On the Mechanism of the Caro Synthesis of Methylene Blue

  • Francisco Sánchez-Viesca Organic Chemistry Department, Faculty of Chemistry, National Autonomous University of Mexico, Mexico City (CDMX), Mexico
  • Reina Gómez Organic Chemistry Department, Faculty of Chemistry, National Autonomous University of Mexico, Mexico City (CDMX), Mexico
Keywords: p-benzoquinone diimine, dibenzothiazine, imino intermediates, radical ions, sulfhydryl radical, thioxo group


The recent interest for new applications of methylene blue as a promising drug for several important ailments prompted us to fill unknown aspects related to this compound. Since there is no mechanism on the Caro synthesis of methylene blue, we provide the electron flow, step by step, from the starting N,N-dimethylphenylenediamine to the dibenzothiazine derivative. It is a free radical generation system due to the oxidizing properties of ferric chloride. We pointed out the alternative reactions that take place with hydrogen sulphide, the reducer from which the thiazine ring is formed.


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How to Cite
Sánchez-Viesca, F., & Gómez, R. (2021). On the Mechanism of the Caro Synthesis of Methylene Blue. Earthline Journal of Chemical Sciences, 6(2), 209-214. https://doi.org/10.34198/ejcs.6221.209214