View source for Chemistry:Polysulfide

[[Image:Pentasulfur-titanocene complex structure.png|thumb|220px|The compound {{chem2|(C5H5)2TiS5}} is an example of a polysulfide complex.]]
'''Polysulfides''' are a class of [[Chemistry:Chemical compound|chemical compound]]s derived from anionic chains of [[Chemistry:Sulfur|sulfur]] atoms.<ref>{{Citation |last1=Kelly |first1=P. F. |title=1.06 - Catenated Sulfur Compounds |date=2013-01-01 |url=https://www.sciencedirect.com/science/article/pii/B978008097774400108X |work=Comprehensive Inorganic Chemistry II (Second Edition) |pages=179–196 |editor-last=Reedijk |editor-first=Jan |place=Amsterdam |publisher=Elsevier |language=en |doi=10.1016/b978-0-08-097774-4.00108-x |isbn=978-0-08-096529-1 |access-date=2022-03-29 |last2=King |first2=R. S. P.|editor2-link=Kenneth Poeppelmeier |editor2-last=Poeppelmeier |editor2-first=Kenneth}}</ref> There are two main classes of polysulfides: inorganic and organic. The inorganic polysulfides have the general formula {{chem|S|''n''|2−}}. These anions are the conjugate bases of [[Chemistry:Polysulfane|polysulfane]]s {{chem2|H2S_{''n''}|}}. Organic polysulfides generally have the formulae {{chem2|R^{1}S_{''n''}R^{2}|}}, where R = [[Chemistry:Alkyl|alkyl]] or [[Chemistry:Aryl|aryl]].<ref name=Steudel>{{cite encyclopedia|first=Ralf|last=Steudel|encyclopedia=Encyclopedia of Inorganic Chemistry|date=2007|publisher=Wiley-VCH|location=Weinheim|doi=10.1002/0470862106.ia233.pub2|chapter=Sulfur: Organic Polysulfanes|isbn=978-0470860786}}</ref>

==Polysulfide salts and complexes==
[[File:Na2S5Packing.tif|thumb|left|220px|Fragment of the solid-state structure of {{chem2|Na2S5}}. The {{chem2|S5(2−)}} chain consists of the yellow-colored atoms.<ref>{{cite journal|last1=Rosén|first1=E.|last2=Tegman|first2=R.|title=Preparative and X-ray powder diffraction study of the polysulfides Na<sub>2</sub>S<sub>2</sub>, Na<sub>2</sub>S<sub>4</sub> and Na<sub>2</sub>S<sub>5</sub>|journal=Acta Chem. Scand.|date=1988|volume=25|pages=3329–3336|doi=10.3891/acta.chem.scand.25-3329|doi-access=free}}</ref>]]
The alkali metal polysulfides arise by treatment of a solution of [[Chemistry:Sulfide|sulfide]], e.g. [[Chemistry:Sodium sulfide|sodium sulfide]], with elemental [[Chemistry:Sulfur|sulfur]]:

:{{chem|S|2-| + ''n'' S → S|''n''+1|2−}}
In some cases, these anions have been obtained as organic salts, which are soluble in organic solvents.<ref>{{cite journal |last1=Dev|first1= S. |last2=Ramli|first2= E. |last3=Rauchfuss|first3= T. B. |last4=Wilson|first4= S. R. | title = Synthesis and Structure of [M(''N''-Methylimidazole)<sub>6</sub>]S<sub>8</sub>: Polysulfide Salts Prepared by the Reaction ''N''-Methylimidazole + Metal Powder + Sulfur | journal = Inorg. Chem. | year = 1991 | volume = 30 | pages = 2514 | doi=10.1021/ic00011a011 | issue = 11}}</ref>

The energy released in the reaction of sodium and elemental sulfur is the basis of battery technology. The [[Engineering:Sodium–sulfur battery|sodium–sulfur battery]] and the [[Engineering:Lithium–sulfur battery|lithium–sulfur battery]] require high temperatures to maintain liquid polysulfide and {{chem2|Na+}}-conductive membranes that are unreactive toward sodium, sulfur, and sodium sulfide.

