Tellurite, sodium

Sodium teUurate [10101-25-8] Na2Te04, (53.7% Te theoretically), is made by oxidizing sodium tellurite solution with hydrogen peroxide. The reaction is exothermic. 

Cadmium acetate and sodium tellurite solutions have similarly been used to grow CdTe films by SILAR. The films were polycrystalline (hexagonal), and the grain size was on the order of 22nm (film thickness 272nm). The optical band gap was 1.41 eV.85... 

Crude tellurium dioxide is dissolved in a strong solution of caustic soda to form sodium tellurite. Electrolysis of sodium tellurite solution deposits tellurium metal on the stainless steel cathode. 

Although this procedure yields tellurium as the same compound found in the original feedstock, the copper telluride is recovered in a comparatively pure state which is readily amenable to processing to commercial elemental tellurium or tellurium dioxide. The upgraded copper telluride is leached with caustic soda and air to produce a sodium tellurite solution. The sodium tellurite solution can be used as the feed for the production of commercial grade tellurium metal or tellurium dioxide. 

If the final product desired is tellurium metal, excess free caustic soda is required in the sodium tellurite solution. The solution is electrolyzed in a cell using stainless steel anodes to produce tellurium metal (20). This technology is used at the CCR Division of Noranda Metalluigy Inc., Canada, and at Pacific Rare Metals Industries Inc., the Philippines. Typical electrolysis conditions are given in Table 2. 

Alternatively, if tellurium dioxide is the product desired, the sodium tellurite solution can be neutralized in a controlled fashion with sulfuric acid. As the pH is lowered, precipitates containing impurities such as lead and silica that form are filtered off. At pH 5.6 the solubility of tellurous acid reaches a minimum and essentially all of the tellurium precipitates (>98%). After filtration and drying, commercial tellurium dioxide is obtained. A diagram for the process of detellurizing of slimes and recovering tellurium products is shown in Figure 1. 

Metal Coatings. Tellurium chlorides, as well as tellurium dioxide in hydrochloric acid solution, impart permanent and attractive black antique finish to silverware, aluminum, and brass. Anodized aluminum is colored dark gold by tellurium electro deposition. A solution containing sodium tellurate and copper ions forms a black or blue-black coating on ferrous and nonferrous metals and alloys. Addition of sodium tellurite improves the corrosion resistance of electroplated nickel. Tellurium diethyldithiocarbamate is an additive in bright copper electroplating (see Electroplating). 

Explosives. Sodium tellurite is used as a jelling promoter in explosive compositions that can be readily poured or pumped into drillholes (91) (see Explosives and propellants, explosives). 

Tellurium in a very finely divided condition may be obtained by mixing aqueous solutions of dextrose (30 per cent.) and sodium tellurite (5 per cent.) and heating to boiling for half an hour.11... 

Sodium Tellurite, Na2Te03.5TI20 Sodium Ditellurite Sodium Tetratellurite, Na2Te40e.4H20. 

Sodium selenate can be produced by electrolytic oxidation of neutral selenite solution.1 On evaporation of the solution, crystals of selenate can be obtained together with a small amount of selenium. The addition of a small quantity of chromate to the bath prevents the cathodic deposition of selenium. F. Foerster2 had previously shown that neutral sulphites give, by electrolytic oxidation, both sulphate and dithionate. No dithion-ate analogue was found by Muller when oxidising the selenites, and in attempting to oxidise sodium tellurite a considerable amount of free tellurium was obtained. 

Aromatic, benzylic, and aliphatic thiols 135 are oxidized to the corresponding disulphides 136 by sodium tellurite under phase transfer conditions200 (Scheme 73). 

Sodium tellurite, prepared by dissolution of tellurium dioxide in aqueous sodium hydroxide, reacted with carboxymethanethiol1 and with 1-carboxy-l-ethanethiol2 to form bis[carboxyalkylthio] tellurium compounds. The reactions must be carried out in acidic solutions, because base decomposes the bis[alkylthio] tellurium derivatives. With an excess of thiol, compounds with more than two alkylthio groups bonded to the tellurium atom were observed1,2. 

