Rongalite method

Cyclic tellurides, including some with a steroidal structure, - have been prepared by the Rongalite method. 

The Rongalite method (see Section 3.1.1.1b,i) can be successfully applied to the preparation of diaryl tellurides from aryl iodides. This method seems to be advantageous compared to the preceding one because of the higher yields and milder experimental conditions. 

Some concurrent reactions sometimes observed in the above methods (dehydrohalo-genation with the tellurium/Rongalite method and formation of tellurocarbamates RTeC(0)NMe2 with the tellurium/NaH/DMF method) that decrease the yields of the desired tellurides can be avoided by a modified procedure, where sodium telluride is generated by heating elemental tellurium and NaH in NMP. The deep purple solution of the reagent prepared under these conditions can be stored for many days (in contrast to the use... 

Under aqueous conditions (Na2Te/Rongalite method) no reduction occurs, the thioke-tone being converted into the ketone. ... 

Epoxides bearing a leaving group in a suitable position, such as chloromethyl epoxides, react with sodium telluride (prepared by the Rongalite method), giving allyhc alcohols. ... 

Methods and Since elemental tellurium is separated during the reaction, the debromination can be performed using only catalytic amounts of tellurium, the reagent being continuously regenerated at the expense of excess Rongalite (method E) and (Et0)2P(0)Na (method E). 

Dibutyl Ditellurium [Rongalite Method]9 Into a 500 ml three-necked flask are placed 9.24 g (0.08 mol) of Rongalite C, 9.0 g (0.23 mol) of sodium hydroxide, and 200 ml of water. The flask is flushed with nitrogen, 15.3 g (0.12 mol) of finely powdered tellurium are added, the stirred mixture is heated under reflux for 5 h under nitrogen, and then 16.4 g (0.12 mol) of butyl bromide are added dropwise. The mixture is then stirred for 30 min, allowed to cool, and extracted with three 100 ml portions of carbon tetrachloride. The combined extracts are dried with calcium chloride, the solvent is removed in vacuum under nitrogen, and the residue is fractionated under vacuum yield 5.1 g (23%) b.p. 112-11571-5 torr. 

When organic dihalides with five atoms between the two halogen atoms were reacted with disodium telluride, prepared by the Rongalite method, the corresponding telluranes were formed2-6. 

The following compounds were similarly prepared from sodium telluride obtained by the Rongalite method ... 

Diaryl Tellurium (Rongalite Method)2,3 A mixture of 128 mg (1.0mmol) powdered tellurium, 339 mg (2.2 mmol) Rongalite, and 1 ml 5M sodium hydroxide is stirred at 60° for 2 h under an atmosphere of nitrogen. The wine-colored solution is evaporated to dryness under reduced pressure. A solution of 2.0 mmol of the aryl iodide in 3 ml dry dimethylformamide is added to the yellow residue. The mixture is stirred at 60° for 10 h. The reaction is quenched with 10 m/ of a 10% aqueous solution of ammonium sulfate and then extracted with 10 m/ diethyl ether. The organic phase is separated, washed with waLer, dried with anhydrous sodium sulfate, and filtered. The solvent is evaporated from the filtrate. The residue is purified by chromatography on silica gel with hexane as the mobile phase. 

Diaryl Tellurium3 (Sodinm Hydride Method) A mixture of 128 mg (1.0 mmol) tellurium, 53 mg (2.2 mmol) sodium hydride (60% suspension in oil washed thoroughly with dry hexane to remove the mineral oil), and 3 ml dry dimethylformamide is heated at 140° for 1 h. The initial deep red color of the mixture faded to pale-yellow within 0,5 h. The yellow mixture is cooled to room temperature and a solution of 2.0 mmol of the aryl iodide in 3 ml dry dimethylformamide is added. The mixture is heated to 130° and kept at 130" for 24 h. The mixture is cooled to 20° and worked up as described for the preparation by the Rongalite method. 

Dihydro-l//-2-benzotelliirin (Rongalite Method) 34 g (0.17 mol) of sodium formaldehyde sulfoxylate, 26 g (0.65 mol) of sodium hydroxide, and 100 ml of water are placed in a flask fitted with a stirrer, a reflux condenser, and a nitrogen inlet tube. The flask is flushed with nitrogen, 15 g (0.12 mol) of fine tellurium powder is added, and the mixture is stirred and heated on a water bath for 30 min. 100 ml of ethanol and a solution of 25 g(0.09 mol) of 2-(2 -bromoethyl)benzyl bromide dissolved in 150 m/ofhot ethanol are added. The mixture is stirred and heated under reflux for 2 h, the ethanol is distilled off, and the residue is ground, then extracted with a mixture of 300 ml of water and 300 ml of diethyl ether. The diethyl ether layer is separated, washed with water, dried with anhydrous sodium sulfate, filtered, and fractionally distilled yield 8.5 g b.p. 116-126°/0.3 torr. The residue from the extraction is boiled with 50 ml of ethanol, the mixture is filtered hot, and the filtrate allowed to cool. The erystals are collected (3.8 g) and the combined product fractions are recrystallized from methanol whereby the methanol solution is cooled in dry ice yield 12.3 g (54%) m.p. 64°. 

Disodium telluride condensed with aryl iodides in dimethylformamide on prolonged heating to give diaryl tellurium products in good yields Sodium telluride prepared by the Rongalite method gave better yields than sodium telluride obtained from tellurium and sodium in liquid ammonia or in aprotic solvents, or from tellurium and sodium hydride in hot dimethylformamide -. ... 

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