Tellurides nitro compounds

Hydrogen telluride and sodium telluride in a protic solvent easily reduce nitroarenes to anilines. In contrast, sodium telluride in an aprotic solvent exhibits a milder reducing capacity and reduces the nitro compounds only to azo compounds. ... 

The reducing power of sodium hydrogen telluride towards nitro compounds is dependent on their structure. Unhindered nitrobenzenes are reduced to azoxybenzenes whereas sterically hindered nitrobenzenes are reduced to anilines by simple stirring with 5 mol equiv of the reagent at room temperature for 1 h. 

The reaction has been suggested as involving a one-electron transfer from sodium hydrogen telluride to the nitro compound followed by the detachment of a nitrite anion from the resulting radical anion. 

The reduction of nitro compounds 38 by tellurium reagents depends on the structure of the substrate and on the solvent used. For example, phenyl tellurol90 and sodium telluride95 reduce nitroarenes to anilines 39 in protic solvents. When an aprotic solvent is used, sodium telluride converts the nitroarenes 38 into the respective azo compounds 40 (Scheme 20).25... 

When aromatic nitro compounds were reduced in dimethylformamide with disodium telluride to aza derivatives, bis[dimethylaminocarbonyl ditellurium was obtained in 5 to 15% yield as a by-product. The formation of this ditellurium compound was attributed to the capture of a telluride anion by a dimethylcarbamoyl radical and subsequent oxidation of the tellurocarbamoyl species5. 

The ditellurium compounds, in which a Te —Te group joins two carbonyl groups, can be considered to be the tellurium analogs of peroxy compounds derived from carbonic acid or benzoic acids (e.g. benzoyl peroxides). Only a few of these compounds are known. During the reduction of aromatic nitro compounds with disodium telluride in dimethylfor-mamide, bis[dimethylaminocarbonyl] ditellurium was formed as a by-product in yields from 5 to 15%. The formation of this compound was attributed to the capture of the dimethylaminocarbonyl radical by the telluride anion and subsequent oxidation of the tellurocarbamoyl species4. 

Tellurides (H2Te, NaTeH, PhTeH and Na2Te) are inexpensive and effective agents for reducing aromatic nitro compounds to hydroxylamines. Catalytic quantities of tellurium, in the presence of sodium borohydride, reduce p-substituted nitrobenzenes to N-arylhydroxylamines (equation 9). Mild reaction conditions, absence of side reactions and experimental simplicity are the main features of this reduction sequence. 

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 reaction of 2-lithio derivative with trans-chlorovinyl iodoso-dichloride and sodium nitrite in dimethylformamide gives with furan, thiophene, and selenophene the corresponding 2-iodo and 2-nitro derivatives. The same reaction, when applied to tellurophene, gives 2-iodotellurophene (16) and the unforeseen compound di-2-tellurienyl telluride (17) the expected 2-nitrotellurophene was not obtained.25 Other attempts to prepare 2-nitrotellurophene were unsuccessful. 

---