Vanillin, reagent

Many known color reactions involve electrophilic substitution at an electron-rich aromatic or heteroaromatic (cf. 4-(dimethylamino)-benzaldehyde - acid reagents and vanillin reagents ). Here aliphatic or aromatic aldehydes react in acid medium to yield polymethyne cations which are intensely colored di- or triarylcarbenium ions [4, 10]. 

In order to be able to recognize the influences exerted by the various mineral acids used in vanillin reagents the three reagent variants listed below were prepared ... 

Evidently the reaction of the indoles investigated with fuming hydrochloric acid is less sensitive as is the case for the two other vanillin reagents. 

VanadiumOO oxide reagent 426 Vanillin reagent 430,434 Van Urk reaction... 

The vanillin method is based on the condensation of the vanillin reagent with proanthocyanidins in acidic solutions. Protonated vanillin, a weak electrophilic radical, reacts with the flavonoid ring at the 6- or 8-position. The vanillin reaction is affected by the acidic nature and concentrations of substrate, the reaction time, the temperature, the vanillin concentration, and water content (Sun and others 1998). 

Colour Tests. Koppanyi-Zwikker Test—violet Mercurous Nitrate—black Vanillin Reagent—brown-orange/violet (transient). 

Colour Test. Vanillin Reagent—brown-orange/brown-orange. 

This triterpene needed only one purification step prior to preparative TLC, and because of its lack of distinctive chromophore, required visualization by spray detection using vanillin reagent (Table 3). 

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