water.

Availability

Aluminium iodide can be bought from chemical suppliers. The anhydrous form is more expensive than the hydrated form.

Preparation

Aluminium iodide can be prepared in a spectacular process from their elements. To a small amount of evenly mixed powdered aluminium metal and elemental iodine, a few drops of water are added. After a few seconds, a vigorous reaction occurs followed by emission of intense purple colored vapors of iodine, due to heat generated by the reaction.

2 Al(s) + 3 I2(s) → 2 AlI3(s)

While good for chemical demonstrations, this route is not very practical for the preparation of bulk AlI3, as most of the final product becomes scattered in air and will rapidly absorb moisture, causing partial hydrolysis.

A much safer method involves passing iodine vapors over large size Al metal granules heated at 500-600 °C, in an inert gas atmosphere. A more convenient route involves refluxing Al granules and iodine in an inert solvent, such as carbon tetrachloride[5][6] The resulting impure AlI3 is collected and further purified by subliming it under vacuum.

The hexahydrate form can be obtained by reacting Al with iodine in water, or by neutralizing aluminium hydroxide with hydroiodic acid. The excess water is removed and the resulting aluminium iodide is dried in a desiccator.

Projects

  • Catalyst in organic reactions
  • Compound collecting
  • Prepare elemental iodine

Handling

Safety

Aluminium iodide is irritant to skin, eyes and respiratory system. Aluminium compounds are known neurotoxins.

Storage

Anhydrous AlI3 should be kept in airtight vessels. Schlenk flasks are a good storage medium.

The hexahydrate form doesn't require special storage, any clean glass bottle will do.

Disposal

Can be neutralized to aluminium oxide, while the iodine should be recycled.

References

  1. Справочник по растворимости. - Т.1, Кн.1. - М.-Л.: ИАН СССР (Solubility Handbook. - Vol. 1, Book 1. - M.-L .: IAN USSR, 1961), 1961
  2. Seidell A. Solubilities of inorganic and metal organic compounds. - 3ed., vol.1. - New York: D. Van Nostrand Company, 1940
  3. Zeitschrift fur Physikalische Chemie. - 1937. - Vol. 179A, No. 1 pp. 47
  4. https://onlinelibrary.wiley.com/doi/10.1002/047084289X.ra083
  5. Inorganic laboratory preparations 15, 1962
  6. https://prepchem.com/synthesis-of-aluminium-iodide/

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