Polysulfur

Even in the presence of considerable moisture, soHd polymer never forms above 30°C (23). Below 30°C, Hquid stabiUty decreases with increasing moisture and decreasing temperature (23). The actual formation of soHd polymer has been hypothesized to involve the formation in the Hquid of high molecular weight polysulfuric acids, followed by precipitation. 

Although the polysulfur macrocycles became more interesting to the scientific community after Pedersen s report of the crown compounds (see Chap. 1), examples of such structures may be found in the literature dating back some time. The first report of a macrocyclic polysulfide appears to be that by Ray who found in 1920 that when 1,2-dimercaptoethane and 1,2-dibromoethane were heated with alcoholic potassium hydrogen sulfide as shown in Eq. (6.2), triethylene trisulfide (2) and a substance presumed to be triethylene tetrasulfide (3) could be isolated. 

At about the same time Pedersen s work was underway, Bradshaw and his coworkers had undertaken the systematic preparation of numerous mono- and polysulfur macrocycles The syntheses were carried out in a fashion similar to that shown in Eq. (6.3). The two principal sources of sulfur in the first paper from this groupwere sodium sulfide and 1,2-ethanedithiol. The latter was utilized in the presence of sodium hydroxide base. Ethanol was generally used as solvent and the reactions were conducted at high dilution. Products were purified either by vacuum distillation or recrystallization as appropriate. The yields were generally in the 5—30% range. 

Ochrymowycz and his coworkers have also prepared a number of polysulfur macrocycles for use in biological or biological model systems . The synthetic methodology is essentially similar to that described above except that certain of the sulfur containing fragments were prepared by addition reactions to ethylene. Two examples of this approach, taken from ref. 59, are shown in Eq. (6.9). 

C. W. Rees, Polysulfur-Nitrogen Heterocyclic Chemistry, J. Heterocycl. Chem., 29, 639 (1992). 

NMR and visible spectra have established that a number of S-N anions are present in such solutions.The primary reduction products are polysulfides Sx, which dissociate to polysulfur radical anions, especially the deep blue 83 ion (/Imax 620nm). In a IM solution the major S-N anion detected by NMR spectroscopy is cycZo-[S7N] with smaller amounts of the [SSNSS] ion and a trace of [SSNS]. The formation of the acyclic anion 5.23 from the decomposition of cyclo-Sjl is well established from chemical investigations (Section 5.4.3). The acyclic anions 5.22 and 5.23 have been detected by their characteristic visible and Raman spectra. It has also been suggested that a Raman band at 858 cm and a visible absorption band at 390 nm may be attributed to the [SaN] anion formed by cleavage of a S-S bond in [SSNS]. ° However, this anion cannot be obtained as a stable species when [SsN] is treated with one equivalent of PPhs. 

CN mucopolysaccharide polysulfuric acid ester sodium salt... 

In the literature tetrathiosulfuranes have been discussed as possible intermediates in the thermal decomposition of sulfanes and other polysulfur compounds. High-level ab initio MO calculations have in fact revealed that such species are local minima on the potential energy hypersurface [34]. However, recent results show that both the Gibbs reaction energies as well as the activation enthalpies for reactions of the type... 

Like other polysulfur compounds, the sulfanes are subject to degradation if treated with strong nucleophiles like aqueous sulfite, arsenite or cyanide ... 

The effect shown in Fig. 9 is a result of the bond-bond interaction which is a characteristic feature for chains and rings of two-valent chalcogen atoms. It can also be recognized from the relatively large bond interaction force constants fir of such compounds. The stretching force constants /r(SS) of polysulfur compounds depend on the SS bond distances as shown in Fig. 10. The data used in this figure include several excited electronic states of the S2 molecule as well as the disulfide anion and a number of sulfur homocycles [77]. 

The discovery in 1973 that polysulfur nitride (SN)X, a polymer comprised only of non-metallic elements, behaves as a superconductor at 0.26 K sparked widespread interest in sulfur-nitrogen (S-N) chemistry. In the past 30 years, the field of inorganic S-N chemistry has reached maturity and interfaces with other areas of chemistry, e.g., theoretical chemistry, materials chemistry, organic synthesis, polymer chemistry and biochemistry, have been established and are under active development. This interest has been extended to Se-N and, to a lesser extent, Te-N systems. 

