Summary on the Chemistry of Traditional Chinese Medicine (5)

Chapter VII Terpenoids and Volatile Oil

Learning points

1. Master the meaning and main classification of terpenoids.

2. Master the definition, universality and chemical composition of volatile oil.

3. Master the extraction and separation methods of volatile oil.

4. Familiar with the structural characteristics and main physical and chemical properties of iridoid glycosides.

5. Be familiar with the structure and biological activity of the main terpenoids in Taxus chinensis?

6. Be familiar with the structural types and extraction and separation methods of the main chemical components in Gentiana.

7. Be familiar with the meaning of chemical constants of volatile oil.

8. Understand the method of identifying volatile oil by gas chromatography.

9. Understand the structural characteristics of the main chemical components in mint.

Key and difficult tips

I. Concepts and classification principles of terpenoids

1. monoterpene is a compound group consisting of two isoprene units, containing 10 carbon atoms; Such as borneol and geraniol.

2. Sesquiterpenes, consisting of 15 carbon atoms and three isoprene units, such as cyclocineole and artemisinin.

3. Diterpenes are composed of 20 carbon atoms and 4 isoprene units, such as ginkgolides and stevioside.

Triterpenes are compounds with 30 carbon atoms and 6 isoprene units as the basic carbon structure.

Second, iridoids

The structure and classification of 1. can be divided according to whether cyclopentane is cracked or not.

① iridoid glycosides, such as aucubin.

② Cleavage iridoid glycosides such as gentiopicroside.

2. Physical and chemical properties

Most of them are white crystals or powders (rarely liquid), which are optically active and bitter.

Iridoid glycoside is easy to hydrolyze, and aglycone can change color when it meets acid, alkali, carbonyl compounds and amino acids. Contact with the skin can also make the skin blue.

3. Extraction and separation

Most iridoid glycosides are extracted by solvents, such as water, methanol, ethanol, allyl acetone and ethyl acetate. Before extraction, appropriate amount of calcium carbonate or barium hydroxide should be mixed into the extraction powder.

Third, the concept, nature and composition of volatile oil.

1. Definition of volatile oil: volatile oil, also known as essential oil, is a general term for a class of volatile oily components that are immiscible with water by steam distillation.

Volatile oil is a mixture containing complex chemical components. There are terpenoids, aliphatic compounds and aromatic compounds.

2. Physical and chemical properties of volatile oil: At room temperature, most volatile oils are colorless or yellowish transparent liquids, and a few volatile oils have other colors, such as stingrays, mostly blue.

The volatile oil can volatilize by itself at room temperature. It is a lipophilic component, insoluble in water and soluble in high concentration alcohol. The boiling point of volatile oil is generally between 70℃ and 300℃.

Acid value, ester value and saponification value are important chemical constants of volatile oils from different sources, and are also important indexes to measure their quality.

Fourth, the extraction methods of volatile oil and their advantages and disadvantages.

1 steam distillation method

The volatile oil is extract by utilizing that characteristic that the volatile oil is volatile and insoluble in water.

The method has the advantages of simple equipment, convenient operation, low cost, high yield and high recovery rate of volatile oil. However, the raw materials are easily burnt by intense heat, or the composition changes, and the aromatic smell of the obtained volatile oil may deteriorate, which often reduces its value as a spice and should be paid attention to.

2 Leaching method

For volatile oil raw materials that are not suitable for steam distillation extraction, organic solvents can be directly used for leaching. Commonly used methods include oil absorption, solvent extraction and supercritical fluid extraction.

① Oil-absorbing oils generally have the property of adsorbing volatile oils, and are often used to extract valuable volatile oils, such as rose oil and jasmine oil.

(2) solvent extraction: petroleum ether (30~60 oc), carbon disulfide, carbon tetrachloride, benzene and other organic solvents are used for extraction. The leaching method can be reflux leaching or cold leaching, and the organic solvent is evaporated under reduced pressure to obtain the extract.

(3) Supercritical fluid extraction of carbon dioxide is similar to solvent extraction technology. The extraction of aromatic volatile oil by this technology has the outstanding advantages of preventing oxidation and pyrolysis and improving quality. The obtained aromatic volatile oil has the same smell as the raw materials, which is obviously superior to other methods. However, the technical requirements are high and the equipment cost is large.

3 cold pressing method

This method is suitable for fresh raw materials, such as oranges, oranges, lemons and other raw materials containing more volatile oil. They can be torn, mashed, cold pressed, left standing and layered, or a crude product can be obtained by centrifugal separation. The volatile oil obtained by this method can maintain its original flavor, but it may dissolve the nonvolatile substances in the raw materials.

Fourth, the separation method of volatile oil

1 freezing treatment

Put the volatile oil below 0℃ for crystallization. If there is no crystallization, the temperature can be reduced to -20℃ and kept. Taking out the crystal and recrystallizing to obtain the pure product.

Fractionation method

Some components in volatile oil are often destroyed at boiling temperature, so decompression fractionation is usually used. Generally, monoterpenes are distilled at 35℃-70℃/ 1333.22pa, monoterpenes and oxygenates are distilled at 70℃-100℃/1333.22 pa, and sesquiterpenes and oxygenates are distilled at 80℃-1/kloc-.

3 chemical methods

(1) is separated by the difference of acidity and alkalinity.

(1) Separation of alkaline components If the volatile oil after the preliminary test contains alkaline components, it can be dissolved with ether, extracted with 10% hydrochloric acid or sulfuric acid, and the acid water layer is separated, alkalized, extracted with ether and evaporated to obtain alkaline components.