The condensation product of 2‐aminophenol and glyoxal. Structure and photochemistry

Abstract

Abstract It has been shown by X ‐ray analysis that the condensation product of 2‐aminophenol and glyoxal is 5a,6,11a,12‐tetrahydro[1,4]benzoxazino[3,2‐ b ][1,4]benzoxazine ( 5 ) and not, as generally assumed, 2,2′‐bibenzoxazoline ( 4 ). The structure of 5 is preserved if it is dissolved in neutral solvents. Thermal oxidation of 5 leads preferentially to the formation of bibenzoxazole 7 and only with small yields to benzoxazinobenzoxazine 8 . The photooxidation reaction of 5 is wavelength dependent. Long wavelength excitation yields exclusively 7 , short wavelength excitation yields also 7 , but in addition 8 . The photooxidation 5→7 requires two photons: The first product is the metastable dihydrobibenzoxazole 10 which is converted by a second photon into 7 . The photooxidation 5→8 is presumably a one‐photon process.