Benzothiadiazoles, radicals from

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). 

In Scheme 1.15, path a can be demonstrated with examples of anion-radicals of amino and hydroxy derivatives of 2,1,3-benzothiadiazole (Asfandiarov et al. 1998) and the azafullerene anion-radical, C59HN (Keshavarz et al. 1996). One of the examples, hydrogen atom detachment from C59HN, is as follows ... 

The photo-reduction of 2,l,3-benzothiadiazole-4,7-dicarbonitrile (13) by EDTA in the presence of micelles gave a stable radical anion which could be observed by ESR <84CC1324>. The observed 17 line ESR signal was attributed to an overlapping quintet of quintets from a radical with (NA) = 0.255 mT and fl(NB) = 0.075 mT. The radical appears to be protected within the micelle when electron transfer is inhibited. 

The radical anions of five isomers of nitrobenzothiazole (4-N02-, 5-N02-, 6-N02-, 7-N02- and 2-N02-) have been obtained by electrochemical reduction in DMSO and easily characterized by ESR spectroscopy [889], To the contrary, the chemical reduction in alkaline solution (t-BuOK in DMSO or glucose and MeOK in MeOH) presented some problems with 6-N02- and 4-N02-benzothiazoles, and 2-N02-benzothiazole did not provide any detectable paramagnetic species [889], Copper(II) complexes of 6-nitrobenzothiazole-A-sulfonamides as protective agents against superoxide anion have been investigated by ESR spectroscopy [890], The ESR spectrum of 5-nitro-2,l,3-benzothiadiazole RA obtained by electrochemical generation in DMF was reported [886], Unfortunately, the HFS constants of this radical anion are absent and we estimated the HFS constants from simulated spectrum (Table 3.40). 

Pyrroles annulated with various kinds of polycyclic aromatic compounds such as the pyrrolo benzothiadiazole (578) have been claimed to be good precursors for polypyrroles. The polymers derived from (578) have a lowered band gap and interesting properties such as the high stability of the cation radicals formed by electrochemical oxidation. They also show ESR signals which are not affected after storage at room temperature for long periods of time in a laboratory atmosphere, <94CC1019>. 

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