Oxidation, of diphenyl disulfide

Methylbis(methylthio)sulfonium hexachloroantimonate ([CH3S(SCH3)2][SbCl6]) was isolated from the reaction mixture at -40°C by the oxidation of nonpoly -merizable dimethyl disulfide [86], This result suggests that the phenylbis(phenyl-thio)sulfonium cation is produced by the oxidation of diphenyl disulfide in the acidic reaction mixture [87-89], This cation acts as the active species for the polymerization and electrophilically reacts with the / -position of the benzene ring to yield PPS [90],... 

Anodic oxidation of diphenyl disulfides in CH2CI2/BU4NBF4 solution in the presence of trifluoroacetic acid yields oligo (p-phenylene) sulfides [41]. Under these conditions the oxidation proceeds via a one-electron transfer, and it is believed that in acidic medium nucleophilic reactions involving the initial cationic product are suppressed. A sulfonium cation formed by reaction of a cation radical with the starting material is suggested as an intermediate ... 

The electrochemical preparation of in organic media being reported, it is worth underlining the interest of disulfides bond under similar conditions. Thus, the anodic oxidation of diphenyl disulfide (in CH2CI2 containing CF3COOH) [293] may lead to an oligomer. 

Anodic oxidation of diaryl disulfides results in polymerization [473, 474]. Thus oxidation of diphenyl disulfide 187, R=Ph, in the presence of trifluoro-acetic acid gave poly(p-phenylene sulfide) 209a. 

Oxidation, of diphenyl disulfide to methyl benzenesulfinate with lead tetraacetate in methanol, 46,62... 

The reagent is prepared by oxidation of diphenyl disulfide with H20a (Tl yield) or tn-chloroperbenzoic acid (96% yield). ... 

Alternative synthetic routes to poly(arylene sulfide)s have been pubHshed (79—82). The general theme explored is the oxidative polymerization of diphenyl disulfide and its substituted analogues by using molecular oxygen as the oxidant, often catalyzed by a variety of reagents ... 

In the oxidation of alkanethiols to disulfides with chloramine-T (CAT), in alkaline solution, the proposed reactive species are hypochlorous acid and TsNCl- anion. A correlation of reaction rate with Taft s dual substituent parameter equation yielded p = -5.28 and 5 = -2.0, indicating the rate-enhancing effect of electron-donating substituents.133 Michaelis-Menten-type kinetics have been observed in the oxidation of atenolol with CAT in alkaline solutions. TsNHCl is assumed to be reactive species. A mechanism has been suggested and the activation parameters for the rate-determining step were calculated.134 The Ru(III)-catalysed oxidation of diphenyl... 

Thiophenol is electrochemically oxidized to diphenyl disulfide near 1.7 V (vs. Ag/AgCl), because the thiophenolate radicals undergo coupling. Although diphenyl disulfide is further oxidized under the given potential of 1.7 V, the cationic species formed are rapidly inactivated by a nucleophilic reaction with... 

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. 

Table 1 Cationic Oxidative Polymerization of Diphenyl Disulfide in the Presence of Catalytic Amounts of Metal Complexes ...

The PPS yield depends on the acidity of the mixture. The oxidative polymerization does not proceed in the absence of acids. Strong acids, such as triflu-oromethanesulfonic acid and trifluoroacetic acid, are required for the VO-cata-lyzed polymerization. The oxidative polymerization of diphenyl disulfide is facilitated by the activated VO(acac)2 produced by the acid. Diphenyl disulfide is not oxidized by 02 only or an equimolar amount of VO(acac)2 in the absence of acid. The VO catalyst is estimated to be an excellent electron mediator, through activation by acids, to promote the electron transfer between diphenyl disulfide and molecular oxygen. 

Although VO(acac)2 acts as an excellent catalyst for the 02-oxidative polymerization of diphenyl disulfide, mechanistic analysis of the redox process involved in... 

Since the oxidative polymerization of diphenyl disulfide catalyzed by VO(acac)2 results in selective formation of thioether bonds without any oxygenated compounds such as sulfoxides and/or sulfones, it should be noted that H20 should be produced predominantly by the reduction of 02 catalyzed by the vanadium complex without the formation of partially reduced side products such as H202. 

