Disulfides and polysulfides

We have noted previously (see Section 2.1) the role played in biochemistry by the thiol disulfide interconversion, and the disulfide unit is a fundamental feature of the structure of peptides and proteins. The sulfur-sulfur bond between two cysteins link remote parts of a peptide chain or cross-link two such chains. Cleavage of these bonds in the hair protein keratin, followed by reoxidation, gives hair its desired shape. 

A number of naturally occurring compounds with a disulfide unit have shown interesting biological activity [28, 29]. Nereistoxin, charatoxin, asparagusic acid, a plant growth inhibitor, and lipoic acid, a key co-factor in the oxidative decarboxylation of pyruvate, are examples taken in the 1,2-dithiolan series. 

Interestingly some 1,2-dithiin compounds have been shown to possess antiviral activity, including anti-HIV activity, and their chemistry is an active area of research associated with that of diatomic sulfur S2 [30,31]. 

The S3 unit is also to be found in compounds of natural origin [28, 32, 33], A very simple one, isolated from an edible mushroom, exhibits both S2 and S3 moieties [34, 35]. 5-Methylthio-l,2,3-trithiane [28] is another example close to charatoxin, and the presence of an allylic trisulfide, and its role as a triggering device for their antitumour activity, in enediyne antibiotics [36, 37], is truly astonishing. 

Some disulfides, particularly dimethyl disulfide (DMDS), and trisulfides are important industrial compounds [13]. Disulfides find a use in synthesis 

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Natural cyclic bissulfides, disulfides, and polysulfides 97UK901. 

Tunicates are by far the most important source of marine metabolites containing disulfides and polysulfides, followed in importance by marine microorganisms and, to a lesser extent, sponges and algae. 

Marine microorganisms have been an important source of disulfide and polysulfide marine metabolites. Among these compounds are the leptosins and the thiomarinols, which form a well-defined group of natural products. 

Chen and co-workers tentatively assigned new signals in the FT-IR spectra of accelerated sulfur-vulcanised NR to the formation of C-S and S-S bonds corresponding to monosulfides, disulfides and polysulfides [68]. The vulcanisation of NR was retarded when clay was added to the NR compound. 

Arretz, E., Lopez, F. Method for preparing organic disulfides and polysulfides from mercaptans and sulfur in the presence of heterogeneous styrene-divinylbenzene copolymer catalysts having pendant guanidine or amidine groups. 1996, WO 9721673. 

The rates of oxidation of both pyrite and pyrrhotite at 25 °C and standard atmospheric oxygen indicate that pyrrhotite can react 20-100 times faster than pyrite. During oxidation of a particle of pyrrhotite, iron diffuses to the exposed surface, thereby creating a sulfur-enriched inner zone that contains disulfide and polysulfide-hke species (Mycroft et al., 1995). 

Owing to preparative problems arising from the instability of hydrogen disulfide and polysulfides, more readily available reagents seem to be... 

There are many organosulfur compounds, which have been used in formulating lubricant additives. The sulfide, disulfide, and polysulfide linkages, incorporated into novel compositions-of-matter, serve various functions, such as corrosion inhibition, oxidation resistance, high-temperature stability, and static prevention. ... 

Disulfides and polysulfides are useful for sulfiding hydrotreating catalysts, used in petroleum refining to convert metal oxides to the preferred metal sulfides. Hydrotreating is an essential process in the refining of petroleum. It removes heteroatoms, nitrogen, and sulfur from crude oil and its fractions, formulated into gasoline and diesel (Table 5). 

Further support for un branched structures in hydrogen polysulfides and polysulfur dichlorides comes from molar volumes, refractions, and viscosities these are discussed in Section V on organic disulfides and polysulfides. 

Sulfides, disulfides, and polysulfides (also called thioethers) are the characterizing components of the alliaceous vegetables (e.g., onion, garlic, leek), although the more subtle attributes of these profiles are contributed by substituted thio compounds. 

Dibenzyl sulfide, disulfide, trisulfide, and tetrasulfide can be separated chromatographically on paper impregnated with 1-bromonaphthalene 80% acetic acid can serve as the mobile phase which is allowed to overrun overnight. Three to five microliters of a 5 —10% solution are applied on the paper. Detection is carried out with potassium iodoplatinate, giving light yellow spots of dibenzyl sulfide and yellow to brown-yellow spots of disulfides and polysulfides on a pink-red background. 

In exchange reactions of disulfides and polysulfides and in sulfur insertion reactions... 

Table 2 Influence of Disulfide and Polysulfide Crosslinks on Properties...

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