Original Title: Chemistry of Traditional Chinese Medicine Terpenes and Volatile Oils (Volatile Oils) Medical Liaison officer Club Volatile oil Definition: Volatile oil, also known as essential oil, is a kind of oily liquid existing in plants, which is volatile, can be distilled with water vapor and is immiscible with water. Most of the volatile oils have aromatic odor and have strong biological activities in many aspects. Note: Volatile oil is a mixture. (I) Chemical composition of volatile oil Type Main composition Representative compound Terpenoids are mainly monoterpenes, sesquiterpenes and their oxygenated derivatives. Mentha oil contains about 80% of menthol and Litsea cubeba oil contains 80% of citral. Aromatic compounds; small molecules; phenylpropanoid derivatives; terpenogens; compounds with C6-C2 or C6-C1 skeletons; cinnamaldehyde in cinnamon; thymol; xanthoxylin Aliphatic compounds, n-nonanol in Pericarpium Citri Reticulatae, panaxynol in Ginseng volatile oil, decanoyl acetaldehyde (i.e. Houttuynium) in Houttuynia volatile oil, methyl n-nonanone, etc. Other compounds can be decomposed into volatile components by steam distillation, such as mustard oil, protoanemonin, garlic oil, etc. (II) General properties of volatile oil 1. Traits At room temperature, most of the volatile oil is colorless or light yellow transparent liquid, and a few of the volatile oil has other colors, such as blue, green and reddish brown. Most of them have strong specific odor (its odor is often an important sign of its quality) and spicy burning sensation. Under cooling conditions, the main components of volatile oil can often precipitate crystals, called "brain", which is commonly known as "brain", such as menthol, camphor and so on. The oil filtered to remove the precipitate is called "dementholized oil", such as the dementholized oil of peppermint oil, which is commonly called "peppermint oil", but still contains about 50% of menthol. 2. Volatility The volatile oil can naturally volatilize at normal temperature. If the volatile oil is coated on a piece of paper and placed for a long time, the volatile oil will volatilize without leaving oil stains, while the fatty oil will leave permanent oil stains, which can be distinguished from each other. The volatile oil can be distilled with water vapor. 3. Solubility Expand the full text Volatile oil is insoluble in water, but soluble in various organic solvents, such as petroleum ether, ether, carbon disulfide, grease and so on. It can be completely dissolved in high concentration ethanol,jacketed glass reactor, while only a part of it can be dissolved in low concentration ethanol. 4. Physical constants Most of the volatile oils are lighter than water, and some are heavier than water (such as clove oil and cinnamon oil). The relative density is generally between 0.85 and 1.065; almost all of them have optical activity; and most of them have strong refractive index. The boiling point of volatile oil is generally between 70 ℃ and 300 ℃. 5. Stability It is easy to oxidize and deteriorate when exposed to light, air and heating. Volatile oil will gradually oxidize and deteriorate after frequent contact with air and light, which will increase the relative density of volatile oil, darken its color, lose its original fragrance and form resin-like substances, which can not be distilled with water vapor. Therefore, the method of preparing volatile oil should be appropriate, and the product should be sealed in a brown bottle and stored at low temperature. 6. Chemical properties Volatile oil often contains double bonds, alcoholic hydroxyl groups, aldehydes, ketones,thin film distillation, acidic groups, lactones and other structures, so it can react with bromine and sodium bisulfite, condensation reaction with hydrazine, silver mirror reaction, iron hydroxamate reaction, saponification reaction and alkali salt formation reaction. (III) Chemical constants of volatile oil Acid value, ester value and saponification value are important chemical constants of volatile oils from different sources, and also important indicators to measure their quality. 1. Acid value It is an index representing the content of free carboxylic acid and phenolic components in volatile oil. Expressed in milligrams of potassium hydroxide consumed to neutralize the free acidic components in 1G of volatile oil. 2. Ester value It is an index representing the content of esters in volatile oil. Expressed in milligrams of potassium hydroxide required to hydrolyze the ester contained in 1 gram of volatile oil. 3. Saponification value It is an indicator of the total amount of free carboxylic acids, phenolic components and combined esters in the volatile oil. Expressed in milligrams of potassium hydroxide consumed to saponify 1 gram of volatile oil. The saponification value is the sum of the acid value and the ester value. Extraction and Separation of Volatile Oil (I) Extraction of volatile oil The extraction method comprises a distillation method, a solvent extraction method, an absorption method, a squeezing method, a carbon dioxide supercritical fluid extraction method and a microwave extraction method. 1. Distillation ： Commonly used method: extraction by co-water distillation, water-proof distillation or steam distillation. Has the advantages of simple equipment, easy operation, low cost, high oil extraction rate and the like. Disadvantages: the volatile oil of heat-unstable components is easy to produce the decomposition of the corresponding components and affect the quality of the volatile oil. 2. Solvent extraction ： Commonly used method: continuous reflux extraction or cold leaching with low boiling point organic solvent. Common solvents: pentane, petroleum ether, carbon disulfide, carbon tetrachloride, etc. (Small polar solvents). Distilling the extracting solution or distilling under reduced pressure to remove the solvent to obtain crude volatile oil. The volatile oil obtained by this method contains more impurities, so it must be further refined and purified. 