Initial steps of the metal-catalysed degradation of L-dehydroascorbic acid in acidic aqueous solutions
1997
Jungbluth, A. | Kolloch, M. | Marx, F. | Pfeilsticker, K.
The initial steps of the degradation of L-dehydroascorbic acid (L-DHA) in acidic aqueous solutions and the catalytic effect of different transition metal ions on this reaction were studied. The main product was identified as 3,6-furanosido-2,3-hexodiulosonic acid-2-hydrate (compound 1). In addition, number of other compounds were detected; they are formed from compound 1 by simple enolisation, lactonisation, hydration and dehydration reactions as well as by cleavage and formation of cyclic half acetal bonds. The chemical structures of these compounds were tentatively deduced by the mass spectra of their TMS derrivatives and a reaction scheme, for their formation is proposed. The velocity and the direction of the reactions were found to be strongly influenced by the presence of catalytic amounts of different transition metal ions. It was concluded that in acidic medium, in contrast to the situation in neutral and alkaline solutions, the opening of the lactone ring of L-DHA is, to a certain degree, a reversible reaction.
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