Phenothiazines. chemistry

Phase transfer catalysis, applications in heterocyclic chemistry, 36, 175 Phenanthridine chemistry, recent developments in, 13, 315 Phenanthrolines, 22, 1 Phenothiazines, chemistry of, 9, 321 Phenoxazines, 8, 83 Photochemistry of heterocycles, 11, I of nitrogen-containing heterocycles, 30, 239... 

From the very beginning of the phenothiazine chemistry, its capacity to give rise to different oxidation products, now explained in terms of a suecessive electron loss, was realized. The first systematic study on these topics was by Kehrmann, in the first decade of the present century. He suceeeded in explaining the observed phenomena, and it has been proved by recent work that most of his statements are essentially correct. A second stage was marked by Michaelis s work, which stressed the remarkable stability of the semiquinonoid forms obtained both by oxidation of phenothiazines and by reduction of quinoneiminoid phenothiazine dyestuffs. The development of electron spin resonance (ESR) spectroscopy allowed the direet investigation of the radical species, and marked the beginning of a third era in the study of redox processes in the phenothiazine class. 

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