Abstract
ANOMALOUS colour changes exhibited by methylene blue (Fig. 1, I) in organic media containing amines in the dark have been reported and rationalized in various ways1–3. These observations are of interest in connexion with studies of the photochemical reduction of I by amines1, the use of I in photosensitized autoxidation of amines4,5 and the investigation of dye-amine catalyst systems for photopolymerization6. We have encountered similar events in our own work in these areas and have identified the cause as base-catalysed self-oxidation7,8 or disproportionation of compound I followed by hydrolysis of the oxidized species VII to the demethylated dye II which is pale red in basic solution. This provides a general explanation for the various observations referred to.
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SCHAEFER, F., ZIMMERMANN, W. Self-oxidation of Methylene Blue. Nature 220, 66–67 (1968). https://doi.org/10.1038/220066a0
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DOI: https://doi.org/10.1038/220066a0
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