Polysulfides determination

Howard B.J. Alley, Determination of Ferric Oxide, Aluminum, and Magnesium Oxide in Polysulfide Propellants , ARGMA TR-1D2R (1960) 6) Anon, Polysulfide, Polymer,... 

The generated polysulfide dianions of different chain-lengths then establish a complex equilibrium mixture with all members up to the octasulfide at least see Eqs. (5) and (6). For this reason, it is not possible to separate the polysulfide dianions by ion chromatography [6]. The maximum possible chain-length can be estimated from the preparation of salts with these anions in various solvents (see above). However, since the reactions at Eqs. (22) and (23) are reversible and Sg precipitates from such solutions if the pH is lowered below a value of 6, the nonasulfide ion must be present also to generate the Sg molecules by the reverse of the reaction at Eq. (22). The latter reaction (precipitation of Sg on acidification) may be used for the gravimetric determination of polysulfides [11]. There is no evidence for the presence of monoprotonated polysulfide ions HS - in aqueous solutions [67, 72]. 

This reaction has also been used for the titrimetric determination of polysulfides [10, 11]. 

Titration of the unreacted hydroxide with standard sulfuric acid allows the determination of the polysulfide [10, 11]. 

The various oxidation states of sulfur have been determined by polarography. The electrochemical oxidation of sulfide ions in aqueous solution may lead to the production of elementary sulfur, polysulfides, sulfate, dithionate, and thiosulfate, depending on the experimental conditions. Disulfides, sulfoxides, and sulfones are typical polarographically active organic compounds. It is also found that thiols (mer-captans), thioureas, and thiobarbiturates facilitate oxidation of Hg resulting thus in anodic waves. 

An interesting idea has been to prepare the photosensitive electrode on site having the liquid play the dual role of a medium for anodic film growth on a metal electrode and a potential-determining redox electrolyte in the electrochemical solar cell. Such integration of the preparation process with PEC realization was demonstrated initially by Miller and Heller [86], who showed that photosensitive sulfide layers could be grown on bismuth and cadmium electrodes in solutions of sodium polysulfide and then used in situ as photoanodes driving the... 

A number of structures with S-rich dianion ligands have been determined (297-299).831 832 For example, (297) can be synthesized by the reaction of [Ni(CN)4]2 with polysulfide.833 Upon further reaction with CS2 or substituted acetylenes it forms perthiocarbonato and dithiolene complexes, respectively. 

S " ") and depolymerization (S " " - Sg + Sy -t- Sg 4-. ..). This free radical mechanism has often been discussed on the basis of the observed first order rate equations found for the formation of it-sulfur and the decomposition of organic polysulfides as well as on the basis of the experimentally determined apparent activation energies (50-150 kJ/mol ). However, this type of mechanism seems rather unlikely at least at moderate temperatures sinc (a) no free radicals have been detected in liquid sulfur below 170 (b) only the... 

The presence of the liquid sulfur phase in the Richard process may favor the formation of the product liquid sulfur by aiding the formation of the intermediate hydrogen polysulfide building block. The success of a 5LTD demonstration plant may well determine whether future sulfur recovery from H2S feed continues to be by... 

In this study, the dipole moments at 298 K and the corresponding temperature coefficient of PDTC are calculated in the RIS approximation. The results are compared to the values determined by experiment. The results indicate that an extra stabilization energy of about 3.8 kj mol-1 must be added to these gauche states relative to trans state. This provides evidence of a large attractive sulfur gauche effect in the polysulfides, about equal in magnitude to that found for the analogous POM. 

The structures of nine of these compounds were determined by spectroscopic methods, while those of the 14 remaining materials were established by GC-MS only. The compounds can be classified into four types (A to D) the 1,2,4-trithiolanes (145-154), 1,2,4,5-tetrathianes (155-157), 1,2,3,5,6-pentathiepanes (158-163), which are all generally quite stable compounds, and the monoalkyl-substituted polysulfides (164-167), which tend to disproportionate into sulfur and disubstituted cyclic polysulfides. These compounds are structurally related to the cyclic polysulfide compounds reported from red alga Chondria californica in 1976 [136] and to compound 168 (3-hexyl-4,5-dithiacycloheptanone) reported from the brown algae of the Dictyopteris genus in 1971 [137]. The latter compound has more recently been found to be a potent inhibitor of bee venom-derived phospholipase A2 (PLA2) [138]. 

