The Ullmann Condensation Reaction of Haloanthraquinoiie Derivatives with Amines in Aprotic Solvents. III. The Formation and Role of Copper(II) Species in the Condensation with 2-Aminoethanol by Copper(I) Catalyst

The ESR spectra of the Ullmann condensation reaction system of 1-bromoanthraquinone-2-aminoethanol-CuBr showed that copper(II) species and 1-bromoanthraquinone radical anion were formed by an electron transfer from copper(I) species to 1-bromoanthraquinone. Although copper(II) species alone had little catalytic activity, the resulting copper(II) species increased the catalytic activity of the copper(I) species, and a pseudo-first order rate constant could be expressed as follows: k=k1[CuI]+k2[CuI][CuII]. According to the magnitude of k1 and k2C0, where C0 is the initial concentration of copper(I) catalyst, the reaction of haloanthraquinone with 2-aminoethanol by copper(I) catalyst can be classified into three modes. When k1<k2C0, an induction period is present. The possible mechanisms of the cooperation between copper(I) and copper(II) species have been proposed. It has been also found that 1-bromoanthraquinone radical anion was responsible for the debromination.