Dialkyl Sulfide Radical Cations

Dialkyl sulfide radical cations have been made from the parent sulfides by a variety of methods including y-radiolysis in matrices at low temperature [280], pulse radiolysis [281-285], photoinduced electron-transfer [286], mass spectroscopic methods [287,288], electrochemical oxidation, and by oxidation with one-electron chemical oxidants. A brief overview of these methods will be presented here even though most of these methods have already been mentioned previously in this review. 

Adducts 134 and 135 absorb with Amax at 330 and 340 nm respectively [293], and adduct H0S(CH2CH2C02Me)2 at Amax=345 nm [294]. In the gas phase no experimental or theoretical evidence [295] was found for Me2SOH as an intermediate. However, other experimental [296] and a high level ab initio calculation [297] find a stable complex weakly bound by 13 3 and 6.0 kcal/m, respectively. Adducts 134 and 135 then form radical cations by three pathways. Ionization of OH from the adduct can occur by a spontaneous or acid catalyzed process. In addition, parent sulfide can displace OH leading to a 2c, 3e species (R2S)2H The adduct of -OH and Me2S is reported to absorb with Amax at 340 [298] or 358 nm 

Direct spectroscopic evidence for the formation of sulfur radical cations was obtained in this reaction after laser flash photolysis. 

However, their anodic oxidation peak potentials in MeCN are 0.69 and 0.34 V vs Ag/0.1 mol I1 AgN03 in MeCN, respectively. That is, 138 is easier to oxidize electrochemically than 137 despite its higher ionization potential. Ab initio calculations support the notion that the S.. S bond of 139 formed on oxidation of 138 is stronger than that for 137 after, but not before, geometry optimization. 

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Table 10. EPR Spectroscopic parameters for dialkyl sulfide radical cations... 

The propensity of dialkyl sulfide radical cations to bond to electron-rich centers exemplified by reaction with parent dialkyl sulfide to form a 2c, 3e S, S bond as shown in Eq. (47) has attracted considerable attention ... 

Species 27 and 2 are generated by one-electron oxidation of the dialkyl sulfide. The interaction between the resulting sulfide cation radical and another sulfide sulfur is overall a bonding interaction since the antibonding orbital is only singly occupied. 

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