Mechanism of the Ullmann condensation reaction. Part III. Role of the copper catalyst

Abstract

The Ullmann condensation of sodium 1-amino-4-bromo-9,10-dihydro-9,10-dioxoanthracene-2-sulphonate (I) with nucleophilic reagents in alkaline, aqueous solution has been investigated. When copper(II) sulphate was used as catalyst and aniline as reagent, e.s.r. studies showed that the hydroxide ion and the amine were co-ordinated to a divalent copper species but no evidence indicating the co-ordination of (I) was obtained. The copper(II)-catalysed reaction was accelerated markedly during the earlier stage by the addition of metal reducing agents (Sn²⁺,Ti³⁺, and Fe²⁺). The distribution of the products depended on pH, the relative yield of the phenolic by-product being minimized at high concentrations of hydroxide ion. Anilines were found to enhance the rate of the reaction of (I) with toluene-p-sulphonamide. The role of the copper catalyst is discussed and a mechanism is proposed.