Tellurium compounds, preparation using

The selectivity in the formation of 1,4-diacetoxy-2-butene (1,4-DAB) is considerably enhanced when tellurium compounds are used as cocatalysts. Thus a heterogeneous catalyst, prepared by impregnation of Pd(N03)2 and Te02 dissolved in HN03 over active charcoal (Pd/Te = 10), can be used for the oxidation of butadiene (by 02 in AcOH at 90 °C) to 63% trans-l,4-DAB, 25% cis-1,4-DAB and 12% 3,4-diacetoxy-l-butene. Conventional soluble catalysts such as Pd(OAc)2/Li(OAc) are much less selective in the formation of 1,4-DAB 429 The gas-phase 1,4-diacetoxylation of butadiene in the presence of Pd-Te catalysts is currently being industrially developed by Mitsubishi and BASF 430... 

Alkyl organo tellurium compounds, prepared from alkane- or arenetellurolates and alkyl halides, react with butyl lithium,. 9ec-butyl lithium, /ert.-butyl lithium, or phenyl lithium. The alkyl group bonded to the tellurium atom is cleaved from the tellurium and is present in solution as the alkyl lithium that can be used for further reactions. This tellurium-lithium exchange reaction is synthetically useful, whenever the alkyl halides cannot be converted to alkyl lithiums by other, more conventional halogen exchange reactions. The following exchange reactions were successfully carried out ... 

The chemistry of sulfur is a broad area that includes such chemicals as sulfuric acid (the compound prepared in the largest quantity) as well as unusual compounds containing nitrogen, phosphorus, and halogens. Although there is an extensive chemistry of selenium and tellurium, much of it follows logically from the chemistry of sulfur if allowance is made for the more metallic character of the heavier elements. All isotopes of polonium are radioactive, and compounds of the element are not items of commerce or great use. Therefore, the chemistry of sulfur will be presented in more detail. 

The ligand chemistry of heterocyclic tellurium compounds has been examined over several years.85 86-92 104-106 The study105 of the monomeric (6) and dimeric (7) complexes, which were obtained from the reaction of Na2PdCl4 and tellurophene and separated by their solubility differences in acetone and chloroform, is illustrative of the preparative chemistry and characterization techniques used in this area of chemistry. 

Organotellurols 1, the tellurium analogs of alcohols, constitute a class of organic tellurium compounds, which have to be prepared and used in situ due to their high succeptibility to oxidation. The participation of this class of compounds in several reactions has been proposed,5-12 but their real existence has never been demonstrated in such processes. A few tellurols exhibiting special structural features could be isolated and characterized (e.g., compound 10, Figure 2).14... 

Tellurium bis[0.0-dimethyl dithiophosphate] (m.p. 91 °) was prepared in 80% yield as described for the diethyl compound but using methanol to wash and recrystallize the compound2. 

Cholesteryloxy tellurium pentafluoride (m.p. 153°) was similarly prepared using 1,2-dimethoxyethane as the solvent. The compound was purified by column chromatography with benzene as the mobile phase4. 

Commercially available butyl lithium was frequently used to prepare aryl lithium compounds from aryl bromides. In these cases the aryl butyl tellurium compounds were the products isolated from the reaction mixtures. 

The extreme sensitivity of tellurolates to moisture and oxygen makes the isolation of these tellurium compounds difficult. Therefore, tellurolates are almost always prepared under an inert atmosphere and used in situ. 

Similarly prepared using organo triphenylstannyl tellurium compounds as starting materials were the following copper tellurolates ... 

A German patent claims the preparation of tellurium-containing propyl alkyl tellurium compounds which are useful as indicators for determining fat absorption1 ... 

Aryl tellurium halides have the capability of adding to carbon-carbon double bonds. This potentially useful method for the preparation of aryl alkyl tellurium compounds has been used to prepare 2-naphthyl 2-oxo-3,3-diphenyl-5-furylmethyl tellurium (yield 61 %)6. 

A promising method for the synthesis of unsymmctrical diorgano tellurium compounds uses carboxylic acid derivatives and diaryl ditellurium as starting materials. The carboxylic acid chloride, prepared in quantitative yield from the acid and oxalyl chloride is added slowly to a mixture of a diary] ditellurium and the sodium salt of 2-mercaptopyridine N-oxide in toluene at 35°. Under normal laboratory light the aryl tellurium radicals... 

Butyl lithium, sec-butyl lithium, tert-butyl lithium, and phenyl lithium cleave Te-phenyl and Te-alkyl bonds in tetrahydrofuran at — 78°. These reactions, in which on organic group bonded to tellurium is exchanged for the organic group associated with the organic lithium compound, are useful for the preparation of organic lithium compounds that are otherwise available only with difficulty or not at all. 

They can be used to prepare Xe(OEF5)2 compounds. The tellurium compound has been used to prepare large, weakly coordinating anions30 such as [M(OTeF5)4]2, M = Co, Ni, Cu, Zn, Pd. 

Most of the complexes have well defined melting points. They appear to be monomeric in solution . An interesting method for the preparation of thiazolidine-2-thione complexes of aryl tellurium trichlorides is the addition of the tellurium compound to a melt of the ligand kept at 110°. Complexes with 1 1, 1 2, and 1 4 stoichiometries (Te-compound ligand) were obtained after recrystallization from dry methanol. Phenyl tellurium trichloride complexes with thiourea appear to form only when an organic solvent is used as the reaction medium in aqueous media the trichloride is reduced to the monochloride that is isolated as the thiourea adduct . 

The limited solubility of long-chain alkyl halides in liquid ammonia makes it advantageous to evaporate the ammonia after the disodium telluride has formed and to dissolve the residue in an appropriate organic solvent. Ethanolic solutions of disodium telluride that had been prepared in liquid ammonia were used for the synthesis of the following heterocyclic tellurium compounds ... 

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