The technological process for the preparation and isolation of phenothiazine

A method of synthesizing phenothiazine is presented that permits obtaining the desired product with a large yield and high quality. It is based on the reaction between diphenylamine and sulfur in the presence of catalytic amounts of iodine crystals in the melt, followed by cooling and recrystallization. For obtaining phenothiazine of the required quality, toluene and ethanol were used as solvents in a specific combination. The recrystallization step proceeded without further crushing of the resulting reaction melt. Introduction of these solvents occurred sequentially, thereby obtaining a final phenothiazine product with high yield and purity. It has been shown in a series of experiments that synthesis of this heterocycle in a solution using o-xylene did not lead to the formation of phenothiazine with a good yield and sufficient quality. Furthermore, it was found that the replacement this solvent of chlorobenzene did not improve the characteristics of the target product. As a result offurther studies, we suggested synthesis ofphenothiazine in the melt followed by a technological method of isolating it. The method ofpreparing and isolating phe-nothiazine described in the article differed from known methods in the literature by the high yield of the desired product, 90%, and high purity, > 99%. The content of impurities in the synthesized heterocycle according to data from high performance liquid chromotography was < 1%, confirming the high purity of the obtained compound. Synthesis conditions described in the article promoted complete reaction and total conversion of the starting material, diphenylamine. The obtained tricyclic compound phenothiazine was reliably characterized by data from nuclear magnetic resonance on nuclei H and C in a solution of deuterated dimethyl sulfoxide. Furthermore, the melting point of the product was determined and fully corresponded to the values shown in the literature. High performance liquid chromatography was used to evaluate the purity of the synthesized sample. The method developed of preparing and isolating the phenothiazine allowed obtaining the desired compound with a yield of > 90% conversion into the dry substance and with a substance content of > 99% The proposed method of synthesis of pheno-thiazine is an excellent basis for obtaining and investigating new biologically active derivatives based on it and also other promising compounds for practical applications.

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