Oxidation to disulfide

Oxidation or "sweetening" is used on gasoline and distillate fractions. A common oxidation process is also a Merox process that uses a solid catalyst bed. Air and a minimum amount of alkaline caustic ("mini-alky" operation) is injected into the hydrocarbon stream. As the hydrocarbon passes through the Merox catalyst bed, sulfur mercaptans are oxidized to disulfide. In the sweetening Merox process, the caustic is not regenerated. The disulfide can remain with the gasoline product, since it does not possess the objectionable odor properties of mercaptans hence, the product has been sweetened. 

These are strong, unstable acids. Oxidation to disulfides takes place readily. Several methods have been used to prepare the dithio acids (I), the most useful of which is the reaction of CS with a Grignard reagent (27). 

Thiols are easily oxidized to disulfides." " Hydrogen peroxide is the most common reagent," but many oxidizing agents give the reaction, among them KMnO ... 

Thiols are easily oxidized to disulfides in solution, but this reaction occurs only very slowly at most electrode surfaces. However, use can be made of the unique reaction between thiols and mercury to detect these compounds at very favorable potentials. The thiol and mercury form a stable complex which is easily oxidized, in a formal sense it is mercury and not the thiol which is actually oxidized in these reactions. For the LCEC determination of thiols a Au/Hg amalgam electrode is used Using a series dual-electrode both thiols and disulfides can be determined in a single chromatographic experiment... 

The data suggest that the hydroxyl groups of 1 are involved in hydrogen bonds to carbonyl oxygens of 32 a, as is shown in Scheme 1. Moreover, although 32 is easily oxidized to disulfide 34 in solution and in the solid state, 32a in 33 is stable. 

In the case of the thiopurines the electrochemical processes do not appear to agree at all with the known biological oxidations. However, again in the case of 6-thiopurine not even a complete picture of the metabolites is available. The electrochemical data indicates that thiopurines are very readily oxidized to disulfides and hence to sulfinic or sulfonic acids. In view of well-known sulfide-disulfide transformations in biological situations (e.g., L-cy-steine to L-cystine), it is not unlikely that part of the metabolic degradation pathway for thiopurines might proceed via reactions of the sulfide moiety. 

In the base-assisted reactions, the hydrogenolysis products are recovered as sodium or potassium thiolates which can either be converted to thiols by acidification with protic acids, or be oxidized to disulfides by exposure to air.184,195 In turn, all of the Rh catalyst of the aqueous biphasic reactions remains in the polar phase for use in a further catalytic run after the thiolate product is extracted as thiol. 

Copper is part of several essential enzymes including tyrosinase (melanin production), dopamine beta-hydroxylase (catecholamine production), copper-zinc superoxide dismutase (free radical detoxification), and cytochrome oxidase and ceruloplasmin (iron conversion) (Aaseth and Norseth 1986). All terrestrial animals contain copper as a constituent of cytochrome c oxidase, monophenol oxidase, plasma monoamine oxidase, and copper protein complexes (Schroeder et al. 1966). Excess copper causes a variety of toxic effects, including altered permeability of cellular membranes. The primary target for free cupric ions in the cellular membranes are thiol groups that reduce cupric (Cu+2) to cuprous (Cu+1) upon simultaneous oxidation to disulfides in the membrane. Cuprous ions are reoxidized to Cu+2 in the presence of molecular oxygen molecular oxygen is thereby converted to the toxic superoxide radical O2, which induces lipoperoxidation (Aaseth and Norseth 1986). 

Locap A process for removing mercaptans from gasoline by catalytic oxidation to disulfides, using a fixed bed of catalyst that is continuously treated with aqueous sodium sulfide. Commercialized by Petrolite Corporation in 1963. 

The SH group of B HnSH2- can be oxidized to disulfides linking two clusters, and further to the disulfide monoxide [57]. The disulfide has tumor-localizing properties superior to Na2Bi2HnSH [58], In acidic conditions, a free radical with intense blue color is obtained as an intermediate, which can be reduced by NaBI-U... 

A simple but accurate potentiometric method for the estimation of mercaptans in 0.01 M perchloric acid is based on their quantitative oxidation to disulfide with 1-chlorobenzotriazole. A backtitration procedure can also be used <90Mi40l-03>. 

Disulfides. Sulfides are oxidized to disulfides usually in 85-95% yield by 1 equivalent of nickel peroxide. 

Low-molecular-mass thiols such as coenzyme A and protein-bound thiol cofactors such as phospho-pantetheine are present in all cells. Their SH groups can also be oxidized to disulfides and it is of interest that in resting bacterial spores these compounds exist largely as disulfides or mixed disulfides. Upon germination of the spores special enzymes reduce the disulfides.136 Some proteins involved in control of protein synthesis contain SH groups that add covalently to C-6 atoms of a uracil ring in specific mRNA molecules. Control of their state of reduction may also be important.137... 

Most sulfur compounds resist the action of active Mn02 at low temperature. For instance, organic sulfides resist active Mn02 during the oxidation of allylic and benzylic alcohols.57 Thiols, being sulfur compouds with a greater oxidation sensitivity, are oxidized to disulfides.56... 

The functional group of thiols is the sulfhydryl group, -SH. Thiols are also called mercaptans because of their reaction with mercury salts to form mercaptides. Thiols have intense, disagreeable odors. They are more acidic than alcohols and are easily oxidized to disulfides. 

The dithiazolylium cation (31) is reduced reversibly to dithiobiuret (80) by a number of thiols, which in turn are oxidized to disulfides. This reaction has been found to be first... 

---