Thianthrene cation radical perchlorate

Dimerization of heterocyclic cation radicals was discovered in recent times. The well known thianthrene cation radical perchlorate forms a dimer in propionitrile solution. This association is, in fact, tetrameric (de Sorgo et al., 1972) that is, the anions are included in the aggregrate (Th +C104)2. Phenoxaselenine cation radical has also been found to form an (M +)2 dimer in sulfuric acid and nitro-methane solutions (Cauquis and Maurey-Mey, 1973). It is not surprising that the very stable metalloporphyrin cation radicals should dimerize, but this was demonstrated only recently with zinc (Fuhrhop et al., 1972), and magnesium (Fajer et al., 1970) octaethyl-porphyrin (MOEP). 

Occasionally, electron transfer is a nuisance and competes with or overshadows a desired nucleophilic reaction. For example, reaction of thianthrene cation radical perchlorate with aniline leads to benzidine (among other products) instead of nucleophilic substitution in thianthrene (Shine and Kim, 1974). 

Thianthrene cation radical perchlorate reacts slowly with alcohols. Reaction with the lower alkanols has not been defined but with... 

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. 

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>. 

The preparation of dibenzo[6,e ][ 1,4]dioxin cation radical (66) has been achieved by oxidation of the heterocycle in ethyl acetate-lithium perchlorate at a platinum anode, using a controlled potential of 1.2 volts vs. Ag-AgC104. The blue solid collected at the anode contained between 85-90% of (66) as the perchlorate (74JHC139). The purple cation radical perchlorate of phenoxathiin, (67), is obtained in high purity by oxidation of phenoxathiin in benzene with 70% perchloric acid-acetic acid (75JOC2756). Similar perchloric acid oxidation of thianthrene affords the dark reddish brown perchlorate of (68) (69JOC3368) and the heterocycle can also be oxidized on a preparative scale with antimony pentachloride (62JCS4963). 

Radical 80 has been prepared as its perchlorate salt by anodic oxidation in ethyl acetate in the presence of hthium perchlorate. The reactivity toward nucleophiles of material so prepared was investigated nitrite and nitrate ions give 2-nitrodibenzo[l,4]dioxin although the mechanisms of the reactions are not clear. Pyridine gives 7V-(2-dibenzo[l,4]dioxinyl)pyridinium ion (84). Other nucleophiles acted as electron donors and largely reduced 80 back to the parent heterocycle they included amines, cyanide ion and water. In an earlier study, the reaction of 80 with water had been examined and the ultimate formation of catechol via dibenzo[l,4]dioxin-2,3-dione was inferred. The cation-radical (80) has been found to accelerate the anisylation of thianthrene cation-radical (Section lII,C,4,b) it has been found to participate in an electrochemiluminescence system with benzo-phenone involving phosphorescence of the latter in a fluid system, and it has been used in a study of relative diffusion coefficients of aromatic cations which shows that it is justified to equate voltammetric potentials for these species with formal thermodynamic redox potentials. The dibenzo[l,4]dioxin semiquinone 85 has been found to result from the alkaline autoxidation of catechol the same species may well be in-... 

Because the cyanide ion is so easily oxidized its apparent ability to react with aromatic cation radicals instead of being oxidized by them reflects the competition so often encountered in cation radical chemistry between nucleophilicity and oxidizability of a nucleophile. The subject has not been treated analytically yet. In the present context, the tri-p-anisylaminium ion is reduced by cyanide ion (Papouchado et al., 1969) in a very fast overall second-order reaction (Blount et al., 1970). The cation radicals of thianthrene, pheno-thiazine, and phenoxathiin are also reduced by cyanide ion (Shine et al., 1974). In none of these cases, incidentally, is the fate known of the cyano radical presumed to be formed. Perylene cation radical perchlorate, on the other hand, reacts with cyanide ion in acetonitrile solution to give low (13%) yields of both 1- and 3-cyano-perylene (Shine and Ristagno, 1972). 

The thianthrene cation-radical (56) shows enhanced stability in trifluoro-acetic acid, which is recommended generally as a solvent in which to prepare cation-radicals. Thianthrenium perchlorate (56 C10 as counter-ion) reacts with substituted benzenes PhR at the para position, rapidly where R = MeO, more slowly where R = Me. The product is a sulphonium salt (58). Kinetic studies show that the reaction is second-order in the thianthrene cation-radical (56). The suggested mechanism features the thianthrene dication (57) as the reactive species, formed in low concentration by disproportionation of the thianthrene cation-radical. 

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). 

In an early paper, Bewick et al. [51] reported the spectrum of the thianth-renonium cation radical obtained from the in-situ oxidation of thianthrene (0.01 M) in acetonitrile at 1.2 V vs. Ag/Ag+. The spectrum was observed on modulating the potential between 0 and 0.2 V and was described as closely comparable with that of an authentic sample of thianthrenonium perchlorate obtained with a conventional spectrometer. 

Perchloric acid oxidizes perylene (Matsunaga, 1961), thianthrene and phenoxathiin (Murata and Shine, 1969) to the cation radicals, but whether or not the acid serves as the oxidizing agent or catalyses oxidation by atmospheric oxygen has not been studied. 

Use of iodine-silver perchlorate may accomplish cation-radical formation before the oxidizing pair can themselves react. In modern usage, silver ion (as the perchlorate usually) is added to a solution of the substrate and iodine, and the complexity of the iodine-silver perchlorate system is avoided, provided that the substrate undergoes reasonably fast oxidation. Such is the case with perylene (Sato et al., 1969 Ristagno and Shine, 1971) and pheno-thiazine, but not the case with diphenylanthracene and thianthrene (Shine et al., 1972). 

Cation radicals of thianthrene (Shine et al., 1972), phenoxathiin, N-methyl- and N-phenylphenothiazine (Shine et al., 1975) react with pyridine as in (138), the pyridinium perchlorates being isolable in... 

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

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... 

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]. 

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