Murexide reaction of caffeine using nitric acid.
作者:HIROSHI KOZUKA、MATAJIRO KOYAMA、TOMOAKI OKITSU
DOI:10.1248/cpb.30.941
日期:——
The murexide reaction of caffeine was investigated to clarify the pathway of the coloration. From the reaction mixture of caffeine with nitric acid, 1, 3-dimethylalloxan (II) and 1, 3, 7-trimethyl-2, 6-dioxo-8-nitro-1H, 3H, 7H-xanthine (IV) were isolated. Compound II was found to be the key intermediate, since it was converted to a purple-red-colored substance, murexoin (III), by treatment with conc. ammonia. It was found that 1-hydroxy-5, 7-dimethyl-2, 4, 6-trioxo-1H, 5H, 7H-oxazolo [4, 5-d] pyrimidine (I), previously obtained by the oxidation of caffeine with hydrogen peroxide and hydrochloric acid, was also transformed to III with conc. ammonia. Consequently, the murexide reaction of caffeine was shown to have two pathways of coloration depending on the oxidizing agent employed. From the spectral data, a symmetrical structure (III) was assigned to murexoin in solution. Amalic acid, which has been reported as an intermediate of the murexide reaction of caffeine, can be ruled out on the basis of our experimental results.
对咖啡因的氧化脲反应进行了研究,以弄清其着色的途径。从咖啡因与硝酸的反应混合物中分离出了 1,3-二甲基阿洛先(II)和 1,3,7-三甲基-2,6-二氧代-8-硝基-1H,3H,7H-黄嘌呤(IV)。发现化合物 II 是关键的中间体,因为它在用浓氨水处理后会转化为紫红色物质,即 murexoin (III)。研究还发现,之前用过氧化氢和盐酸氧化咖啡因得到的 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(I)也在浓氨水的作用下转化为 III。结果表明,咖啡因的脲氧化反应有两种着色途径,取决于所使用的氧化剂。从光谱数据来看,溶液中的金合欢素具有对称结构 (III)。根据我们的实验结果,可以排除作为咖啡因金霉素反应中间体的水杨酸的可能性。