Sulfonium cation

Interestingly, the sulfanes H2S are both proton acceptors and donors. In the first case sulfonium ions H3S are formed, in the second case hydrogen polysulfide anions HS are the result. While the latter have never been isolated in salts, several salts with sulfonium cations derived from the sulfanes with n = 1, 2, and 4 have been published. However, none of these salts has been structurally characterized by a diffraction technique. Therefore, the structures of the HsSn cations and HS anions are known from theoretical calculations only. 

The validity of equation (12) has been checked for several families of alkyl halides for which D and E /x- are known (Ref. 32, see particularly figure 6 therein). It was thus found that for v = 0.1 V s the constant is equal to 0.3 eV at 20°C (expressing D in eV and the potentials in V). Equation (12) was then applied to the approximate determination of unknown BDEs in several series of compounds undergoing dissociative electron transfer, namely, TV-halosultams,32 sulfonium cations,33 vicinal dihalides,34 1,3-dihaloadamantes, 1,4-dihalo-bicyclo[2.2.2]octanes, and l,3-dihalobicyclo[l.l.l]pentanes.35 In the latter case, the mutual influence of the two halogens could be rationalized thanks to the conversion of the peak potential data to bond dissociation energies. 

The electrochemical reduction of sulfonium cations in acetonitrile according to Scheme 433 offers a striking example of the combined roles of the bond... 

Fig. 4 Electrochemical reduction of a sulfonium cation (Scheme 6) showing the transition from the concerted to the stepwise mechanism as driving force increases upon raising the scan rate.33 The apparent transfer coefficient, a, is derived from the peak width according to equation (17).

The preparative oxidation of vinyl sulfides is thought to proceed via an intermediate bridged sulfonium cation that can be attacked by an external nucleophile from the less encumbered side to give two isomers (Scheme 21) [87]. 

The proposed mechanism of the oxidative cleavage of S-protecting groups by the chlorosilane/sulfoxide procedure is outlined in Scheme 8. 95 The first reaction is considered to be formation of the sulfonium cation 9 from diphenyl sulfoxide (7) and the oxygenophilic silyl compound 8. The formation of a sulfonium ion of this type is known and has been utilized for the reduction of sulfoxides. 97 Subsequent electrophilic attack of 9 on the sulfur atom of the S-protected cysteine residue leads to the formation of intermediate 10, whereby the nature of the silyl chloride employed should be the main factor that influences the electrophilicity of 9. The postulated intermediate 10 may then act as the electrophile and react with another S-protected cysteine residue to generate the disulfide 11 and the inert byproduct diphenyl sulfide (12). This final step is analogous to the reaction of a sulfenyl iodide as discussed in Section 6.1.1.2.1. 

A comparable positive influence as experienced with anodic dimerization of olefins, styrene in particular, exerts carbon anodes on the anodic formation of trisarene sulfonium cations by anodic coupling of diarylsulfide radical cations to arenes (226-228). 

Deuterium-labeling studies support the involvement of tricyclic sulfonium cations (152 and 153) in the photorearrangement of phenylthiazoles (154)13 3 the proposed general mechanism is shown in Scheme 12. Highly strained thiirans (155) have been similarly obtained on irradiation of the mesoionic 2-alkylthiothiazol-4-ones (156),134 and an analogous intermediate (157) has been proposed to account for the conversion of the mesoionic species (158)... 

The tertiary cage sulfonium cation 78 was generated and characterized by NMR spectroscopy as early as 1963196 [Eq. (4.46)]. 

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],... 

The ylide initially acts as a nucleophile toward the carbonyl compound. The resulting oxygen anion then reacts as an intramolecular nucleophile toward the now electrophilic ylide carbon, which bears a sulfonium cation as a good leaving group ... 

Oniu m Cations. Major families of ILs are composed of quaternary onium cations such as imidazolium, pyridinium, ammonium, phosphonium, sulfonium cations and so on. As described above, the fact that most ILs are composed of organic cations is attributed to weaker electrostatic interaction among component ions. There have been several reports on the effect of cation structure on the Tm of ILs. The relationship between Tm and the basic structure of onium cations is important in developing a protocol to prepare low melting ILs. 

The idea of lone pairs was originated by W. J. Pope of Cambridge in 1900 who extended the concept of the three-dimensionality of carbon and nitrogen compounds to those of sulfur. His resolution of sulfonium cations RR R"S+ with three different substituents into optically active enantiomers suggested that these species were tetrahedral with an invisible substituent. The influence of these lone pairs can hardly be detected in transition metal compounds, but the situation is different for post-transition group central atoms such as Ge(II) As(III), Se(IV), and Br(V) with 30 electrons, In(I), Sn(II), Sb(III), Te(IV), I(V), and Xe(VI) with 48 electrons, and Au( —I), T1(I), Pb(II), and Bi(III) with 80 electrons (90). 

Cationic propagating species that contain positively charged sulfur atoms include sulfonium and sulfonylium cations. Sulfonium cations have been suggested to be involved in the synthesis of poly(phenylene sulfide) (PPS). 

The phenyl bis(phenylthio) sulfonium cation, 203, was detected by, 3C NMR analysis of a reaction mixture of diphenyl disulfide and SbCl5 in CH2CI2 at -40° C. No signals due to radical species were detected by ESR. The generation of 203 in the presence of excess diphenyl disulfide leads only to the formation of trimer 205 (Fig. 32). The equimolar addition... 

Figure 32 Evidence of a stepwise polymerization mechanism by the formation of trimer 205 upon treatment of the phenyl bis(phenylthio) sulfonium cation with excess diphenyl disulfide. (From Ref. 115.)...

The synthesis of high molecular weight PPS via a cationic oxidative polymerization route was inhibited by premature precipitation of PPS. A method for the synthesis of high molecular weight PPS from a soluble precursor under mild conditions was developed. Poly(sulfonium cation) was used as a precursor to PPS [Eq. (31)] [118]. 

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