Polysulfane

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A polysulfane is a chemical compound of formula H 2 S n, where n > 1 (although disulfane (H2S2) is sometimes excluded). [1] [2] [3] Compounds containing 2 – 8 sulfur atoms have been isolated, longer chain compounds have been detected, but only in solution. [4] H2S2 is colourless, higher members are yellow with the colour increasing with the sulfur content.In the chemical literature the term polysulfanes is sometimes used for compounds containing −(S)n−, e.g. organic polysulfanes R1−(S)n−R2.

Contents

Structures

Polysulfanes consist of unbranched chains of sulfur atoms terminated with hydrogen atoms. The branched isomer of tetrasulfane H2S4, in which the fourth sulfur is bonded to the central sulfur, would be described as trithiosulfurous acid, S=S(−SH)2. Computations suggests that it is less stable than the linear isomer HSSSSH. [5] The S-S-S angles approach 90° in H2S3 and higher polysulfanes. [4]

Reactions and properties

Polysulfanes can easily be oxidised, and are thermodynamically unstable with respect to decomposition (disproportionation) readily to H2S and sulfur:

8 H2Sn → 8 H2S + (n − 1) S8 (S8 is cyclo-octasulfur, one of the allotropes of sulfur)

This decomposition reaction is catalyzed by alkali. To suppress this behavior, containers for polysulfanes are often pretreated with acid to remove traces of alkali. [6]

In contrast to the thermodynamic instability of polysulfates, polysulfide anions form spontaneously by treatment of S2− with elemental sulfur:

S2− + (n − 1) S → [Sn]2−

Beyond H2S and H2S2, many higher polysulfanes H2Sn (n = 3 – 8) are known. [7] They have unbranched sulfur chains. Starting with disulfane H2S2, all known polysulfanes are liquids at room temperature. The density, boiling point and viscosity correlate with chain length. Physical properties of polysulfanes are given in the table below. [6]

Compound Density at 20 °C (g·cm−3) Vapour pressure (mmHg)Extrapolated boiling point (°C)
H2S1.363 (g·dm−3)1740 (kPa, 21 °C)−60
H2S21.33487.770
H2S31.4911.4170
H2S41.5820.035240
H2S51.6440.0012285
H2S61.688??
H2S71.721??
H2S81.747??

They also react with sulfite and cyanide producing thiosulfate and thiocyanate respectively. [6]

Polysulfanes can be made from polysulfides by pouring a solution of a polysulfide salt into cooled concentrated hydrochloric acid. A mixture of metastable polysulfanes separates as a yellow oil, from which individual compounds may be separated by fractional distillation. Other more selective syntheses are:

Na2Sn + 2 HCl → 2 NaCl + H2Sn (n = 4, 5, 6)
SnCl2 + 2 H2Sm → 2 HCl + H2Sn+2m

The reaction of polysulfanes with sulfur dichloride or disulfur dichloride produces long-chain dichloropolysulfanes:

2 SCl2 + H2Sn → 2 HCl + S2+nCl2
2 S2Cl2 + H2Sn → 2 HCl + S4+nCl2

The reaction with a sulfite salt (a base) quantitatively decomposes the polysulfane to produce thiosulfate and hydrogen sulfide:

(n − 1) SO2−3 + H2Sn → (n − 1) S2O2−3 + H2S

Related Research Articles

<span class="mw-page-title-main">Sodium thiosulfate</span> Chemical compound

Sodium thiosulfate is an inorganic compound with the formula Na2S2O3·xH2O, where x indicates the number of water molecules in the compound. Typically it is available as the white or colorless pentahydrate, Na2S2O3·5H2O. The solid is an efflorescent crystalline substance that dissolves well in water.

<span class="mw-page-title-main">Polysulfide</span>

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 = alkyl or aryl.

<span class="mw-page-title-main">Calcium sulfide</span> Chemical compound of formula CaS

Calcium sulfide is the chemical compound with the formula CaS. This white material crystallizes in cubes like rock salt. CaS has been studied as a component in a process that would recycle gypsum, a product of flue-gas desulfurization. Like many salts containing sulfide ions, CaS typically has an odour of H2S, which results from small amount of this gas formed by hydrolysis of the salt.

In horticulture, lime sulphur (American spelling lime sulfur) is mainly a mixture of calcium polysulfides and thiosulfate (plus other reaction by-products as sulfite and sulfate) formed by reacting calcium hydroxide with elemental sulfur, used in pest control. It can be prepared by boiling in water a suspension of poorly soluble calcium hydroxide (lime) and solid sulfur together with a small amount of surfactant to facilitate the dispersion of these solids in water. After elimination of any residual solids (flocculation, decantation and filtration), it is normally used as an aqueous solution, which is reddish-yellow in colour and has a distinctive offensive odour of hydrogen sulfide (H2S, rotten eggs).

<span class="mw-page-title-main">Tetrasulfur tetranitride</span> Chemical compound

Tetrasulfur tetranitride is an inorganic compound with the formula S4N4. This gold-poppy coloured solid is the most important binary sulfur nitride, which are compounds that contain only the elements sulfur and nitrogen. It is a precursor to many S-N compounds and has attracted wide interest for its unusual structure and bonding.

Sulfur compounds are chemical compounds formed the element sulfur (S). Common oxidation states of sulfur range from −2 to +6. Sulfur forms stable compounds with all elements except the noble gases.

<span class="mw-page-title-main">Sulfur dichloride</span> Chemical compound

Sulfur dichloride is the chemical compound with the formula SCl2. This cherry-red liquid is the simplest sulfur chloride and one of the most common, and it is used as a precursor to organosulfur compounds. It is a highly corrosive and toxic substance, and it reacts on contact with water to form chlorine-containing acids.

