Dialkyl disulfides, oxidation

Methylene blue irradiation Thiolsuliinic acid esters from dialkyl disulfides Oxidation with singlet oxygen... 

In wet acetonitrile, the oxidation of diaryldisuUrdes [119] and dialkyl disulfides (Aik 7 f-Bu) [120] affords the corresponding aryl and alkylthiosulfonates in good synthetic yields (Eq. 15). Thus, the oxidation of a cyclic disulfide, dibenzo(c,e)-1,2-dithiin (1,1) does not affect the S—S bond and results in a corresponding thiosulfonate, dibenzo(c,e)-l,2-dithiin-l,l-dioxide(Scheme 27) [121]. Such oxidized products can form in wet acetonitrile as well as in a dry solvent, but in the latter case this is probably a result of disproportionation of the primarily... 

In the case of the double NPS-protected lysine methyl ester, oxidation selectively takes place at the 6-sulfenamide function under spontaneous cyclization via the a-sulphe-namido group as nucleophile. Only one diastereoisomer of the A,A -bis(NPS)-protected methyl 6-amino-piperidine-2-yl-carboxylate seems to be formed. The transformation of a-amino alkanoates and diaryl or dialkyl disulfides to the aryl- or alkylsulfenimine derivatives can be performed electrochemically using MgBr2 as a mediator system. This reaction can either proceed in one step or starting from the corresponding sulfenamide [170]. 

Anodic oxidation of dialkyl disulfides in MeCN/H20 solutions at a Pt electrode yields alkyl alkanethiosulfonates both under controlled potential and current conditions, as in Eq. (10) [38]. 

Symmetrical disulfides (73) may be prepared by reaction of alkyl halides with disodium disulfide (Scheme 43). The product is contaminated with triand polysulfides owing to the presence of impurities in the disodium disulfide however, lower members of the series of dialkyl disulfides may be purified by fractional distillation. Disulfides can also be obtained from thiols by mild oxidation, e.g. by treatment with iodine or dimethyl sulfoxide (DMSO) (Scheme 44). In the reaction with iodine, the hydriodic acid formed must be removed, otherwise the disulfide is largely reduced back to the thiol by hydriodic acid which is a powerful reducing agent. Pure unsymmetrical disulfides are more difficult to prepare owing to their tendency to undergo disproportionation they can, however, be synthesised from thiols by treatment with imides (see p. 59) or sulfenyl halides (51) (Scheme 45). 

Chen, J Preparation of Alkane Sulfonic Acids and Sulfonyl Chlorides by Oxidation of Alkanethiols and Dialkyl Disulfides. U.S. Patent 6,124,497,, Sep 26, 2000. 

Husain, A. Wheaton, G.A Production of Alkanesulfonic Acids by Oxidation of Alkanethiols or Dialkyl Disulfides in the Presence of DMSO. European Patent 424,616, Feb 2, 1991 Chem. Abstr. 115, 8085. 

These species were prepared by y-radiolysis of their corresponding dialkyl disulfides 187 at 77 K, treatment of the cyclic disulfides 188-191 or their corresponding dithiols with aluminum chloride in dichloromethane or sulfuric acid, by anodic oxidation of aryl disulfides 192,193a, and 194a, by bromine oxidation of 195 and iodine oxidation of 196. 

In 2000, Guy reported the stoichiometric coupling of alkane thiols and arylboronic acids, which was initially thought to be mediated by Cu(ll) [71]. Liebeskind proposed that the reaction was more likely catalyzed by Cu(l), generated by oxidation of the alkane thiols into dialkyl disulfides. Based on this hypothesis, Liebeskind predicted that disulfides and disulfide equivalents should be effective reagents for thioether formation [34]. This process would constitute a modification of the Chan-Evans-Lam, which involves the coupling of arylboronic acids and amines or alcohols in the presence of tertiary amine bases, generating aryl amines and ethers, respectively. Indeed, the coupling of diphenyl disulfide with phenyl boronic acid would yield diphenyl sulfide. 

Oae and Numata proposed intermediate formation of a S-S dication 5 in order to explain migration of the oxygen occurred when 4 was treated with concentrated sulfuric acid. Similarly, Ruffato and Miotti proposed formation of a disulfonium dication as a result of intramolecular interaction during the oxygen atom transfer from arylmethylsulfoxide to dialkyl disulfide. In 1974, Simonet et al suggested transient formation of an extremely unstable S-S dication 7 (Scheme 3) during electrochemical oxidation of thioketals 6 to afford disulfides 9 and carbonyl compounds 8 after hydrolysis. 

