Thorium chloride is an inorganic chemical compound. In addition to the anhydrous ThCl4, two hydrates have been reported: ThCl44 and ThCl48. These hygroscopic salts are water-soluble and white, at room temperature. Similar to other thorium complexes thorium chloride has a high melting point 770 °C and a boiling point of 921 °C. Like all the other actinides, thorium is radioactive and has sometimes been used in the production of nuclear energy. Thorium chloride does not appear naturally but instead is derived from Thorite, Thorianite, or Monazite which are naturally occurring formations.
History
Thorium was first discovered by Jons Jacob Berzelius in 1828. After receiving a sample of minerals from his colleague Jens Esmarck, Berzelius was able to isolate thorium using a method that had been used for other metals like cerium, zirconium, and titanium. This process involved using alkali metals to disassociate the thorium from its prior ligand form ThSiO4 . An intermediate in the isolation process was thorium chloride and thus the compound was discovered.
Structures
The structure of thorium chloride is square planar with a symmetry of D4h. In this coordinate compound the bond length between the Th-Cl bond is 2.690 Å. The structure has been reported as hydrous or anhydrous. Due to the compound’s hydroscopic nature in the presence of water it can form either ThCl44 and ThCl48.
Synthesis
Thorium Chloride can be produced in a variety of ways but the most common starting reactant is either thorium dioxide or Thorium orthosilicate. One way thorium chloride is synthesized is through a carbothermic reaction. The carbothermic reaction require very high temperature ranging from 700 °C to 2600 °C. What necessitates these extreme environments are thorium dioxides melting temperature of 3,390 °C. The reaction between graphite and thorium dioxide usually takes place in a stream of chlorine gas forming the thorium chloride. However the chlorination reaction can be done by another compound Cl2-CCl4 which is a more stable reactant than pure Chlorine gas. Cl2-CCl4 is formed by passing a gas mixture of Cl2 through a wash bottle filled with CCl4. ThO2 + 2 C + 4 Cl2 → ThCl4 + 2 CO Another less common method of synthesis relies on heating thorium metal with NH4Cl at 300 °C for 30 h making a 2ThCl6. This product is then heated at 350 °C under a high vacuum to produce ThCl4.
Application
Thorium chloride is an intermediate in many different experiments. The first type of experiment is the purification of Thorium. 1. Reduction of ThCl4 with alkali metals. 2. Electrolysis of anhydrous thorium chloride in fused mixture of NaCl and KCl. 3. Ca reduction of Thorium Chloride mixed with anhydrous zinc chloride. The process of producing pure thorium is normally for its production as the initial stage of producing a nuclear fuel. Thorium is sometimes mistaken for a nuclear fuel like uranium however it is not and requires neutron bombardment or other modifications to be applicable in the nuclear fuel cycle. The other application of thorium chloride is a perquisite for other thorium complexes. In these reactions Thorium Chloride is the initial reagent but it is first changed into ThCl42. ThCl42 is a versatile reagent that can be converted into ThCl42, ThBr42.and others.
