摘要
为了探索一种简便的鉴别儿茶酚及其保护基类型的方法,比较了苯酚与儿茶酚在水溶液里的颜色反应及其在可见光区域的吸收谱,测试了 30余种酚类物质与FeCl3在TLC硅胶板上的颜色反应,对比了 4种氯化物与酚类物质在硅胶板上的显色效果,建立了酚类浓度梯度与样品点显色深浅的关系,最后研究了缩丙酮保护在稀FeCl3乙醇溶液中分解的反应动力学.结果表明:在TLC硅胶板上,络合能力弱的酚类与FeCl3不发生显色反应,儿茶酚等具有强螯合能力的酚类可以发生颜色反应,儿茶酚样品点显示的青(蓝)黑色来自于其与Fe(Ⅲ)形成的一配位和二配位络合物,与三配位络合物无关.由于作为路易斯酸的FeCl3具有选择性脱保护的特性,不同类型保护基保护的儿茶酚显色现象不同:对弱酸不稳定的,在室温缓慢显色;对强酸不稳定的,室温不显色在110℃烤板5 min后显色;对强酸稳定的,2种条件下都不显色.在4种金属氯化物中,FeCl3是最佳的检测试剂,酚类检测浓度最合适的范围为10～50 mmol·L-1.
Abstract
To explore a simple analytical method for identifying catecholsand the types of their protecting groups,the colors of phenol and catechol with FeC13 in aqueous solutions and their visible absorption spectra were compared,and over thirty phenolic substances were tested for color developments with FeCl3 on TLC silica-gel plates.Color-developing effectiveness between phenols and four metal chlorides were evaluated to establish a correlation between catechol concentrations and shades of spot colors.The kinetics of acetonide decomposition in dilute FeCl3 ethanol solution were analyzed.The experiments demonstrated that phenols with weak binding abilities did not develop colors with FeCl3 on TLC silica-gel plates while phenols with strong chelating abilities such as catechol did.The greenish/bluish black color on the spots of catechol samples arose from the mono-and bi-coordinated Fe(Ⅲ)complexes,not from the tri-coordinated ones.Since FeCl3 is a strong Lewis acid and can selectively cleave phenol protections,catechols protected by various types of protecting groups showed different color changes.Catechols protected by weak-acid labile protecting groups exhibited slow color development at room temperature;those protected by strong-acid labile protecting groups displayed no color at room temperature but bluish-black after heated on the silica-gel plate at 110℃ for 5 min;those protected by strong-acid stable protecting groups showed no color change under both conditions.The results also indicated that FeCl3 was the best color-developing agent among the four metal chlorides in testing phenols,with the optimum concentration of the phenols ranging from 10 to 50 mmol·L-1.
维普
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