Highly reactive uranium and thorium

1 Two Methods for Preparation of Highly Reactive Uranium and Thorium Use of a Novel Reducing Agent Naphthalene Dianion 

Highly dispersed and reactive metal powders have commanded a great deal of interest for their applications in catalytic and stoichiometric chemical syntheses, as well as their uses in materials science. Numerous methods exist for the preparation of these metal powders. Most of these methods for preparing metal powders involve the reduction of a metal salt or oxide by hydrogen (usually at high temperatures) [2-4] or by other chemical or electrochemical means [3, 5-10]. In addition to reductive techniques, pyrolysis [3, 11,12] and metal atom vaporization [13-19] have been employed. An excellent review of the preparation, reactivity, and physical properties of unsupported metal particles has appeared [20]. 

Because of the commercial importance of uranium, a number of methods for generating finely divided chemically reactive uranium metal have been developed. Pyrophoric uranium metal powders have been prepared by thermal decomposition of uranium amalgam [21-23] or uranium hydride [24, 25]. Many methods have involved reduction of uranium oxides [26]. Other methods employed are melt electrolysis [26] and potassium reduction of (i/ -C6H5)4U [27]. 

Chemical Synthesis Using Highly Reactive Metals, First Edition. Reuben D. Rieke. 2017 John Wiley Sons, Inc. Published 2017 by John Wiley Sons, Inc. 

The oxophilicity of titanium has been exploited in the well-known reductive carbonyl coupling reactions pioneered by McMurry [37-41] and others [42,43] using low-valent titanium. This reaction has been shown to occur with many other early transition metals [44, 45]. The oxophilicity of the early transition metals, lanthanides, and actinides is well known. The standard enthalpies of 

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The homogeneous reactor experiment-2 (HRE-2) was tested as a power-breeder in the late 1950s. The core contained highly enriched uranyl sulfate in heavy water and the reflector contained a slurry of thorium oxide [1314-20-1J, Th02, in D2O. The reactor thus produced fissile uranium-233 by absorption of neutrons in thorium-232 [7440-29-1J, the essentially stable single isotope of thorium. Local deposits of uranium caused reactivity excursions and intense sources of heat that melted holes in the container (18), and the project was terrninated. 

Uranium(IV) and thorium(IV) form true sandwich cyclooctatetraenide complexes uranocene U(CgH8)2 and Th(C8H8)2 with the average 180) of the sixteen U-C distances 2.647 A and Th-C distances 2.701 A. Cerium(III) forms a far more reactive anion Ce(C8H8)2- with the quite high average 2.74 A of the sixteen Ce-C distances. 

Evidence for the high reactivity of uranium and some uranium compounds is found in the report by Hartman, Nagy and Jacobson that uranium metal in thin layers ignites at room temperature within a few minutes after exposure, as do uranium hydride (UH3) and thorium hydride (ThHj). 

The solutions in acetic acid contain scarcely dissociated ion-pairs owing to its low dielectric constant. Some reactions lead to solvolysis products, such as FeCl(RCOO)2. Partial hydrolysis is found to occur with ferric and aluminium chloride, titanium(IV), niobium(V) and tantalum(V)-chlorides, while halides of arsenic(III), zirconium(IV), thorium(IV) and uranium(IV) are completely solvo-lysed. The high reactivity is undoubtedly due to the presence of acetate ions, and ethylacetate gives many more adducts with acceptor molecules than does acetic acid. 

Calcium serves as a reductant for such reactive metals as zirconium, thorium, vanadium, and uranium. In zirconium reduction, zirconium fluoride is reacted with culcium metal. The high heat of the reaction melts the zirconium. The zirconium ingot resulting is remelted undet vacuum for purilicatinn. Thorium and uranium oxides are reduced with an excess of calcium in reactors or trays under an atmosphere of argon. The resulting tnetals are leached with acetic acid tu remove the lime. 

The actinides are reactive metals, typified by the reactions of thorium and uranium shown in Figures 10.1 and 10.2. These binary compounds frequently have useful properties. Thus, choosing examples from thorium chemistry, Th2S3 is a high-temperature crucible material, ThN is a superconductor, and Th3P4 and Th3As4 are semiconductors. 

In all three decay series, isotopes of relatively soluble elements like U, Ra, and Rn, decay to isotopes of highly particle-reactive elements (Th, Pa, Po, Pb), and vice versa (Figure 1), resulting in widely different distributions in the water column (Table 2) see Uranium-Thorium Series Isotopes in Ocean Profiles). 

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