From Tellurium Dichlorides

Tellurium dichloride and 2,2 -dilithiobiphenyl produced dibenzotellurophene in 54% yields 

Dibenzotellurophene h A solution of 61.6 mmol of 2,2 -dilithiobiphenyl in 300 jm/ of dry diethyl ether is prepared under nitrogen and cooled to — 70°. 10.6 g (53.4 mmol) of tellurium dichloride are added and the stirred mixture is allowed slowly to warm to 20°. After 15 h the mixture is hydrolyzed, filtered, and the organic phase is separated. The ether is evaporated, the pasty residue is dissolved in petroleum ether (b.p, 40-60°), and the solution is chromatographed on a column of neutral alumina yield 8.0 g (54%) m.p. 94°. 

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The catalyst is allowed to cool under nitrogen, and 400 ml. of bis-(2-methoxyethyl) ether is added from the dropping funnel. The stopper is then temporarily removed to add 20.6 g. (0.05 mole) of bis(4-methoxyphenyl)tellurium dichloride. The mixture is refluxed for 8 hours. Altered while still hot, and the solvent evaporated under reduced pressure (10-20 mm.). The residue was recrystallized from ethanol to afford 8.5-9.8 g. (78-90%) of the product, m.p. 175-176° (Note 9). 

The checkers distilled the anisole from calcium sulfate before use. This reagent functions not only as a reactant, but also as solvent. In some similar preparations the intermediate trichloride is rather insoluble, as in the case of bis(3-methyl-4-methoxyphenyl)tellurium dichloride. The addition of co-solvents such as bis-(2-methoxyethyl) ether is beneficial. ... 

Bis[2-(2,3-dihydrobenzofuranyl)methyl]tellurium dichloride (typical procedure) Te02 (2.4 g, 15.0 mmol), 2-allylphenol (4.0 g, 30.0 mmol) and LiCl (3.0 g, 70.8 mmol) are refluxed in HOAc (50 mL) for 1.5 h. The clear solution is then filtered hot from a small amount of elemental tellurium and, upon cooling (freezing), the product crystallizes as a white solid [5.4 g (78%)]. The product is recrystallized from EtOH/CH2Cl2 (1 1) (m.p. 180-184°C). 

Synthesis of enones and cyclopropanes from bis(oxoalkyl)tellurium dichlorides... 

Stable representatives of telluroketones were not available until recently. 2,5-Dihydro-1,3,4-telluradiazole 172 can be prepared from hydrazones 171 and tellurium tetrachloride or tetrabromide in yields of 19-48 and 42-55%, respectively (Scheme 8.39) (237). Ketazines 173 were obtained as byproducts of this reaction in 32 5% yield. It was proposed that XeX4 is hrst reduced to TeX2 in the reaction medium. The latter species probably generates both the diazo compound and the telluroketone derived from hydrazone 3 and then a [3+2] cycloaddition occurs. In fact, both 172 and 173 were obtained when hydrazones 3a-c were treated with the difhcult-to-handle tellurium dichloride in the presence of triethylamine. 

When in a state of fine division, tellurium dichloride has a yellowish-green colour. On account of its miscibility with tellurium the chloride is difficult to obtain pure and the recorded melting-points range from 209° to 175° C. the boiling-point is near 324° C.3 The reddish vapour at 450° C. lias a density in keeping with the unimolecular formula TeClg.4... 

Di-o-tolyl tellurium dichloride, (CH3.C6H4)2TeCl2,is prepared in a similar manner to the corresponding phenyl compound. It is best recrystallised from absolute alcohol, separating as small monoclinic tablets. M.pt. 183° C., readily soluble in benzene, toluene or xylene, but sparingly soluble in ligroin, methyl or ethyl alcohol. 

Di-p-tolyl tellurium dichloride, (CH3.C6H4)2TeCl2,1 is obtained in a similar way to the phenyl compound. It separates from absolute alcohol as small needles or plates of the triclinic system, M.pt. 160° to 167° C., soluble in chloroform, benzene, toluene, xylene or ligroin, sparingly soluble in methyl alcohol. 

Re cry st alii sation of the foregoing green solid from absolute alcohol gives the telluridichloride as primrose-yellow crystals, almost insoluble in benzene, chloroform, carbon tetrachloride or ethyl acetate, slightly soluble in acetone and readily soluble in hot absolute alcohol. Boiling with 95 per cent, alcohol precipitates tellurium dioxide and the tellurium dichloride passes into solution, but on boiling with 90 per cent, alcohol more than 90 per cent, of unchanged dichloride is recovered. When a hot aqueous sodium carbonate solution of the dichloride is acidified with hydrochloric acid the telluronium chloride is precipitated quantitatively. 

Tellurium dibutyrylmethane trichloride (Formula III).—This is isolated when the final mother-liquors from the dichloride are concentrated and cooled to 0° C. It yields large tabular crystals, melting and blackening at 87° to 88° C. Unlike the dichloride it develops a blood-red coloration with aquo-alcoholic ferric chloride. It is decomposed by moisture, and is very soluble in chloroform. 