Sulfur dissolves in liquid ammonia to give intensely coloured solutions. The colour is concentration-dependent and the solutions are photosensitive. Several S-N anions are present in such solutions.76,77 The primary reduction products are polysulfides Sx2, which dissociate to polysulfur radical anions, notably the deep blue S3 ion. In a 1M solution, the major S-N anion is cyc/0-[S7N] with smaller amounts of 21 and a trace of 20.76... 

Other related compounds are the diphosphine disulfides R2P(S)P(S)R2 14, which contain a direct phosphorus-phosphorus bond, and polysulfur fe(dior-ganophosphine sulfides) R2P(S)-S -P(S)R2 in which the two phosphorus centres are connected by a chain of one of more sulfur atoms. R2P(S)P(S)R2 compounds are accessible from heating secondary phosphine sulfides with thiophosphinic chlorides (Equation 10) or by reaction of fephosphines with... 

A tree, Scorodocarpus borneensis, native to Borneo and the Malay peninsula, has a garlic-like smell and is known as wood garlic . The fruit is used locally for seasoning. The major volatile flavor compounds from wood garlic are similar to those of garlic itself. Some of these materials are polysulfur compounds and have antimicrobial activity against some bacteria and fungi. These materials contain four sulfur atoms.75 They are either 2,4,6-trithiaheptane-5-thione-2,2-dioxide (CH3-SO2-CH2-S-CS-S-CH3) or derivatives of tetrathia-octane (CH3-S-CH2-S-S-CH2-S-CH 3, CH3-SO2-CH2-S-S-CH2-S-CH3, CH3-S-CH2-SO2-S-CH2-S-CH3). 

Clear white to yellow-pink deliquescent crystals with an odor like rotten eggs due to formation of hydrogen sulfide. Commercial material may be yellow or brick-red lumps or flakes. It is unstable and discolors upon exposure to air. It undergoes autoxidation to form polysulfur, thiosulfate, and sulfate. It absorbs carbon dioxide from the air to form sodium carbonate. Moist sodium sulfide is spontaneously flammable upon drying in air. This material is hazardous through ingestion and produces local skin/eye impacts. 

Although these equations held true for some strains of bacteria under some growth conditions, they did not help explain the commonly observed quantitative conversion of both sulfur atoms of thiosulfate to sulfate, rather than the liberation of the sulfane-sulfur mainly as elemental sulfur. During the 1960s, cyclic reactions of polythionates and other polysulfur compounds continued to be postulated as mechanisms for thiosulfate and polythionate metabolism (Trudinger 1967), but none of these was supported at the time by strong biochemical evidence. The time was opportune for a new approach to the problem of thiosulfate oxidation in thiobacilli. 

More curious and unexpected reactions were observed when complex 219 was heated with triethylamine often used as an "inert" base in many reactions with sulfur monochloride. Thienopentathiepin 229 (30%) together with heptathiocane 230 (10%) were produced their polysulfur rings had the anticipated chair and crown conformations, respectively (20030L1939 Scheme 122). 

The iron-catalyzed reaction of 1,3-dimethoxybenzene with sulfur monochloride in dilute chloroform gave two polysulfur heterocycles 245 and 246 with six sulfur atoms in the molecule, yields were very low (1979JCS(P1)1712 Scheme 131). 

Treatment of mesitylene or dimesityl sulfide with sulfur monochloride led to the same polysulfur macrocycle 247 yields in both cases were identical (1977T337 Scheme 132). 

Sulfur is present in the petrochemicals derived from once-living matter as it is present in certain amino acids. Because of its removal from industrial waste, sulfur has been stockpiled and is available at a low price in large amounts. While the stable form of sulfur at room temperature is cyclooctasulfur (Sg), linear polysulfur is formed on heating. Unfortunately, the thermodynamically stable form of sulfur is the cyclooctasulfur monomer and the polymer undergoes depolymerization after sometime. 

Methods have been studied to inhibit this reversal process. Some have involved the addition of olefins such as limonene, myrcene, and cyclopentadiene to the ends to inhibit the depolymerization. Such stabilized polysulfur has been incorporated into concrete and asphalt mixes to strengthen them. Concrete blocks, posts, and parking tire restrainers containing polysulfur... 

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