Thiosulphates, reduction

Electrochemical study of the gold thiosulphate reduction, A. M. SuUivan and P. A. Kohl, J. Electrochem. 

Sodium sulphide, NajS, formed by reduction Na2S04 with CO or H2- Aqueous solutions are oxidized to sodium thiosulphate. 

The NH2 groups can be diazotized and reduced in the presence of thiosulphates and different metal ions. The effect of some metal ions, namely Fe ", Sn, Cu +, and Co on the graft yield of cotton modified with aryl diazonium groups via its reaction with 2,4-dichloro-6-(p-nitroaniline)-5-triazine in the presence of alkali and followed by reduction of nitro group was studied [4]. 

Silyl enol ethers, 23, 77, 99-117,128 Silyl enolates, 77 Silyl peroxides, 57 Silyl triflate, 94 Silyl vinyl lithium, 11 (E)-l -Silylalk-1 -enes, 8 Silylalumimum, 8 Silylation, 94 reductive, 26 a-C-Silylation, 113 O-Silylation.99,100 / -SilyIketone, 54 non-cydic, 55 Silylmagnesium, 8 Silyloxydienes, 112 Sodium hexamethyldisilazide, 89 Sodium thiosulphate pentahydrate, 59 Stannylation, see Hydrostannylation Stannylethene, 11 (Z)-Stilbene, 70 (E)-Stilbene oxide, 70 /3-Styryltrimethylsilane, 141 Swern oxidation. 84,88... 

At high ratios of reductant to oxidant, conditions which favour tetrathionate formation at the expense of sulphate, the Cr(Vl) oxidation of thiosulphate follows kinetics ... 

These and similar results can be explained if the simultaneous reduction of hydrogen peroxide is due to an induced reaction. To show the characteristic features of this reaction some results are presented in Table 19 and Table 20. The procedure for these measurements was as follows. The solution of peroxy compounds given in columns 1 and 2 was made up to 20 ml and the pH was adjusted to the given value. Then potassium thiocyanate solution was added and, after the reaction time noted, the process was quenched by adding potassium iodide solution (0.3 g KI). After 5 sec the solution was acidified with 1 ml 2 iV sulphuric acid then using, molybdate catalyst solution, the iodine liberated was titrated with standard thiosulphate. 

Aftertreatment with detergent (2-5 g/1) and sodium carbonate (2-5 g/1) often enhances whiteness and may improve fabric absorbency, particularly if the goods have not been scoured before bleaching. Antichlor treatment is unnecessary for white goods but may be required before coloration. A convenient antichlor treatment involves combining the detergent aftertreatment with sodium perborate, percarbonate or thiosulphate [143]. Traditional reductive antichlors such as sodium bisulphite are not recommended, since their residues can be just as troublesome as chlorite residues. 

In the cell, chlorate and bromate are converted to chloride and bromide at the cathode by reduction with nascent hydrogen, although the chlorate reacts only partially. The chlorate remaining in the cell-liquor can be reduced with thiosulphate or another chemical reducing agent ... 

An unusual reaction of methoxythiocarbonyl chloride with tetra-n-butylammo-nium iodide in the presence of sodium thiosulphate leads to the formation of 0,5-dimethyl dithiocarbonate [49], The reaction appears to involve a reduction step, with the iodide anion being regenerated from the released iodine by the thiosulphate ions (Scheme 4.7). In the absence of the thiosulphate ions, the thiocarbonyl chloride decomposes to yield chloromethane and carbonyl sulphide. 

The mechanism of the thiosulphate reaction is not clear. Lokhande, in his studies, has suggested an internal reduction involving the reaction... 

Many sulphides have been deposited using thioacetamide in acidic solutions (Chapter 6 describes most of these). For depositions using thioacetamide, as with thiosulphate, there are no detailed mechanistic studies. Both H2S formation and complex decomposition are possible in acid solutions, as discussed in Section 3.2.1.3. Deposition of CdS was accomplished using thioacetamide in acidic solution by exploiting electrolytic proton reduction to increase the pH locally at the cathode (substrate), and the mechanism was believed to be a surface-catalyzed decomposition of a Cd-thioacetamide complex [80]. 

Thiosulphate and sulphite are sufficiently reducing to reduce Cu to Cu. Therefore the Cu in solutions of Cu containing sufficient thiosulphate, seleno-sulphate, or sulphite should be predominantly in the monovalent form. This would lead to the expectation that the main product will be something close to Cu2S(e). While this is often the case, CuS(e) is deposited in some cases. However, it is arguable whether this reduction of Cu is, in fact, important in practice. The reason is based on an XPS study that showed that Cu in its compounds with S, Se, and Te is normally in the monovalent state it is the chalcogenide ion (or polyion) that is believed to change oxidation states in these compounds [41]. 

This seems to suggest that the sulphur unit is S2. This unit is capable of uniting with hydrogen sulphide to form the trisulphide, H2S3 but sodium sulphite can only combine with one atom of sulphur to yield thiosulphate. The catalytic activity of the hydrogen sulphide would thus appear to be due to its ability to absorb a whole sulphur unit, Sa, and subsequently to give up, on reduction, each atom of sulphur separately, thus ... 

Other reactions readily available for the detection of a thiosulphate include reduction to hydrogen sulphide by most reducing agents, for instance by zinc and hydrochloric acid, oxidation to sulphuric add or a sulphate, and formation of a thiocyanate on warming with an alkaline solution of a cyanide 5... 

The evidence supplied by the method of formation and the occurrence of isomerism as to analogous structures for the thiosulphates and selenosulphates, is amplified by the chemical behaviour of the potassium alkyl selenosulphates, obtained by treatment of potassium selenosulphates with alkyl halides.1 These, on electrolytic reduction and also on oxidation with hydrogen peroxide, yield the corresponding di-selenides (compare the thiosulphates, p. 203). The structure of the selenosulphates therefore involves a selenium atom directly attached to... 

F. Hefti and W. Schilt, hydrogen sulphide, to thiosulphate, sulphur—and ammonia. N. R. Dhar studied the induced reaction involving the effect of nitrites on the reduction of mercuric chloride by oxalic acid. 

Volumetric methods have been suggested, notably that of Klobbie,4 which consists in treating a solution of osmium tetroxide in dilute sulphuric acid with potassium iodide and titrating the liberated iodine with sodium thiosulphate. One molecule of osmium tetroxide liberates four atoms of iodine. The solution becomes dark green, but no further reduction takes place even after several days. 

Adding an excess of sodium thiosulphate to the solution, tri-iodide ions are reduced to colourless iodide ions and die white colour of the precipitate becomes visible. The reduction with thiosulphate yields tetrathionate ions ... 

Interference of iron(III) ions can be eliminated by adding some potassium fluoride. The colourless hexafluoroferrate(III) [FeF6]3- complex does not interfere. Alternately, iron(III) can be reduced with sodium thiosulphate or ascorbic acid (a few ml of a 0- 1m solution of either), and iron(II) ions, formed in the reduction, do not interfere any more. 

The overall reaction can be written as the reduction of iron(III) by thiosulphate 2S20f-+2Fe3+ - S40 -+2Fe2+... 

Both iron and copper interfere. If, however, potassium iodide solution is added, they are reduced to the non-reactive iron(II) and copper(I) ions the liberated iodine may be decolourized with sodium thiosulphate solution. Alternatively, the reduction may be carried out with sodium thiosulphate solution alone on a spot plate, the copper acting as a catalyst for the reduction of the iron ... 

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