Sulphur and Selenium

Oxygen, sulphur and selenium are known to exist in more than one allotropic form. 

Sulphur and selenium form the chlorides disulphur dichloride S2CI2 and diselenium dichloride Se2Cl2. They are made by the direct combination of the elements. Both are covalent, yellow liquids which are readily hydrolysed by water ... 

A number of halide oxides are formed by sulphur and selenium but only one is considered here. 

Recent developments in the studies of titanium and vanadium porphyrins with special emphasis on oxygen adducts, low valent metalloporphyrins and related systems of sulphur and selenium. R. Gui-lard and C. Lecomte, Coord. Chem. Rev., 1985, 65, 87 (76). 

Reactions of carbon subsulphide and of elementary phosphorus, sulphur and selenium with complexes of the platinum metals Sulphur dioxide insertion reactions of transition metal alkyls and related complexes... 

Sulphur and selenium have a high tendency to form homochain polymeric compounds. 

The analysis of close contacts at divalent sulphur and selenium centres reveals a picture very similar to that observed for halogen atoms. Close contacts again fall into two classes (Ramasubbu et al., 1986 Sakurai et al., 1963 Rosenfield et al., 1977), depending on whether the second centre involved is an electrophile E (a metal cation or an electrophilic hydrogen, or carbon halogen atom), or a nucleophilic anion Nu. Similar preferences are observed for S-S contacts (Ramasubbu et al., 1986). 

Occurrence. It is found in close association with sulphur and selenium. Tellurium is often found as gold telluride (calaverite), occasionally observed as free element. 

These reactions are of particular interest since the corresponding sulphur and selenium compounds give unsatisfactory results. 

Another class of compounds, dihydrotellurophenes, exhibits antioxidant activity together with the oxygen, sulphur and selenium analogues. ... 

Sulphur and selenium donor ligands. The reaction between AgNOj and the series of thiocarbazide derivatives RCONHNHC(S)NHNH2 (R == Me, Ph, or C6H4N) has produced white diamagnetic solids for which the polymeric structures (94) are proposed. Support for these structures comes from their low solubility, and i.r. data suggesting terdentate co-ordination via the terminal N, the amido N, and the S atom. The Ag ion attains its usual co-ordination... 

Goodall (53) has synthesised a series of sulphur and selenium containing ligands related to the ligands used by Kouwenhoven. These are the sulphide and selenide ligands shown in Fig. 39. 

Chemical deposition of both M0S2 and MoSei has been reported from ammonium molybdate solution [76,77], For the sulphur and selenium sources, thioacetamide and selenosulphate were used, respectively. Ammonium hydroxide was added to the sulphide solution, while an acetic acid/ammonium acetate buffer was used with the selenide solution (pH values were not given). Reducing agents (either hydrazine [76] or sodium dithionite [77]) were added to the baths. Deposition was started at 90-100°C, followed by lowering to room temperature. 

Sulphur and selenium unite when warmed with the metal 51 when sulphur is triturated with sodium, the reaction proceeds with explosive violence which can be moderated by dilution with common salt. Under boiling toluene, sulphur forms the trisulphide Na2S3. Selenium forms the monoselenide, Na2Se, when heated with sodium. Sodium is attacked by hydrogen sulphide at ordinary temp., and at the fusion point the metal bums in the gas. Gaseous ammonia reacts readily with sodium, and liquid ammonia forms blue soln.—the so-called alkali-ammoniums. 

The most important range for inorganio chemicals is between 1 40 and 1 70. But there are some substances, such as certain oxides and sulphides, whose indices lie well above this range, or even well above 2 0. Media which are liquid at room temperature and have such high refractive indices are not available, but certain mixtures of substances which solidify to glasses may be used. A little of the medium is melted on a microscope slide, the substance under examination is dusted into the melt, a cover-glass is pressed on, and the slide is then allowed to cool. Substances which have been used in this way are mixtures of piperine with arsenic and antimony tri-iodides (for indices 1 7-2 1), mixtures of sulphur and selenium (2-0-2-7)—for details, see Larsen and Berman (1934)—and mixtures of the halides of thallium (Barth, 1929). 

This behaviour contrasts with that of the halides of oxygon, which witli water produce halogen oxyaeids. Sulphur and selenium do not combine with iodine. 

Attempts to use selenium either in place of or in conjunction with sulphur in the vulcanisation of rubber do not appear to be completely successful,2 although it is claimed that rubber vulcanised with sulphur and selenium in the presence of an organic accelerator exhibits enhanced rigidity and resistance to abrasion.3 The incorporation of powdered selenium in ordinary rubber for vulcanisation by sulphur is said to provide crystalline selenium nuclei which induce the internal crystallisation of any superfluous sulphur and so prevent the undesirable surface crystallisation (or bloom ). The effect is attributed to the isomor-plious character of selenium and sulphur. 

Small quantities of selenium in solution may be detected by the test described by Meunier,1 which is similar to Marsh s test for arsenic. If there is a relatively large amount of selenium present it is readily detected by its red colour, but if the amount of the element be small the deposit closely resembles that of arsenic, and in this case the following process may be adopted to detect the selenium. A current of hydrogen sulphide is passed into the hot solution containing a little sulphurous acid. The precipitate of finely divided sulphur carries down with it any selenium present and arsenic as arsenious sulphide, and it is clotted by stirring. In the presence of selenium the clots are brown they may be dried and the sulphur and selenium separated by careful sublimation in a closed tube. 

The method of estimation of selenium in sulphur depends upon the fact that sulphur and selenium bromides are decomposed by water according to the equations ... 

Hydrogen sulphide reduces selenious acid solution with formation of a mixture of selenium and sulphur.13 The proportion of the two elements in the precipitate varies with the conditions. At one time this precipitate was regarded as a definite sulphide of selenium, but the sulphur can be entirely extracted by a mixture of benzene and carbon disulphide. The so-called sulphur selenide obtained by fusing together sulphur and selenium probably is also not a true compound, but only mixed crystals of the elements.14... 

The production of the hydrogen sulphide serves to prevent the selenate being oxidised to the ferric state. There may also be a slight secondary reaction resulting in the precipitation of both sulphur and selenium according to the equation on p. 335. From the solution unstable monoclinic crystals of hydrated ferrous selenate, FeSe04.7H20, may be deposited. 

There are, however, compounds containing sulphur and selenium, with one or more additional elements, in which the selenium may be regarded as having partially displaced sulphur from a compound containing more than one atomic proportion of this element. 

Physical Properties.—Tellurium is known in amorphous and crystalline forms, but it appears to differ from sulphur and selenium in... 

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