Disulfides oxidation potentials

Hot surfaces and electric sparks are potential ignition sources for carbon disulfide. The ignition temperature depends on specific conditions, and values from 90 to 120°C in air have been reported (2,22). Data on carbon disulfide oxidation and combustion have been summarized (18). Oxidation products ate generally sulfur dioxide [7446-09-5] and carbon dioxide [124-58-9J ... 

CH2CI2, sulfolane, THF) in the presence of alkenes, whose oxidation potential is lower than that of the disulfide, results in the addition of the MeS group on the double bond. Since then, the anodic sulfeanylation of multiple bonds received many synthetic applications. 

Aromatics for oxidative polymerization usually show high oxidation potentials. The direct oxidation of these monomers by 02 does not proceed because of the large potential gap between the monomers and 02. A novel catalysis by vanadyl complexes is applicable to the synthesis of PPS by the 02-oxidative polymerization of diphenyl disulfide (Eq. 10) [93-103], In the presence of VO(acac)2, the polymerization is accompanied by a quantitative 02 uptake. Dioxygen is essential for the VO-catalyzed oxidative polymerization of diphenyl disulfide. 

Oxidation potentials determined by cyclic voltammetry in MeCN are considerable higher for monosulfides than those for the disulfides (XII) with w = = 3, w = 3, = 4,... 

Dication (35) reacted with aniline and A(,Af-dimethylaniline according to Scheme 4. Aliphatic amines like diisopropylamine did not react. Thiophenol was oxidized by (35) to diphenyl disulfide the difference is probably due to difference in oxidation potentials <90CL393>. 

The reactivity of the diselenide dication (51) towards various nucleophiles and in redox reactions is investigated. The diselenide dication undergoes electrophilic substitution reactions with activated aromatic compounds to give para-substituted selenonium salts (57), but oxidizes benzenethiol into diphenyl disulfide <90CL393>, both of which are analogous chemical behaviors to those of the disulfide dication (36). Thus, the Se-dication can both function as an electrophile and as an oxidant. The oxidation potential of the aromatic compound it reacts with determines the mode of reaction. Indeed, the reaction with phenothiazine, whose oxidation potential is known to be lower than that of the Se-dication (51), generates a cation radical detected by the color of the reaction mixture and the UV-visible absorptions at 436 and 515 nm. 

Austin C D, Wen X, Gazzard L, et al. (2005). Oxidizing potential of endosomes and lysosomes limits intracellular cleavage of disulfide-based antibody-drug conjugates, Proc. of the National Academy of Sciences of the United States of America. 102 17987-17992. 

The SAM consists of a mixture of octadecyl mercaptan (OM) and two short chain disulfides, which form -S-CH2-CH2-CH2-COO" and -S-CH2-CH2-NH3+ on the surface. The short chain, charged modifiers may provide defects, or pockets, in the OM layer where the enzyme may adsorb through electrostatic interactions. At oxidizing potentials, the electrode generates a catalytic current at densities up to about 10 pA/cm when exposed to fructose solution. The enzyme electrode exhibits a response time well under a minute and the calibration curve is linear at fructose concentrations up to 0.8 mM. The biosensor prototype exhibits low susceptibility to positive interference by ascorbic acid indicating that this construct could be useful for fructose analysis of citrus fruit juice. 

A soln. of diphenyl disulfide in 0.1 M tetra- -butylammonium bromide (as both mediator and electrolyte) in dichloromethane electrolysed under argon in a divided cell with platinum electrodes at a constant current of 0.02-0.03 A (current density 3 mA/cmO until 10 As of charge consumed, 0.5 eqs. 4-pentenol added, and electrolysis continued until reaction complete by g.c. or t.l.c. 2-(phenylthiomethyl)tetr hydro-furan. Y 72%. The method is inexpensive, less toxic than Se-based methodologies, and generally applicable to 5- and 6-membered O-heterocyclics reaction may also be achieved (preferably) by direct electrolysis with bis(4-methoxyphenyl) disulfide (having a much lower oxidation potential than diphenyl disulfide). F.e. and stereoselectivity, also 2-(aryIthio)lactones from ethylenecarboxylic adds, s. S. Toteberg-Kaulen, E. Steckhan, Tetrahedron 44, 4389-97 (1988). 

We can at last turn to the question of the quantitative examination of the mercaptan-disulfide redox system. For about thirty years chemists and biochemists (Prof. H. T. Clarke among the earliest) have been trying to determine the oxidation potential of Ibis system ... 

The special properties of lipoic acid arise from the ring strain experienced by oxidized lipoic acid. The closed ring form is approximately 20 kj higher in energy than the open-chain form, and this results in a strong negative reduction potential of about —0.30 V. The oxidized form readily oxidizes cyanides to isothiocyanates and sulfhydryl groups to mixed disulfides. 

This thiol-disulfide interconversion is a key part of numerous biological processes. WeTJ see in Chapter 26, for instance, that disulfide formation is involved in defining the structure and three-dimensional conformations of proteins, where disulfide "bridges" often form cross-links between q steine amino acid units in the protein chains. Disulfide formation is also involved in the process by which cells protect themselves from oxidative degradation. A cellular component called glutathione removes potentially harmful oxidants and is itself oxidized to glutathione disulfide in the process. Reduction back to the thiol requires the coenzyme flavin adenine dinucleotide (reduced), abbreviated FADH2. 

Thiol (s), 652, 667-668 disulfides from, 668 electrostatic potential map of, 75 from alkyl halides, 667 hybridization of, 20 naming, 667 odor of, 667 oxidation of, 668 pKa of, 604... 

With its oxygen functionality, graphite oxide has chemical properties more akin to those of layered disulfides or sheet silicates than to those of graphite (Gi, T1,A2). Many studies have been of an extremely applied nature the possibility of fluorination (LI, N1), redox potentials in the presence of hydrogen peroxide (V2), the apparent density (L2), the adsorption isotherms with nitrogen (L3), and the diffusion of Cs in graphite oxide (R2). 

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... 

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