Sulphide oxidation periodates

There are many transition metal ion oxidants used in organic chemistry for the interconversion of functional groups. Those which have been used for the preparation of sulphones from sulphoxides will be discussed below. It is very interesting to note that this type of oxidant often reacts more rapidly with sulphoxides than with sulphides and so sulphoxides may be selectively oxidized with transition metal ion oxidants in the presence of sulphides. This is in direct contrast to the oxidation of sulphides and sulphoxides with peracids and periodate, for example, where the rate of reaction of the sulphide is more than 100 times that for the corresponding sulphoxide. 

Although there are other more cost effective and efficient procedures, the periodate oxidation of dialkyl sulphides to the sulphoxides has been shown to proceed in high yield [24, 25, 29] thiols are oxidized to disulphides (95-100%) [29]. The potency of the quaternary ammonium periodate for the oxidation of sulphides is improved by the addition of wieso-tetraphenylporphinatoironflll) chloride [TPPFe(III)Cl] [27]. In contrast with the oxidation conducted in the absence of TPPFe(III)Cl [24,25], aryl sulphides are oxidized more rapidly than alkyl sulphides. 

An oxometalloporphyrin is probably the actual oxidizing agent the threo erythro ratio (35 65) of the diastereomeric sulphoxides obtained from racemic sulphides is close to that obtained for the corresponding oxidation using cytochrome P450 oxidase and differs from that (58 42) obtained by the oxidation using periodate in the absence of the porphyrin [27]. The cytochrome-induced demethylation of N,N-dimethylaniline can also be mimicked with periodate and the metalloporphyrin. 

Correlations between catalytic activity and a variety of bulk properties of semiconductors have been reported (i) the average band gap of III-V and II-VI semiconductors and activity towards hydrogenation of isopropanol (ii) enthalpy of oxides and their activity towards oxidation of propylene and (iii) number of d-electrons (and crystal field stabilization energy) or 3rf-metal oxides and their activity towards N2O decomposition. The last correlation, due to Dowden (1972), is important since it provides a connection between heterogeneous catalysis and coordination chemistry of transition-metal compounds. A correlation between the catalytic activity of transition-metal sulphides towards hydrodesulphurization of aromatic compounds and the position of the transition metal in the periodic table has been made by Whittingham ... 

It is due to the decrease of the heat of formation that, at the end of the periods, the highest halides, oxides, sulphides and nitrides become unstable. In the second period no normal halides are formed after carbon. In the third period the fluorides extend to SFe, in the fifth group to IF7. The normal oxides, too, extend to higher valencies in the third period, where are S03 and C1207, than in the second, where N2Os is the highest oxide. 

Hydrogen sulphide is sometimes estimated volumetrically by treating a solution containing less than 0-04 per cent, with excess of standard iodine and then after a short period titrating the residual iodine in the usual manner with sodium thiosulphate or arsenious oxide accurate direct titration is not possible 3... 

When dry arsenious oxide is fused with sodium thiosulphate a mixture of the di- and tri-sulphides results.13 In aqueous solution and in acidified solutions of arsenites the addition of aqueous sodium thiosulphate causes the precipitation of arsenious sulphide after a sharply defined induction period, the duration of which is in inverse proportion to the thiosulphate concentration and practically independent... 

---