Polysulphides, Organic

Also known as vulcanite and (mainly in the USA) hard rubber . The hard, horn-like product obtained when natural rubber and some synthetic rubbers such as nitrile (NBR) are vulcanised with a high proportion of sulphur or organic nonsulphur vulcanising agent. Butyl rubber and polysulphide rubber do not form ebonites. Ebullioscopy... 

The first commercial sulphur dye was discovered accidentally in 1873 by Croissant and BretonniSre who heated lignin-containing organic waste, such as sawdust, with sodium polysulphide at about 300 °C the product was sold under the name Cachou de Laval [52]. Even today an equivalent dye (Cl Sulphur Brown 1) is derived from lignin sulphonate, which is readily available from waste liquors from wood pulp manufacture. The real pioneer of sulphur dyes was Vidal, the first chemist to obtain dyes of this type from specific organic compounds. In particular, Sulphur Black T (Cl Sulphur Black 1) was made from 2,4-dinitrophenol in 1899. At the turn of the century many of the intermediates available were subjected to sulphurisation (thionation), that is, treatment with sulphur, sodium sulphide or sodium polysulphide to introduce sulphur linkages. 

The high mechanical strength of natural and organic rubbers as used in tires is due to the incorporation of pyrogenic carbon blacks as active fillers. Elastomers of a more polar polymer backbone, such as polyacrylates, polyurethanes or polysulphides, require fillers of higher polarity. In particular the performance of polydimethylsiloxane elastomers (silicone rubber) is basically related to the addition of fumed silica. 

Bacterial attack and fungal growth are the two biochemical effects which influence the durability of a sealant. Bacterial attack results in the chemical breakdown of the sealant. Fungi attach themselves to the surface of the sealant and live as parasites, feeding on the organic matter present. The use of polysulphide sealants in the water industry has proved to be a versatile method for overcoming the above-mentioned problems. 

The reaction is catalysed by an organic base, usually an amine, which in the past has nearly always been the tertiary amine 2,4,6-tri(dimethyl aminomethyl) phenol. Such LP-modified epoxy resins have been in existence for more than 30 years. Their popularity declined because of the mercaptan odour of the polysulphide polymers in the uncured state and because of the use of a tertiary aromatic amine. 

Except in ozone, the alkali-metal ozonates, the unstable O4F2, and a number of organic peroxides and trioxides (e.g. F3C, 000. CF3), the covalent linking of 0 to 0 does not proceed beyond 0=0 or -0—0—. Sulphur, on the other hand, presents a very different picture, a feature of its chemistry being the easy formation of chains of S atoms—in the element itself, in halides S ,X2, polysulphides, and polythionates. 

At the surface of some marine sediments, organic sulphur can comprise as much as 50% of the total sulphur present (Francois, 1987) due to biosynthesis which incorporates sulphur of all oxidation states, but also, because of the reactivity of sulphides and polysulphides, by chemical addition. There is usually an increasing S/C ratio with depth in sediments, partly associated with humic substances, and most of this increase occurs in the oxic and suboxic zones. This organic repository may be the source of the sulphur required to convert metastable iron sulphides, formed in the lower part of the sulphur reduction zone, to framboidal pyrite, which is often found closely associated with organic matter. 

Sulphur (S, at. mass 32.06) occurs in the oxidation states -II (in sulphide), IV (in SO2 and sulphite), and VI (in H2SO4 and sulphate). Sulphur dissolves in certain organic solvents (e.g., CS2 and CeHe) when dissolved in an alkali metal sulphide solution, it yields yellow polysulphides (S + nS —> Sn+i j. When heated with an alkaline solution of sulphite, sulphur forms thiosulphate. Sulphide, sulphite, and thiosulphate are reducing agents. Persulphate has strongly oxidizing properties. Complexes are formed by sulphide e.g., with As, Sb, Mo), and also by thiosulphate [e.g., with Ag, Cu, and Fe(lII)]. The most stable sulphur species is sulphate, which forms sparingly soluble compounds, for example with Ba and Pb, and stable soluble complexes with Zr and Th. 

Kohnen M.E.L., Sinninghe Damste J.S., ten Haven H.L., de Leeuw J.W. (1989) Early incorporation of polysulphides in sedimentary organic matter. Nature 341, 640-1. 

Vairavamurthy M. A., Mopper K. and Taylor B. F. (1992) Occurrence of particle-bonded polysulphides and significance of their reaction with organic matter in marine sediments. Geophys. Res. Lett. 19, 2043-2046. 

Sulphur derivatives. A preliminary polarographic scan is recommended to provide sufficient information as to the presence or absence of hydrogen sulphide, elemental sulphur, mercaptans (thiols), disulphides and organic polysulphides. This preliminary... 

It may be noted that chemical and physical evidence shows that the sulphur chains in inorganic and organic polysulphides are unquestionably linear and not branched as was once believed. 

In a simulation of the reaction of glucose and cellulose with hydrogen sulphide and polysulphide at ambient temperature in aqueous solution the formation of organic sulphur compounds was observed which yielded thiophene on pyrolysis/evaporation. By such a process carbohydrates in nature might be converted into sulphur compound which, being resistant to microbial attack, would be preserved in sediments. ... 

Table 16.3 Organic sulphides, mercaptans, disulphides, and polysulphides C-S and S- -S stretching vibrations...

Mercaptans, -SH, Disulphides, -S-S-, and Polysulphides, -(-S-S-) -Compounds containing S=0 Organic Sulphoxides,... 

These results consistently contributed to improvements in the technology of lithium/sulphur battery however, some residual issues still remain to prevent full practical application of this high-energy battery system. Most of the recent works rely on conventional liquid organic carbonate solution as the preferred electrolyte although the sulphur and/or the lithium sulphide are shielded into a carbon matrix, either mesoporous [46] or spherical [50], thus in principle preventing the direct contact with the electrolyte, it is not yet fully established whether the solubility of the polysulphides is effectively blocked. Another issue still to be solved is in the relatively modest power capability of these batteries. 

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