Uranium tetrachloride

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Uranium tetrachloride
ThCl4.png
UCl4 Powder.jpg
Names
IUPAC name
Uranium(IV) chloride
Other names
Tetrachlorouranium
Uranium tetrachloride
Uranous chloride
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.030.040 OOjs UI icon edit-ltr-progressive.svg
EC Number
  • 233-057-7
PubChem CID
UNII
  • InChI=1S/4ClH.2U/h4*1H;;/q;;;;2*+2/p-4 Yes check.svgY
    Key: AYQSGSWJZFIBLR-UHFFFAOYSA-J Yes check.svgY
  • InChI=1/4ClH.2U/h4*1H;;/q;;;;2*+2/p-4
    Key: AYQSGSWJZFIBLR-XBHQNQODAS
  • [U+4].[Cl-].[Cl-].[Cl-].[Cl-]
Properties
UCl4
Molar mass 379.84 g/mol
Density 4.87 g/cm3
Melting point 590 °C (1,094 °F; 863 K)
Boiling point 791 °C (1,456 °F; 1,064 K)
Structure
Octahedral
Related compounds
Related compounds
uranium trichloride, uranium pentachloride, uranium hexachloride
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 inorganic compound, a salt of uranium and chlorine, with the formula UCl4. It is a hygroscopic olive-green solid. It was used in the electromagnetic isotope separation (EMIS) process of uranium enrichment. It is one of the main starting materials for organouranium chemistry.

Contents

Synthesis and structure

Single crystals of uranium tetrachloride (field of view about 7 mm) UCl4 single crystals.jpg
Single crystals of uranium tetrachloride (field of view about 7 mm)

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.

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. [1]

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 [2] ) is strongly hydrolyzed.

[U(H2O)x]4+ [U(H2O)x−1(OH)]3+ + H+

The pKa for this reaction is ca. 1.6, [3] 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. [3]

With alcohols, partial solvolysis may occur.

UCl4 + xROH UCl4−x(OR)x + xHCl

Uranium tetrachloride dissolves in non-protic solvents such as tetrahydrofuran, acetonitrile, dimethyl formamide etc. that can act as Lewis bases. Solvates of formula UCl4Lx are formed which may be isolated. The solvent must be completely free of dissolved water, or hydrolysis will occur, with the solvent, S, picking up the released proton.

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 carbon tetrachloride with pure uranium dioxide UO2 at 370 °C. It has been used as feed in the electromagnetic isotope separation (EMIS) process of uranium enrichment. Beginning in 1944, the Oak Ridge Y-12 Plant converted UO3 to UCl4 feed for the Ernest O. Lawrence's Alpha Calutrons. Its major benefit being the uranium tetrachloride used in the calutrons is not as corrosive as the uranium hexafluoride used in most other enrichment technologies This process was abandoned in the 1950s. In the 1980s, however, Iraq unexpectedly revived this option as part of its nuclear weapons program. In the enrichment process, uranium tetrachloride is ionized into a uranium plasma.

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 molten salt reactors. Uranium tetrachloride melts dissolved in a lithium chloridepotassium chloride eutectic have also been explored as a means to recover actinides from irradiated nuclear fuels through pyrochemical nuclear reprocessing. [4]

Safety

Like all water soluble uranium salts, uranium tetrachloride is nephrotoxic (poisonous to the kidney) and can cause severe renal damage and acute renal failure if ingested.

Related Research Articles

The actinide or actinoid series encompasses the 15 metallic chemical elements with atomic numbers from 89 to 103, actinium through lawrencium. The actinide series derives its name from the first element in the series, actinium. The informal chemical symbol An is used in general discussions of actinide chemistry to refer to any actinide.

Chlorine Chemical element, symbol Cl and atomic number 17

Chlorine is a chemical element with the symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between them. Chlorine is a yellow-green gas at room temperature. It is an extremely reactive element and a strong oxidising agent: among the elements, it has the highest electron affinity and the third-highest electronegativity on the revised Pauling scale, behind only oxygen and fluorine. On several scales other than the revised Pauling scale, nitrogen's electronegativity is also listed as greater than chlorine's, such as on the Allen, Allred-Rochow, Martynov-Batsanov, Mulliken-Jaffe, Nagle, and Noorizadeh-Shakerzadeh electronegativity scales.

