Polysulfide

Key takeaways

Polysulfide belongs to chemistry; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Polysulfide to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Polysulfide from memory before moving on to harder problems.

Reference excerpt

Polysulfides are a class of chemical compounds derived from anionic chains of sulfur atoms. There are two main classes of polysulfides: inorganic and organic. The inorganic polysulfides have the general formula S2−n. These anions are the conjugate bases of polysulfanes H2Sn. Organic polysulfides generally have the formulae R1SnR2, where R is an alkyl or aryl group.

Polysulfide salts and complexes

The alkali metal polysulfides arise by treatment of a solution of the sulfide with elemental sulfur, e.g. sodium sulfide to sodium polysulfide: S2−+ n S → S2−n+1 In some cases, these anions have been obtained as organic salts, which are soluble in organic solvents. 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 ligands in coordination chemistry. Examples of transition metal polysulfido complexes include (C5H5)2TiS5, [Ni(S4)2]2−, and [Pt(S5)3]2−. Main group elements also form polysulfides.

Organic polysulfides

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 (ClCH2CH2OCH2OCH2CH2Cl), 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. 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

Many commercial elastomers contain polysulfides as 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 return to their original shape after being stretched or compressed. Because of this memory for their original cured shape, elastomers are commonly referred to as 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.

Properties Polysulfides, like sulfides, can induce stress corrosion cracking in carbon steel and stainless steel. Polysulfides exist in biology as downstream metabolites of hydrogen sulfide and hydropersulfides. They are thought to play an important role in redox biology by acting as reservoirs for hydropersulfides (RSSH) and hydrogen polysulfides (RSSnSH) upon cleavage of polysulfane chains by biological thiols.

See also Disulfide – Functional group with the chemical structure R–S–S–R′ Trisulfide – Functional group Hydropersulfide – Functional group with the chemical structure R–S–S–H Polyselenide - selenium analog Polytelluride - tellurium analog Polyiodide – Anions composed of many iodine atoms Catenation – Bonding of atoms of the same element into chains or rings

References

Illustrations

Worked examples

Example 1 — a first encounter with Polysulfide

Start with the simplest possible case. Write down what Polysulfide claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Polysulfide before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Polysulfide ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Polysulfide

In research: Polysulfide appears in chemistry research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Polysulfide in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Polysulfide is common in secondary-school and first-year university syllabi. It links to neighbouring topics Anions, Corrosion, Homonuclear ions, so understanding it makes those chapters shorter.
In everyday life: Look for Polysulfide outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study Polysulfide in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Polysulfide means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Polysulfide out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Polysulfide in simple terms?

Polysulfides are a class of chemical compounds derived from anionic chains of sulfur atoms. There are two main classes of polysulfides: inorganic and organic.

Why does Polysulfide matter?

Because it connects several chemistry ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Polysulfide?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Polysulfide.