Tellurium dioxide with thiourea

Alkyl Aryl Telluriums (Reduction with Thiourea Dioxide) To a solution of 1.0 mmol diaryl ditellurium in 7.5 ml tetrahydrofuran are added 0.108 g (1.0 mmol) thiourea dioxide, 30 mg 2HT (phase transfer reagent), and 2.0 mmol of the alkyl bromide. To this mixture are added 7.5 ml of a 50% aqueous solution of sodium hydroxide. The mixture is stirred for several hours at 20°. The organic phase is separated. The aqueous phase is extraeted three times with 20 ml ethyl acetate. The organic phase and the ethyl aeetate extracts are combined and dried with anhydrous magnesium sulfate. The mixture is filtered and the solvents evaporated from the filtrate. The residue is chromatographed on silica gel with ethyl acetate as mobile phase. 

During work on nucleophilic substitution at divalent sulfur,64 65 a series of tellurium derivatives with sulfur-containing ligands were prepared in a straightforward manner by addition of a warm aqueous solution of, for example, thiourea to tellurium dioxide dissolved in warm hydrochloric or hydrobromic acid, and which involved the reduction of tellurium(IV) to tellurium(II). 

Tellurium dioxide complexes with thiourea, 305 Tellurium dithiocyanate complexes, 303 Tellurium hexafluoride complexes, 303 with amines, 304 Tellurium sulfate complexes, 303 Tellurium tetrabromide complexes, 302 Tellurium tetrachloride complexes with acetamide, 304 with amines, 304 with pyridine N-oxide, 304 Tellurium tetrafluoride complexes with amines, 304 with dioxane, 304 Tellurotungstates, 1042 Tempera ture-jump studies molybdenum(VI) complexes, 1259 Terbium complexes p diketones, 1081... 

Dialkyl Ditellurium (Thiourea Dioxide Method)2 A mixture of 128 mg (1.0 mmol) of elemental tellurium, 4 mg (0.01 mmol) of cetyltrimethylammonium bromide, 0.75 ml tetrahydrofuran, and 0.5 ml dimethyl sulfoxide is heated at 80° for 15 min under an atmosphere of deoxygenated nitrogen. To this mixture is added 100 mg (1.0 mmol) of thiourea dioxide, 112 mg (2.6 mmol) sodium hydroxide, and 0.75 ml water. The resulting mixture is refluxed for 1 h. The purple solution is then cooled to 15°. Alkyl halide (2.0 mmol) is added and the mixture is stirred at 20° for 1 h. After normal work-up, the dark-red oils were passed through a pad of Celite with dichloromethane as the mobile phase. 

Bis[2-methylphenyl] Ditellurium [Thiourea Dioxide Method]4 A mixture of 0.65 g (2.0 mmol) 2-methylphenyl tellurium trichloride and 5 ml of 2 M aqueous sodium hydroxide solution is vigorously stirred at 20° for 15 min. To this mixture are added 0.43 g (4.0 mmol) thiourea dioxide and 5 ml petroleum ether (30-60°). The mixture is stirred at 20° for 15 min. The phases are separated. The organic phase is dried with anhydrous magnesium sulfate, filtered, and the solvent evaporated from the filtrate. The product was isolated in 76% yield. 

Tellurium is reduced by thiourea dioxide in alkaline medium to the telluride dianion that is alkylated with alkyl halides2. 

Bis[6-(tetrahydropyran-2-yl-oxy)-l-hexyl] Tellurium2 (Thiourea Dioxide Method) Under an atmosphere of nitrogen 200 mg (2 mmol) thiourea dioxide, 112 mg (2.6 mmol) sodium hydroxide, 0.75 mt water, 0.75 ml tetrahydrofuran and 128 mg (1 mmol) tellurium are mixed. The mixture is refluxed for 1 h. Then 2 mmol of the alkyl halide and 4 mg cetyltrimethylammonium bromide are added to the pale-pink solution.The mixture is refluxed for 1 h and then worked up in the usual way. The residue is purified by column chromatography on silica gel with petroleum ether as the mobile phase. The product is isolated in 72% yield. Similarly prepared were2 ... 

Diorgano tellurium dihalides react with reducing agents (sodium sulfide, sulfites, hydrazine, thiourea dioxide, sodium borohydride) under mild conditions to give the corresponding diorgano tellurium derivatives in high yields. 

Disodium ditelluride can be prepared from tellurium and sodium in liquid ammonia, lithium triethylborohydride in THF, sodium borohydride in ethanol or THF" lithium or sodium in ethylenediamine , sodium hydride in DMF , hydrazine hydrate in aqueous sodium hydroxide , thiourea dioxide in DMF/THF/aqueous sodium hydroxide, and sodium formaldehyde sulfoxylate (Rongalite C) " in aqueous sodium hydroxide. The reducing agents compatible with organic solvents provide reaction media in which long-chain aliphatic halides are soluble. Such halides are insoluble in liquid ammonia, or aqueous media. 

The reaction of disodium telluride with alkyl halides is the oldest known method for the preparation of dialkyl telluriums. The required solutions of disodium telluride can be prepared from tellurium and sodium formaldehyde sulfoxylate (Rongalite C) in aqueous sodium hydroxide (Vol. IX, p. 1048), from tellurium and sodium in liquid ammonia " dimethylformamide or tetrahydrofuran in the presence of naphthalene , from tellurium and hydrazine hydrate/sodium hydroxide in water or dimethylformamide °, from tellurium and thiourea dioxide in aqueous tetrahydrofuranor from tellurium and sodium borohydride in methanol, ethanol, tetrahydrofuran, or aqueous sodium hydroxide ... 

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