Definition: Any compound derived from the polymerization of isoprene, a class of compounds whose molecular formula conforms to the general formula (C5H8)n

Terpenoids are the most common type of compounds in natural substances, such as volatile oils, rubber, resins and carotenes. Many substances with strong physiological or biological activities are used clinically. Such as: menthol (monoterpene), artemisinin (monocyclic sesquiterpene), andrographolide (bicyclic diterpene), glycyrrhizic acid (pentacyclic triterpene, oleanane type), etc.

Terpenoids: Derived from isoprene, they are polymers or derivatives of isoprene. Ruzicka proposed the "empirical isoprene rule": the precursor of terpenes is active isoprene

Terpenoids are a class of compounds derived through the mevaleric acid pathway, with the general formula (C5H8)n. In actual work, experimental isoprene rules are still the main method.

Note that one unit is a hemiterpene!

chain monoterpenes

cyclic monoterpenes

Metamorphic monoterpenes

Definition: Consists of 3 isoprene units and contains 15 carbon atoms. It is the main component of the high-boiling range part of volatile oils. It mostly exists in the form of alcohols, ketones, lactones or glycosides, or alkaloids. It is the category with the largest number and skeleton structure types among terpenoids.

Classification

Definition: A group of compounds composed of 4 isoprene units and containing 20 carbon atoms. Diterpenes usually exist in the form of resins, bitter substances, plant alcohols, etc.

Classification

Two rings, three rings, four rings, open chain

form: • Monoterpenes and sesquiterpenes are mostly oily liquids and a few are solid, with special aroma. • As the molecular weight and double bonds increase, the functional groups increase, the volatility of the compound decreases, and the melting point and boiling point increase accordingly. They can be separated by fractional distillation. • Diterpenes and sesquiterpenes are mostly crystalline solids.

Taste: Most terpenoids have a bitter taste, also known as bitters

Optical rotation and refractive properties: Most terpenes have asymmetric carbon atoms and are optically active, and many of them exist in isomers.

Solubility: • Terpenoids are highly lipophilic and easily soluble in alcohol and fat-soluble organic solvents. Terpenoids with lactone structure can be dissolved in alkaline water and re-precipitate after acidification. This property can be used for the separation and purification of terpenes with lactone structure (alkali extraction and acid precipitation). • Terpenes are sensitive to high heat, light and acid and alkali, so care should be taken during extraction and separation.

addition reaction

oxidation reaction

dehydrogenation reaction

molecular rearrangement reaction

Volatile oils mostly have expectorant, cough-relieving, asthma-relieving, wind-relieving, stomach-tonifying, antipyretic, analgesic, antibacterial and anti-inflammatory effects. For example: clove oil has local anesthesia and analgesic effects; nepeta oil has anthelmintic effects; peppermint oil has cooling, carminative, anti-inflammatory, local anesthetic effects, etc. It is widely used in the spice industry. Volatile oil is an important raw material in the daily food industry and chemical industry.

terpenoids

aromatic compounds

aliphatic compounds

Other compounds

Form: Volatile oil is a transparent liquid at room temperature, and some of its main components may precipitate and crystallize when cooled. Precipitates are often called "brain", such as menthol, camphor, etc.

Volatility: Volatile oil can evaporate on its own at room temperature without leaving any traces. This is the essential difference between volatile oil and fatty oil.

Solubility: Volatile oils and fats are highly soluble and insoluble in water, but easily soluble in various organic solvents, such as petroleum ether, diethyl ether, carbon disulfide, grease, etc. It can be completely dissolved in high-concentration ethanol, but can only be partially dissolved in low-concentration ethanol.

Physical constants: The boiling point is generally between 70 and 300°C, and it has the characteristic of distilling with water vapor; the specific gravity is between Between 0.85 and 1.065 (divided into light and heavy oils); almost all of them are optically active and have strong refractive properties.

stability: • When volatile oil comes into contact with air and light, it often gradually oxidizes and deteriorates, causing its specific gravity to increase, its color to darken, its original fragrance to be lost, and it can form a resin-like substance that can no longer be distilled with water vapor. • Therefore the product should be stored in brown bottles, filled, tightly corked and stored at low temperature in a cool place.

Steam distillation method: Volatile oil and water do not mix. When heated, when the sum of the vapor pressures of the two is equal to the atmospheric pressure, the solution boils, and the volatile oil can be distilled out with the water vapor. If the steam distillate of volatile oil is not easy to stratify because the solubility of the volatile oil in water is slightly greater or the content of volatile oil is low, saturated brine can be added to it to promote the separation of oil and water by salting out; or at the same time, use low boiling point The organic solvent is used as a two-phase solvent to extract volatile oil, and then the organic solvent is distilled to recover the volatile oil.

Leaching method: Commonly used methods include oil absorption method, solvent extraction method, and supercritical fluid extraction method. Grease absorption method: Extract valuable volatile oils by utilizing the properties of greases that generally absorb volatile oils.

Solvent extraction method: reflux leaching method, cold soaking method, etc. Impurities can also be removed by taking advantage of the fact that the solubility of fat-soluble impurities such as vegetable waxes in ethanol decreases as the temperature decreases.

Supercritical fluid extraction (supercritical fluid extraction SFE): utilizes the special fluid properties of solvents under supercritical conditions to extract samples. Using this technology to extract aromatic volatile oils has the outstanding advantages of preventing oxidation, pyrolysis and improving quality.

Cold pressing method • This method is suitable for fresh raw materials, such as raw materials with orange, mandarin, and lemon peels containing more volatile oils. • Advantages: The volatile oil obtained by this method can maintain its original fresh fragrance. • Disadvantages: But it may dissolve non-volatile substances in raw materials.

Freezing method: Place the volatile oil below 0°C to precipitate crystals. If no crystals precipitate, lower the temperature to -20°C and continue to place it. The pure product can be obtained by taking out the crystals and recrystallizing them.

Fractional distillation method: Separation takes advantage of the different boiling points of the components and the different gasification sequences. Boiling point law: • As the number of carbon atoms increases, the boiling point increases. • The higher the number of double bonds, the higher the boiling point • The greater the polarity of the functional group, the higher the boiling point, ether＜ketone＜aldehyde＜alcohol＜acid • The trans boiling point is higher than the boiling point of the cis structure

Chemical method: separation using different acids and bases; separation using functional group characteristics

Chromatographic separation method: Among the chromatographic methods, silica gel and alumina adsorption column chromatography are the most widely used. But silica gel chromatography is powerless when separating two cis-trans isomers. Therefore, AgNO3 complex chromatography is often used.

Determination of physical constants: Determination of physical constants such as relative density, specific rotation, refractive index and freezing point.

Determination of chemical constants: acid value (mg of potassium hydroxide required to neutralize free carboxylic acids and phenols contained in 1g of volatile oil), saponification value (saponification value is equal to the sum of acid value and ester value), and ester value are important Chemical constants are important indicators of quality.

Chromatographic identification