Anisaldehyde - sulfuric acid is a universal reagent for natural products, that makes color differentiation possible. It is a reagent for anitoxidants, steroids, prostaglandins, carbohydrates, phenols, glycosides, sapogenins, essential oil components or terpenes, antibiotics and mycotoxins.
This stain is an excellent multipurpose visualization method for examining TLC plates. It is sensitive to most functional groups, especially those which are strongly and weakly nucleophilic. It tends to be insensitive to alkenes, alkynes, and aromatic compounds unless other functional groups are present in the molecules which are being analyzed.
It tends to stain the TLC plate itself, upon mild heating, to a light pink color, while other functional groups tend to vary with respect to coloration.
The mechanism with steroids has not been elucidated. Various nonquantitative reactions occur simultaneously. Cyclopentenyl cations have been postulated as intermediates which condense with anisaldehyde to yield colored compounds. It is probable that triphenylmethane dyes are also formed with aromatic compounds.
Reference : Stahl E and Glatz A. J Chromatogr. 1982, 240: 518-521; 243: 139-143.
Anisaldehyde - sulfuric acid is a universal reagent for natural products, that makes color differentiation possible. It is a reagent for anitoxidants, steroids, prostaglandins, carbohydrates, phenols, glycosides, sapogenins, essential oil components or terpenes, antibiotics and mycotoxins.
This stain is an excellent multipurpose visualization method for examining TLC plates. It is sensitive to most functional groups, especially those which are strongly and weakly nucleophilic. It tends to be insensitive to alkenes, alkynes, and aromatic compounds unless other functional groups are present in the molecules which are being analyzed.
It tends to stain the TLC plate itself, upon mild heating, to a light pink color, while other functional groups tend to vary with respect to coloration.
The mechanism with steroids has not been elucidated. Various nonquantitative reactions occur simultaneously. Cyclopentenyl cations have been postulated as intermediates which condense with anisaldehyde to yield colored compounds. It is probable that triphenylmethane dyes are also formed with aromatic compounds.
Reference : Stahl E and Glatz A. J Chromatogr. 1982, 240: 518-521; 243: 139-143.
The mechanism for anisaldehyde dyes is similar to that for vanillin.
The formation of triarylmethane dyes are thought to be actively responsible for the colourant. Anisaldehyde can form such dyes in a generally non-quantitative fashion in the presence of sulfuric acid and oxygen, which causes the background colour. The reaction proceeds through sensitive cationic intermediates via a Friedel-Crafts like process and is therefore extremely sensitive to the presence of other compounds which become chaotically incorporated, resulting a variation of colours.
Aldehydes are already very susceptible nucleophilic addition reactions, and in the presence of a bronsted acid as strong as sulfuric acid they spend a lot of time as the oxocarbenium resonance form. That charge on the oxygen is going to kick up your pi-electrons and polarize the carbonyl even more. In short, p-anisaldehyde is shockingly electrophilic. Now add a heat gun and all of your recently separated reaction products adsorbed onto a TLC plate and the possibilities are endless. Beyond that, the various additions and/or condensation products are going to yield a palette of chromophores with MO bandgaps that fall within the spectrum of visible light.
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