The Ullmann Condensation Reaction of Haloanthraquinone Derivatives with Amines in Aprotic Solvents. II. The Presence of an Induction Period in the Condensation with 2-Aminoethanol

An induction period was present in the Ullmann condensation reactions of 1-bromoanthraquinone(AQBr) with 2-aminoethanol(AE) in the presence of CuBr or CuI in aprotic solvents under a nitrogen atmosphere, while there was no induction period in the reaction systems of 1-iodoanthraquinone(AQI)–AE–CuBr, AQI–AE–CuI, and AQBr–AE–[Cu(CH3CN)4]ClO4. In the condensation system with a copper(I) catalyst, the Cu(I) species was oxidized to the Cu(II) species by means of an electron transfer from Cu(I) to haloanthraquinone as the reaction proceeded. By adding copper(II) bromide, the induction period vanished in the reaction system of AQBr–AE–CuBr. The copper(II) species increased the catalytic activity of the copper(I) species. The formation of the copper(II) species was responsible for the presence of an induction period and played an important role in the Ullmann condensation reaction of haloanthraquinones with amines in the presence of copper(I) salt as a catalyst.