Tellurium dibromides

Tellurium dibromide, TeBr2, m.p. 2lO C, b.p. 339 C. Unstable compound formed Te plus TeBr4 in Et20. 

Tellurium Dibromide. Tellurium dibromide [7789-54-0] TeBr2, must be prepared very carefully, because it is unstable and has a strong tendency to disproportionate to TeBr and Te. 

Type 5 tellurenyl bromides are not easily accessible. They were prepared by refluxing an acetic acid solution of tellurium dibromides 6 in the presence of catalytic amounts of HBr [96ZOK1434 97JOM(536-537)233]. The reaction is not easily reproducible, affording the tellurenyl bromides in rather low yields. 

This method is similar to that employed in the synthesis of isoselenazoles (73JHC267). However, owing to the thermal stability of the tellurium dibromides 6, one can perform the reaction at room temperature, whereas with selenium dibromides it must be carried out at -70°C. 

Dibenzo[d,g][l,5]telluroazocines 65 are the only representatives of Te, N-containing eight-membered heterocycles known thus far. Treatment of bis(2-bromomethylphenyl)tellurium dibromide 66 with methylamine followed by reduction of the reaction mixture with sodium sulfide gives, instead of the expected... 

A -methyl-5//,7//-dibenzo[d,.g][l,5]telluroazocine 65, its thiooxide 67a (X=S, R= Me) (95JA6388). The same type of reaction with benzylamine and sodium selenide gives A-benzyl-5//,7//-dibenzo[d,g][l,5]telluroazocine selenoxide 67b (X = Se, R = CH2Ph). Reaction of the tellurium dibromide 66 with sodium sulfide carried out in the absence of the primary amines affords the eight-member Te,S-containing heterocycle 5//,7//-dibenzo[d,g][l,5]telluroazocine (92CL151). 

Tellurium-containing donors, synthesis and manufacture of, 22 212 Tellurium-copper alloys, 24 425-426 Tellurium crystals, 24 405-406 Tellurium decafluoride, 24 419 Tellurium dibromide, 24 420 Tellurium dichloride, 24 419-420 Tellurium diethyldithiocarbamate, 24 411 Tellurium dimethylthiocarbamate, 24 428 Tellurium dioxide, 24 407-408, 409, 411, 420, 428... 

Tellurium dibromide (TeBr ) forms blackish-green needles that are very hygroscopic (readily absorbs water). It is toxic when inhaled. 

The starting telluroxides (see Section 3.1) are prepared by hydrolysis of the corresponding tellurium dibromides (method a) or by direct oxidation of the tellurides (MCPBA is the more appropriate oxidizing agenH) (method b). By the first method the telluroxides are obtained as hydrates and normally higher elimination yields are achieved. 

Method a + c. The tellurium dibromide (1.0 mmol) in THF (20 mL) is treated with 0.5 N NaOH (10 mL) at room temperature with stirring, and the resnlting solntion is stirred for 1 h, the colour of the solution turning to orange. The mixtnre is dilnted with brine and extracted with ether. The extracts are dried (MgS04), evaporated nnder vacnnm and the residue purified from diphenyl ditelluride by Si02 chromatography (elntion with hexane). The pure olefin is isolated by distillation of the residne. 

The group VIB cyanides, thiocyanates and selenocyanates and their complexes with species such as thiourea have been described.1,45 For example, the tellurium dithiocyanate complex has been prepared45 by treatment of tellurium dichloride or tellurium dibromide with ammonium thiocyanate. It seems that little information exists on the preparation of tellurocyanates and there is a sparsity of data on polonium derivatives. Indeed, the only known cyanide of polonium is probably a salt of the quadrivalent element.1... 

The dichloride reacts with magnesium phenyl bromide, CeHs.MgBr, in ether solution, with formation of diphenyl telluride, (C6H5)2Te. Tellurium dibromide and di-iodide give a similar result.8 In ether solution the dichloride absorbs bromine and iodine, but the products, presumably the chlorobromide and chloro-iodide, respectively, have not been isolated.9... 

Tellurium Dibromide, TeBr2.—Just as the tetrachloride can be reduced to the dichloride, so can tellurium tetrabromide be made to yield the dibromide by treatment in dry ether solution in the dark with finely divided tellurium. The solution so obtained is chocolate-brown in colour and is decomposed by water 8... 

Dimethyl tellurium dibromide, (CH3)2TeBr2, is formed when the preceding di-iodide is treated with hvdrobromic acid. Another method consists in dissolving the di-iodide in ammonium hydroxide, precipitating the iodine with ammoniacal silver nitrate, and treating the dimethyl tellurium dinitrate with hvdrobromic acid. The reaction is very complicated, but may be summarised as follows ... 

By treating aryl magnesium bromides in ether solution with tellurium dibromide (in the case of diphenyl telluride the by-products consist of diphenyl ditelluride, diphenyl and tellurium). 

Only one mixed telluride, RTeR, is known, namely, phenyl-p-tolyl telluride, and this is prepared by the interaction of magnesium phenyl bromide and di-p-tolyl tellurium dibromide. 

When the preparations are effected by use of the Grignard reagent it is customary to transform the crude diaryl telluride into the diaryl tellurium dibromide, then reduce the latter to obtain the pure diaryl telluride. 

Diphenyl tellurium dibromide, (C6H5)2TeBr2, occurs when diphenyl telluride reacts with bromine,3 or when the bromine is replaced by hydrobromic acid and the process conducted in the manner described for the corresponding dichloride.4 The dibromide may be crystallised from chloroform, melts at 203 5° C., and when heated to 280° C. the bromine still remains attached to the tellurium atom. It forms crystals belonging to the tetragonal system and a second modification which is triclinic and gives the following values 5... 

This forms compact prisms, M.pt. 223° to 224° C., soluble in alcohol, chloroform or water, reduction by sulphurous acid giving the telluride. Di-p-chlorodiphenyl tellurium dibromide,1... 

Di-o-tolyl tellurium dibromide,1 (CH3.C6H4)2TeBr2, obtained in the usual way, dissolves in chloroform, benzene or toluene, but is sparingly soluble in alcohols or cold ligroin, more soluble in hot ligroin. 

Di-m-tolyl tellurium dibromide, (CH3.C6H4)2TeBr2, forms pale yellow needles, sintering at 163° C. and melting at 165° to 166° C. Its solubility is similar to that of the preceding cldoride. 

Di-p-anisyl tellurium dibromide, (CH3O.C6H4)2TeBr2, is insoluble in methyl alcohol, otherwise it has a similar solubility to the foregoing compound. For purposes of analysis the dibromide is dried at 135° C. 

Di-o-phenetyl tellurium dibromide, (C2H5O.C6H4)2TcBr2, forms small pale yellow needles when an ether solution of di-o-phenetyl telluride is treated with bromine. It crystallises as four-sided columns, sintering at 180° C., melting at 183° to 184° C., and having a similar solubility to the dichloride. 

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