Radical cations of thianthrenes

Fluorescence was used to investigate the excited-state dynamics of the radical cation of thianthrene (TH ) <2001PCA6594>. The frequencies of the fundamental modes of the molecules of some dioxins in the ground electronic state were also determined by analysis of their fine-structure phosphorescence spectra <19990PS(86)239, 19970PS(83)92, 20000PS(89)42, 20000PS(88)339>. 

Electron transfer may also dominate the excited state chemistry of open shell radical ions. The fluorescence of the radical anions of anthraquinone and 9,10-dicyanoanthracene and the radical cation of thianthrene are quenched by electron acceptors and donors, respectively, although detailed kinetic analysis of the electron exchange do not correspond exactly either with Weller or Marcus theory (258). The use of excited radical cations as effective electron acceptors represents a... 

Reversible dimerizations are observed less frequently, since often the reactions are not fast enough to be treated as thermodynamic equilibria. Examples are the dimerization of the radical cations of thianthrenes [110] and thiophene derivatives [111]. 

For mesitylene and durene, the kinetics have been followed by specular reflectance spectroscopy [17]. The results indicated that mesitylene produces a fairly stable radical cation that dimerizes. That of durene, however, is less stable and loses a proton to form a benzyl radical, which subsequently leads to a diphenylmethane. The stability of the radical cation increases with increasing charge delocalization, blocking of reactive sites, and stabilization by specific functional groups (phenyl, alkoxy, and amino) [18]. The complex reaction mechanisms of radical cations and methods of their investigation have been reviewed in detail [19a]. Fast-scan cyclovoltammetry gave kinetic evidence for the reversible dimerization of the radical cations of thianthrene and the tetramethoxy derivative of it. Rate constants and enthalpy values are reported for this dimerization [19b]. 

Thianthrene, radical cation of and its reactivity 85PS(23)111 84ACR243. 

There is a scant data on the radical behavior of thianthrene radical cation [58]. As pointed out above, thianthrene radical cation couples with radicals. It shows little reactivity toward oxygen but this may be ascribed to its positive charge which should render it an electrophilic radical. It initiates the polymerization of styrene [59,60], a-methyl styrene [59], and ethyl vinyl ether [59,60],but not that of vinyl pyridine [61], vinyltrimethylsilane [59], methyl acrylate [59, 61], or acrylonitrile [59,61 ]. These results can be explained by cationic rather than radical polymerization. 

Unsaturated ketones react with phenyUiydrazines to form hydrazones, which under acidic conditions cyclize to pyrazolines (35). Oxidation, instead of acid treatment, of the hydrazone with thianthrene radical cation (TH " ) perchlorate yields pyrazoles this oxidative cyclization does not proceed via the pyrazoline (eq. 4). 

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... 

Thianthrene cation radical tetrafluoroborate 139 has been found to add to 2,3-dimethyl-2-butene 138 at —15 °C to give adduct 2,3-dimethyl-2,3-(5,10-thianthreniumdiyl)butane ditetrafluoroborate 140, which was isolated and characterized by 111 NMR spectroscopy at —15 °C (see Equation 40) <2006JOC3737>. The adduct 140 was stable in CD3CN solution at —15 °C but decomposed quickly at 23 °C, forming the salt of 2,4,4,5,5-pentamethyl-2-oxazoline with loss of thianthrene. 

An energy-sufficient mixed chemiluminescent radical-ion reaction is that of thianthrene (TH) radical cation 101 and 2.5-diphenyl-1.3.4-oxadiazole (DPO) radical anion 102 156> ... 

Emission spectra have been recorded for electron injection into Au and Ag spherical electrodes and hole injection into Au(lll) planar electrodes. These processes were brought about in solutions of acetonitrile containing tetrabutylammonium hexafluoro-phosphate (TBAHP), using the trans-stilbene radical anion as the electron injector and the thianthrene radical cation as hole injector. The spectrum for the hole injection process into planar Au(lll) electrodes has been resolved into the P S-polarised components of the emitted light. A comparison of the spectral distribution of emitted light for the above electron injection process, occurring at both Au and Ag... 

The spectra recorded for the hole injection process by the thianthrene radical cation into the Au(lll) electrode are shown in Fig 4, for three different excitation energies. Once again, square wave modulation was employed with a fixed positive value of +1.0V where the cation radical is produced /4/ to negative values... 

Figure 17. 1,4-Dithiin 21 and the molecular structure of its radical-cation salt 2f+SbF6 determined by X-ray crystallography. The observed lengths (A) of Cl-S and C1-C2 in 2f+SbF6 are 1.72(1) and 1.31(2) to be compared with 1.324(3) and 1.760(2) determined for neutral 21, respectively. Also shown is the thianthrene radical cation 23 +. 

The homogeneous oxidation of compounds 14 and 15 with thianthrene radical cation perchlorate (Th C104) was studied later by Kovelski and Shine... 

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. ... 

The reaction in Scheme 5.11 gives the snlfoninm salt (anion CIO4 ) in a 90% yield (ronte a). One-electron reduction of the thianthrene cation-radical by anisole is the side reaction (ronte b). Route b leads to products with a 10% total yield. Addition of the dibenzodioxine cation-radical accelerates the reaction 200 times. The cation-radicals of thianthrene and dibenzodioxine are stable. Having been prepared separately, they are introdnced into the reaction as perchlorate salts. 

To increase the stationary concentration of complex (HetH - - - ArH) +, a stronger oxidizer, as compared to the cation-radical of thianthrene, should be introduced into the reaction. This is the cation-radical of dibenzodioxine. It increases the rate of the reaction by 2 orders. 

The same way was used by Yoon and Kim (2005) for the preparation of 5-(p-methoxyphenyl)thian threnium ion incorporated in a calyx[4]arene. Namely, the ratio of starting materials, methoxycal-ixarene to the thianthrene cation-radical perchorate, was 1 10. The product of such 5-anisylation of thianthrene was further transformed into a calixarene bearing an additional o-phenylene thio-macrocycle. This macrocylization is beyond the scope of this book the original paper by Yoon and Kim (2005) could be recommended for those who interested in. It is worth noting only one practical importance of the calixarene-phenylene thiomacrocycle here It selectively extracts silver(l-l-) by both calixarene and thiomacrocycle. Each molecule of this combined complexon takes up two silver cations, so that extractability achieves 165%. 

Thianthrene, 68 X = Y = S, radical-cation is obtained by oxidation in trifluoro-acetic acid containing perchloric acid and the evaporation of the solvent [232], It shows electrophilic behaviour on the sulphur atom. When the electrochemical oxidation of thianthrene is carried out in aqueous acetic acid, the monoxide is obtained... 

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... 

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). 

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. 

A quite different mode of reaction was observed for the reactions between thianthrene radical ion(l+) and the heterocyclic bases pyridine (72JOC2691) and 2,3-diazabicyclo[2,2,2]oct-2-ene (88JA7880) thianthren-2-yl-N salts were obtained in each case. It was shown that 2 mol equivalents of the radical cation are required, the byproduct being thianthrene. 

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). 

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