Polysulfides samples

Vibrational spectroscopy and in particular Raman spectroscopy is by far the most useful spectroscopic technique to qualitatively characterize polysulfide samples. The fundamental vibrations of the polysulfide dianions with between 4 and 8 atoms have been calculated by Steudel and Schuster [96] using force constants derived partly from the vibrational spectra of NayS4 and (NH4)2Ss and partly from cydo-Sg. It turned out that not only species of differing molecular size but also rotational isomers like Ss of either Cy or Cs symmetry can be recognized from pronounced differences in their spectra. The latter two anions are present, for instance, in NaySg (Cs) and KySg (Cy), respectively (see Table 2). 

In anoxic hypolimnion samples collected from Lower Mystic Lake, MA, hexachloroethane was abiotically transformed into tetrachloroethylene via reductive elimination and to pentachloro-ethane via hydrogenolysis. Tetrachloroethylene accounted for 70% of hexachloroethane in unaltered lake water and 62% in filter-sterilized water after 10 d. Trichloroethylene and pent-achloroethane accounted for <1 and 2% in unaltered lake water and filter-sterilized water, respectively. Disappearance rate constants for hexachloroethane were 0.33/d for unaltered water and 0.26/d for filter-sterilized water. At least 80% of the hexachloroethane disappearance in unaltered water was abiotic in origin due to the reactions with naturally occurring aqueous polysulfides, H2S and (Miller et al, 1998a). 

Fig. 33 Effect of nanoclay content on adhesive strength of polysulfide elastomer/clay nanocomposites samples containing 0, 2, 4, and 8 phr of nanoclay are designated as PSCO, PSC2, PSC4, and PSC8, respectively...

Fig. 35 a Failure pattern in the neat polysulfide adhesive sample PSCO. b Failure pattern in clay-loaded sample PSC8... 

Varacin (114), a cytotoxic compound closely related to lissoclinotoxin A (106), was isolated from a Fijian sample of L vareau and a benzopentathiepin structure was proposed on the basis of spectral data [131]. Two total syntheses of varacin (114) have been carried out [132,133] and later, further syntheses were described [134-135]. N,N-dimethyl-5-(methylthio)varacin (115) and the corresponding trithiane (116) were obtained from L. japonicum from Palau and 3,4-desmethylvaracin (117) was isolated from a Eudistoma sp. from Pohnpei [136], An inseparable mixture of 5-(methylthio)varacin (118) and the corresponding trithiane (119) was obtained from a Pohnpeian Lissoclinum sp. [136]. Three additional antimicrobial polysulfides of the varacin family (120-122) were isolated from Polycitor sp., collected by dredging in the Sea of Japan [137]. 

Equilibrium calculations suggested that Hg complexation varies greatly among redox and pH levels typical of the regions of lakes sampled during this study. In an oxic lake, pore water, and groundwater, Hg complexation with organic matter most likely dominates. Under anoxic conditions in the hypolimnion and pore waters, Hg most likely forms soluble bisulfide and polysulfide complexes. 

This study indicates that the sulfur of our sulfide samples was susceptible to bacterial attack in two of the three cases. The aliphatic sulfides could be ranked in the order of their ease of oxidation as di-ferf-butyl polysulfide > di-fert-butyl disulfide > di-tert-butyl sulfide. 

The polarographic and potentiometric methods are not HPLC-run. The polarographic method relies upon the measurement of half-wave potentials of various sulfur compounds reacting with a mercury electrode. It is sensitive to submicromolar concentrations (Luther, pers. com.). While sulfide, thiosulfate, polysulfide and polythionates can be measured, the initial sample must be subdivided and pretreated in different ways. The disadvantages are that sample preparation ana analysis are time-consuming and there is no way to preserve samples for later analysis nor to study organic thiols with precision., ... 

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). 

The notion that naturally occurring organic polysulfides in coal decompose to form elemental sulfur has also been tested in another way. Buchanan and his associates have shown that the 32S/34S ratios of the elemental sulfur and the pyrite in another Illinois Basin Coal Sample Program coal are similar and different from the 32S/34S ratio for the organic material in the same coal (Buchanan, D., private communication, 1989). This result infers that pyrite is the source of elemental sulfur. Thus, we conclude that oxidative chemical and bacteriological processes convert pyrite to elemental sulfur when pristine coals are exposed to the atmosphere. 

At low cure times, only Ale and A2c polysulfidic structures (50 ppm) are observed. At longer cure times, Ale and A2c polysulfidic structures reduce in sulfur rank to monosulfide (45 ppm), and Blc (58 ppm). Bit (64 ppm) and Clc (45 ppm) polysulfidic structures are observed. A small amount of ds-to-trans isomerisation was observed, which increased with sulfur content. The reversion reactions of TBSI-accelerated systems result in a lower degree of sulfurisation as opposed to TBBS-accelerated samples. Based on the equilibrium swelling measurements, TBSI is found to be a less efficient accelerator than TBBS. 

Melsheimer and co workers (Melsheimer and Schlogl, 1997 Melsheimer et al., 1997) investigated the oxidation of H2S with 02 or SO2 on alumina catalysts. A transmission and a diffuse reflectance experiment were compared (Melsheimer et al., 1997). In the transmission experiments, the gas-phase spectra of the reactive gases had to be subtracted. A spectral response could always be observed, but conversions were difficult or impossible to detect because of the small mass of sample in a wafer. Spectra of adsorbed SO2 obtained in the two experiments were similar to each other. During oxidation of H2S with SO2, a number of bands were recorded that were assigned to polysulfide species. The height of a band at approximately 435 nm was inferred to follow a parallel course to the H2S conversion, and hence Sg2 species were inferred to be "responsible for the steady-state conversion". 

The Final Analysis. The SEM analysis of the liquid extrusion shows that sulfur is present in quantities much greater than the monosulfide of calcium could provide. The most probable explanation is that part of the sulfur is present in polysulfide anions, as the infiltration conditions appear to favor their formation (18). A sample of the yellow solution obtained by leaching fragments under nitrogen was therefore analyzed by laser Raman spectrometry to determine if the absorption... 

A useful procedure for the isolation of humic substances from groundwater is that of Thurman and Malcolm (1981) with the following modifications. Hydrochloric acid should be added immediately to the water sample to prevent the precipitation of iron hydroxide, and the sample should be evacuated with a vacuum pump to remove hydrogen sulfide. If the sulfide is not removed, it can react to form both elemental sulfur and polysulfides that adsorb onto and clog the XAD resin (Leenheer and Noyes, in press Thurman, 1979). 

Polysulfides can be generated via two major pathways. First, polysulfides can be formed by the oxidation of dissolved sulfide and sulfide minerals(l, 2). Second, they can be formed by the reaction of elemental sulfur with bisulfide ion(35). Polysulfide levels can be predicted for the second process as described in previous studies(, 36-38). Equilibrium calculations as described in a previous study(22) were performed for the polysulfide levels in these samples. The ratio of S(0) experimental to S(0) calculated for all samples from Great Sippewissett were 0.145 (4-8 cm), 0.137 (8-13 cm) and 0.128 (23-28 cm). Because these ratios are less than 1.0, these results indicate that polysulfides should form primarily from the reaction of bisulfide ion with elemental sulfur(5) rather than sulfide oxidation. This data set is... 

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