Tellurium Tetrahalides

In contras t with dially lamines and their sulfonyl derivatives, IV-acy Idially lamines react with tellurium tetrahalides to give zwitterionic oxazolines 29 containing five-coordinated tellurium (85T1607). Molecular and crystal structures of one of this type of compound (29, R = Me, X = Cl) were studied by X-rays (85T1607). 

N-Bridged tellurium-containing heterocycles are exemplified by derivatives of l,4-tellurazine[2,3-g/i]carbazole 107 and heterocycle 108. One-pot reaction of A-propargylcarbazole with tellurium tetrahalides under conditions of the two-phase tellurohalogenation (Section n,B,l) leads to halogenomethylene derivatives 107 (90KGS126). The reaction proceeds as the spontaneous electrophilic cycliza-tion of initially formed tellurium trihalides 109. 

By addition of tellurium tetrahalides and aryltellurium trihalides to acetylenes... 

Tellurium tetrachloride 16 is the most commonly used tellurium tetrahalide. It is a very hygroscopic white solid, which decomposes immediately upon contact with metallic spatulas. Thus, porcelain spatulas must be used to manipulate this reagent. It reacts immediately with air moisture. When manipulated in contact with air, the operation must be performed as fast as possible. 

Tellurium tetrachloride and tellurium tetrabromide were converted to tellurium dithiocarboxylate halides in reactions with two or fewer molar equivalents of dithiocarboxylic acids1,2 or their piperidinium salts1. Reactions with a 3 1 molar ratio of the reagents (dithiocarboxylate/tellurium tetrahalide) were not carried out. 

The free orthotellurous acid is unknown. However, orthotellurous halides (tellurium tetrahalides), the mixed anhydrides derived from orthotellurous acid and hydrogen halides, are well known. 

Tellurium derivatives of a purely inorganic nature, such as tellurium tetrahalides, that form coordination compounds with organic ligands, such as amines, are not included in this chapter. 

The product was isolated as described for the reactions using tellurium tetrahalides as starting materials. 

Tellurium tetrakis[fluoroalkoxides] reacted with tellurium tetrahalides in benzene or tetrahydrofuran to yield fluoroalkoxy tellurium halides with one, two, or three flu-oroalkoxy groups in the molecule depending on the molar ratio of the reagents2. 

Tellurium tetrahalides and sodium dialkyldithiocarbamates (1 2 molar ratio) reacted in dioxane to form tellurium bis[dithiocarbamate] dihalides3,4. 

The reactions between Grignard reagents and tellurium dihalides frequently reported in the older literature (Vol. IX, p. 1051) produced mixtures of diaryl tellurium products and other organic tellurium compounds that were difficult to separate. Tellurium dihalides are rather unstable compounds with a strong tendency to disproportionate to tellurium and tellurium tetrahalides. The Grignard reagents, which had to be used in excess of the stoichiometri-cally required amounts, then reacted with the tellurium (p. 172) and the tellurium tetrahalide and probably not with the tellurium dihalide. 

Hexadiene and tellurium tetrahalides under similar conditions yielded 2,5-bis[halomethyl]-tetrahydrotellurophene 1,1-dihalides1 2. 

Tellurium tetrachloride and tetraaryl tin compounds reacted under similar conditions to give diphenyl tellurium dichloride (75% yield)2,3 and bis[4-methylphenyl tellurium dichloride (86% yield)4. Tellurium tetraiodide and tetraphenyl tin reacted to give diphenyl tellurium diiodide (m.p. 236°) in only 20% yield1. Tetraethyl tin and tellurium tetrahalides produced reaction mixtures from which the diethyl tellurium dihalides could not be isolated1. 

Triphenyl telluronium halides reacted with tellurium tetrahalides or phenyl tellurium trihalides to produce telluronium salts with tellurium in the cation as well as in the anion8. 

During the search for homogeneous systems in which the tetravalent perhalotellurium compounds would undergo addition to an alkene, trimethylchlorosilane, acetyl chloride, or acetyl bromide were found to be a convenient source of halogens for the conversion of tellurium dioxide to a tellurium tetrahalide88. Addition of twice the stoichiometrically required amount of cyclohexene to a solution of tellurium tetrahalide, thus generated in either acetic acid, dichloromethane or ethanol-free chloroform leads to the formation of (fra i-2-halocyclo-hexyl)tellurium trihalides in ca. 70% yield. When dry methanol is used as solvent, trans-2-... 

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