Polysulfide

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The compound (C5H5)2TiS5 is an example of a polysulfide complex

Polysulfides are a class of

alkyl or aryl group.[2]

Polysulfide salts and complexes

Fragment of the solid-state structure of Na2S5. The S2−5 chain consists of the yellow-colored atoms.[3]

The alkali metal polysulfides arise by treatment of a solution of sulfide, e.g. sodium sulfide, with elemental sulfur:

S2−
+ n S → S2−
n+1

In some cases, these anions have been obtained as organic salts, which are soluble in organic solvents.[4]

The energy released in the reaction of sodium and elemental sulfur is the basis of battery technology. The sodium–sulfur battery and the lithium–sulfur battery require high temperatures to maintain liquid polysulfide and Na+-conductive membranes that are unreactive toward sodium, sulfur, and sodium sulfide.

Polysulfides are

coordination chemistry. Examples of transition metal polysulfido complexes include (C5H5)2TiS5, [Ni(S4)2]2−, and [Pt(S5)3]2−.[5] Main group elements also form polysulfides.[6]

Organic polysulfides

shiitake mushrooms

In commerce, the term "polysulfide" usually refers to a class of polymers with alternating chains of several sulfur atoms and hydrocarbons. They have the formula R1SnR2. In this formula n indicates the number of sulfur atoms (or "rank"). Polysulfide polymers can be synthesized by

condensation polymerization
reactions between organic dihalides and alkali metal salts of polysulfide anions:

n Na2S5 + n ClCH2CH2Cl → [CH2CH2S5]n + 2n NaCl

Dihalides used in this condensation polymerization are dichloroalkanes (such as 1,2-dichloroethane, bis-(2-chloroethoxy)methane and 1,3-dichloropropane). The polymers are called thiokols. In some cases, polysulfide polymers can be formed by ring-opening polymerization reactions.

Polysulfide polymers are also prepared by the addition of polysulfanes to alkenes. An idealized equation is:

2 RCH=CH2 + H2Sn → (RCH2CH2)2Sn

In reality, homogeneous samples of H2Sn are difficult to prepare.[2]

Polysulfide polymers are insoluble in water, oils, and many other organic solvents. Because of their solvent resistance, these materials find use as sealants to fill the joints in pavement, automotive window glass, and aircraft structures.

Polymers containing one or two sulfur atoms separated by hydrocarbon sequences are usually not classified polysulfides, e.g.

poly(p-phenylene) sulfide
(C6H4S)n.

Polysulfides in vulcanized rubber

Idealized structure of two strands (blue and green) of natural rubber after vulcanization with elemental sulfur, which forms polysulfide linkages.

Many commercial

rubbers. The process of crosslinking the polymer chains in these polymers with sulfur is called vulcanization. The sulfur chains attach themselves to the allylic carbon atoms, which are adjacent to C=C linkages. Vulcanization is a step in the processing of several classes of rubbers, including polychloroprene (Neoprene), styrene-butadiene, and polyisoprene, which is chemically similar to natural rubber. Charles Goodyear
's discovery of vulcanization, involving the heating of polyisoprene with sulfur, was revolutionary because it converted a sticky and almost useless material into an elastomer that could be fabricated into useful products.

Occurrence in gas giants

In addition to water and ammonia, the clouds in the atmospheres of the gas giant planets contain ammonium sulfides. The reddish-brownish clouds are attributed to polysulfides, arising from the exposure of the ammonium sulfides to light.[7]

Properties

Polysulfides, like sulfides, can induce stress corrosion cracking in carbon steel and stainless steel.

See also

  • Disulfide – Functional group with the chemical structure R−S−S−R′
  • Trisulfide – Functional group
  • Polyiodide – Anions composed of many iodine atoms
  • Catenation – Bonding of atoms of the same element into chains or rings

References

  1. ISBN 978-0-08-096529-1
    , retrieved 2022-03-29
  2. ^
    ISBN 978-0470860786
    .
  3. doi:10.3891/acta.chem.scand.25-3329
    .
  4. doi:10.1021/ic00011a011
    .
  5. doi:10.1002/anie.198507421
    .
  6. ISBN 3-540-40378-7
    .
  7. ^ "Jupiter: Cloud composition". Encyclopædia Britannica. 6 June 2023.
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