Polysulfides are [[Chemistry:Ligand|ligand]]s in coordination chemistry. Examples of transition metal polysulfido complexes include [[Chemistry:Titanocene pentasulfide|{{chem2|(C5H5)2TiS5}}]], {{chem2|[Ni(S4)2](2−)}}, and {{chem2|[Pt(S5)3](2−)}}.<ref>{{cite journal|last1=Draganjac|first1= M. E.|last2= Rauchfuss|first2= T. B.|title= Transition Metal Polysulfides: Coordination Compounds with Purely Inorganic Chelate Ligands|journal= Angew. Chem. Int. Ed. Engl.|date= 1985| volume= 24|issue= 9|page= 742 |doi=10.1002/anie.198507421}}</ref> Main group elements also form polysulfides.<ref>{{cite book|last1=Takeda|first1= N.|last2= Tokitoh|first2= N. |last3=Okazaki|first3= R. |date=2003 |title=Polysulfido Complexes of Main Group and Transition Metals |volume=231 |pages=153–202 |isbn= 3-540-40378-7 |doi=10.1007/b13184|series= Topics in Current Chemistry}}</ref>

==Organic polysulfides==
[[Image:Lenthionine-2D-skeletal.png|thumb|130px|left|[[Chemistry:Lenthionine|Lenthionine]] is an organic polysulfide found in 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 {{chem2|R^{1}S_{''n''}R^{2}|}}. 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:

:{{chem2|''n'' Na2S5 + ''n'' ClCH2CH2Cl → [CH2CH2S5]_{''n''} + 2''n'' NaCl}}

Dihalides used in this condensation polymerization are dichloroalkanes (such as [[Chemistry:1,2-Dichloroethane|1,2-dichloroethane]], bis-(2-chloroethyl)formal ({{chem2|ClCH2CH2OCH2OCH2CH2Cl}}), and 1,3-dichloropropane). The polymers are called [[Chemistry:Thiokol (polymer)|thiokols]]. In some cases, polysulfide polymers can be formed by [[Chemistry:Ring-opening polymerization|ring-opening polymerization]] reactions.

Polysulfide polymers are also prepared by the addition of polysulfanes to alkenes. An idealized equation is:
:{{chem2|2 RCH\dCH2 + H2S_{''n''} → (RCH2CH2)2S_{''n''}|}}
In reality, homogeneous samples of {{chem2|H2S_{''n''}|}} are difficult to prepare.<ref name=Steudel/>

Polysulfide polymers are insoluble in water, oils, and many other organic solvents. Because of their solvent resistance, these materials find use as [[Chemistry:Sealant|sealant]]s 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 {{chem2|(C6H4S)_{''n''}|}}.

===Polysulfides in vulcanized rubber===
[[File:Vulcanization of POLYIsoprene V.2.png|thumb|320px|right|Idealized structure of two strands ({{color|blue|'''blue'''}} and {{color|green|'''green'''}}) of natural rubber after vulcanization with elemental sulfur, which forms polysulfide linkages.]]
Many commercial [[Physics:Elastomer|elastomer]]s contain polysulfides as [[Chemistry:Cross-link|crosslinks]]. These crosslinks interconnect neighboring polymer chains, thereby conferring rigidity. The degree of rigidity is related to the number of crosslinks. Elastomers, therefore, have a characteristic ability to "snap back" to their original shape after being stretched or compressed. Because of this memory for their original [[Chemistry:Curing|cured]] shape, elastomers are commonly referred to as [[Chemistry:Rubber|rubber]]s. The process of crosslinking the polymer chains in these polymers with sulfur is called [[Chemistry:Vulcanization|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 poly[[Chemistry:Chloroprene|chloroprene]] ([[Chemistry:Neoprene|Neoprene]]), styrene-butadiene, and poly[[Chemistry:Isoprene|isoprene]], which is chemically similar to natural rubber. [[Biography:Charles Goodyear|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 [[Chemistry:Water|water]] and [[Chemistry:Ammonia|ammonia]], the clouds in the atmospheres of the [[Astronomy:Gas giant|gas giant]] planets contain ammonium sulfides. The reddish-brownish clouds are attributed to polysulfides, arising from the exposure of the ammonium sulfides to light.<ref>{{cite web|url=http://www.britannica.com/eb/article-54256/Jupiter |title=Jupiter: Cloud composition |website=[[Encyclopædia Britannica]]|date=6 June 2023 }}</ref>

==Properties==
Polysulfides, like sulfides, can induce [[Chemistry:Stress corrosion cracking|stress corrosion cracking]] in [[Engineering:Carbon steel|carbon steel]] and [[Chemistry:Stainless steel|stainless steel]].

== See also ==
* {{annotated link|Biology:Disulfide}}
* {{annotated link|Chemistry:Polyiodide}}
* {{annotated link|Chemistry:Catenation}}

==References==
{{reflist}}


[[Category:Sulfur compounds]]
[[Category:Anions]]
[[Category:Inorganic polymers]]
[[Category:Corrosion]]

{{Sourceattribution|Polysulfide}}