Thianthrene, radicals from

Species 4, produced from thianthrene by loss of an electron from a sulfur, is correctly known as thianthrene radical ion(l+) most authors have referred to it as the thianthrene radical cation or the thianthrene cation radical. The species produced by loss of two electrons from the central ring, and for which 5 is probably a resonance contributor, is termed thianthrenediium. Sulfonium salts (6) produced formally by utilizing a sulfur lone-pair in bonding to, are 5-R-thianthrenium salts. Thianthrene... 

A great deal of work has been carried out on the thianthrene radical ion(l+), which can be produced from thianthrene by a variety of one-electron oxidations. The radical cation reacts at sulfur with nucleophilic species, giving rise to 5-substituted products, oxides, ylids, and 5-R-thianthrenium salts. 

V. Reactions of thianthrene radical ion(l+) with nucleophiles. As discussed previously, thianthrene radical ion(H-) reacts rapidly with water, giving thianthrene and its 5-oxide. So from most reactions that have been described, these two products are also isolated, resulting from reaction... 

Thianthrene radical cation undergoes self exchange, i.e., transfer of an electron from thianthrene to its radical cation and the rate of this process measured [43]. In addition, this exchange has been studied by measurement of the equi-... 

Disporportionation, as shown in Eq. (8) involves electron transfer from one thianthrene radical to another ... 

If fragmentation of the radical cation from 25 afforded radical 26 then five-membered ring products derived from intramolecular cyclization of this radical should be formed. Treatment of 25 with thianthrene radical cation gave 27-29,... 

Intermediates in the thermal oxidations of thioethers with NO are generally difficult to detect owing to the limiting reaction rates. The exceptions are oxidations of strong sulphur-containing donors derived from thianthrene. The stoichiometric oxidation of thianthrene in dichloromethane at -78 °C produces a pink-coloured solution ( max =-544 nm) that finally leads to a pale-yellow solution from which thianthrene 5-oxide was isolated in 94% yield. This process involves the intermediate stage of the thianthrene radical cation formation [23] ... 

Phenyl radicals react with 1,2,3-benzothiadiazole to give diphenyl sulphide, dibenzothiophen, thianthrene, 4-phenylthiodibenzothiophen, and l,2-bis(phenyl-thio)benzene. It is suggested that the reaction involves attack of phenyl radicals on the sulphur atom of the reactant, to produce an intermediate o-(phenylthio)-phenyl radical, from which each of the products may be derived. Similarly, methyl radicals yield a mixture of thioanisole, thianthrene, 4-methylthiodi-benzothiophen, and l-methylthio-2-phenylthiobenzene. The experiments are claimed to be the first examples of the attack of a radical on a hetero-aromatic sulphur atom (see Vol. 3, p. 678). 

The most evident of these is the marked stability of radical cations formed in an aprotic medium by the oxidation of compounds where the first ionization potential (in the sense of photoelectron spectroscopy) is for the removal of an electron from a non-bonding orbital, e. g. thianthrene... 

The restriction for a nucleophile to penetrate and react with the confined cation-radical sometimes leads to unexpected results. Comparing the reactions of thianthrene cation-radicals, Ran-gappa and Shine (2006) refer to the zeolite situation. When thianthrene is absorbed by zeolites, either by thermal evaporation or from solution, thianthrene cation-radical is formed. The adsorbed cation-radical is stable in zeolite for a very long time. If isooctane (2,2,4-trimethylpentane) was used as a solvent, tert-butylthianthrene was formed in high yield. The authors noted it is apparent that the solvent underwent rupture, but the mechanism of the reaction remains unsolved. ... 

When the concentration of the thianthrene cation-radical drops from 10 -10 M to 10 M, the reaction results change The sulfonium salt is not produced at all (route a becomes closed) and... 

To decrease the stationary concentration of complex (HetH- - - ArH) +, it will suffice to lower the concentration of the oxidizer, that is, substrate (HetH)+. This also decreases the equilibrium concentration of the cation-radical complex (HetH- - ArH)+. The rate of anisylation—the main process—drops sharply. The side process, one-electron transfer from anisole to the cation-radical of thianthrene, also decelerates, but not so markedly. So this side process (route b on Scheme 5.11) remains the only one. 

One-electron removal from thianthrene also enforces conjugation within the internal electronic system and leads to the flattening of the molecular carcass. If the neutral parent molecule is bent, the cation-radical becomes considerably flattened (Bock et al. 1994). 

Molecular ions obtained from thianthrenes are normally the base peak in their mass spectra. The principal fragmentation involves loss of sulfur (87PS377), and this is interpreted as formation of a dibenzothiophen radical cation (16). Further loss of sulfur then occurs. CSH is lost from both the dibenzothiophen fragment ion and from the molecular ion species such as 17, from the parent ion, are proposed (74JHC287). The mass spectroscopic fragmentation pattern of fluorothianthrenes is comparable (720MS373). 

Azoadamantane exposed to 2 mol equivalents of T CIO4 at room temperature rapidly and quantitatively evolved nitrogen, and thianthrene and products derived from the adamantyl cation were obtained. Equations (38)-(40) (AA, azo-adamantane Ad, adamantane) make clear why 2 mol equivalents of the radical oxidant are required (85JA2561). The comparable interaction of T with phenylazotriphenylmethane and di-ter/-butyl diazene, using a 2 1 ratio of radical cation to substrate, also leads to the formation of thianthrene and nitrogen (85PS111). 

The preparation of a number of 5-(alkyl)thianthrenium perchlorates has been performed from the thianthrene cation radical with dialkylmercurials and tetraalkyltins (R4Sn) <1983JOC143>. Thianthrene as well as phenoxathiin cation radical perchlorates react with alkenes. The former add stereospecifically to cycloalkenes although the latter afforded a mixture of mono- and bis-adducts in which the configuration of the alkene was retained <2003JOC8910>. 

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