Sulfur-based compounds

The possibility to vary the parameters governing the physical properties of (TM>2X compounds (nature of cation or anion, pressure and application of a magnetic field) allows an exploration moving continuously from half-filled band 1-D Mott insulators in sulfur based compounds to conducting systems in selenium or strongly pressurized sulfur based compounds (Fig. 4). 

The exact mechanism of toxicity has not been elucidated, although there is a lot of information on how sulfur-based compounds are detoxified by the liver. Sodium sulfite is a mild reducing agent that would most likely cause burning or irritation at the site of exposure or application by altering oxidation-reduction potential and pH. 

Some sulfur-based compounds (especially those with thiol functions) make a positive contribution to the varietal aromas of certain grape varieties. The role of 4-methyl-4-mercaptopentanone in Sauvignon Blanc aroma is well known (Section 7.4.1). However, most sulfur derivatives have a very bad smell and have detection thresholds as low as 1 p,g/l. These compounds are known as mercaptans, referring to their capacity to be precipitated by mercury salts. 

Most liquids and gases that contain sulfur tend to have rather noxious odors. Notable examples include sulfur dioxide (SO ), hydrogen sulfide (FI S), and mercaptans the class of sulfur-based compounds that are responsible for the intense odor of a skunks spray. 

The liquid (sulfur-based compounds) and sohd sulfur cathodes (items 6 and 7) do not develop surface chemistry that can be separated from their main electrochemical redox reactions. Hence, when the reduction of sulfur SO2 or SOCI2 produces insoluble species such as LiCl, LijS, and LijO, they precipitate on the current collector [9]. When formed, LijS can be reoxidized, up to elemental sulfur, via various LLS intermediate compounds [10]. Hence, the current collector, which may be aluminum (Al) plus carbon in the case of sulfur cathodes or carbon in the case of SOCI2 cathodes, does not develop intrinsic surface chemistry beyond the precipitation of the reduction products of the active mass. 

There have been several papers dealing with the oxidation reactions of nitrogen and sulfur-based compounds. Hindered amines, such as substituted 2,2,6,6-tetramethylpiperidines, are easily oxidized by electron-transfer reactions to the corresponding cation, by the sulfate radical anion, and by sensitized electron transfer to carbonyl triplets. Radicals derived from tertiary piperidines were observed directly by optical spectroscopy and deprotonated to a-alkylamine radicals. The amine radical cation derived from secondary piperidines deprotonated to give aminyl radicals. In the presence of oxygen, both classes were oxidized to give nitroxyl radicals, but by different proposed mechanisms. Both oxidation and fragmentation pathways have been observed in the photochemical reaction of alkyl phenyl sulfides with tetranitromethane. The oxidation of various A-(arylthio)-4-substituted-2,6-diarylanilines (18) with PbOa yielded, in most cases, persistent radicals that could... 

As discussed for Figure 10.3B, a large baseline signal is encountered in HPLC-PAD for the oxide-catalyzed detections of amino acids and sulfur compounds (Mode n). Furthermore, the large baseline current is frequently observed to drift to large anodic values, especially for new or freshly polished electrodes. This drift is the consequence of a slow growth in the true electrode surface area as a result of surface reconstruction caused by the oxide on-off cycles in the applied multistep waveforms. As listed in Table 10.2, Mode II detections performed with PAD are subject to a number of disadvantages because of the formation of surface oxide, which is required and concomitant with the detection of amine- and sulfur-based compounds. 

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