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The preparation of some 1-derivatives of phenothiazine by thionation and their 10-acetyl derivatives are described.The preparation of phenothiazines by thionation of diarylamines was discussed recently as a part of the review of the chemistry of phenothiazines.2 The thionation reaction is being systematically studied in this laboratory, with particular emphasis on the use of catalysts, solvents, and temperature, and this paper describes some observations on the results obtained using solvents in the preparation of 1-substituted phenothiazines.The comparison of the thionation reaction of diphenylamine in various solvents showed that pyridine and dimethylformamide were completely unsatisfactory, benzene and naphthalene gave highly impure products, and xylene and o-diehlorobenzene were most suitable. Using the last mentioned solvent there were obtained good yields of rather pure 1-methyl-and 1-methoxy-phenothiazines. The 1-ehlorophenothiazine presented difficulties because of the simultaneous formation of phenothiazine. A similar observation has been made by Roe and Little3 in the preparation of l-fluorophenothiazine from 2-fluorodiphenylamine.1-Carboxyphenothiazine, previously prepared by metalation4 was obtained in low yield by the thionation of N-phenylanthranilic acid in o-dichlorobenzene. The larger part of the acid was decarboxylated so that a 75% yield of phenothiazine was obtained. Previous attempts4 to obtain this compound by thionation gave neither the phenothiazine acid nor phenothiazine; only starting material was recovered. The formation of 1-carboxyphenothiazine, even in small yield, suggests that if a catalyst could be found which lowers the reaction temperature, the anthranilic acid might give the carboxyphenothiazine directly. Studies in this direction are in progress.

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