The oxidation of phenols with copper‐amine catalysts and its relation to the mode of action of tyrosinase: I. The catalytic oxidation of monohydric phenols to orthoquinone derivatives

In an attempt to imitate the action of the enzyme tyrosinase by means of simple homogeneous catalytic systems we have found some rapid reactions which convert monohydric phenols directly into amine‐substituted orthoquinone derivatives. These reactions proceed rapidly at room temperature with molecular oxygen as an oxidant and copper‐amine complexes as catalysts. The reactions may be applied to a variety of phenols and of primary or secondary amines. It is argued that the monohydric phenols are primarily converted into the corresponding orthoquinones. Paraquinones are not formed or formed in traces only. The quinones are subject to rapid spontaneous addition reactions with the primary or secondary amines, thus giving rise to substituted catechols, which are oxidized to the corresponding orthoquinones. In the instances studied, the orthoquinone derivatives were formed in high yield. As they are converted easily in the corresponding phenazines and hydroxyquinones, the latter compounds may thus be synthesized in a convenient way from monohydric phenols and naphthols. The present paper deals with the nature of the reaction products only. Kinetics and reaction mechanism are discussed in following papers. The reactions studied in some detail are: The conversion of phenol into dimorpholino‐orthobenzoquinone (yield 64%) and of α‐ and β‐naphthol into 4‐morpholino‐1,2‐naphthaquinone (37 and 84%). The effect of morpholino substituents on the redox potential of quinones has been measured. The following new compounds are described in this paper: 4,5‐dimorpholino‐orthobenzoquinone, 2,3‐dimorpholinophenazine, 4‐morpholino‐1,2‐benzophenazine.