Although the Ullmann condensation has played an important role in a larger number of chemical manufacturing industries, especially those of dyestuffs, drugs, and many other chemicals, the mechanistic studies have been scarcely reported in the literature. From the practical point of view, the information as to catalytic species will be expected to allow the setting up of the more effective synthetic conditions.
We have studied the mechanism of the Ullmann codensation reaction in order to aquire more knowledge as the “true” catalytic species in this reaction. In this paper our results obtained by mechanistic and kinetic studies on the Ullmann condensation reaction between haloanthraquinones and amines are briefly reviewed.
In the reaction of bromamic acid with anilines in the alkaline aqueous solution, the active catalyst was concluded to be the monomeric cupric species, having a cuprous character, on the basis of the kinetic results, the ESR observations, and the effects of the added anions and chelates. The addition of reducing agents, such as FeSO
4, astonishingly enhanced the reaction rate. The reactivities of amines are showed to depend on both their basicities and polarizabilities.
On the other hand, in the case of the reaction between haloanthraquinones and amines in non-aqueous solution the cuprous species was showed to be active as catalyst, while the cupric one was almostly inactive. In this reaction system the cupric species, formed in the course of the reaction, increased the reaction rate. The role of the cupric species in the reaction are discussed from the stand point of kinetics.
The reaction mechaism of those reactions and the role of the copper species as catalyst are tentatively proposed and discussed.
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