Abstract
The murexide reaction was investigated to clarify the mechanism of the coloration, with caffeine as a model compound. From the reaction mixture of caffeine with hydrogen peroxide and hydrochloric acid, 1-hydroxy-5, 7-dimethyl-2, 4, 6-trioxo-1H, 5H, 7H-oxazolo-[4, 5-d] pyrimidine (yellow oil) (I) and 1, 3, 7-trimethyl-2, 6, 8-trioxo-9-hydroxy-1H, 3H, 7H-xanthine (red powder) (II) were isolated, and these two compounds were shown to be responsible for the murexide reaction of caffeine. Compound I was regarded as a key intermediate, since its purple coloration with dil. ammonia was similar to that of caffeine developed by the murexide reaction. The absorption maximum of II corresponds to that of the red-colored solution obtained from the reaction of caffeine with hydrogen peroxide and hydrochloric acid.
