Benzotellurophene dichlorides

In turn, benzotellurophene dichlorides are reduced back to benzotellurophenes by sodium disulphite or sodium sulphide nonahydrate. ° ... 

Bromobenzntellurophene1 3-Bromobenzotellurophene dichloride is suspended in diethyl ether and an excess of 5% aqueous sodium disulfite solution is added. The mixture is shaken thoroughly until all of the organic material has dissolved. The organic layer is separated, dried with anhydrous calcium chloride, filtered, and the filtrate is evaporated. The oily residue is pure 3-bromobenzotellurophene-, yield 100%. See Table 20 for similary prepared benzotellurophene dichlorides and benzotellurophenes. 

Phenylacetylenes (3 mol) react with Te02 (1 mol) and excess of lithium halide in refluxing HOAc to produce 3-halobenzotellurophenes via the addition of a Te(IV) acetate halide to the triple bond, cychzation (probably by loss of HOAc) and reduction of the Te(IV) cyclic product to 3-halobenzotellurophene by an excess of the phenylacetylene. Owing to isolation facihties, the product is converted into the crystalhne dichlorides that is reduced to the benzotellurophenes. °... 

To facilitate the isolation of the benzotellurophenes, many of which are oils, they were converted to the benzotellurophene 7e,7e-dichlorides. After the crystalline dichlorides had been purified by recrystallization, they were reduced to the benzotellurophenes with aqueous sodium disulfite1. 

Starting Materials Reflux lime [h] Product. .. -benzotellurophene (1,1-dichloride) 1,1 -Dichloride Benzotellurophene ... 

Similarly prepared were 3-chloro-6-methyl-benzotellurophene 1,1-dichloride (m.p. 230") and 6-bromo-3-chlorobenzotellurophene 1,1-dichloride (m.p. 281 )4. 

Benzotellurophene 1,1-dichlorides were reduced to benzotellurophenes by aqueous sodium disulfite4 or sodium sulfide nonahydrate5. 

When l,3-dihydro-2-benzotellurophene 2,2-dichloride and the corresponding dibromide are dissolved in DMF, halogen exchange occurs. The rate of exchange is slow on the NMR time scale. The broadened Te-NMR signals of the dichloride and the chloride bromide were observed The equilibrium constant for this reaction was not determined. It is likely that in solution diorgano tellurium dihalides with two different halogen atoms are in equilibrium with the two symmetrical dihalides. Isolation attempts will disturb the... 

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