オルガノシリル遊離基による塩素原子引き抜き反応の相対速度 : 水素化有機ケイ素化合物を用いる還元反応(第3報)

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Relative rates of chlorine atom abstraction by organosilyl radicals were determined by allowing six different polychloroalkanes to compete in pairs for an insufficient amount of triethylsilane, phenyldimethylsilane, diphenylmethylsilane and ethyldichlorosilane at 80°C in the presence of benzoyl peroxide. Relative reactivities per chlorine atom of the trichloromethyl groups in X-CCl<SUB>3</SUB> towards the four organosilyl radicals are satisfactorily correlated with the Taft σ values of the substituents X. These relationships can be interpreted in terms of the polar factor which is important in determining the reactivities of the chlorine atoms in this class of substrates. In the absence of solvent, the Hammett ρ values for the reactions of triethylsilyl, phenyldimethylsilyl, diphenylmethylsilyl and ethyldichlorosilyl radicals are 0.29, 0.27, 0.29 and 0.29, respectively. It was also found that the selectivity of the reaciton in methyl ethyl ketone or methyl acetate was somewhat greater than that in cyclohexane, benzene and chlorobenzene.
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