Thianthrenes, radical cations

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). 

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 5. The P-polarised emission spectrum obtained for hole injection by the thianthrene radical cation into Au(lll) for emission angle = 30° and excitation energy Eex = 3.0eV. (NB.

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... 

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... 

Another general problem, perhaps with somewhat more impact on homogeneous solution chemistry, is whether the reactions of radical ions with nucleophiles or electrophiles, depending upon the charge, go directly via the radical ions or if reactive doubly charged ions must first be formed by disproportionation. The reaction of thianthrene radical cation with water (Murata and Shine, 1969 Shine and Murata, 1969) is a typical example which was proposed to involve the disproportionation mechanism (71 and 72). The... 

Step. As an example the role of an ET step in the interaction between dibenzodioxin and thianthrene radical cation with aromatic donors such as anisole and anthracene has been evaluated through kinetic studies [37]. 

A different approach, MSRS, involves modulation of the electrode potential by a periodic function, e.g., a sine wave or a pulse [340-345]. Absorbance variations other than those that are synchronized with the modulation frequency are discriminated by help of a lock-in amplifier, leaving the system almost insensitive to absorbance of products built up during the experiment. In this way it has been possible to obtain the visible spectrum of perylene radical anion in the presence of acetic acid (Fig. 50) and thianthrene radical cation in the presence of water [341]. Other examples include the oxidation of N,N-... 

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

These results support the suggestion that the energy difference between folded and planar thianthrene conformations is small. However, 2,3,7,8-tetramethoxy-thianthrene radical cation [22], as both the hexachloroantimonate and triiodide salts, and thianthrene radical cation [20], as its tetrachloroaluminate salt, have been shown to be planar in the solid state. The dihedral angles 0 are 180° and 174°, respectively. These results provide strong evidence for delocalization in... 

The reactions of thianthrene radical cation have recently been reviewed [10]. Consequently, this discussion will emphasize the major reaction motifs and reactions reported subsequent to the previous review. However, some of the previously reviewed material will be presented here so that a complete picture may be painted. 

In competition with this radical coupling reaction is electron transfer between the alkyl radical and thianthrene radical cation. If the radical R- is of sufficiently low oxidation potential (and the reorganization energy permits), e.g., terf-butyl radical, then electron transfer occurs to yield the corresponding cation R+. Evidence for electron-transfer in these reactions was also convincingly demonstrated by the use of unsymmetrical organometallic species. Kochi [29] has shown that the alkyl group that is preferentially cleaved... 

Thianthrene radical cation is also an excellent one-electron oxidant of iron porphyrin complexes. Such oxidation of Fem(0Cl03)(TPP), where TPP is meso-tetraphenylporphyrin, provides the corresponding porphyrin 7r-cation radical analytically pure [32]. Similar oxidation of the AT-methyl porphyrin complex (N-MeTPP)FenCl, where AT-MeTPP is AT-methyl-meso-tetraphenylporphyrin, afforded [N-MeTPPFemCl]+ which was not further oxidized [33]. Thus thianthrene radical cation selectively oxidized the aromatic porphyrin ligand in one case and the metal center in the other. Ligand oxidation at a phenolic moiety has also been reported [34] on treatment of a 1,4,7-triazacyclononane appended with one or two phenol moieties ligated to Cu(II) complex with thianthrene radical cation. 

Formation of 7r-cation radicals has also been suggested [35] in the reaction of stable enols with thianthrene radical cation and other one-electron oxidants. Thus enol 10 on treatment with thianthrene radical cation affords benzofuran derivative 11 in 87 % yield. The initial step in this reaction is suggested to be one-electron transfer forming the cation radical of 10, which has been unequivocally identified in a related system [36]. 

This cation radical rapidly deprotonates, undergoes further oxidation (or disproportionates) to the corresponding a-carbonyl cation. Cyclization of this cation and rearrangement [37] yield ultimately 11. It should be noted that an alternative reaction path has been identified in the reaction apparently of enols with thianthrene radical cation. Ketones [38, 39] and aldehydes [40] on treatment with thianthrene radical cation form sulfonium salts 12 and thianthrene. 

Cyclized products 13 and 14 are formed in 0.7 and 12% yields, respectively, in the reaction of lithium dialkylamide 15 with thianthrene radical cation [41]. 

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-... 

This equilibrium has attracted much attention because of the mechanism first suggested for the reaction of thianthrene radical cation with water. In this reaction, the second order dependence of the rate on the concentration of TH was explained by disproportionation followed by nucleophilic attack on the dication. The equilibrium constant KD for the reaction shown in Eq. (8) may be determined electrochemically. The difference in E° for the two one-electron processes shown in Eqs. (9) and (10) determine KD. Interestingly, this value depends strongly on solvent and counterion and pKD ranges between 5-13 [46-48] ... 

Oxidation of azo compounds by thianthrene radical cation has been reported. Thus treatment of l,l -azoadamantane 19 with two equivalents of thianthrene radical cation perchlorate in acetonitrile produced AT-adamantylacetamide 20 in 90% yield and thianthrene quantitatively [53]. 

This led to the interesting suggestion that the azo compound underwent one-electron oxidation to the then little known azoalkane radical cation. This species subsequently lost dinitrogen to form 1-adamantyl cation and 1-adamantyl radical. This latter species was then oxidized by thianthrene radical cation to 1-adamantyl cation. The 1-adamantyl cation thus formed underwent Ritter reaction to produce AT-adamantyl acetamide 20. 

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