Study on the murexide reaction. V

Although the reaction of caffeine with hydrogen peroxide/hydrochloric acid or nitric acid and then with ammonia has been known to give a purple coloration (Murexide reaction), the use of hydrazine instead of ammonia is found to provide no purple coloration. The reaction of caffeine with hydrogen peroxide/hydrochloric acid and then with hydrazine hydrate afforded a yellow reaction mixture, from which 4‐methyl‐6‐( N ‐methylcarbamoyl)‐3,5‐dioxo‐2,3,4,5‐tetrahydrotriazine 9 , oxalyl hydrazide 10 and hydroxylamine hydrochloride were isolated. The reaction of caffeine with nitric acid and then with hydrazine hydrate furnished a yellow reaction mixture, from which 8‐amino‐1,3,7‐trimethyl‐2,6‐dioxo‐1 H ,3 H ,7 H ‐xanthine 11, 9 and hydroxylamine nitrate were isolated. Compound 9 was clarified to be produced from 3‐hydroxy‐4,6‐dimethyloxazolo[4,5‐ d ]pyrimidine‐2,5,7(3 H ,4 H ,6 H )‐trione 3 and 1,3‐dimethylalloxan 7 by the ring transformation with hydrazine.