Telluride, dialkyl

Diorganyl tellurides have low molecular mass and are colourless or yellowish liquids with an unpleasant and penetrating odour. Dimethyl teUuride is a metabolite of tellurium and tellurium compounds in a variety of living organisms, including humans. Higher dialkyl tellurides and most diaryl tellurides are solids with low melting points (diphenyl telluride is a liquid). 

Because of the above-mentioned organoleptic properties, it is recommended that contact between dialkyl tellurides and the skin is avoided, and that, in general, all work involving diorganyl tellurides is performed under a well-ventilated hood. 

Dialkyl tellurides (generalprocedure) Elemental Te is added in 0.5 g portions to a well-stirred solution of Na in liquid NHj until the solution decolourizes, forming a colourless suspension (2 g-atom Na/1 g-atom Te). The quantities of the materials are chosen to give a suspension of -0.7 M. The alkylating agent is added dropwise in 10% excess to the suspension of NUjTe. The reaction mixture is stirred until the NHj evaporates. H2O is then added, the mixture extracted with ether and the ethereal solution worked up in the usual manner. 

Dialkyl tellurides (general procedure).Te powder (3.58 g, 28 mmol), Na chips (1.29 g, 56 mmol), and naphthalene (0.72 g, 5.6 mmol) in THF (25 mL) are refluxed under N2 and stirred for 3 h. The heterogeneous white mixture is cooled at 0°C and the alkyl halide (56 mmol) is added slowly, stirring for 30 min. After 30 min of additional stirring, the mixture is filtered, the solution evaporated and the residue distilled under vacuum, giving the telluride. 

Dialkyl tellurides (general procedure) A mixture of TUDO (0.2 g, 2 mmol), NaOH (0.112 g, 2.6 mmol), Te powder (0.128 g, 1 mmol) in H2O (0.75 mL) and THF (0.75 ml) is refluxed for 1 h. The alkyl halide (2 mmol) and (cetyl trimethyl ammonium bromide) CTBA (0.004 g, 1.1 X 10 mmol) in THF (0.5 mL) are added to the pale pink solution. After 1 h of additional reflux the mixture is worked up in the usual manner and the residue purified by column chromatography on Si02 (elution with petroleum ether 40-60°C). 

Dialkyl tellurides (general procedure) Bis(triphenylstannyl) telluride (1 equiv), alkyl halide (2 equiv), excess CsF (4 equiv) and the solvent (MeCN or MeCN/THF) are mixed, kept nnder N2 and monitored by thin layer chromatography (TLC) (or NMR). Usual work-up of the mixture yields the telluride. 

In the presence of alkyl halides under pressurized acetylene, alkylvinyl tellurides in medium to good yields are obtained along with variable amounts of divinyl and dialkyl tellurides. ... 

Similar reactions were also performed with alkylphenyl and dialkyl tellurides. The following scheme illustrates a cycUzation process probably proceeding via a radical intermediate. 

TetralkylteUnriiims, prepared in situ by the reaction of tellurium tetrachloride with 4 equiv of alkyllithiums, react with arylacetylenes to afford dialkyl tellurides A, alkylation products B, an alkene C and minor amounts of a vinyl telluride D. ... 

Organic tellurides are known and clearly show the tendency of tellurium to pass from the bivalent condition to one of higher valency 2 thus the dialkyl tellurides act in an unsaturated manner and readily form dihalides, oxides and hydroxides, for example, (C,H5)2TeCl2,... 

Considerably less work has been done on the aliphatic derivatives of tellurium than on those of selenium, and whereas the latter element yields the types RSeH, R2Se and RSeR, only the type R2Te is at present known with certainty in the case of tellurium. The methods of preparation used for the dialkyl tellurides are as follows ... 

The dialkyl tellurides are heavy oils, which tend to decompose on keeping. Combination takes place slowly with water, probably forming the hydroxides, R2Te(OH)2. Oxidation by hydrogen peroxide gives the oxides R2TeO and finally tellurones, R2Te02. 

