UV-Photolyse von 5-Joduracil, IV Reaktionen des Uracilradikals mit primären und sekundären Alkoholen in wäßriger, sauerstoffgesättigter Lösung / Photochemistry of 5-Iodouracil in Aqueous Oxygenated Solution in Presence of Primary and Secondary Alcohols

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Abstract
UV-Photolysis (λ=254 nm) of 5-iodouracil in aqueous oxygenated solution in presence of ethanol, ethylene glycol and i-propanol was investigated at pH = 6. Isodialuric acid, uracil, H2O2 and iodine were found in all solutions. In addition to the above products in presence of ethanol, ethylene glycol and i-propanol acetaldehyde, glycolaldehyde and acetone respectively were formed. The yields of these products were determined as a function of the alcohol concentrations. The results suggest that the primary step is a homolytic splitting of the C-I-bond forming a uracil radical and an iodine atom. The uracil radical reacts with oxygen to form isodialuric acid and with alcohols to give uracil and an alkylhydroxyradical. The ratio of the rate constants between the addition of oxygen and the H-atom abstraction of the uracil radical has been determined for the following H-donors: ethanol, ethylene glycol, i-propanol and glycerine (Table 1). The reactions of the alkylhydroxyradicals with oxygen give the corresponding aldehyde or ketone respectively and H2O2. In the absence of oxygen the UV-photolysis of iodouracil in the presence of i-propanol leads to uracil, acetone and iodide. Consideration of the material balance leads to a reaction scheme which explains all the final products.

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