Thiosulfates

Thio acids have already been defined (Chap. 18) as acids related to their parent oxyacids by replacement of one or more oxygen atoms by sulfur. Most thio acids themselves are unstable, but their salts are stable and some (particularly the thiosulfates and thiocyanates) are quite familiar. Organic derivatives of monothiophosphoric acid, (HO)3PS, have recently found application as insecticides. 

Thiosulfates are best made by the action of sulfites on elemental sulfur, a reaction analogous formally (and possibly mechanistically) to that yielding disulfides and thiocyanates (Exercise 10)  

If a similar experiment is carried out, adding Ag+ instead of acid to the labeled thiosulfate, Ag2S and S0 4 are formed (Chap. 11, Exercise 4), all of the radioactivity this time being carried with the Ag2S. 

The thiosulfate ion, 820 is a stmctural analogue of the sulfate ion where one oxygen atom is replaced by one sulfur atom. The two sulfur atoms of thiosulfate thus are not equivalent. Indeed, the unique chemistry of the thiosulfate ion is dominated by the sulfide-like sulfur atom which is responsible for both the reducing properties and complexing abiUties. The abiUty of thiosulfates to dissolve silver haUdes through complex formation is the basis for their commercial appHcation in photography (qv). 

Structure. The thiosulfate sulfur atoms have been shown to be nonequivalent by radioactive sulfur exchange studies (1). When a sulfite is treated with radioactive sulfur and the resulting thiosulfate decomposed to sulfur and sulfite by acids, the radioactivity appears in the sulfur  

When the silver salt of the radioactive thiosulfate [83682-20-6] is decomposed, the radioactivity appears in the sulfide  

If both sulfur atoms were equivalent, the radioactivity would be equally divided between the two products. 

Calculations from binding-force measurements (2) indicate the limiting stmctural forms of the thiosulfate ion  

The reduction of the tris(oxolato)cobalt(III) ion, [ 0(0204)3] , induced by the reaction of copper(II) with thiosulfate has been reported. The mechanistic scheme is as shown in equations (41) (44), with the complexation of the intermediate Cu(I) ion by thiosulfate accounting for the inhibition of the reaction of high 

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Silver chloride Aqueous ammonia or sodium thiosulfate. 

The following factors are the equivalent of 1 mL of normal sodium thiosulfate. Where the normality of the solution being used is other than normal, multiply the factors given in the table below by the normality of the solution employed. 

Iodine, Q.IN (0 to 1 —). Dissolve 12.690 g of resublimed iodine in 25 mL of a solution containing 15 g of KI which is free from iodate. After all the solid has dissolved, dilute to 1 L. If desired, check against a standard arsenite or standard thiosulfate solution. 

Sodium thiosulfate, O.IA. Weigh 24.818 g of fresh crystals of Na2S203 5H2O, dissolve in distilled water. Add 0.5 g of Na2C03 and 0.5 mL of chloroform as preservative. Dilute to 1 L. 

Add KI and back-titrate iodine liberated with thiosulfate. Cd/8 = 14.05... 

Titrate liberated iodine with thiosulfate Ee/1 = 55.847 Ee203/2 = 79.845 I2 + 2 820 = 2 D + 8401 [titrate solution (pH ° 7.0) with thiosulfate until color is pale yellow. Add K1 and starch and continue titration to disappearance of blue color. I2/2 =... 

NaCl—HCl solution, add KI, and titrate I2 with thiosulfate solution. 

S H2S + F(excess) = S + 2 1 + 2 Back-titrate excess F with standard thiosulfate solution. 

H2S + 4 Br2 + 4 H2O = SO + 8 Br + 10 H" Use excess KBr and standard KBr03 solution. Fet stand until clear, add excess KI, and titrate with standard thiosulfate solution. 

Br , citrate, CE, 2,3-dimercaptopropanol, dithizone, EDTA, E, OH , NagP30io, SCN , tartrate, thiosulfate, thiourea, triethanolamine BE4, citrate, V,V-dihydroxyethylglycine, EDTA, E , polyphosphates, tartrate Citrate, CN , 2,3-dimercaptopropanol, dimercaptosuccinic acid, dithizone, EDTA, glycine, E, malonate, NH3, 1,10-phenanthroline, SCN , 820 , tartrate Citrate, V,V-dihydroxyethylglycine, EDTA, E , PO , reducing agents (ascorbic acid), tartrate, tiron... 

BrOg Reduction with arsenate(III), hydrazine, sulfite, or thiosulfate... 

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