Oxidation of Thiols and Disulfides to Sulfonic Acids. Sulfonic acids have been prepared from the corresponding thiols with MTO/H2O2 as the oxidizing system. The protocol is simple, eco-triendly, and produces high yields (eq 60). The same catalytic system was satisfactorily employed in the oxidation of diaryl- and dialkyl disulfides, in acetonitrile at 20 °C with high yields in short... 

Field, L., Harle, H., Owen, T.C., and Ferretti, A. (1964) Preparation and oxidation of some asymmetrical dialkyl and alkyl pyridnium disulfides./. Org. Chem. 29, 1632-1635. 

R = Et) yields, by the familiar Hugershoff cyclization,114 the substituted benzthiazole 128 and not the thiadiazolidine 129. In 1,5-dialkyl-aryl group suitable for benzthiazole formation, oxidation by iodine or bromine causes mainly S-dealkylation and subsequent formation of cyclic disulfides (126)137 in two cases, however, the formation of thiadiazolines (129 R = PhCH2, R = Me, R" = Me or Et and R = CH2=CHCH2, R=p-C6H4Me, R" = Me)137-138 as additional products in undisclosed yields, has been observed. 

A kinetic study of the oxidation of some hexameric silver(I) dialkyl dithiocarbamate complexes by thiuram disulfides to the silver(II) complexes has been reported.543 Although a 100-fold excess of the thiuram disulfide was used, the formation of the Ag111 complex reported earlier was not considered. 

Decomposition of ZDDP takes place in the presence of oxygen, either coming from oxygen dissolved in engine oil or from peroxy radicals and hydroperoxides. Solution studies of the oxidation of zinc dialkyl dithiophosphates by peroxy radicals have shown that disulfides are major reaction products (Paddy et al., 1990 Rossi and Imparato, 1971 Willermet, 1998 Willermet et al., 1983 Willermetand Kandah, 1984). 

The preparation of disulfides can be achieved by reacting the thiol or its salts with aqueous hydrogen peroxide358 under alkaline conditions. However, the pH needs to be closely monitored, since if too high, the disulfide selectivity will drop.359 Dialkyl dithiocarbamates can be oxidized to tetraalkylthiuram disulfides (Figure 3.92).360... 

The typical S-oxidation with BVMOs allows the formation of chiral sulfoxides from organic sulfides. This oxidation has received much interest in organic chemistry due to its use in the synthesis of enantiomerically enriched materials as chiral auxiliaries or directly as biologically active ingredients. This reaction has been studied extensively with CHMO from Adnetohacter showing high enantioselectivi-ties in the sulfoxidation of alkyl aryl sulfides, disulfides, dialkyl sulfides, and cychc and acyclic 1,3-dithioacetals [90]. CHMO also catalyzes the enantioselective oxida-hon of organic cyclic sulfites to sulfates [91]. 

Dialkyl sulfoxides such as DMSO work as oxidants for the selective preparation of disulfides. The order of thiol reactivity is ArSH > ArCH2SH > RSH. Several amine oxides, such as pyridine N-o -ides and triethylamine oxide, also oxidize sulfides to sulfoxides, but the reaction generally requires higher temperatures. 

Little has so far been reported on the chemistry of teUurones. The preparation of several dialkyl tellurones by H2O2 or air oxidation of the corresponding tellurides or telluroxides has been claimed, but it is doubtful whether those compounds were isolated in a pure tellurone form. In 1982 the first definitely characterized tellurone, bis(4-methoxyphenyl) tellurone (60), was prepared by periodate oxidation of the corresponding telluroxide (59 equation 50). Both (59) and (60) woric as mild useful oxidants which show some chemoselectivities and readily oxidize thiols to disulfides. The preparation of dodecyl 4-methoxyphenyl tellurone by a similar method has also been claimed. ... 

Cation radicals are intermediates in the anodic oxidation of simple dialkyl and diaryl disulfides, RSSR, but are too short-lived to be observed at the time scale of slow-sweep voltammetry, although their existence has been established by pulse radiolysis [29] and electron spin resonance (ESR) spectroscopy [30]. Their detection by voltammetric technique was achieved in the case of more complex molecules like NDS [31], and when two disulfide linkages are present as in TTN, TTA, and TTT, even the generated dications are stable [32, 33]. 

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