Uranium tetrachloride
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Names | |
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IUPAC name
Uranium(IV) chloride
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Other names
Tetrachlorouranium
Uranium tetrachloride Uranous chloride | |
Identifiers | |
3D model (
JSmol ) |
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ChemSpider | |
ECHA InfoCard
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100.030.040 |
EC Number |
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PubChem CID
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UNII | |
CompTox Dashboard (EPA)
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Properties | |
UCl4 | |
Molar mass | 379.84 g/mol |
Appearance | olive green solid |
Density | 4.87 g/cm3 |
Melting point | 590 °C (1,094 °F; 863 K) |
Boiling point | 791 °C (1,456 °F; 1,064 K) |
Hydrolysis | |
Solubility | Soluble in hydrochloric acid |
Structure | |
Octahedral | |
Related compounds | |
Related compounds
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uranium trichloride, uranium pentachloride, uranium hexachloride
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Uranium tetrachloride is an
Synthesis and structure
Uranium tetrachloride is synthesised generally by the reaction of uranium trioxide (UO3) and hexachloropropene. Solvent UCl4 adducts can be formed by a simpler reaction of UI4 with hydrogen chloride in organic solvents.
Uranium tetrachloride also forms the nonahydrate, which can be produced by evaporating a mildly acidic solution of UCl4.[1]
According to X-ray crystallography the uranium centers are eight-coordinate, being surrounded by eight chlorine atoms, four at 264 pm and the other four at 287pm.[2]
Chemical properties
Dissolution in protic solvents is more complicated. When UCl4 is added to water the uranium aqua ion is formed.
- UCl4 + xH2O → [U(H2O)x]4+ + 4Cl−
The aqua ion [U(H2O)x]4+, (x is 8 or 9[3]) is strongly hydrolyzed.
- [U(H2O)x]4+ ⇌ [U(H2O)x−1(OH)]3+ + H+
The pKa for this reaction is ca. 1.6,[4] so hydrolysis is absent only in solutions of acid strength 1 mol dm−3 or stronger (pH < 0). Further hydrolysis occurs at pH > 3. Weak chloro complexes of the aqua ion may be formed. Published estimates of the log K value for the formation of [UCl]3+(aq) vary from −0.5 to +3 because of difficulty in dealing with simultaneous hydrolysis.[4]
With alcohols, partial solvolysis may occur.
- UCl4 + xROH ⇌ UCl4−x(OR)x + xHCl
Uranium tetrachloride dissolves in non-protic solvents such as
- UCl4 + H2O + S ⇌ UCl3(OH) + SH+ +Cl−
The solvent molecules may be replaced by other ligand in a reaction such as
- UCl4 + 2Cl− → [UCl6]2−.
The solvent is not shown, just as when complexes of other metal ions are formed in aqueous solution.
Solutions of UCl4 are susceptible to oxidation by air, resulting in the production of complexes of the uranyl ion.
Applications
Uranium tetrachloride is produced commercially by the reaction of
The uranium ions are then accelerated and passed through a strong magnetic field. After traveling along half of a circle, the beam is split into a region nearer the outside wall, which is depleted, and a region nearer the inside wall, which is enriched in 235U. The large amounts of energy required in maintaining the strong magnetic fields as well as the low recovery rates of the uranium feed material and slower more inconvenient facility operation make this an unlikely choice for large scale enrichment plants.
Work is being done in the use of molten uranium chloride–alkali chloride mixtures as reactor fuels in
Safety
Like all water soluble uranium salts, uranium tetrachloride is
References
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- ^ a b IUPAC SC-Database[permanent dead link] A comprehensive database of published data on equilibrium constants of metal complexes and ligands