<span class="mw-page-title-main">Disulfur dichloride</span> Chemical compound

Disulfur dichloride is the inorganic compound of sulfur and chlorine with the formula S2Cl2. It is an amber oily liquid.

Thiosulfuric acid is the inorganic compound with the formula H2S2O3. It has attracted academic interest as a simple, easily accessed compound that is labile. It has few practical uses.

<span class="mw-page-title-main">Allotropes of sulfur</span> Class of substances

The element sulfur exists as many allotropes. In number of allotropes, sulfur is second only to carbon. In addition to the allotropes, each allotrope often exists in polymorphs delineated by Greek prefixes.

<span class="mw-page-title-main">Hydrogen disulfide</span> Chemical compound

Hydrogen disulfide is the inorganic compound with the formula H2S2. This hydrogen chalcogenide is a pale yellow volatile liquid with a camphor-like odor. It decomposes readily to hydrogen sulfide and elemental sulfur.

Selenium monochloride or diselenium dichloride is an inorganic compound with the formula Se2Cl2. Although a common name for the compound is selenium monochloride, reflecting its empirical formula, IUPAC does not recommend that name, instead preferring the more descriptive diselenium dichloride.

<span class="mw-page-title-main">Trisulfane</span> Chemical compound

Trisulfane is the inorganic compound with the formula H2S3. It is a pale yellow volatile liquid with a camphor-like odor. It decomposes readily to hydrogen sulfide (H2S) and elemental sulfur. It is produced by distillation of the polysulfane oil obtained by acidification of polysulfide salts.

<span class="mw-page-title-main">Titanocene pentasulfide</span> Chemical compound

Titanocene pentasulfide is the organotitanium compound with the formula (C5H5)2TiS5, commonly abbreviated as Cp2TiS5. This metallocene exists as a bright red solid that is soluble in organic solvents. It is of academic interest as a precursor to unusual allotropes of elemental sulfur as well as some related inorganic rings.

<span class="mw-page-title-main">Sodium polysulfide</span> Chemical compound

Sodium polysulfide is a general term for salts with the formula Na2Sx, where x = 2 to 5. The species Sx2−, called polysulfide anions, include disulfide (S22−), trisulfide (S32−), tetrasulfide (S42−), and pentasulfide (S52−). In principle, but not in practice, the chain lengths could be longer. The salts are dark red solids that dissolve in water to give highly alkaline and corrosive solutions. In air, these salts oxidize, and they evolve hydrogen sulfide by hydrolysis.

<span class="mw-page-title-main">Thiosulfurous acid</span> Chemical compound

Thiosulfurous acid is a hypothetical chemical compound with the formula HS−S(=O)−OH or HO−S(=S)−OH. Attempted synthesis leads to polymers. It is a low oxidation state (+1) sulfur acid. It is the Arrhenius acid for disulfur monoxide. Salts derived from thiosulfurous acid, which are also unknown, are named "thiosulfites" or "sulfurothioites". The ion is S=SO2−
2.

Hydrogen chalcogenides are binary compounds of hydrogen with chalcogen atoms. Water, the first chemical compound in this series, contains one oxygen atom and two hydrogen atoms, and is the most common compound on the Earth's surface.

<span class="mw-page-title-main">Sulfoxylic acid</span> Chemical compound

Sulfoxylic acid (H2SO2) (also known as hyposulfurous acid or sulfur dihydroxide) is an unstable oxoacid of sulfur in an intermediate oxidation state between hydrogen sulfide and dithionous acid. It consists of two hydroxy groups attached to a sulfur atom. Sulfoxylic acid contains sulfur in an oxidation state of +2. Sulfur monoxide (SO) can be considered as a theoretical anhydride for sulfoxylic acid, but it is not actually known to react with water.

Polonium sulfide is an inorganic compound of polonium and sulfur with the chemical formula PoS. The compound is radioactive and forms black crystals.

<span class="mw-page-title-main">Disulfur diiodide</span> Chemical compound

Disulfur diiodide is an unstable inorganic chemical compound with the chemical formula S2I2. Its empirical formula is SI. It is a red-brown solid that decomposes above −30 °C to elemental sulfur and iodine.

References

  1. ↑ IUPAC , Compendium of Chemical Terminology , 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006–) " polysulfanes ". doi : 10.1351/goldbook.P04753
  2. ↑ Wiberg, E.; Holleman, A. F.; Wiberg, Nils (2001). Inorganic Chemistry. San Diego : Academic Press; New York : De Gruyter. ISBN   978-0-12-352651-9. OCLC   48056955.{{cite book}}: CS1 maint: location missing publisher (link)
  3. ↑ Greenwood, N. N.; Earnshaw, A. (2012-12-02). Chemistry of the Elements. Boston, Massachusetts, MA: Elsevier. ISBN   978-0-08-050109-3. OCLC   48138330.
  4. 1 2 R. Steudel "Inorganic Polysulfanes H2Sn with n > 1" in Elemental Sulfur and Sulfur-Rich Compounds II (Topics in Current Chemistry) 2003, Volume 231, pp 99–125. doi : 10.1007/b13182
  5. ↑ Laitinen, Risto S.; Pakkanen, Tapani A.; Steudel, Ralf (1987). "Ab initio study of hypervalent sulfur hydrides as model intermediates in the interconversion reactions of compounds containing sulfur–sulfur bonds". J. Am. Chem. Soc. 109 (3): 710–714. doi:10.1021/ja00237a012.
  6. 1 2 3 Greenwood and Earnshaw, p. 683
  7. ↑ R. Steudel "Inorganic Polysulfanes H2S2 with n > 1" in Elemental Sulfur and Sulfur-Rich Compounds II (Topics in Current Chemistry) 2003, Volume 231, pp 99-125. doi : 10.1007/b13182
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