Bis[carboxymethylthio] tellurium was detected in solution, but was too unstable to allow its isolation1. When sodium tellurite and carboxymethanethiol (1 8 molar ratio) reacted in 1N sulfuric acid, moisture-sensitive dihydrogen tetrakis[carboxymethylthiolato tellura-te(II) was isolated. The compound was stable at 0°, but gradually decomposed to tellurium at 30cl. 

Dihydrogen TctrakisicarboxymethylthioIatoltellurateCII)1 Sodium tellurite and mercaptoacetic acid are combined in a 1 8 molar ratio in 1 normal sulfuric acid. The resultant mixture is extracted with ethyl acetate, the organic phase is shaken repeatedly with aqueous cadmium chloride solution to remove excess mercaptoacetic acid, the organic phase is dried with sodium sulfate, the mixture is filtered, and the solvent is evaporated at 0° under reduced pressure to leave yellow crystals of the product. 

Tellurium bis[thiolobenzoate] was obtained from sodium tellurite and thiobenzoic acid in strongly acidic medium. The compound was recrystallized from benzene. A single-crystal X-ray structural analyses showed the thiolobenzoate groups to be bidentate2. 

Solutions of sodium tellurite in water1,2 or prepared from tellurium dioxide and aqueous sodium hydroxide3 were acidified with sulfuric acid and treated with freshly prepared solutions of bis[2-hydroxyethyl]dithiocarbamic acid in aqueous methanol. Addition of aqueous solutions of potassium chloride, iodide, or thiocyanate led to the deposition of crystalline tris[bis(2-hydroxyethyl)dithiocarbamate] halides. 

Tellurium Tris[bis(2-hydroxyethyl)dithiocarbamate] Iodide 20 ml (1 mmol) of a 0.05 molar aqueous solution of sodium tellurite are mixed with 50 ml of 1 molar sulfuric acid, 60 ml (30 mmol) of a 0.5 molar 20% aqueous/methanolic solution of bis[2-hydroxyethyl]dithiocarbamic acid. The mixture is stirred and 40 ml (4 mmol) of a 0.1 molar aqueous solution of potassium iodide arc added dropwise over 30 min. The red crystals deposited are collected, washed with water, and dried over sulfuric acid yield 0.8 g (100%) m.p. 160° (dec.)... 

Sodium tellurite dissolved in aqueous sulfuric acid reacted with a methanolic solution of the dithiocarbamic acid to produce the corresponding bis[tris(dithiocarbamato)tellurium] oxide1. 

Bis[tris(/V-methyl-/V-2-hyilroxyethyldithiocarbainato)telluriuin] Oxide1 0.44 g (2 mmol) of sodium tellurite are dissolved in 20 ml of water, 5 ml concentrated sulfuric acid and then 50 mmol of AT-ethyl-AT-2-hydroxyethyldithiocarbamic acid in methanol are added. The mixture is stirred until the red solution deposits yellow crystals. The mixture is filtered, the crystals are washed with water, methanol, and acetone, and dried over anhydrous calcium chloride yield 1.1 g (90%) m.p. 165 ... 

With sodium tellurite instead of tellurium, the same products were obtained in half the yields4. 

Cobalt Tellurite, CoTe03.H20, results as a dark purple-blue precipitate when sodium tellurite solution is added to one of cobalt chloride.3 When heated to 300-400° C. it melts without change of colour, and loses water. 

Nickel Tellurite may be obtained as a pale greenish yellow precipitate of composition NiTe03.2Ha0, by addition of sodium tellurite solution to one of nickel chloride.8 When heated it loses water, becoming light brown in colour. 

Lenher and Wolesensky, J. Artur. Ohem. Soc., 1913, 35, 718. The sodium tellurite is obtained by fusing eqnmiolecular quantities of sodium carbonate and tellurium dioxide. It readily dissolves in water and crystallises with 5 molecules of water, thus Na4TeOa.5H,0. 

Reactions of tellurites To study these reactions use a 0-1 m solution of potassium tellurite, K2Te03, or sodium tellurite, Na2Te03. 

Sodium tellurite (0-1m). Dissolve 22-2 g sodium tellurite, Na2Te03, in water and dilute to 1 litre. 

I On sodium tellurite, compare Lenher and Wolesensky, J. Amer. Ghem. Soc., 1913, 35. 718. 

---