Lithium tellurolates

Air is then bubbled through it to oxidize the lithium tellurolate. The red oily ditelluride that separates is extracted with ethyl ether (200 mL). The organic phase is washed with H2O (2X50 niL), dried (CaCl2) and evaporated to give 2.83 g of a viscous red oil. Distillation of 5.66 g of the crude material prepared in this manner affords 4.87 g of pure di-n-butyl ditelluride (89% based on Te b.p. 103-105°C/0.8 torr). 

Moreover, since organic tellurides are easily accessible from lithium tellurolates and organic halides, a one-pot procedure can be performed, overcoming the isolation of the tel-luride (method C). 

Dihydrogen telluride is an acid in aqueous solution and is comparable in strength with phosphoric acid. Tellurols, especially arenetellurols, are expected to be at least as acidic as dihydrogen telluride. Therefore, tellurols should react easily with alkali metal hydroxides to form alkali metal tellurolates. Because tellurols are difficult to prepare, alkali metal tellurolates are best obtained by methods which avoid the tellurols. Sodium and lithium tellurolates are the most frequently used tellurolates. Although the tellurolates are not as sensitive to oxidation as the tellurols, tellurolates are almost always used in situ and are prepared and stored under nitrogen. Sodium benzenetellurolate was isolated as a moisture-and air-sensitive, grey powder. Its solutions in tetrahydrofuran or acetone were found to be stable for months when kept under nitrogen6. 

The insertion of elemental tellurium into C — Li or C — Na bonds is a convenient method for the preparation of alkali metal tellurolates. Many organic lithium compounds are commercially available or can be prepared, for instance, by halogen-lithium or hydrogen-lithium exchange. The reactions of the organic lithium compounds with elemental tellurium are performed in inert organic solvents such as diethyl other, tetrahydrofuran, tetrahydrofuran/hexane, or diethyl ether/benzene at temperatures (— 196° to + 20°) compatible with the stability of the organic lithium compound. The applicability of this reaction for the synthesis of aliphatic, aromatic, and heteroaromatic lithium tellurolates is documented in Table 1 (p. 155). 

Table 1 Lithium Tellurolates from Organic Lithium Compounds and Tellurium...

R-Hal Preparation of R-Li Solvent Produtt R-Te-Li lithium ... -tellurolate Refer- ence... 

For l25Te-NMR investigations, dialkyl and diaryl ditellurium derivatives were converted to the lithium tellurolates through reactions with lithium in tetrahydrofuran at room temperature under an atmosphere of argon4. In this manner, the following lithium tellurolates were generated for NMR studies. 

Solutions of lithium tellurolates were prepared by reacting a diaryl ditellurium5-7 or dibutyl ditellurium7 with lithium aluminum hydride. Diethyl ether5, dioxane6, or a mixture... 

Lithium tellurolate reacted exothermically with an equimolar amount of elemental sulfur in tetrahydrofuran. The organotellurothiolates were identified as the products by 125Te-NMR spectroscopy2. 

The addition of sodium or lithium tellurolates to carbon-carbon triple bonds can occur intramolecularly when an ethynyl group is suitably located within the molecule to allow the formation of a tellurium-containing heterocyclic compound3,4. 

Heterocyclic lithium tellurolates reacted with dichloromethane at 20°. Chloromethyl organo tellurium derivatives, the products of the first step in these reactions, could not be isolated. It was postulated that the second nucleophilic substitution is much faster than the first one3. 

Instead of air, potassium hexacyanoferrate(III) can also be used to oxidize tellurols to diaryl ditellurium products. This method produced the following JV-heterocyclic ditellurium compounds from the lithium tellurolates ... 

The reaction has been rationalized as involving an attack of lithium tellurolate on a lithi-ated sulphone, promoting the elimination of lithium phenyl sulphinate and the formation of a labile epitelluride that readily collapses into stilbene and elemental tellurium. 

The insertion tendency decreases in the order f-BuLi > 5-BuLi > n-BuLi > PhLi > MeLi. These insertions can be carried out by using lithium alkanides, alkenides, alkynides, and aromatic or heterocyclic lithium compounds. The lithiation should not be carried out by using alkyl halides, because the lithium tellurolates that are formed in the reaction may react with the alkyl halide reagent to produce organyl alkyl tellurides. ... 

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