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-h][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 -4 3 is presumably a one-photon process.
Struktur und Photochemie eines Kondensationsproduktes aus ZAminophenol und GlyoxalMit Hilfe der Rontgen-Strukturanalyse konnte gezeigt werden, daB bei der Kondensation Bei kurzwelliger Anregung entsteht ebenfalls 7, daneben jedoch auch 8. Zur Photooxidation 5+7 sind zwei Photonen erforderlich. Zunachst bildet sich das metastabile Dihydrobibenzoxazol 10, aus dem nach der Absorption eines zweiten Photons 7 entsteht. Die Photooxidation 5-8 ist wahrscheinlich ein Ein-Quanten-ProzeB.
The Structure of the Condensation ProductFor the condensation product (CP) of 2-aminophenol (1) and glyoxal (2) the structures 3 to 6 are conceivable (Scheme 1). Since CP forms chelates with a number of divalent cations (e.g. Cu2@, Mg2@, Ca2@), Bayer') first assumed that the Schiff base 3 is the chelating reagent. CP is commercially available (Fluka)