Tellurinic Acid

Only a few tellurinic acids have been prepared and characterized. The aliphatic tellurinic acids reported in the older literature are not pure compounds but mixtures of tellurinic acid and diorganyl telluroxide. The aromatic tellurinic acids appear to be polymeric. They are insoluble in common organic solvents and have rather high melting or decomposition temperatures. 

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Kinetic studies on racemization, oxygen exchange reaction using H2lsO, and theoretical studies clarified the mechanism for racemization of optically active chalcogenic acids.34,37 The mechanism of racemization of tellurinic acids is different from that of the corresponding seleninic acids. In fact, the mechanism for racemization of optically active tellurinic acids was found to involve an... 

Diorgano diselenides have been used extensively as precursors to seleninic acids in the presence of hydrogen peroxide.The catalytic activity of preformed seleninic acids and seleninic acids generated in situ are identical. Diorgano ditellurides have also been used as catalysts in thiolperoxidase-like reactions for the oxidation of thiols with various peroxides. However, tellurinic acids are not thought to be involved even though RTe(=0)SPh types of structures are proposed as intermediates. 

Epoxidation of olefins catalysed by polystyrene-supported tellurinic acid... 

The catalytic activity is dependent on the polymeric structure of the reagent, no epoxidation being observed with free tellurinic acids. 

Electrophilic addition reactions of tetravalent tellurium compounds have been reviewed.64 2-Naph-thyltellurium trichloride (ArTeCb) adds to alkenes in an anti stereospecific manner (equation 11), whereas tellurium tetrachloride gives mixtures of 2 1 adducts with both syn and anti addition.72 A one-pot alkene inversion procedure has been developed, based upon TeCU addition to alkenes followed by treatment of the (3-chloroalkyltellurium trichloride adduct with aqueous Na2S (Scheme 37).73 Tellurium compounds such as tellurinyl acetates, ArTe(0)0Ac, prepared in situ through reaction of tellurinic acid anhydrides with acetic acid, can be employed in oxytelluration and aminotelluration procedures (Schemes 38 and 39).74 In the oxytelluration reaction intermediate triacetates of the type RCH2Te(OAc)2Ph are reduced with hydrazine to the corresponding tellurides. 

Treatment of aryl tellurium halides with base (ethanolic potassium hydroxide6, aqueous sodium hydroxide7, triethylamine8, tris[< -propyl] phosphite8, triphenylphosphane8) leads to the formation of diaryl ditellurium compounds (p. 273). In the hydrolytically induced disproportionation reactions, aryl tellurinic acids are the other tellurium-containing products7,9. 

Oxidizing agents such as nitric acid, air, hydrogen peroxide, and lead tetraacetate convert ditellurium compounds to tellurinic acid derivatives. Diphenyl ditellurium suspended in hot dilute nitric acid formed benzenetellurinic acid nitrate5. Air oxidizes dissolved diaryl ditellurium compounds to tellurinic acid anhydrides6. Diphenyl ditellurium and lead tetraacetate in benzene solution form phenyl tellurium triacetate7,8. 

Tellurinic acids and their derivatives contain tetravalent tellurium. The following types of compounds are known ... 

Tellurinic Acids and Dcrivatcs Organo Tellurium Trihalides... 

Organo tellurium trihalides are the best known and most numerous compounds among the tellurinic acid derivatives. Most of the other derivatives are represented only by a few compounds, some of which have not been adequately characterized. Frequently, different products are claimed for similar reactions with identical starting materials. Much more work needs to be done with the various hydrolysis products of organo tellurium halides before this area of organic tellurium chemistry can be considered to be adequately explored. 

Aryl tellurium trihalides treated with water are converted to arenetellurinyl halides. The susceptibility to hydrolysis decreases from the trichlorides to the triiodides2,3. With basic aqueous solutions (sodium carbonate, sodium hydroxide) tellurinic acids or tellurinic acid anhydrides are formed2 5. 

Organo tellurium trihalides are converted by aqueous solutions of sodium hydroxide1 or sodium carbonate2 or by boiling water3 to tellurinic acids. 

Aryl tellurium trihalides were hydrolyzed with aqueous sodium hydroxide solution. The tellurinic acids were precipitated by acidification of the reaction mixture with acetic, hydrochloric1 or sulfuric acid4. 

Dialkyl tellurium compounds when exposed to air for long periods were reported to form alkanetellurinic acids. In the most cases the isolated substances were mixtures of the tellurinic acid and the dialkyl tellurium oxide3,4. 

With two moles of nitric acid per mole of tellurinic acid, 4-hydroxy-3,5-dinitrobenzenetellurinic acid was isolated in 60% yield1. 

Hydroxy-3,5-dinitrobenzenetellurinic acid nitrate was saponified to the tellurinic acid in refluxing 20% aqueous sulfuric acid1. 

When aryl tellurium trichlorides or tribromides were treated with aqueous solutions of sodium carbonate or sodium hydroxide4,5 and the resulting solutions acidified with 10% acetic acid, tellurinic acid anhydrides precipitated. 

Similarly prepared were the following tellurinic acid anhydrides ... 

Oxidation of diaryl ditellurium compounds with selenium dioxide in pyridine at 80-90° produced mixed anhydrides of tellurinic acids and selenotellurenic acids1. 

Tellurinic Acid 3,5-Dinitro-4-hydroxy-benzene- El2b, 348 (H - N02)... 

Tellurinic Acid 4-Hydroxy-benzol-E12b, 346 (TeCl3—TeO — OH)... 

Tellurinic Acid O-Trifluoracetyl-benzene- E12b, 350 (R-TeO-O-TeO-R + R-COOH)... 

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