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.
以
咖啡因为模型化合物,研究了氧化
脲反应,以澄清着色的机理。在
咖啡因与
过氧化氢和
盐酸的反应混合物中,产生了 1-羟基-5,7-二甲基-2,4,6-三氧代-1H,5H,7H-
恶唑并[4,5-d]
嘧啶(黄色油状物)(I)和 1、分离出了 1,3,7-三甲基-2,6,8-三氧代-9-羟基-1H,3H,7H-
黄嘌呤(红色粉末)(II),并证明这两种化合物是
咖啡因发生
脲氧化反应的原因。化合物 I 被认为是一个关键的中间体,因为它在稀
氨水中呈现的紫色与
咖啡因通过
金霉素反应生成的紫色相似。II 的吸收最大值与
咖啡因与
过氧化氢和
盐酸反应生成的红色溶液的吸收最大值一致。