Thiols oxidative dimerization

Aromatic and aliphatic thiols are oxidized by quaternary ammonium dichromate salts to disulphides (8, 13]. Yields are very good, even with the oxidative dimerization of diethyl phosphorothiolothionate to the corresponding disulphide (79%). 

In order to maintain adequate levels of GSH, the oxidized dimer is then reduced back to the original thiol components. This is achieved using the enzyme GSH reductase in a reaction involving NADPH and FAD cofactors (see Section 15.1.1). 

The thiophene ring is opened and sulfur extruded as hydrogen sulfide when 3,4-dinitrothiophene is reacted with piperidine. The product contains two nitroenamine units coupled to each other (Scheme 140). Other secondary amines react similarly (69CC549). Secondary aliphatic amines also react with 2-nitrothiophene to form the nitrodienamines (426) in 50-80% yield. It is believed that the reaction involves addition of the amine at position 5, followed by proton transfer and ring opening to give the thiol which, in the presence of air, oxidatively dimerizes to (426) (Scheme 141). In one case the thiol has been trapped as the silver salt and methylated (74JCS(P1)2357). 

Thiols have been linked to insoluble supports as acid-labile benzyl thioethers, as aryl thioethers, as S-carbamoyl derivatives, and as unsymmetrical disulfides (Table 3.37). Because thiols often undergo oxidative dimerization in air to yield symmetric... 

The oxidative dimerization of thiols was catalyzed by anhydrous FeCl3 and sodium iodide under air at room temperature in acetonitrile (Table 3.5) [154]. The corresponding disulfides were formed in excellent yields (96-99%). 

Anionic organic complexes of Mo have been immobilized on LDHs. For example, a Mo(VI)02 complex containing 2-mercapto-2,2-diphenyl-ethanoate ligands (14) was supported on ZnAl LDH and used for the catalytic air oxidation of thiols (269-271). Although the homogeneous dioxoMo complex has some catalytic activity, it is rapidly deactivated as a result of the formation of dimers. By intercalation of the complex in an LDH structure, dimerization could be avoided, resulting in improved longevity. 

The inefficient trapping of thiyl radicals by dodecene-1 was attributed to the effective interception of the radicals by Mn(III), resulting in electron transfer oxidation to the thioxonium ion. By contrast, thiyl radicals formed in the oxidation of thiols by the weaker oxidant, ferric octanoate, were scavenged by dodecene-1. Disulfide was formed by dimerization of thiyl radicals.352 Thus, the mechanism for disulfide formation is dependent on the nature of the metal oxidant. 

Oxidations. Clean products are generally obtained by using alumina-supported reagents. For the oxidative dimerization of thiols by OMSO or NalOj, the conversion of hydroquinones to quinones and 2-naphthols to BINOLs in the presence of CuSO, the formation of lactones from a,co-diols under the influence of NaBrOj, and the hydrolytic defluorination of certain perfluoroalkylarenes, alumina has unique or positive effects. 

Oxidation of sulfur compounds. The copper(lI) nitrate complexed with dimerizes thiols to afford disulfides and oxidizes sulfides to sulfoxides. 

C-C bond formations. Iron(III) perchlorate effects cyclization of 1,5-cyclooctadienes to bicyclo[3.3.0]octane derivatives and oxidative dimerization of naphthalenes. Thiols are also oxidized to give disulfides. 

Previous study [18] on oxidation of thiols by transition metal oxide(s) in the presence of olefins resulted in the formation of corresponding sulphides indicating a free radical addition reaction in which metal oxide acts as an initiator for the production of thiyl radicals(RS-). The disulphide is formed by the dimerization of thiyl radieals (RS )- Based on this, a mechanism for thiol oxidation by manganese nodule (Only oxides of Mn, Fe, Co and Cu in manganese nodule are responsible for oxidation of thiols) is delineated as follows ... 

Oxidative dimerization. Conversion of thiols to disulfides hy the Burgess reagent is reported, despite the economic irrationality involved. ... 

Disulfides. Bu4N[R3SnF2] act as nucleophiles toward sulfur. Oxidative dimerization of the thiols initially formed, results in disulfides. 

Disulfides. The oxidative dimerization of thiols is easily achieved with iodine-morpholine. 

Oxidation of thiols by Fe(Oct)8 has been carried out in acetone and xylene . Kinetic studies indicate that the reaction follows a second-order rate law. It is suggested that disulphide arises from dimerization of thiyl radicals which are formed in the rate-determining reaction of thiol with Fe(Oct)8 (equations 49, 50). 

Formation of a bis-fluorous sulfide is accomplished by the alkylation of a fluorous thiol phosphate salt with a fluorous alkyl bromide (eq 8). The salt is prepared from the fluorous thiol to avoid the oxidative dimerization of the thiol to form the disulfide. 

Tri-tert-butoxidesilanethiolate forms complexes with both Co11 and Co111. Reaction of the thiol with a Co11 ammine in water yields a dimer which undergoes oxidation in an ammonia-saturated atmosphere to form octahedral [Co(SSi(0-t-Bu)3)2(NH3)4]+, the first silanethiolate characterized structurally.1044... 

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