Benzothiazoles radicals from

Benzothiazole is acylated selectively in the 2-position by acyl radicals generated from a variety of aldehydes under the influence of the redox system f-butylhydroperoxide-ferrous sulfate. The nucleophilicity of acyl radicals is confirmed by the higher reactivity of 6-nitrobenzothiazole. The reaction, which could detect acyl radicals in the oxidation of aldehydes by various oxidizing agents, could serve as a diagnostic test for the presence of such radicals (71JCS(C)1747). 

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). 

Due to inductive electron withdrawal, nucleophilic attack at position 2 is favored. Deprotonation at this position also occurs in the presence of a strong base, and organometallic reagents so derived react with electrophiles in the usual manner. The reactivity of thiazoles and benzothiazoles toward nucleophiles, electrophiles, and radicals is well explained by data from MO calculations and has been covered thoroughly in CHEC(1984) and CHEC-IK1996). 

Photolysis experiments have elucidated the mechanism for the efficient production of phenyl benzoate, the geminate product, from direct and sensitized irradiations of dibenzoyl peroxide in solution.Photolysis has also been used to obtain rate constants for addition of benzothiazole-2-thiyl radical to vinyl monomers. Rate constants of 6.3 x 10 to 2.5 x 10 M s were obtained for reactions with vinyl acetate and styrene monomers. 

After irradiation, the HABI molecules decompose into lophyl radicals which subsequently abstract protons from a donor, e.g. thiols [BER 14] (Figure 4.9), heteroaromatic thiols, benzothiazoles, benzooxazoles, tertiary amines, alcohols, thiocarboxylic acids [BLA 09] or dyes [BEN 02], If used in a dental composite, they lead to improved compressive, yield and flexural strengths compared to conventional composites with CQ/DMABE. Furthermore, the sensitivity to ambient light could be decreased [BLA 09]. 

In an extensive study of the selective homolytic amidation of heteroaromatic bases, the behaviour of benzothiazole has been described." Carbamoyl and a-N-amidoalkyl radicals (generated from formamide or N-alkylacetamides) attack its 2-position, producing 2-carboxamido- or 2-acetamidomethyl-benzothiazoles, generally in satisfactory yields."... 

Toshiyuki Ishikawa, Masayo Sato, Yuko Itoh, Hrroki (Research Center, Mitsubishi Chemical Corporation, Yokohama, Japan). J. Photopolym. Sci. Technol. (1999), 12 (5), 711-716. Quenching of imidazoyl radical (Im ) produced in 2-[p-(diethyl-amino)styryl]naphtho[l, 2-d]thiazole (NAS) sensitized photolysis of 2,2 -bis(2-chlorophenyl)-4,4, 5,5Gtetraphenyl-l,l -bi-lH-imidazole (BI) in PMMA film in the presence of 2-mercapto-benzothiazole (MBT) was studied by laser flash photolysis using a total reflection cell. It was obsd. that MBT acted as an accelerator increasing the initial concn. of Im by slowing down the back electron-transfer from BI anion to NASA cation, and also quenched Im radical by hydrogen transfer. 

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