Hydrogen polysulphides

Shock-tube experiments on the decomposition of hydrogen sulphide have been performed but were unsuccessful because traces of oxygen and other oxidizers could not be removed from the reactant24. No data are available on the homogeneous decomposition of hydrogen polysulphides, nor have the kinetics of pyrolysis of selenium and tellurium hydrides been studied. 

The gas was first liquefied in 1828 by M. Faraday, who, twenty-two years later, successfully reduced the temperature by means of a mixture of solid carbon dioxide and ether to such a degree that the substance solidified.3 In Faraday s method, using an inverted U-tube, liquid hydrogen sulphide is obtained by placing in one limb materials such as hydrogen polysulphide or charcoal 4 saturated with hydrogen sulphide,... 

General Properties.—All the known hydrogen polysulphides, as well... 

Sulphur dissolves in the various hydrogen polysulphides as already described 3 the solutions deposit crystalline sulphur when cooled or on the addition of benzene.4 As solutions of sulphur in hydrogen disulphide or trisulphide behave in this way, whereas the fresh crude polysulphidc does not yield its excess of sulphur on similar treatment, this supplies further evidence of the existence of a higher polysulphide in the crude persulphide. ... 

The hydrogen polysulphides arc miscible with benzene, toluene, chloroform, bromofomi, carbon disulphide, ether and heptane, giving relatively stable solutions,5 and the use of such solutions has been suggested in place of sulphur chloride for the vulcanisation of caoutchouc at the ordinary temperature. The addition of alcohol to the benzene solutions induces rapid decomposition, with formation of nacreous sulphur, which slowly undergoes conversion into ordinary sulphur (p. 25). Ketones, nitrobenzene, aniline and pyridine also catalyse the decomposition. 

Hydrogen trisulphide is much more easily combustible than the crude parent hydrogen polysulphide. Exposure to light tends to accelerate its decomposition. It slowly reduces concentrated sulphuric acid to sulphur dioxide, whilst on contact with dry silver oxide, cupric oxide, lead dioxide or mercuric oxide, it bursts into explosive combustion,2 a residue of the metallic sulphide being obtained. Many other metallic oxides and most salts bring about a less vigorous decomposition metals in the massive condition only react with it slowly. With potassium permanganate or dichromate the reaction is violent. 

Hydrogen Disulphide, H2S2, in addition to being obtained from the distillation of crude hydrogen persulphide, is also formed when hydrogen trisulphide is distilled at 100° C. under a pressure of 20 mm. approximately one-third of the trisulphide is converted into disulphide, whilst the remainder passes into hydrogen sulphide and sulphur. The disulphide, therefore, is the most stable of the hydrogen polysulphides towards heat, and can actually be distilled under atmospheric pressure at 71° to 75° C. with only partial decomposition. 

According to this view the intermediate sulphur atoms are probably arranged in a similar manner in the polythionic acids and the hydrogen polysulphides, and tetrathionic acid may be considered as a sulphur analogue to perdisulphuric acid.2... 

For hydrogen polysulphide H2S3 a chain structure has been established, also for H3C—S—S—S—CH3. Recently such a structure has been found for Cs2S6, with spirals of six sulphur atoms [distance alternatively 2.00 and 2.14 A, bond angle 1080 Abrahams and Grison]. 

Two basic methods are used for the manufacture of sulphur dyes. In one, the starting materials are baked either with sulphur alone or with sulphur and sodium sulphide at a temperature between 180 and 350 °C. Alternatively the intermediates are heated under reflux in aqueous or alcoholic sodium polysulphide this process may also be carried out under pressure at temperatures up to about 130 °C. Following sulphurisation the dye is precipitated by means of air or chemical oxidation, acidification or a combination of these methods. The sulphurisation process results in the evolution of hydrogen sulphide, which is usually absorbed in aqueous sodium hydroxide for use elsewhere - in the reduction of nitro compounds, for example. 

According to G. Calcagni, 100 c.c. of a cold 66 per cent, of sodium hydroxide dissolves 24 55 grms. of sulphur or 57 parts of sulphur per 23 parts of sodium while 100 c.c. of a similar soln. of potassium hydroxide dissolves 17 70 grms. of sulphur, or 59 35 parts of sulphur per 39 15 parts of potassium. The soln. reacts for sulphides, polysulphides, thiosulphates, and sulphites. The reaction between alkali hydroxides and sulphur is complex probably sulphides are first formed from which thiosulphates are produced, and by the dissolution of more sulphur, polysulphides the thiosulphates Ipse part of their sulphur forming sulphites. In the more cone. soln. of sulphur part of the latter appears to be uncombined because these soln. yield sulphur to hot benzene. All the soln. are decomposed by carbon dioxide yielding sulphur and hydrogen sulphide. 

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