Aluminium perchlorate
Chemical compound
From Wikipedia, the free encyclopedia
Aluminium perchlorate is an inorganic chemical compound of aluminium with the formula Al(ClO4)3·nH2O, where n can range from 0 to 9. It is most commonly found as the nonahydrate Al(ClO4)3·9H2O, but other hydrates, such as the trihydrate, have also been reported. All forms of aluminium perchlorate are hygroscopic white solids that are soluble in water.
_perchlorate.svg)
| |
| Names | |
|---|---|
Other names
| |
| Identifiers | |
| |
3D model (JSmol) |
|
| ChemSpider | |
| ECHA InfoCard | 100.034.927 |
| EC Number |
|
PubChem CID |
|
| UNII | |
CompTox Dashboard (EPA) |
|
| |
| |
| Properties | |
| Al(ClO4)3 | |
| Molar mass | 325.33 g/mol (anhydrous) 487.46 g/mol (nonahydrate) |
| Appearance | White solid |
| Density | 2.30 g/cm3 (anhydrous)[1] 1.86 g/cm3 (nonahydrate)[2] |
| Melting point | 82 °C (180 °F; 355 K)[3] (nonahydrate, decomposition) |
| nonahydrate 180.4 g/100 mL (0 °C) 209.6 g/100 mL (25 °C)[3][4] | |
| Solubility | Soluble in ethanol, insoluble in chloroform and dichloromethane[3][5] |
| Structure[2] | |
| Trigonal | |
| R3c | |
a = 10.12 Å α = 106.7°, β = 106.7°, γ = 106.7° | |
Lattice volume (V) |
869.5 Å3 |
| Thermochemistry | |
Std enthalpy of formation (ΔfH⦵298) |
–571.1 kJ/mol[6] |
| Hazards | |
| GHS labelling: | |
  | |
| Danger | |
| H272, H314 | |
| P210, P220, P260, P264, P280, P301+P330+P331, P302+P361+P354, P304+P340, P305+P354+P338, P316, P321, P363, P370+P378, P405, P501 | |
| NFPA 704 (fire diamond) | |
| Related compounds | |
Other anions |
Aluminium nitrate |
Other cations |
Gallium perchlorate Indium perchlorate |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
| |
Preparation
The nonahydrate is produced by the dissolution of aluminium hydroxide in aqueous perchloric acid, followed by the evaporation of the solution:[2]
- Al(OH)3 + 3 HClO4 → Al(ClO4)3 + 3 H2O
The dehydration of the nonahydrate by heating at 82 °C produces a basic perchlorate. However, heating at 80 °C under vacuum produces the trihydrate. Further heating of the trihydrate does not form the anhydrous form; instead, it decomposes to aluminium oxide.[1][7][3][8][9]
Anhydrous aluminium perchlorate is produced by the reaction of aluminium chloride and dichlorine hexoxide at –20 °C:[10][11]
- 8 Cl2O6 + 2 AlCl3 → 2 ClO2Al(ClO4)4 + 6 ClO2 + 3 Cl2
The resulting ClO2Al(ClO4)4 is then heated to 90 °C under vacuum to yield anhydrous aluminium perchlorate.[11]
Structure
The nonahydrate, structurally [Al(H2O)6](ClO4)3(H2O)3, has a trigonal crystal structure and consists of octahedral [Al(H2O)6]3+ centers as well as perchlorate and three molecules of water of crystallization.[2]
The anhydrous form, on the other hand, consists of bidentate perchlorate ligands with a hexagonal crystal lattice.[1]
Reactions and complexes
Aluminium perchlorate dissolves in water to form discrete [Al(H2O)6]3+ and ClO4– ions. The [Al(H2O)6]3+ partially hydrolyses, similar to the hexaaquoiron(III) ion:[12]
- [Al(H2O)6]3+ ⇌ [Al(H2O)5OH]2+ + H+
This can be suppressed by the addition of perchloric acid. Like other aqueous Al3+ solutions, the addition of base, such as ammonium hydroxide or sodium hydroxide results in the precipitation of aluminium hydroxide; when base is further added, the precipitate redissolves to form [Al(OH)4]–.[12][13][14]
The hydrates, the tri- and nonahydrate, are soluble in various organic solvents and are used to prepare multiple complexes with organic ligands, such as pyridine, dimethylacetamide, dimethyl sulfoxide, and acetonitrile. Specifically, the dimethyl sulfoxide complex, [Al(DMSO)6](ClO4)3 is explosive. Other aluminium perchlorate complexes tetraperchloratoaluminate and hexaperchloratoaluminate are also known.[5][15][16][17][18]
Anhydrous aluminium perchlorate decomposes when heated to 160 °C to Al2O(ClO4)4:[1]
- 4 Al(ClO4)3 → 2 Al2O(ClO4)4 + 2 Cl2 + 7 O2
The oxyperchlorate decomposes to aluminium oxide if further heated to 450 °C.[1]