All these alkaloids can react with the precipitant of alkaloids to form precipitates. There are several chemical reactions to identify these alkaloids:
① Mercury chloride reaction: scopolamine and scopolamine can be distinguished. Anisodamine can react with ethanol solution of mercuric chloride to form yellow precipitate, which turns red after heating. Under the same conditions, scopolamine can only produce white precipitate. This is due to the strong alkalinity of scopolamine, which converts mercuric chloride into brick-red mercuric oxide when heated, while scopolamine is weak in alkalinity and can only form white molecular double salt with mercuric chloride.
② Vitaly reaction: Except anisodamine, alkaloids with scopolamine structure in Datura stramonium were nitrated by fuming nitric acid, and then reacted with alcohol solution of caustic soda, resulting in double bond rearrangement to generate derivatives with quinone structure, which appeared deep purple and finally disappeared.
③ Acetylacetone periodate reaction: used to identify anisodine. The hydroxyl scopolamine in anisodine molecule has o-dihydroxy structure, which can be oxidized by periodate to form formaldehyde, and then reacted with acetylacetone in acetic acid to form yellow diacetyl dimethyl dihydropyridine.