Reduced elemental sulphur, reaction

Reaction of 1,2-benzoquinone with reduced elemental sulphur (H2S ) gives a low yield of the pentathiabenzocycloheptene-l,2-diol 149. A mechanism of formation, summarised in Scheme 37, has been proposed (07JCX72951). The reaction is of some interest because similar cytotoxic natural products contain dopamine fragments and may be derived from the corresponding orf/zo-quinone. 

The reaction is a sensitive one, but is subject to a number of interferences. The solution must be free from large amounts of lead, thallium (I), copper, tin, arsenic, antimony, gold, silver, platinum, and palladium, and from elements in sufficient quantity to colour the solution, e.g. nickel. Metals giving insoluble iodides must be absent, or present in amounts not yielding a precipitate. Substances which liberate iodine from potassium iodide interfere, for example iron(III) the latter should be reduced with sulphurous acid and the excess of gas boiled off, or by a 30 per cent solution of hypophosphorous acid. Chloride ion reduces the intensity of the bismuth colour. Separation of bismuth from copper can be effected by extraction of the bismuth as dithizonate by treatment in ammoniacal potassium cyanide solution with a 0.1 per cent solution of dithizone in chloroform if lead is present, shaking of the chloroform solution of lead and bismuth dithizonates with a buffer solution of pH 3.4 results in the lead alone passing into the aqueous phase. The bismuth complex is soluble in a pentan-l-ol-ethyl acetate mixture, and this fact can be utilised for the determination in the presence of coloured ions, such as nickel, cobalt, chromium, and uranium. 

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 ... 

Carrying out the reaction under different reaction conditions (solvent, mercaptide concentration, presence of elemental sulphur) gives rise to variable ratios of reaction products. These results are interpreted in terms of competing 1,7-diradical and 1,5-nucleophilic pathways. The former is reduced in importance relatively to the latter on increasing the mercaptide concentration ... 

A spectroscopic study212 of solutions of alkali-metal polysulphides in DMF has shown the blue coloration to be due to the formation of the trisulphur radical anion S3. This result is contrary to that previously published (W. Giggenbach, J. C. S. Dalton, 1973, 729), which identified the species as the supersulphide ion S2. Further information on the formation of S3 in solutions of elemental sulphur in HMPA was also obtained, and it is now thought that the elemental sulphur is reduced by impurities present in the solvent, probably by dimethylamine. The reaction of piperidyl-lithium with S8 in HMPA was studied in order to determine the stoicheiometry and the nature of the final products. The stoicheiometry of the reaction was found to be ... 

Sphalerite reacts with the dissolved ferric sulphate to produce soluble zinc sulphate and elemental sulphur, with the iron being reduced from the ferric to ferrous state, as in reaction (2). 

The reduction of sulphur dioxide with hydrogen, carbon or carhon compounds such as methane or carbon monoxide is also of industrial interest. These reactions require high temperatures or catalysts or both. They result in mixtures of elemental sulphur with hydrogen sulphide. If carbon or a carbon compound has been used as the reducing agent, carbon-containing species such as carbon dioxide, carbonyl sulphide and carbon disulphide will be formed as well. 

Lithium triethylborohydride continues to be a useful synthetic reagent. It has been reported that this reagent in THF reduces the toluene-p-sulphonates of primary and secondary alcohols to the corresponding alkanes. The reduction is even applicable to tosylates of cycloalkanols, hindered alcohols, and polyhydroxy derivatives. The reaction of lithium triethylborohydride with elemental sulphur has been reported to form rapidly Li aS or Li aS a (depending upon the stoicheiometry), which can then be used to prepare sulphides, RaS, and disulphides, RaS a, in high yield. Similarly, the publication of a convenient... 

Tellurous acid is rapidly reduced to the element by sulphurous acid in the presence of potassium iodide.3 Owing, however, to the affinity which tellurium has for iodine and the consequent formation of varying proportions of tellurium tetra-iodide, the trustworthiness of the quantitative method based on this reaction is questionable.4... 

In natural waters occur not one but several oxidation-reduction reactions. These reactions are associated with the presence of several elements, which are capable of changing their charge, and run in parallel. For this reason, total oxidation potential of the solution is defined by the nature and concentration of all redox-couples. Components which noticeably affect the solution s oxidation-reduction potential are called electroactive. Elements whose concentration and form of existence actually control solution s oxidation are culled potential-setting. In natural waters these are usually O, S, C, N and Fe. The medium whose oxidation potential value almost does not change with the addition of oxidizers or reducers is called redox-buffers. The redox-buffer may be associated with composition of the water itself, of its host rocks or with the effect of atmosphere. In the subsurface redox-buffers are associated, as a rule, with the content of iron, sulphur or manganese. Stably high Eh value in the surface and ground waters is caused by the inexhaustible source of in the atmosphere. 

The element will combine vigorously with halogens, with sulphur and many metals. It is a reducing agent and with concentrated alkalies, phosphine and hydrogen are produced (4.13,4.14). Phosphine is produced in reactions (4.15) and (4.16) [23], and under the appropriate conditions, white P can be reduced to P4H2, P4H and various other hydrides (Section 4.4),... 

The reactions between TiCl., TiBr., TiCl, VCl, VCl, and VBr with a range of monodentate sulphur ligands, have been investigated. The ligands used include the aliphatic thioethers, R S, for R =Me, Et, Pr, and Bu, and tetrahydrothiophen and pentamethylenesulphide. Notable differences have been observed in the reactions of the halides of the two elements. Thus, whereas the tetrahalides of titanium form simple adducts with all ligands tried, vanadium(IV) chloride is reduced rapidly and quantitatively to the tervalent state. Furthermore, tervalent vanadium forms a series of well-defined complexes with sulphur ligands, but the complexes formed by tervalent... 

---