Aromatic ditellurides

The Te2 group is a chromophore, and aliphatic and aromatic ditellurides exhibit a characteristic orange to pale or dark red colour (absorption maximum at 400 nm). 

The aromatic ditellurides RTe=TeR are intensely coloured substances, often bearing a striking resemblance to the azo-compounds, and the prime cause of the colour is the group —Te=Te—. 

The dimethoxylation of aromatic olefins can also be performed by employing a catalytic amount of ditelluride, e.g. styrene (5 mmol), (PhTe)2 (0.5 mmol), f-BuOOH (5.5 mmol added in 10 portions) and H2SO4 (2 mmol). MeOH (10 mL, reflux for 3.8 days) give 1,2-dimethoxy-l-phenylethane in a yield of 88%. ... 

Organic selenides and tellurides Ludvik and Nygard etal. [133, 134] have studied electroreduction of aromatic diselenides and ditellurides (ArEEAr) at mercury electrodes. They have found that the charge-transfer process is preceded by a spontaneous heterogeneous reaction between these compounds and mercury. 

In general, from among the protic solvents, only liquid ammonia (the first used)1 is particularly useful, and is still used more than any other solvent despite the low temperature at which reactions have to be carried out (b.p. -33 °C) and the fact that solubilities of some aromatic substrates and salts (M+Nu-) are poor. Ammonia has the added advantage of being easily purified by distillation, being an ideal system for production of solvated electrons, and has very low reactivity with basic nucleophiles and radical anions, and aryl radicals. Also, poor solubilities can sometimes be ameliorated by use of cosolvents such as THF. In addition it can be used as a solvent for the in situ reductive generation of nucleophiles such as ArSe- and ArTe- ions, e.g. the formation of PhTe- from diphenyl ditelluride (equation 16).54 55... 

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. 

Diorganyl mono- and ditellurides are the best-known classes of organic tellurium compounds comprising symmetric and unsymmetric alkyl, aryl, and alkyl-aryl tellurides. In addition to acyclic tellurides, heterocychc aliphatic telluroethers as well as aromatic tellurophene-derivatives are known (for a review, see Ref 36). 

If the diaryl ditelluride is previously converted in situ into the corresponding tellurenyl halide, both the electrophilic tellurium moieties are used. (The stable crystaUine 2-naph-thylteUurenyl iodide (see Section 3.7) reacts similarly.) The reaction is of general application, giving high yields of the expected tellurides with aromatic, aliphatic, cycloaliphatic, vinylid and acetylenic Grignard reagents, under mild conditions. 

Aromatic disulphides and diselenides adopt a conformation in which the torsion angle between the C—S—S— and —S—S—C— planes lies between 70 and 90°. Related studies of aliphatic disulphides have also been undertaken. Comparisons of S, Se, and O analogues represented by ArXMe, (At = Ph or mem-substituted phenyl) and aryl diarylmethyl sulphides have been made, in terms of their conformational behaviour. Studies of diaryl ditellurides ArTeTeAr and phenyl tellurobenzoates PhCOTeR provide dipole-moment data consistent with a non-planar C conformation and planar Z conformation,... 

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