Thiosulfate

The mechanism of the oxidation of sulfide sulfur to sulfate is probably much more complex than a simple fixation of oxygen. Fromageot and Royer (51) have presented the hypothesis that the oxidation of hydrogen sulfide to sulfate involves formation of thiosulfate as intermediary. They base this hypothesis on the constant presence of thiosulfate in the urine of higher animals, and also on the ease with which hydrogen sulfide is oxidized to thiosulfate by inorganic catalysts in the presence of air (106). 

These results show that urinary thiosulfate comes from the animal metabolism proper, and not, as had been believed for some time, from bacterial action in the digestive tract. It thus represents an intermediary 

To the thiosulfate in the urine, thiocyanate should be added, which according to Lang (72) arises from the following reaction between thiosulfate and hydrogen cyanide  

This reaction is catalyzed by an enzyme, rhodanese, which is present in different tissues. 

The mechanism of thiosulfate formation in animals is still obscure. Three theories can actually be proposed for this problem according to one by Medes and Floyd (86), thiosulfate would be formed from sulfoxylic acid according to one by Fromageot and Royer (51), it would be formed by oxidation of hydrogen sulfide and finally one may think thiosulfate would result froifi the reaction between free sulfur and sulfite. 

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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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