An electrolyte is a medium containing ions that is electrically conducting through the movement of ions, but not conducting electrons. This includes most soluble salts, acids, and bases dissolved in a polar solvent, such as water. Upon dissolving, the substance separates into cations and anions, which disperse uniformly throughout the solvent. Solid-state electrolytes also exist. In medicine and sometimes in chemistry, the term electrolyte refers to the substance that is dissolved.

Aqua regia Mixture of nitric acid and hydrochloric acid in a 1:3 molar ratio

Aqua regia is a mixture of nitric acid and hydrochloric acid, optimally in a molar ratio of 1:3. Aqua regia is a fuming liquid. Freshly prepared aqua regia is colorless, but it turns yellow, orange or red within seconds, so named by alchemists because it can dissolve the noble metals gold and platinum, though not all metals.

Zinc chloride Chemical compound

Zinc chloride is the name of chemical compounds with the formula ZnCl2 and its hydrates. Zinc chlorides, of which nine crystalline forms are known, are colorless or white, and are highly soluble in water. This white salt is hygroscopic and even deliquescent. Samples should therefore be protected from sources of moisture, including the water vapor present in ambient air. Zinc chloride finds wide application in textile processing, metallurgical fluxes, and chemical synthesis. No mineral with this chemical composition is known aside from the very rare mineral simonkolleite, Zn5(OH)8Cl2·H2O.

Titanium tetrachloride Inorganic chemical compound

Titanium tetrachloride is the inorganic compound with the formula TiCl4. It is an important intermediate in the production of titanium metal and the pigment titanium dioxide. TiCl4 is a volatile liquid. Upon contact with humid air, it forms thick clouds of titanium dioxide and hydrochloric acid, a reaction that was formerly exploited for use in smoke machines. It is sometimes referred to as "tickle" or "tickle 4" due to the phonetic resemblance of its molecular formula to the word.

Copper(II) chloride Chemical compound

Copper(II) chloride is the chemical compound with the chemical formula CuCl2. The anhydrous form is yellowish brown but slowly absorbs moisture to form a blue-green dihydrate.

Tantalum(V) chloride Chemical compound

Tantalum(V) chloride, also known as tantalum pentachloride, is an inorganic compound with the formula TaCl5. It takes the form of a white powder and is commonly used as a starting material in tantalum chemistry. It readily hydrolyzes to form tantalum(V) oxychloride (TaOCl3) and eventually tantalum pentoxide (Ta2O5); this requires that it be synthesised and manipulated under anhydrous conditions, using air-free techniques.

Uranyl chloride Chemical compound

Uranyl chloride refers to inorganic compounds with the formula UO2Cl2(H2O)n where n = 0, 1, or 3. These are yellow-colored solids.

Uranium(III) chloride Chemical compound

Uranium(III) chloride, UCl3, is a water soluble salt of uranium. UCl3 is used mostly to reprocess spent nuclear fuel. Uranium(III) chloride is synthesized in various ways from uranium(IV) chloride; however, UCl3 is less stable than UCl4.

Platinum(IV) chloride Chemical compound

Platinum(IV) chloride is the inorganic compound of platinum and chlorine with the empirical formula PtCl4. This brown solid features platinum in the 4+ oxidation state.

Organoactinide chemistry

Organoactinide chemistry is the science exploring the properties, structure and reactivity of organoactinide compounds, which are organometallic compounds containing a carbon to actinide chemical bond.

Chloroauric acid Chemical compound

Chloroauric acid refers to inorganic compounds with the chemical formula H[AuCl4nH2O. Both the trihydrate and tetrahydrate are known. Both are orange-yellow solids consisting of the planar [AuCl4] anion. Often chloroauric acid is handled as a solution, such as those obtained by dissolution of gold in aqua regia. These solutions can be converted to other gold complexes or reduced to metallic gold or gold nanoparticles.

