Dimethylamino -benzaldehyde-Acid Reagents

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]. 

A whole series of derivatization reagents contain 4-(dimethylamino)-benzaldehyde as a fundamental component. They differ in the type and concentration of the mineral acid components used in their preparation. Other components of the reagent generally play a minor role. 

Ehrlich s reagent as 4-(dimethylamino)-benzaldehyde — hydrochloric acid and... 

Van Urk s reagent as 4-(dimethylamino)-benzaldehyde - sulfuric acid, but the experimental section incorrectly refers to a solution of 4-(dimethylamino)-benzaldehyde in hydrochloric acid/ethanol as Van Urk s reagent [1]. 

It can be concluded from the publications of Rohde [2] and Freund and Lebach [3, 4] that it was Ehrlich who first suggested the use of 4-(dimethylamino)-benzalde-hyde in the presence of hydrochloric acid for color reactions with methylketols that was found also to apply to indole derivatives [S]. Auterhoff [6] designated a reagent for urobilinogen, consisting of a solution of 2 g 4-(dimethylamino)-benzaldehyde in 20 percent hydrochloric acid, correctly as Ehrlich s solution. Hence, it is essentially correct to refer to all reagents which contmn these components as Ehrlich s reagent. 

Auterhoff described a reagent made up of 4-(dimethylamino)-benzaldehyde, sulfuric acid with additional iron(lll) ions as Van Urk s reagent solution . A more correct name would have been Van Urk-Salkowski reagent, since the Salkowski reagent (iron(lll) chloride/sulfuric acid) has been used alongside the Van Urk s reagent [8]. 

Dimethylamino)-benzaldehyde-Acetic Acid-Phosphoric Acid Reagent... 

Note The individual components of the reagent can also be applied separately one after the other [12, IS], e.g. the chromatogram is first immersed in an 8% methanolic 4-(dimethylamino)-benzaldehyde solution and then, after intermediate drying, sprayed v th 25% sulfuric acid [12]. 4-(Dimethylamino)-benzaldehyde can be replaced in the reagent with 4-(dimethylamino)-ciimamaldehyde [1]. 

Tin(II) Chloride-Hydrochloric Acid-4-(Dimethylamino)-benzaldehyde Reagent... 

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