Oxidative trimerization of indole: on the formation of dications and radical cations by reaction of indole and nitrosobenzene in the presence of acids

The reactions of indole with nitrosobenzene in the presence of acetic, monochloroacetic, monobromoacetic and trichloroacetic acid afford as the main product a deep-green precipitate, which in a preceding study had been erroneously identified as the aminyl radical of a trimer indole. The identity of the minor products was confirmed. This paper deals with the determination of the correct structure of the compounds contained in the precipitate through a study based on chemical reactions, electrochemical measurements and X-ray analysis.