# Polysulfides

The polysulfides are a group of chemical compounds which contain chains of sulfur atoms .

## Inorganic polysulphides

Inorganic polysulfides (polysulfanes) are salts of polysulfuric hydrogen. They contain a polysulfide with a double negative charge as an anion .

### Manufacturing

Alkali metal polysulfides are obtained by reacting alkali metal monosulfide with excess sulfur . For example, when sodium sulfide is melted with sulfur, yellow to red-brown sodium polysulfide is formed:

${\ displaystyle \ mathrm {Na_ {2} S + n \; S \ longrightarrow Na_ {2} S_ {n + 1}}}$

The reaction of sodium hydrogen sulfide with sulfur also leads to sodium polysulfides, which in this case are characterized by a high degree of purity.

On an industrial scale, polysulphides are obtained by reacting caustic soda with sulfur and immediately processed further in an aqueous solution, since pure, solid alkali polysulphide is difficult to handle.

### use

Polysulfides used in analytical chemistry for the detection of cyanide ions.

## Organic polysulfides

Organic polysulphides are organic compounds which as a functional group of sulfur contained in the form of sulfur-sulfur bond.

### Manufacture and use

Organic polysulfides are of great technical importance for the production of sealants , especially for use in the manufacture of insulating glass. Aliphatic, organic polysulphides are obtained in a multi-stage process. By reacting 2-chloroethanol with formaldehyde , bis (2-chloroethyl) formal is obtained in a first stage:

${\ displaystyle \ mathrm {2 \ HO {-} CH_ {2} {-} CH_ {2} {-} Cl + H_ {2} CO \ longrightarrow Cl {-} CH_ {2} {-} CH_ {2} {-} O {-} CH_ {2} {-} O {-} CH_ {2} {-} CH_ {2} {-} Cl}}$

The formal is implemented with sodium polysulphide with the addition of a trifunctional crosslinker to form the aliphatic polysulphide with the following simplified structure:

${\ displaystyle \ mathrm {HS {-} CH_ {2} {-} CH_ {2} {-} O {-} CH_ {2} {-} O {-} CH_ {2} {-} CH_ {2} {-} (SS {-} CH_ {2} {-} CH_ {2} {-} O {-} CH_ {2} {-} O {-} CH_ {2} {-} CH_ {2}) _ {23} {-} SH \}}$

This viscous prepolymer can be easily oxidatively crosslinked via the terminal mercapto groups, for example with manganese dioxide , but also with lead dioxide and dichromates , and as a binder in corresponding adhesive and sealant formulations, it results in rubber-elastic products. This heterogeneous oxidation reaction does not proceed stoichiometrically and is therefore relatively insensitive to incorrect dosing of the hardener, which, like the base component, is usually formulated to have a paste-like consistency.

The properties of the cured polysulfide compounds are good weathering stability, high resistance to fuels and many other chemicals, low gas permeability, especially for noble gases , and a certain relaxation in the case of adhesions or seals under mechanical tension. This combination of properties is the reason for the wide use of polysulfide adhesives and sealants , e.g. B. in the manufacture of insulating glass units (main use), sealants for aviation, filling station seals, chemical-resistant coatings and sealants for civil engineering.