Sulfanes Polysulfides

A mixture of sulfanes is obtained when aqueous sodium polysulfide is rapidly acidified with concentrated hydrochloric acid at low temperatures [16, 18] ... 

Since the chain-lengths of the molecules present in crude sulfane oil is different from the chain-length of the anions in the original sodium polysulfide solution one has to conclude that in addition to the reaction at Eq. (4) the reactions at Eqs. (5) and (6) also take place during the preparation by protonation of the polysulfide anions. 

MeO)2S [36]. These evidently originated from the reaction of the dichloro-sulfanes with the methanol solvent used in the preparation of the sulfanes by mixing sodium polysulfide with dichlorosulfanes. 

Interestingly, the sulfanes H2S are both proton acceptors and donors. In the first case sulfonium ions H3S are formed, in the second case hydrogen polysulfide anions HS are the result. While the latter have never been isolated in salts, several salts with sulfonium cations derived from the sulfanes with n = 1, 2, and 4 have been published. However, none of these salts has been structurally characterized by a diffraction technique. Therefore, the structures of the HsSn cations and HS anions are known from theoretical calculations only. 

However, some interconversion reactions take place simultaneously and therefore the composition of the sulfane mixtime is not a mirror image of the composition of the polysulfide solution [103]. The sulfane mixture forms a yellow oily hydrophobic liquid which precipitates from the aqueous phase. At 20 °C it decomposes more or less rapidly to H2S and Sg. 

Since heptasulfane is difficult to prepare, a mixture of polysulfanes known as crude sulfane oil was used instead (average composition H2S6.2, accessible from sodium polysulfide and hydrochloric acid [71]). From 104 g of... 

Negative ions of sulfur exist in aqueous polysulfide solutions 112a) and nonaqueous solutions 16). The structure of these ions is presumed to be similar to that of Feher s sulfanes 87) and their corresponding salts. Figure 1 shows that in these compounds cis-cis or trans-trans configurations are possible. Some bond data are given in Table II. Typical values are 101)... 

Sulfur has a strong tendency to catenation, which manifests itself not only in the many forms of the element that all contain S rings of various sizes, but in polysulfide ions S - which may be discrete in highly ionic salts or serve as chelating ligands towards transition metals, sulfanes (XS X) (where X... 

Simple sulfides are discussed elsewhere. However, the chemistry of polysulfides relates to that of the sulfanes, and some discussion is provided here. 

Such sulfinate compounds are water soluble and may be used as antiradiation drugs (see Section 7.4). Bis(sulfinato)trisulfanes may be converted to the corresponding bisalkyl esters by reaction with either diazomethane or a solution of BF3 in diethyl ether. When sodium polysulfide is apphed in equation (59) the resulting poly-sulfanes (equation 60) contain up to six sulfur atoms. However, bis(sulfinato)polysulfanes with more than four catenated sulfur atoms are unstable in water, and elemental sulfur is slowly precipitated. When the thiosulfonate RS(0)-(CH2)2-SS02C6H4Me was used in equations (59) and (60), the bis(sulfoxido)trisulfane [RS(0)-(CH2)2]2S3 resulted. ... 

Polysulfanes with the general formula H2S (n — 2-S) are reactive oils in their pure state. Heating aqueous sulfide solutions yields polysulfide ions most typically with n = 3 or 4. The presence of sulfanes has been used to explain the high concentrations of sulfur compounds in some hydrothermal fluids (Migdisov and Bychkov, 1998). 

Preparation of S12 from S2CI2 and a polysulfane mixture H2S sulfanes H2S and dichlorosulfanes S Cl2 react with each other with elimination of HCl forming new S-S bonds. Since piue sulfanes with more than two sulfur atoms are difficult to prepare, this synthesis uses a mixture of sulfanes, called crude sulfane oil , which can easily be prepared from aqueous sodium polysulfide and concentrated hydrochloric acid at 0 °C [39, 40] ... 

Since the aqueous sodium polysulfide contains already several polysulfide anions in equilibrium and since the acidification results in some interconversion reactions, a sulfane mixture H2S c is obtained rather than pure H2S4. This mixture nevertheless reacts in dry CS2/Et20 mixture at 20 °C with dichlorodisulfane, besides other products, to S12 which has been isolated in 4% yield by extraction with CS2 and fractional crystallization [41] ... 

In principle, deprotonation of any of the sulfanes gives polysulfide anions In practice, this route is not employed and rather fewer anions are known compared with the sulfanes. It was established last century that sulfur dissolves in basic media to give intensely colored (often blue) solutions. The well-known polysulfide solution [NH4]2Sjt, which contains mostly X = 4 and 5, is obtained by bubbling H2S through a suspension of sulfur in ammonium hydroxide. It is accepted nowadays that the blue coloration of many of these solutions is a consequence of the 83 radical. This species has characteristic EPR, visible, and Raman spectra that have enabled its detection in a variety of solutions including liquid ammonia,DMF, and HMPA. 82 can be introduced as an impurity into alkali metal halides. In lapis lazuli (lazurite that is made synthetically as ultramarine blue Na8[Al68i6024]8 , n = 2-4), the blue color is due to the presence of 83 radicals, which has also been identified by Resonance Raman Spectroscopy ... 

Before we present the results of these calculations, it is useful to consider the expected results. Sulfur rings are isovalent to cycloalkanes (CH2)n and might be expected to have large gaps between the top filled and lowest empty orbitals. The sulfanes HSnH, formerly called polysulfides, would be expected also to have large gaps between the top filled and lowest empty orbitals in analogy to the isovalent linear alkanes. On the other hand, the open chain S allotropes are isovalent to alkane diradicals and would be expected to be colored. We considered also the possibility of branched chain allotropes, whose properties we could not predict in advance. The extended Hiickel calculation was used to see whether the expected properties were supported by the simplest model orbital calculation, to determine the dependence on number of sulfur atoms, and to see if branched chain structures are reasonable. Moreover,... 

Let s reflect for a moment on how the chemistry just described compares with the chemistry of the sulfanes described in the last section. Like the sulfane SH groups, the oxygens of H2O2 can act as nucleophiles. Like the sulfur atoms within polysulfide chains, the oxygens in H2O2 can also act as electrophiles. One distinct feature of H2O2 chemistry is of course its potential for oxidation to O2. Sulfanes too are prone to oxidation but not to diatomic S2, which is unstable, but rather to medium-sized S rings. 

If acid is added to polysulfides (see Section 12.3.2), a mixture of acids containing S—S bonds results H2S2, H2S3, H2S4, etc. As these are analogues of carbon and silicon hydrides, they are called sulfanes. Sulfur has the highest tendency after carbon to form bonds to itself, that is, to catenate. 

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