MECHANISM OF FREE-RADICAL OXIDATION OF CAFFEINE IN AQUEOUS-SOLUTION

The oxidation of caffeine with persulfate and hydroxyl radicals in aqu eous solution has been studied by EPR spectroscopy and HPLC analysis. In both cases the formation of 1,3,7-trimethyluric acid is observed as the main final product, A C8-OH radical adduct is postulated as the i ntermediate after reaction with OH', and leads to the final product af ter further oxidation, This radical is too short-lived to be observed by EPR. After oxidation of caffeine with SO4.- its radical cation is d etected by EPR. This radical reacts with water to produce the above me ntioned C8-OH radical adduct after deprotonation. In the presence of d ibasic phosphate a spectrum attributed to the C8-phosphate radical add uct is observed. This radical results from the nucleophilic attack of the buffer on the radical cation of caffeine, Hydrolysis and oxidation of the phosphate radical intermediate results in the formation of 1,3 ,7-trimethyluric acid.