Facile synthesis of catechol azo dyes
Facile synthesis of catechol azo dyes
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DOI：
10.1021/jo972151z
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发表时间：
1998-06-26
影响因子：
3.6
通讯作者：
Tan, EW
中科院分区：
文献类型：
--
作者：
Haghbeen, K;Tan, EW
邻苯二酚（1，2-二羟基苯）的偶氮染料由于其发色性质和其邻位酚羟基的双齿特征而受到关注。这些特性使它们可用于金属络合研究1和阳离子浓度的光谱测量。2，3由于缺乏普遍适用但有效的综合方法，它们的广泛用途受到限制。现有方法4 -8的局限性在我们尝试制备用作氧化还原酶的发色底物的邻苯二酚偶氮化合物2a-d时变得明显。邻苯二酚与重氮盐的偶联反应（方案1）伴随有副反应，这些副反应尚未被彻底研究。邻苯二酚在重氮偶合反应中需要考虑的一个重要方面是它倾向于氧化成不稳定的邻醌。儿茶酚的氧化随着碱性pH值的增加而变得越来越快。然而，高pH值也增加了儿茶酚对重氮偶联的反应性。邻苯二酚的这两个特性的平衡导致反应产率的折衷。已经报道了几种方法来解决与邻苯二酚的重氮偶联的这两个方面。这些包括碱性条件，4 pH 4的醋酸盐缓冲溶液，
Azo dyes of catechol (1, 2-dihydroxybenzene) are of interest due to their chromophoric nature and the bidentate character of their ortho phenolic hydroxyl groups. These properties have made them useful for metal complexation studies1 and for spectroscopic measurement of cation concentrations. 2, 3 Their wider utility is limited by a lack of generally applicable, yet efficient, methods for their synthesis. The limitations of existing methods4-8 became obvious in our attempts to prepare catechol azo compounds 2a-d for use as chromophoric substrates for redox enzymes.The coupling reaction of catechol with a diazonium salt (Scheme 1) is accompanied by side reactions that have not been thoroughly studied. An important aspect to consider for catechol in a diazo coupling reaction is its tendency to oxidize to unstable o-quinone. Oxidation of catechol becomes increasingly rapid with increasing alkaline pH. However, a high pH also increases the reactivity of catechol to diazo coupling. It is the balancing of these two characteristics of catechol which leads to compromises in the yield of reaction. Several methods have been reported to address these two aspects of diazo coupling with catechol. These have included alkaline conditions, 4 an acetate-buffered solution at pH 4 using