Unsymmetrical Anodic C-C Coupling of 2,6-Di-tert-butyl-4-methylphenol

概要

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Cyclic voltammetry of 2,6-di-tert-butyl-4-methyphenol (1) in acetonitrile in the presence of an aliphatic amine such as ethyl-, diethyl-, or triethylamine shows an ill-defined anodic wave-a socalled kinetic wave-around 0.5 V vs. aqueous saturated calomel electrode, indicating an electron-transfer process preceded by a slow chemical reaction. Based on the estimated pK_a value of 1 (pK_a=12.55 in water at 25℃), the chemical reaction was ascribed to a slow hydrogen-bonding association of 1 and the added amine. Controlled potential electrolysis of 1 at the potential of the anodic wave gave an unsymmetrical dimer, 2,6-di-tert-butyl-4-(3,5-di-tert-butyl-4-hydroxyphenyl)-4-methyl-2,5-cyclohexadiene-1-one, as the main product. Side-chain aminated derivatives of 1,Ar-CH_2NHEt, Ar-CH_2NEt_2,and Ar-CH_2N^+NEt_3 (Ar=3,5-di-tert-butyl-4-hydroxyphenyl), are suggested to be the intermediates; that is, the process of dimer formation is explained in terms of cross-coupling of the phenoxyl radicals derived from 1 and the side-chain aminated phenols followed by expulsion of the aminomethyl group.
公益社団法人日本薬学会の論文
1986-02-25