Diorgano Tellurium Dihalides

Organo magnesium halides and organo lithium compounds are readily accessible alkylation and arylation reagents. However, they have little practical importance for the preparation of diorgano tellurium derivatives. Tellurium tetrachloride cannot be alkylated or arylated stepwise to give, for instance, diorgano tellurium dihalides, which could... 

Diorgano tellurium dihalides are often the primary products of reactions producing compounds with two tellurium-carbon bonds. Such reactions arc the condensation of tellurium tetrachloride with aromatic compounds (p. 527), the addition of tellurium tetrachloride or organo tellurium trichlorides to carbon-carbon multiple bonds (p. 530, 544), and the alkylation or arylation of organo tellurium trihalides (p. 549). The symmetrical and unsymmetrical diorgano tellurium dihalides are convenient starting materials for the preparation of diorgano tellurium derivatives. 

Reaction of Diorgano Tellurium Dihalides with Sodium Sulfide General Procedure A 15-fold molar excess of sodium sulfide nonahydrate is mixed with the diorgano tellurium di halide and the mixture is heated at 90-95° on a boiling water bath. When the mixture has become liquid, it is stirred for an additional 10 min. and then cooled. Water is added to dissolve the sulfide and the mixture is filtered to collect the solid diorgano tellurium product. Liquid diorgano tellurium products are extracted into petroleum ether. Products are purified by recrystallization or distillation. 

Reductions of diorgano tellurium dihalides with hydrazine or hydrazine hydrate are carried out in ethanol. Diaryl, alkyl aryl, and dialkyl tellurium dihalides have been reduced in this manner. The isolation of the product is simple because hydrazine is converted to gaseous nitrogen. 

To Diorgano Tellurium Dihalides/Pseudo halides/ Carboxylates... 

Interhalogen compounds produce diorgano tellurium dihalides with two different halogen/pseudohalogen atoms bonded to tellurium15. 

Organic compounds of mercury, tin, and lead do not suffer from these shortcomings and convert tellurium tetrachloride and tetrabromide to diorgano tellurium dihalides in excellent yields. 

Because a number of these organometallic compounds are commercially available, they are convenient starting materials for the preparation of certain aliphatic and aromatic diorgano tellurium dihalides. Tetraorgano tin and lead compounds transfer only two of their four organic groups to tellurium. Experiments with dialkyl-diaryl compounds showed that only the aryl groups are transferred. 

Diorgano tellurium compounds are easily oxidized by elemental halogens to diorgano tellurium dihalides. Generally, the reactions are carried out with solutions of the reagents in inert organic solvents such as diethyl ether, methanol, acetonitrile, dichloromethane, chloroform, carbon tetrachloride, fluorotrichloromethane, benzene, or toluene. Often, the diorgano tellurium dihalides precipitate quantitatively from the reaction mixture. Soluble products are isolated by evaporation of the solvent or by addition of petroleum ether or hexane. 

Diorgano tellurium compounds that contain a carbon-carbon double or triple bond in the molecule react with equimolar amounts of bromine or iodine to form the diorgano tellurium dihalides. Under these conditions, the halogens do not attack the carbon-carbon multiple bonds. The following diorgano tellurium dihalides with olefinic or acetylenic organic groups were obtained in this manner ... 

Diorgano tellurium compounds can be easily converted to diorgano tellurium dihalides in reactions with sulfuryl chloride, bromide, and iodide. Carbon tetrachloride, dichlorometh-ane, diethyl ether, petroleum ether, or benzene have been used as reaction media. Chlorinations with sulfuryl chloride, a liquid reagent, avoid the use of gaseous chlorine. Required amounts of sulfuryl chloride can be more easily measured than those of chlorine. Sulfur dioxide formed during the reaction escapes the reaction mixture as a gas, thus facilitating the isolation of the product. For these reasons, sulfuryl chloride has been frequently used, whereas sulfuryl bromide and iodide5-6 have been only infrequently employed. 

Diorgano tellurium dihalides were prepared in this manner from dialkyl, alkyl aryl, and diaryl tellurium compounds, and from tellurium heterocycles. However, 1-oxo-1,3-dihydro-2-benzotellurophene experienced ring cleavage when reacted with sulfuryl chloride7. 

The diorgano tellurium oxides or dihydroxides need not be isolated. Treatment of diorgano tellurium dihalides with silver oxide2,3 or ammonia and silver nitrate4 forms solutions of diorgano tellurium dihydroxides, which can be immediately reacted with hydrohalic acids. 

Diorgano tellurium dihalides, when refluxed with silver fluoride in toluene, tetrahydro-furan, or acetone, precipitate silver halides. The diorgano tellurium difluorides crystallize upon cooling the filtrate of the reaction mixture or evaporating the filtrate under vacuum. 

Diorgano tellurium dihalides form complexes with iodine and interhalogen compounds organic compounds with N, P, O, S, and Se donor atoms boron, aluminum, and gallium trihalides antimony pentachloride and mercury(II) halides. 

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