Berberine: yellow, tetrahydroberberine: colorless; hematine: yellow, colorless after salt formation

Free base: A small number of phenolic bases, which are insoluble in alkaline water for various reasons. For example, demethyltetrandrine is insoluble in alkaline water due to steric hindrance and the ability to form intermolecular hydrogen bonds. Non-phenolic alkaloids are insoluble in alkaline water, so they are in the chloroform layer during extraction.

Salt-forming Alk: • Mostly soluble in water, insoluble or poorly soluble in organic solvents. Hydrophilic alkaloids usually refer to quaternary ammonium alkaloids and alkaloids with N→O coordination bonds • Oxylate salts tend to be more water-soluble. • Poor solubility with salt water formed by macromolecular organic acids • Good solubility with small molecular organic acids or inorganic acids to form salt water

The larger the pKa, the smaller the degree of ionization of the conjugate acid, and the stronger the binding ability of nitrogen atoms to H, that is, the stronger the alkalinity.

Hybridization method

Electronic effect: The density of the electron cloud increases, and the stronger the ability to accept protons, the stronger the alkalinity.

Steric effect: steric hindrance

intramolecular hydrogen bonding

Intramolecular tautomerism: aza ketal, protonation to form quaternary ammonium base

Alk protonation is mostly on β-C, not nitrogen atoms

The N atom at the bridgehead of the fused ring cannot form a salt in the form of an imine

When the lone electron pair of the N atom is spatially close to the ketone group, a cross-ring effect occurs.

Metal salts • Iodine-potassium iodide (Wagner) KI-I2 tan precipitate • Potassium bismuth iodide (Dragendoff) BiI3×KI reddish brown precipitate • Potassium mercury iodide (Mayer reagent) HgI2×2KI off-white precipitate; if excess reagent is added, the precipitate will be dissolved again • Gold chloride (3%) (Suric chloride) HAuCl4 yellow crystalline precipitate

Acids - silicotungstic acid (Bertrand reagent) SiO2×12WO3 milky white

Phenolic acids - picric acid (Hager's reagent) 2,4,6-trinitrophenol yellow

Double salt—Ammoniumreineckate chromium ammonium thiocyanate reagent, produced Into insoluble double salt purple red

(1) It is usually carried out in the state of salt formation of alkaloids in acidic aqueous solution; (if it is under alkaline conditions, the reagent itself will precipitate) (2) When in dilute alcohol or fat-soluble solution, the water content is >50%; (when the alcohol content is >50%, the precipitate can be dissolved) (3) It is not easy to add large amounts of precipitation reagents. (For example: excess potassium mercury iodide can dissolve the precipitate produced)

(1) More than three precipitation reagents need to be used for each Alk during identification: precipitation reagents have different sensitivities to various Alks. (2) Directly carry out precipitation reaction on the acid extract of traditional Chinese medicine, then Positive result - cannot determine the presence of Alk A negative result indicates that there is no presence of Alk (3) Amino acids, proteins, polysaccharides, tannins, etc. Precipitation reagents - precipitation

Acid water - 0.1% ~ 1% H2SO4, HCl, HOAc, etc. Alkaloids and their salts are easily soluble in methanol, ethanol, etc., so methanol or ethanol is often used as the extraction solvent, and extraction is performed by reflux, dipping or percolation methods. Most free alkaloids are lipophilic, so they can be extracted with lipophilic organic solvents such as chloroform, dichloromethane, toluene, etc.

Acid water extraction has many disadvantages, so here are some solutions:

Methods to determine pH value: Buffer paper chromatography (small Rf value means high alkalinity), use pKa value to determine pH value (pH=pKa 2). When mixing alkaloid acid aqueous solutions and extracting and separating them using the pH gradient method, the pH of the solution should gradually increase from low to high. When separating alkaloids from chloroform by pH gradient extraction, you can extract from 8-3 buffer sequentially (from high to low pH)

Determine the ease of separation - number of extractions

Features: M or M -1 are mostly base peaks or strong peaks. Characteristic ions resulting from framework fragmentation are generally not observed. Mainly includes two categories: ①The overall or main structure of the molecules composed of the aromatic system; such as quinolines, acridones, etc. ②Alkaloids with multiple ring systems and tight molecular structures; such as matrines, colchicines, etc.

• The main cleavage method is α-cleavage centered on nitrogen atoms, and it mostly involves the cleavage of the skeleton. • Characteristics: Most of the base peaks or strong peaks are nitrogen-containing groups or parts. • Main types of alkaloids: cinchonines, steroidal alkaloids, etc.

• Features: After cleavage, a pair of strong complementary ions are produced, from which the nature and number of substituents on the ring can be determined. • Mainly include: tetrahydroprotoberberines, non-N-alkyl-substituted aporphyrins, etc. • Tetrahydroprotoberberine type alkaloids are mainly cleaved from the C ring and undergo reverse Diels Alder reaction (RDA reaction). For example: the cleavage process of cyclanoline is expressed as follows:

• Features: Same as 3. That is, a pair of strong complementary ions is produced after fragmentation • Such as: benzyl tetrahydroisoquinolines, bisbenzyl tetrahydroisoquinolines, etc. • For example: 1-benzyl-tetrahydroisoquinoline alkaloids in the isoquinoline type easily lose the benzyl group during the cracking process, resulting in strong spectral lines dominated by tetrahydroisoquinoline fragments