Tellurium tetrachloride

Tellurium tetrachloride is the inorganic compound with the empirical formula TeCl₄. The compound is volatile, subliming at 200 Ã‚°C at 0.1 mmHg. Molten TeCl₄ is ionic, dissociating into TeCl₃⁺ and Te₂Cl₁₀^2−.

Structure

TeCl₄ is monomeric in the gas phase, with a structure similar to that of SF₄. In the solid state, it is a tetrameric cubane-type cluster, consisting of a Te₄Cl₄ core and three terminal chloride ligands for each Te. Alternatively, this tetrameric structure can be considered as a Te₄ tetrahedron with face-capping chlorines and three terminal chlorines per tellurium atom, giving each tellurium atom a distorted octahedral environment

Synthesis

TeCl₄ is prepared by chlorination of tellurium powder:

Te + 2 Cl₂ → TeCl₄

The reaction is initiated with heat. The product is isolated by distillation. Crude TeCl₄ can be purified by distillation under an atmosphere of chlorine.

Alternatively TeCl₄ can be prepared using sulfuryl chloride (SO₂Cl₂) as a chlorine source. Yet another method involves the reaction of tellurium with sulfur monochloride (S₂Cl₂) at room temperature. This exothermic reaction rapidly forms white needle-like crystals of TeCl₄.

Reactions

Tellurium tetrachloride is the gateway compound for high valent organotellurium compounds. Arylation gives, depending on conditions, .

TeCl₄ has few applications in organic synthesis. Its equivalent weight is high, and the toxicity of organotellurium compounds is problematic. Possible applications of tellurium tetrachloride to organic synthesis have been reported. It adds to alkenes to give Cl-C-C-TeCl₃ derivatives, wherein the Te can be subsequently removed with sodium sulfide. Electron-rich arenes react to give aryl Te compounds. Thus, anisole gives TeCl₂(C₆H₄OMe)₂, which can be reduced to the diaryl telluride. TeCl₄ is a precursor to tellurium-containing heterocycles like tellurophenes.

Heating a mixture of TeCl₄ and metallic tellurium gives tellurium dichloride (TeCl₂).

In moist air, TeCl₄ forms tellurium oxychloride (TeOCl₂), which further decomposes with excess water to form tellurous acid (H₂TeO₃).

Safety considerations

As is the case for other tellurium compounds, TeCl₄ is toxic. It also releases HCl upon hydrolysis.

References