Tellurium iodine anions

In the anion electrochemical series, sulfur, being the less noble element compared to its heavier congeners, occupies an intermediate position between iodine and selenium [(+)F, Cl, Br, I, S, Se, Te(-)]. Selenium, regarded as a metalloid, is a relatively noble element. Tellurium is rather an amphoteric element it can enter into solution in the form of both cations and anions. Regarded as a metal, i.e., with respect to its cations, tellurium occupies a position between copper and mercury. Regarded as a metalloid, i.e., with respect to its anions, it is located on the extreme right of the above series. 

Biphenyldiyl 2-bromo-2 -biphenyl telluronium bromide (m.p. 264°, yield 79%) and the corresponding iodine compound (m.p. 265c, yield 63%) were similarly prepared2,3. Tetraphenyl tellurium transferred an anionic phenyl group to benzaldehydc and triphenyl boron yielding triphenyl telluronium salts4. 

The iodine is removed by adding a thiosulphate, and the selenium remains as a reddish-brown powder. Tellurites react under these conditions forming the complex anion, [Tel6]2, which also has a reddish-brown colour it is, however, decomposed and decolourized by a thiosulphate, thus permitting the detection of selenium in the presence of not too large an excess of tellurium. 

Trialkyl phosphites have been converted to dialkyl chlorophosphates (32) in a mild and efficient way by tellurium tetrachloride. Tris(dimethylamino)phosphine abstracts iodine from 1-iodoperfluoroalkanes to give metal-free perfluoroalkyl anions which have basic but poor nucleophilic properties. The bicyclic phosphite (33) with chlorine gave a sole product (34) resulting from opening of the five-membered and not the seven-membered ring. ... 

The color of the iodine is removed by adding thiosulfate, and the selenium is left as a red-brown powder. Under the same conditions, tellurous acid reacts with hydriodic acid, forming the complex red-brown [Tele]" anion. However, this tellurium compound can be decomposed and decolorized by sodium thiosulfate. Selenium can thus be detected successfully, even in the presence of considerable quantities of tellurium. 

---