Thiosulphate ions reactions

Three thiosulphate ion reactions which may profit from discussion together involve exchange of oxygen with water (1), exchange of sulphur with bisulphide ion (2) and the displacement reaction with water (3), viz. 

However, the sulphide ion can attach to itself further atoms of sulphur to give polysulphide ions, for example Sj , Sj , and so these are found in solution also. Further, the sulphite ion can add on a sulphur atom to give the thiosulphate ion, S203 which is also found in the reaction mixture. 

The intermediate reacts with thiosulphate ion to provide the main course of the overall reaction ... 

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. 

One possible reaction which hinders the total removal of the silver is the formation of a complex between silver and thiosulphate ions (Eq. 6.15). Whilst the removal of such a large quantity of sodium thiosulphate (220 g L- prior to discharge of silver is not economically feasible, removal (discharge) of thiosulphate is improved in the presence of ultrasound (Tab. 6.10). 

This reaction can be applied to distinguish sulphite and thiosulphate ions (cf. Section IV.4, reaction 6). 

In the classical case, R is sulphite and Ox sulphate. Three classes of related reactions have been recognised. To the first belong the sulphite, thiosulphate and stannous ion reactions, and with these (4) is always faster than (3) so that the starch-iodine colour emerges very suddenly when all the reductant is exhausted (by excess iodate). The second type can attain equal rates of iodine production, through (2) and (3), and decomposition (4). Starch-iodine colour is seen at about that point, with partial removal of the reductant e.g. arsenite, ferrocyanide, Fe(II) complexed with oxalate or EDTA). In the third type, reaction (3) is so much faster than (4) that the necessary iodide concentration to give starch-iodine colour is only attained late in reaction. Iodine is then present early but the blue colouration only develops later. A number of organic reductants fall into this class. The rates of colour development in the normal reaction system have been treated in semiquantitative fashion . ... 

The rate of oxidation of thiosulphate ion by chlorate and bromate is not small by comparison with other reactions of these halates. The chlorate reaction appears to have received only very fragmentary kinetic examination. The latter has been studied , but only reported as having a rate equal to fc[ ][BrOJ ] ]. The iodate reaction has been reported to have the stoichiometry... 

The stoicheiometry and kinetics of reaction of aqueous ammonia solutions of copper(ii) ions with thiosulphate ion in the presence of oxygen have been examined. The amount of oxygen consumed and the relative amounts of the final sulphur products, namely trithionate and sulphate ions, are dependent on the initial 8203 concentration and pH. The most active species for SjOe" formation is a tetra-amminecopper(ii) complex having one axial 8303 and one axial O2 ligand. A complex having both axial and equatorial 8203 ligands as well as an axial O2 was suggested as the reactive intermediate for sulphate formation. 

The reduction of selenite ions by some selenothionate and thiosulphate ions has been studied. 8e03 reacts with 80830 in acidic solutions to form selenanemonosulphanedisulphonates with <6 8e atoms in the chain. The ions 805830 and 803830 were detected for the first time. 80 and 80830 reduce 8eO in acidic solutions to selenium metal but selenane-disulphonates are produced as intermediate products. In neutral systems, species exist with <4 Se atoms in the chain in acidic solutions species with <7 8e atoms in the chain were formed, including the new species 867830 . 8elenium metal is precipitated by the decomposition of the longest-chain intermediates, 8eO reacts with 820 to form 868 0 and 8406 . Excess SgO " reacts with 80840 in neutral solutions to form 8eS80 , which decomposes to selenium. In acidic solutions, this reaction is of less importance, and only minor precipitation of selenium is observed instead a sequence of build-up reactions takes place. 

The reaction between hydrogen peroxide and iodide ions Hydrogen peroxide can react as an oxidant or a reductant. In the titrimetric determination of hydrogen peroxide, it usually reacts as a reductant when a strong oxidant is used as a titrant. In the reaction with iodide, hydrogen peroxide reacts as an oxidant. The iodine produced in this reaction can be reduced by thiosulphate back to iodide. In presence of thiosulphate, the reaction is similar to the reaction in Sec.7.6.1. It was found that molybdates act as catalysts. This fact is the basis of a titrimetric method for determination of the latter ions. 

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]. 

The Co(III) complexes Co(NH3)6 " and Co(NH3)sOH bring about oxidation of stannate(II) ion in strongly basic solution . The rates were found to be independent of the concentration of the Co(III) complex. It is proposed that stannate(Il) exists as a dimer, and that the monomer is the reactive species, the rate being close to half-order in stannate(II). Cyanide and thiosulphate catalyse the reaction but Co(CN)g is immune to attack by stannate(II) ion. The experimental difficulties encountered in this study preclude a full analysis as regards mechanism. 

Among the most important indirect methods of analysis which employ redox reactions are the bromination procedures for the determination of aromatic amines, phenols, and other compounds which undergo stoichiometric bromine substitution or addition. Bromine may be liberated quantitatively by the acidification of a bromate-bromide solution mixed with the sample. The excess, unreacted bromine can then be determined by reaction with iodide ions to liberate iodine, followed by titration of the iodine with sodium thiosulphate. An interesting extension of the bromination method employs 8-hydroxyquinoline (oxine) to effect a separation of a metal by solvent extraction or precipitation. The metal-oxine complex can then be determined by bromine substitution. 

It has been suggested that the thiosulphate, a reducing agent, may act as an electron donor and rednce the elemental sulphur formed in Reactions (3.21) and (3.22), forming sulphide ions ... 

These electrons reduce elemental S formed in Reaction (3.21) or (3.22) to give sulphide (or hydrosulphide) ions, as in Reaction (3.24), which react with the metal ions. The general mechanism of sulphide generation has been assumed in most studies using thiosulphate, e.g., Nair et al [78] for SbzSs deposition and Groz-danov et al. in their study of Cu S deposition from Cu-thiosulphate solutions [76], although in this latter study it is noted that the mechanism may be more complicated in this Cu-S system. 

A variant of CD was based on illnmination of a solntion containing thiosulphate and cadmium ions by UV light [26,70,71]. CdS was deposited only on the illnminated portion of the snbstrate. Since only light absorbed by thiosulphate (wavelength shorter than 300 nm) was effective, the effect was attributed to photodecomposition of thiosnlphate to elemental S and solvated electrons and snbse-qnent reaction with Cd. ... 

This precipitate dissolves in thiosulphate to form a thiosulphate complex, which, in common with other metal thiosulphate complexes, decomposes when heated to the metal snlphide (see Sec. 3.3.3). Besides direct decomposition of the thiosnlphate complex, another possibility suggested in this study is formation of snlphide ion by alkaline hydrolysis of thiosulphate [Eqs. (3.20) to (3.24)] and reaction with Hg to form HgS. The substrates were glass precoated with a very thin film of CD PbS (presnmably this improved adherence and/or homogeneity). 

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