Thiosulphate ions

The slow oxidation of 8203 required to explain the kinetics is most anomalous radical-anions are normally most powerful reducing agents, reaction being dif- 

H2SO3 is oxidised to two sets of products by both ferric ion and ferricyanide depending upon the reaction conditions, e.g. 

When a large excess of ferric ion was employed to promote the sulphate-forming reaction under nitrogen, it was found that a plot of versus [Fe(II)]o + 2 [H2S03]q is a straight line and in general the rate equation 

Colour changes indicate the role of the bisulphite complex. 

Higginson and Marshall s have examined the catalytic effect upon this reaction of Cu(II) ions these oxidise HS03- about 10 times faster than does Fe(m). 

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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 oxidation of the thiosulphate ion SjOj to tetrathionate ion, is used to estimate iodine. 

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

A yellow solution is formed when nitrous acid is added to thiosulphate ion in water84. This is believed to be due to the formation of nitrosyl thiosulphate [O3SSNOI, although this has not been isolated and even in solution decomposition is fairly rapid. The equilibrium constant for its formation Wxno is 1.66 x 107 dm6 mol 2 at 25 °C and the UV-visible absorption spectrum is very similar to that of other S -nitroso compounds85. The rate constant for its formation is very large and is believed to represent a diffusion controlled process. Thiosulphate ion does appear to catalyse nitrosation but, over the range studied... 

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). 

The chemical shift in AES is illustrated for S203A the thiosulphate ion, in solid Na2S203 in Figure 8.24. The ion has a tetrahedral shape and, therefore, two types of sulphur atom, one in a + 6 and the other in a — 2 oxidation state, giving rise to two peaks in the spectrum. The Auger process involved is KLnmLnm, the difference in chemical shift between Ln and Lm not being resolved. The core state of sulphur produced by the processes in Equations (8.12)... 

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

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. 

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... 

Those with the shortest sulphur chains x = 3) have a moderate thermal stability but this decreases with the length of the chain. Hydrolytic stability also falls, the compounds with longer sulphur chains being particularly susceptible to attack by alkahs and giving sulphur, SOg and thiosulphate ions. 

Delayed ischaemic anoxia may also result from cyanide poisoning as a result of circulatory effects. There are several antidotal treatments, but the blood level of cyanide should be determined if possible as treatment may be hazardous in some cases. Cyanide is metabolized in the body, indeed up to 50% of the cyanide in the circulation may be metabolized in 1 h. This metabolic pathway involves the enzyme rhodanese and thiosulphate ion which produces thiocyanate (figure 7.461. However, the crucial part of the treatment is to reduce the level of cyanide in the blood as soon as possible and allow the cyanide to dissociate from the cytochrome oxidase. This is achieved by several means. Methaemoglobin will bind cyanide more avidly than cytochrome oxidase and therefore competes for the available cyanide. 

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. 

A specific rate constant for the rapid complexation of Ag" ion by thiosulphate ion in aqueous solution has been determined, using the recently developed laser optical-acoustic technique for measurement of sound absorption. In aqueous solution the predominant complexed species is the 1 2 ion [Ag(8203)2] ". 

I Iodine reacts with thiosulphate ions according to the equation ... 

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