[Mechanism of the autocatalytic formation of ferrihemoglobin by dimethylaniline oxide: analysis of the explanation of the structure of 2-dimethylamino-4-(N-methylanilino)phenol].

1. The autocatalytic oxidation of haemoglobin to ferrihaemoglobin (methaemoglobin) by dimethylaniline N-oxide (DANO) has been further investigated with special emphasis on the condensation product of 2-dimethylaminophenol and N-methylaniline. 2. From incubations of DANO with ferrihaemoglobin or ferricytochrome c, N-methylaniline, N,N-dimethylaniline, formaldhyde, 2-dimethylaminophenol, and 4-dimethylaminophenol were identified as reaction products. 3. The structure of the leuco compound, which is also formed in the incubation mixture, was shown by X-ray analysis to be 2-dimethylamino-4-(N-methylanilino)phenol, a condensation product of N-methylaniline and 2-dimethylaminophenol. Chemical and physicochemical investigations confirmed this assignment. 4. The purple dye produced from the leuco compound by withdrawal of two electrons, and also found in the incubation mixtures, may be considered as a resonance hybrid of the two structures, 2-dimethylamino-N-methyl-N-phenyl-1,4-benzoquinone-4-imonium and 4-(methylphenylamino)-N,N-dimethyl-1,2-benzoquinone-2-imonium. 5. With clarification of the structures of the leuco compound and the purple dye, and of the mechanism of their formation, the autocatalytic formation of ferrihaemoglobin by DANO can now be described as shown in figure 5 (cf. Kiese and Renner 1976).