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1991 (1)
1982 (1)
1Author    Thomas Buhse, Wolfram ThiemannRequires cookie*
 Title    Chiral Intermediates and the Oscillatory Effect of Circular Dichroism in the Belousov -Zhabotinskii Type Reaction of L-Ascorbic Acid  
 Abstract    Investigating the Belousov-Z habotinskii (BZ) type reaction of an acidic L-ascorbic acid (AA) / potassium brom ate / cerous sulfate system, an oscillatory effect of circular dichroism is detectable at A = 300 nm. HPLC analysis o f the oscillatory mixture and spectroscopic experi­ ments indicate that this effect is caused by 3,4,5-trihydroxy-2-oxo-L-valeraldehyde (TVA) -a C5 oxidation fragment of AA. Because of the bromide ion production occurring before the metal catalyst addition the AA system shows no preoscillatory phase and a rather short entire length of oscillation up to a maximum of 20 min. Since AA is not brom inated but oxidized by bromine which is formed by the Landolt typ "clock reaction" o f AA with acidic brom ate, par­ tially bromine-hydrolysis-controlled (BHC) oscillations are discussed for the overall mecha­ nism of this BZ system. 
  Reference    Z. Naturforsch. 46b, 1406—1414 (1991); received 
  Published    1991 
  Keywords    M arch 1, 1991 Chemical Oscillations, CD Spectra, L-Ascorbic Acid, B elousov-Z habotinskii Reaction, Bromate 
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 TEI-XML for    default:Reihe_B/46/ZNB-1991-46b-1406.pdf 
 Identifier    ZNB-1991-46b-1406 
 Volume    46 
2Author    Sa-Ouk Kang, Helmut Sapper, Wolfgang LohmannRequires cookie*
 Title    The Oxidative Degradation of L-Ascorbic Acid via an a-Ketoaldehyde  
 Abstract    Dehydro-L-ascorbic acid, the oxidation product of L-ascorbic acid, is unstable in aqueous solution and decomposed by a hydrolytic disruption of its ring structure to 2,3-diketo-L-gulonic acid. It is shown by means of UV, 'H-, and 13C-NMR spectroscopy that after decarboxylation 3,4,5-trihydroxy-2-keto-L-valeraldehyde, an a-ketoaldehyde, is formed. This substance is oxidized further to L-erythroascorbic acid, coupled with a reduction of 2,3-diketo-L-gulonic acid to L-ascorbic acid. 
  Reference    Z. Naturforsch. 37c, 1064—1069 (1982); received August 24 1982 
  Published    1982 
  Keywords    L-Ascorbic Acid, Dehydro-L-Ascorbic Acid, a-Ketoaldehyde, L-Erythroascorbic Acid, NMR 
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 TEI-XML for    default:Reihe_C/37/ZNC-1982-37c-1064.pdf 
 Identifier    ZNC-1982-37c-1064 
 Volume    37