Modified Waksman s medium was prepared in a Fernbach culture flask. An amount of organic sulfide normalized to an equivalent sulfur content of the standard medium (10 g/1.) was added followed by an emulsifier. The medium was then autoclaved for 30 min at 15 psi (121°C), or, as with the polysulfide and elemental sulfur, sterilization was achieved by membrane filtration. Upon cooling, the medium was inoculated with 10 cc of the pure strain of Thiobacillus thiooxidans. The culture s initial pH value was read, and an initial gravimetric sulfate assay was performed. Thereafter, pH and sulfate values were determined at two-day intervals for 25 days. 

The first preparation and structure determination of optically pure cyclic polysulfides, 6,10-diethyltrithiolo[ ]ben-zopentathiepin monoxides, were described in 1997 <1997TL1607>. Then the oxidation reaction and properties of... 

One such difficulty is that, while it appears that [Sn2 ] levels may be as high as 400 /iM in some hypoxic environments, the precise number (n) of sulfur atoms in these polysulfide species, or even the range of n, is uncertain. Bouleague (16) discusses some of the thermodynamic equilibrium calculations which may be used to estimate the distribution of s[Sn2 ] among the various polysulfide species. Another difficulty with these data is that the structures of the thiols (RSH) detected are not well known. Mopper and Taylor (14) identified 13 different thiols in slurries of intertidal sediments from Biscayne Bay (FL), and found at least 20 more thiols whose structures could not be determined. Their observations (Table III) indicate that thiols encountered in natural waters will probably exhibit a broad variety of structures in any one location, but that a relatively small number of compounds may dominate the mixture. 

The results obtained for reaction of acrylic acid (200 /iM) with tetrasulfide (1.25 mM 5 mM) as well as bisulfide (5 mM) are shown in Figurel. In the reaction with HS, the concentration of 3-MPA did not noticeably increase after treatment with TBP. If polysulfide ion was the actual reactive species in this reaction, then TBP treatment should have caused a significant increase of 3-MPA, in comparison to that without TBP. Therefore, these results indicate that HS was the reactive species in the sulfide medium. However, in the reaction of acrylate with the polysulfide ion, S42, determination of 3-MPA concentration after TBP treatment revealed a large increase, indicating that S42 reacted with acrylate to produce 3-tetrasulfidopropionic acid. The reactivity of tetrasulfide with acrylate was much higher than that of bisulfide. Similar results were also obtained for reaction of acrylonitrile with HS and S42 (Figure 2). The kinetic data are summarized in Table I. In the polysulfide senes low concentrations of 3-MPA were also observed without TBP treatment. It is possible that this 3-MPA was formed from uncatalyzed dissociation of the polysulfide addition product... 

The potentiometric measurement of hydrogen sulfide via a Ag/Ag2 electrode is well known and such electrodes are commercially available. Boulggue (22) has used the electrode to measure changes in potential during a titration with HgC. This method can measure sulfide, polysulfide, thiols, sulfite and thiosulfate. Weaknesses of die method are the following there is no method of sample preservation the pH must be adjusted to pH 13 for the measurement of sulfide, thiol and polysulfide then adjusted to pH 7 for the measurement of thiosulfate and sulfite polysulfide is determined by difference after attack on the polysulfides with added sulfite (if elemental sulfur is present in the sample it will also participate in this reaction) the identity of the organic thiols is unknown and sulfite can not be measured in seawater samples because of competition with halides (21). 

Figure 2. Radioactivity chromatogram of sulfur compounds derivatized with monobromobimane. The reversed-phase HPLC separation is based on the hydrophobic properties of the bimane-sulfur adducts but peak area is based on "S-radioactivity of the compounds. At time 0 sulfite and thiosulfate impurities are present before addition of the hepatopancrease tissue homogenate. This was a 60 min experiment to determine the sulfide detoxifying functions of the hepatopancrease of the hydrothermal vent crab Bythograea thermydron. During this time the proportion of radioactivity in sulfide rapidly decreases and thiosulfate and sulfate accumulate as end products. Two intermediates, pi and p2 accumulate then decrease during the experiment. The two intermediates are believed to be polysulfides based on similar elution times of polysulfide standards. (Figure is the unpublished chromatograms from the data in Vetter et al. (24)-) continued on next page.

The rate constants kt and k2 were found to be 0.5 M 1 min-1 and 29.0 M-1 min-1 respectively at pH 5.05 and 25 C. The rate law and other data suggest a nucleophilic displacement by the bisulfide ion (HS ) on H202 as the rate-determining step with subsequent formation of polysulfide as intermediates. The rate of the reaction was found to decrease as HS ion in solution decreases and hence the optimal pH for oxidation was determined to be 7. They postulated the following mechanism for the second term in the rate expression ... 

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