A molecular conversion system based on a four-electron transfer to 02 was accomplished in the 02-oxidative polymerization of diphenyl disulfide (Figure 14) [116]. This is the first example of a multielectron mediator that is applied to molecular conversion systems. The multielectron transfer process from the reduced vanadium(III) complex (VOV+) to 02 not only revealed the 02 oxidation mechanism but also provided additional insight into the unique chemistry of vanadium with possible relevance to metal mono-oxygenases. 

Figure 14 Proposed mechanism for the VO-catalyzed 02-oxidative polymerization of diphenyl disulfide.

In 1979 it was reported20 that by converting the 2-a-hydroxy group of 2-a-hydro-xyethyl-3,4-dimethylthiazolium salts to an ether, the enamine could be generated, as deduced from its product with the oxidizing agent diphenyl disulfide, generating a tetrahedral intermediate at the C2a position by sulfenylation (equation 2). This would be consistent with nucleophilic and/or redox reactivity of the enamine at the C2a position. 

The role of VO(acac) is presumably identical with that of the oxidative polymerization of diphenyl disulfide. The V(IV) catalysts disproportionate to give a V(ll) and V(III) species. The V(V) species oxidizes monomer 311 producing cation-radical 328 and V(1V). V(III) is readily oxidized in triflic acid by oxygen to regenerate the V(IV) catalyst [211]. 

Oxidation of aryl amines and phenols. Phenol and aniline are not oxidized by KO2, but 0- and p-phenylenediamine are oxidized to diaminoazobenzenes and o-and p-aminophenols are oxidized to dihydroxyazobenzenes. Thiophenol is oxidized to diphenyl disulfide." ... 

Scheme 1.70. Pro-oxidant activity of alkyl mercaptans (a) and both pro-oxidant and delayed antioxidant activity of diphenyl disulfides (b) during melt processing of polymer PH containing hydroperoxide groups POOH. After Scott (1993b).

The sulfoxide is prepared by treatment of diphenyl disulfide with vinyllithium followed by peracid oxidation. 

Electrophilic aromatic substitution is not observed with benzenethiol either. Instead, the treatment of two equivalents of benzene thiol with the S-dication, as shown in Equation (15), gives the oxidation product, diphenyl disulfide, and the monocyclic bis-sulfide as the reduced 5-dication. The disulfide dication (36) similarly oxidizes 1,2-diphenylhydrazine into azobenzene without any accompanying substitution products <93T1605>. 

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. 

The oxidative polymerization of diphenyl disulfides with quinones to form ultrapme poly(l-p-phenylene sulfide)s is discussed in Section 4 [37b]. 

The oxidative polymerization of diphenyl disulfides or of thiophenal with quinones at room temperature has been reported to produce pure poly(p-phenylene sulfides) [37cJ. This will be described in more detail in Section 4. 

This reaction has been characterized for a wide variety of Rh(I) complexes. The behavior of (/x-dpm)2Rh2(CNi )4 shown in reaction 14 is typical. Oxidants capable of performing this reaction include chlorine, bromine, iodine, and trifluoromethyl disulfide. However, dihydrogen does not add to these Rh(I) compounds. The dimeric Rh(II) products are quite stable. Treating these with excess oxidant does not result in the formation of the more usual Rh(III) complexes. However, some oxidants, including diphenyl disulfide, pentafluorophenyl disulfide, and diphynel diselenide, react with (/x-dpm)2Rh2(CNR)4 to form Rh(III) products, (dpm)Rh(CNR)2(X)2 ", exclusively. The difference in behavior of these oxidants has not been explained. 

Kita s group also described an intermolecular version that resembles the procedure of Engler [8]. This is shown in Scheme 5 and again features phenyliodine(ni) bis(trifluoroacetate) (FIFA) reaction with Al-tosylaniline, followed by nucleophilic attack by an activated olefin, and cyclization to give either Af-tosylindoline (equation 1) or Af-tosylindole (equation 2). The latter is the product when phenyl vinyl sulfides are employed. The thiophenol byproduct was oxidized to diphenyl disulfide with excess FIFA. Four indoles that were prepared in this study are also shown. 

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