MUREXIDE REACTION OF CAFFEINE WITH HYDROGEN-PEROXIDE AND HYDROCHLORIC-ACID .2.

In continuation of the study on the murexide reaction of caffeine with 3% hydrogen peroxide/hydrochloric acid and then with ammonia giving a purple coloration, we investigated the oxidation reaction of caffeine with 6% hydrogen peroxide/hydrochloric acid to isolate ten reaction products, 3‐hydroxy‐4,6‐dimethyloxazolo[4,5‐d]pyrimidine‐2,5,7(3H,4H,6H)‐trione 1, 1,3‐dimethylalloxan 2, murexoin 3, 1,3,7‐trimethyl‐2,6,8‐trioxo‐9‐hydroxy‐1H,3H,7H‐xanthine 5, 1,3,7‐trimethyl‐2,6,8‐trioxo‐1H,3H,7H‐xanthine 6, 1,3,7‐trimethyl‐2,6‐dioxo‐8‐chloro‐1H,3H,7H‐xanthine 7, 5‐(1,3‐dimethyl‐1,2,3,4,5,6‐hexahydro‐2,4,6‐trioxopyrimidin‐5‐yl)‐aminomethylene‐1,3‐dimethyl‐1,2,3,4,5,6‐hexahydro‐2,4,6‐trioxopyrimidine ammonium salt 9, 1,3‐dimethylpalabanic acid 10, 1‐methyl‐2,4,5‐trioxoimidazole 11, 3‐hydroxy‐5,7‐dimethyloxazolo[5,4‐d]pyrimidine‐2,4,6(3H,5H,7H)‐trione 12 and 4,6,8‐trimethyl‐1,2,4‐dioxazino[6,5‐d]pyrimidine‐3,5,7(4H,6H,8H)‐trione 13. The oxidation reaction using 6% hydrogen peroxide/hydrochloric acid was found to produce a similar purple coloration to that of the murexide reaction despite no subsequent addition of ammonia, indicating the liberation of ammonia by the oxidation of caffeine. Among the above compounds, the purple colored substance murexoin 3 and the yellow colored compound 9 were both ammonium salts, and compound 5 was the red colored substance. In the present investigation, these three compounds were found to contribute to the coloration. Copyright © 1990 Journal of Heterocyclic Chemistry