Radical accumulators whose presence might facilitate addition to / -mono and / ,/ -disubstituted olefins were conceived. It seemed to us that alkylaryl or dialkyl tellurides should react with alkyl radicals and give an intermediate radical of type R1R2R8Te (an expanded valence shell) which might have a relatively longer life on the radical time scale. A secondary objective would be the exchange of one radical against another. In this way, the special nucleophilic properties of the aryl telluride anion for example, could be exploited to make complex natural product derived radicals. 

The diaryl or aryl alkyl tellurides are dense yellow oils or crystalline solids, which are easier to handle than the dialkyl tellurides of similar molecular weight. Some of the diaryl derivatives are almost odorless solids. The same comments are valid for the diorganoditellurides 4, which are dark red oils (aliphatic derivatives) and dark red solids (aromatic derivatives). It is recommended that solutions of tellurides or ditellurides should not be kept in contact with air, since an amorphous white solid will form after some time. For some compounds, this reaction with oxygen is very fast. Aliphatic derivatives are more air sensitive than the aromatic ones. In view of this fact, it is recommended to bubble nitrogen into the solutions while a column or thin-layer chromatographic separation is performed. Evaporation of the solvent, however, minimizes the air oxidation. Pure liquids or solids can be handled in air with no need for special precautions, but prolonged exposure to air and to ambient light should be avoided. 

Alkali tellurides 13 and 14, or ditellurides 15, are potent nucleophiles and react rapidly with alkyl halides. Table 1 presents some representative examples of such reactions leading to dialkyl tellurides 3 and dialkyl ditellurides 4. Alkali organotellurolates 2 are also potent nucleophiles and are used to prepare symmetrical and unsymmetrical tellurides (Table 2). 

LTAl oxidizes diaiyl telhirides to diaiylteUurium diacetates. whUe the treatment of diaryl, divinyl, alkyl aiyl and dialkyl tellurides widi Pd(OAc)2 or Li2PdQ4 results in a new carbon-carbon bond bang formed (equations 48 and 49). 

A combination of titanium(IV) chloride and dialkyl telluride in relatively inert solvent systems reduces nitroarenes to arylamines in moderate yields." Presumably, titanium(IV) chloride is reduced to a low valent titanium species which subsequently reacts with aromatic nitro compounds to afford the corresponding amines (equation 18). 

The diaryl telluride, alkyl aryl telluride, and dialkyl telluride carrying sulfopropyl groups were prepared and were found to be the most efficient tellurium based inhibitors of thioredoxin reductase ever tested. The results clearly showed that of the four cyclic aryl alkyl chalcogenides 162-165, all primitive analogues of vitamin E, only the tellurium compound, 165, showed interesting inhibition characteristics. 

In addition to the selective synthesis of selenides and diselenides, symmetrical dialkyl tellurides [5a, 47-49, 50a, 58] and ditellurides [48a, 51a, c, 59] can be prepared with high selectivity by alkylation of Na2Te and Na2Te2, respectively, with alkyl halides (Scheme 15.20). 

Sodium telluride and ditelluride are readily generated in situ from Te by reduction with thiourea dioxide, and subsequent treatment with alkyl halide provides the corresponding dialkyl tellurides and ditellurides. E Thiourea dioxide and NaOH in 1 1 water/THF added to Te under N2, the mixture refluxed for 1 h, n-octyl halide and a little cetyltrimethylammonium bromide in THF added, and refluxing continued for 1 h - dioctyl telluride. Y 85%. The method is cheap, simple and does not require very dry conditions. F.e. and sym. ditellurides s. J.T.B. Ferreira et al., Synth. Commun. 19, 239-44 (1989) prepn. of Na2Te from ultra-pure Te-ingots/Na-naphthalenide, or from Te/Na and a little naphthalene, s. K.T. Higa, D.C. Harris, Organometallics 8, 1674-8 (1989). 

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