The plutonyl ion is an oxycation of plutonium in the oxidation state +6, with the chemical formula PuO2+
2
. It is isostructural with the uranyl ion, compared to which it has a slightly shorter M–O bond. It is easily reduced to plutonium(III). The plutonyl ion forms many complexes, particularly with ligands that have oxygen donor atoms. Complexes of the plutonyl ion are important in nuclear fuel reprocessing.

A metal ion in aqueous solution or aqua ion is a cation, dissolved in water, of chemical formula [M(H2O)n]z+. The solvation number, n, determined by a variety of experimental methods is 4 for Li+ and Be2+ and 6 for elements in periods 3 and 4 of the periodic table. Lanthanide and actinide aqua ions have a solvation number of 8 or 9. The strength of the bonds between the metal ion and water molecules in the primary solvation shell increases with the electrical charge, z, on the metal ion and decreases as its ionic radius, r, increases. Aqua ions are subject to hydrolysis. The logarithm of the first hydrolysis constant is proportional to z2/r for most aqua ions.

Metal halides

Metal halides are compounds between metals and halogens. Some, such as sodium chloride are ionic, while others are covalently bonded. A few metal halides are discrete molecules, such as uranium hexafluoride, but most adopt polymeric structures, such as palladium chloride.

Uranium pentachloride Chemical compound

Uranium pentachloride is an inorganic chemical compound composed of uranium in the +5 oxidation state and five chlorine atoms.

Uranium hexachloride Chemical compound

Uranium hexachloride (UCl6) is an inorganic chemical compound of uranium in the +6 oxidation state. UCl6 is a metal halide composed of uranium and chlorine. It is a multi-luminescent dark green crystalline solid with a vapor pressure between 1-3 mmHg at 373.15 K. UCl6 is stable in a vacuum, dry air, nitrogen and helium at room temperature. It is soluble in carbon tetrachloride (CCl4). Compared to the other uranium halides, little is known about UCl6.

Actinide chemistry Branch of nuclear chemistry

Actinide chemistry is one of the main branches of nuclear chemistry that investigates the processes and molecular systems of the actinides. The actinides derive their name from the group 3 element actinium. The informal chemical symbol An is used in general discussions of actinide chemistry to refer to any actinide. All but one of the actinides are f-block elements, corresponding to the filling of the 5f electron shell; lawrencium, a d-block element, is also generally considered an actinide. In comparison with the lanthanides, also mostly f-block elements, the actinides show much more variable valence. The actinide series encompasses the 15 metallic chemical elements with atomic numbers from 89 to 103, actinium through lawrencium.

Thorium compounds

Many compounds of thorium are known: this is because thorium and uranium are the most stable and accessible actinides and are the only actinides that can be studied safely and legally in bulk in a normal laboratory. As such, they have the best-known chemistry of the actinides, along with that of plutonium, as the self-heating and radiation from them is not enough to cause radiolysis of chemical bonds as it is for the other actinides. While the later actinides from americium onwards are predominantly trivalent and behave more similarly to the corresponding lanthanides, as one would expect from periodic trends, the early actinides up to plutonium have relativistically destabilised and hence delocalised 5f and 6d electrons that participate in chemistry in a similar way to the early transition metals of group 3 through 8: thus, all their valence electrons can participate in chemical reactions, although this is not common for neptunium and plutonium.

References

  1. Taylor, J.C.; Wilson, P.W. (1973). "A neutron-diffraction study of anhydrous uranium tetrachloride". Acta Crystallogr. B. 29 (9): 1942–1944. doi: 10.1107/S0567740873005790 .
  2. David, F. (1986). "Thermodynamic properties of lanthanide and actinide ions in aqueous solution". Journal of the Less Common Metals. 121: 27–42. doi:10.1016/0022-5088(86)90511-4.
  3. 1 2 IUPAC SC-Database [ permanent dead link ] A comprehensive database of published data on equilibrium constants of metal complexes and ligands
  4. Olander, D. R. and Camahort, J. L. (1966), Reaction of chlorine and uranium tetrachloride in the fused lithium chloride-potassium chloride eutectic. AIChE Journal, 12: 693–699. doi : 10.1002/aic.690120414