Identification of catechols and their protecting groups usin gcolor reactions
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.
万方数据
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