Tellurium dipropionylmethane (2 6-Dimethylcyclotelluro-pentanedione) (Formula II), obtained from the dichloride by bisulphite reduction, crystallises from methyl alcohol, benzene or aqueous ethyl alcohol as well-defined golden-yellow needles, M.pt. 151° C. with slight decomposition. Under diminished pressure it sublimes at 110° C. as slender needles, which slowly pass at this temperature into compact prisms. It readily dissolves in organic solvents, except light petroleum in water it is sparingly soluble, the solution giving no enolic reactions. 

Tellurium Bis[(diphenylthionophosphinimido(diphenylthiolophosphinate] 0.20 g (0.38 mmol) of lelrakis-[thiourea]tellurium dichloride dihydrate are dissolved in 20 ml of methanol, the solution is stirred, and 0.47 g (1.0 mmol) of ammonium (diphenylthionophosphinimino)diphenylthiophosphinate dissolved in 80 ml of methanol are added. The resultant yellow solid is washed with ethanol and dried yield 0.3 g (75%) m.p. 257° (dec.) (from chloroform). 

Tellurium Bis[bis(2-hydroxyethyl)dithiocarbamate] 20 ml (50 mmol) of a 20% aqueous methanol solution of bis[2-hydroxyethyl]dithiocarbamic acid, prepared from carbon disulfide and bis[hydroxyethyl]amine, are slowly added to 5.0 g (10 mmol) of tetrakis[thiourea]tellurium dichloride are suspended in 50 ml of methanol containing 1 g of thiourea. The product separates as orange needles that are collected and recrystallizcd from methanol yield 4.4 g (90%) dec. 150°. 

Bis[morpholino] tellurium dichloride was also obtained from bis[tetrafluoropropoxy] tellurium dichloride or tris[tetrafluoropropoxy] tellurium chloride and iV-trimethylsilyl-morpholine3. 

Bis[acylmethyl] tellurium dichlorides and aryl benzoylmethyl tellurium dichlorides lose the acylmethyl group under conditions generally used for the reduction of diorganyl tellurium dichlorides. However, these acylmethyl tellurium dichlorides were successfully reduced in a two-phase system consisting of dichloromethane and an aqueous solution of disodium disulfite. The acylmethyl tellurium compounds escape into the organic phase and are protected from further attack by the reducing agent1. 

Bisfbenzoylmethyl] Tellurium A solution of 1.09 g (2.3 mmol) of bis[benzoylmethyl] tellurium dichloride in 100 m/ dichloromethane is shaken vigorously in a separatory funnel for 15 min with a solution of 0.50 g (2.6 mmol) disodium disulfite in 50 ml water. The yellow organic phase is separated, washed once with water, and then dried for 10 min with anhydrous calcium chloride. The mixture is filtered and the filtrate evaporated. The residue is recrystallized from petroleum ether (40-60°) yield 53% m.p. 79°. 

Bis[4-methoxyphenyl] Tellurium2 8.3 g (0.02 mol) of bis[4-methoxyphenyl] tellurium dichloride are suspended in a mixture of 150 m/ of ethanol and 15 ml of water. The mixture is heated to reflux and 3.2 g (0.1 mol) of hydrazine are added dropwise to the refluxing suspension, vigorous evolution of nitrogen. When further addition of hydrazine does not cause evolution of nitrogen, the mixture is poured into 700 ml of water, and extracted with two 300-ml portions of diethyl ether. The combined extracts are washed with water, dried, and evaporated. The residue is recrystallized from methanol which is cooled to — 25° yield 5.2 g (77%) m.p. 57°. 

Dialkyl, alkyl aryl, and diaryl tellurium dichlorides were reduced by thiourea dioxide in a 2 molar aqueous solution of sodium hydroxide to the corresponding diorgano tellurium compounds4,5. The tellurium species actually reduced are the diorgano tellurium oxides or dihydroxides that are formed from the dichlorides in the basic medium. 

Diorgano Tellurium5 (Thiourea Dioxide Method) A mixture of 2 mmol of the diorgano tellurium dichloride and 10 ml of 2 molar aqueous sodium hydroxide solution is stirred for 15 min at 20°. Then, 0.432 g (4 mmol) thiourea dioxide and 10 m/ petroleum ether (30-60°) are added. The mixture is stirred at 20° until it becomes clear. The phases are separated. The aqueous phase is extracted three times with diethyl ether. The combined organic phases are dried with anhydrous magnesium sulfate, the dried mixture is filtered, and the solvent evaporated from the filtrate. The residue is placed on a silica-gel column. The product is eluted with petroleum ether. 

Sodium sulfide will split the benzoylmethyl group from 4-methoxyphenyl phenacyl tellurium dichloride as evidenced by the formation of bis[4-methoxyphenyl] ditellurium5. The aryl phenacyl tellurium is the intermediate in this reaction. 

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