Potassium hydroxide reagent

The course of the reaction has not been fully clarified. Hydrolytic and aromatization processes are probably responsible for the formation of colored or fluorescent deriva4 tives (cf. Potassium Hydroxide Reagent). For instance, sevin is converted to a-naphthalkali metal salt of the o-hydroxycinnamic acid pro- duced by hydrolytic cleavage of the pyrone ring is converted from the non-fluorescent cis- to the fluorescent trans-form by the action of long-wavelength UV light (X = 365 nm) [2]. 

Note It is occasionally recommended that after it has been sprayed the plate should be covered with a glass plate for several minutes until optimum reaction has occurred [11], or be irradiated with long-wavelength UV light (X = 365 nm) [2]. Methanolic potassium hydroxide solution can also be used in place of sodium hydroxide [12] (see Potassium Hydroxide Reagent). The formation of colors and fluorescences depends on the length of heating and on the temperature employed optimum conditions must be discovered empirically [12]. 

Aromatic aldehydes react in basic as well acidic medium. Thus vanillin and primary amines yield Schiff s bases (cf. vanillin-potassium hydroxide reagent in Volume 1 a). Colored phenolates are formed at the same time. As would be expected secondary amines, indole derivatives and lysergic acid derivatives do not react. 

Ninhydrinr-Collidine-Ethanolic Potassium Hydroxide Reagent (S54)—(Leudne/Isoleudne/etc.)... 

Fig. 8 A UNO,-potassium hydroxide reagent (HNO,/KOH No.30) -4 UV-365nin B Sodium metaperiodate reagent (see 2.3 Detection) -4 UV-365nm...

The most frequently used color reactions are those developed by Vital and Gerrard and may be briefly described as follows The Vitali Reaction (1). A minute quantity (as little as 0.0001 mg. is sufficient) of solid atropine, Z-hyoscyamine or Z-scopolamine, on a watch glass, is treated with a drop of fuming nitric acid and the liquid evaporated to dryness at 100°. The residue when treated with a drop of freshly prepared solution of ethanolic potassium hydroxide develops a bright purple coloration which slowly fades to a dark red and finally to a colorless liquid. The color sequence can be reproduced by the addition of more potassium hydroxide reagent. 

The same color display is observed in the case of the modified Vitali test. The alkaloid is ground with sodium nitrate and moistened with sulfuric acid, and subsequently treated with potassium hydroxide reagent. This color reaction has been applied to sixty alkaloids and only veratrine Z-Scopolamine will be used throughout this chapter in preference to Z-hyoscine so as to avoid any possibility of confusion of this alkaloid with Z-hyoscyamine. 

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