Reaction of spironaphthoxazine with acid

The reaction of spironaphthoxazine (SNO) with acid in ethanol was investigated by spectroscopic analyses SNO was protonated and then transformed into a complex in an acidic ethanol solution in the dark. It is presumed that the complex contains a hydrated proton and its structure is similar to that of the metal complex of a merocyanine-type isomer photoderived from SNO based on its UV–vis absorption and fluorescence spectra. The complex dissociated into SNO by adding base. The complex was further changed under acidic conditions after a long time. Highly concentrated acid decomposed SNO to an indoline compound having a carboxyl group and 1-amino-2-naphthol, which was revealed by fluorescence, IR, and GC–MS analyses. These reaction processes were promoted by UV irradiation.

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► SNO was protonated and then transformed into a complex in an acidic ethanol solution.
► The complex contains a hydrated proton and has the metal complex-like structure.
► The complex dissociated and reproduced SNO by adding base.
► Highly concentrated acid decomposed SNO to an indoline and 1-amino-2-naphthol.
► These reaction processes were promoted by UV irradiation.