3. Absorption method ： Oils and fats generally have the property of absorbing volatile oil, which is often used to extract valuable volatile oil, rotovap distillation ,wiped film evaporator, such as rose oil, jasmine oil and so on. There are two kinds of absorption methods, namely cold absorption method and warm immersion absorption method. The oil after absorbing the volatile oil can be directly used in the perfume industry, and can also be added with absolute ethyl alcohol, and the alcohol solution is distilled under reduced pressure to remove the ethanol to obtain the essential oil. 4. Squeezing ： This method is suitable for raw materials containing more volatile oil, such as fresh tangerine, orange, lemon peel, etc. Advantages: simple, no heating. Disadvantages: many impurities. The product obtained by the method is impure and may contain impurities such as water, chlorophyll, mucilage, cell tissue and the like and is in a turbid state, and meanwhile, the volatile oil is difficult to be completely squeezed out, so the residue after squeezing can be subjected to steam distillation to completely extract the volatile oil. The volatile oil obtained by the pressing method can keep the original fresh fragrance. 5. Carbon dioxide supercritical fluid extraction ： Carbon dioxide supercritical fluid is applied to extracting aromatic volatile oil. Has the advantages of preventing oxidation and pyrolysis and improving quality. For example, perillaldehyde, which is a special flavor component in perilla, is extracted. In the extraction of orange peel oil, lemon oil, osmanthus oil and vanillin, the application of this method has achieved good results. Disadvantages: high technical requirements, large investment in equipment costs. 6. Microwave extraction ： The method has that advantage of shortening the experiment and production time, reduce the energy consumption, reducing the solvent consumption and the generation of waste, and better meeting the requirement of 'green' environmental protection. Imultaneously, that yield and the purity of the extract can be improve. Compared with supercritical fluid extraction, the equipment is simpler and cheaper, and has a wider range of applications, and is less limited by the polarity of the extracted substance (supercritical fluid extraction is still difficult to apply to substances with strong polarity). Compared with the traditional method, the method for extracting the volatile oil of clove, Artemisia leaves, safflower, Agastache rugosa, Eupatorium and the like by adopting the method greatly shortens the extraction time and greatly improves the extraction yield. (2) Separation of volatile oil Separation methods: freezing crystallization, fractional distillation, chemical separation, chromatographic separation. 1. Freezing crystallization method The volatile oil is placed below 0 deg C to separate out crystals, if no crystals are separated out, the temperature can be reduced to -20 deg C, the volatile oil is continuously placed until the crystals are separated out, and then the monomer crystals can be obtained by recrystallization. Main separation objects: menthol and camphor. Note: This method is easy to operate, but the separation of some volatile monomers is not complete, and most of the volatile oil can not be crystallized after freezing. 2. Fractional distillation The boiling point of monoterpenes increases with the increase of double bonds, that is, triene diene monoene. The boiling point of oxygenated monoterpenes increases with the polarity of the functional group, i.e., ether ketone aldehyde alcohol acid. The ester has a higher boiling point than the corresponding alcohol. Some components in the volatile oil are often destroyed when they are close to their boiling point, so vacuum fractionation is usually used. Each fraction obtained by fractionation may still be a mixture, so it is necessary to further rectify or combine freezing, recrystallization, chromatography and other methods to obtain a single component. 3. Chemical separation Ingredient type reagent and method Separation of alkaline components 1% sulfuric acid or hydrochloric acid extraction in alkalization Separation of phenol and acidic components Extraction with 5% sodium bicarbonate — — Separation of acidic components Extraction with 2% sodium hydroxide — — Separation of weak acidic components Separation of Alcohols Malonic acid monochloride or phthalic anhydride or malonic acid reacts to produce an acidic monoester Aldehyde and ketone components are separated to remove the volatile oil mother solution of phenol and acid components, and sodium sulfite or Girard reagent is added Separation of other components Distillation or chromatographic separation of ester components Salting of ether components with concentrated sulfuric acid Components containing double bonds are added to double bonds by bromine, hydrogen chloride, hydrogen bromide, nitrosyl chloride and other reagents 4. Chromatographic separation (1) Adsorption chromatography Adsorbent: silica gel, alumina. Eluent: use petroleum ether or hexane, mixed with ethyl acetate in different proportions. (2) Silver Nitrate Chromatography Principle: The separation is based on the difference of the degree of difficulty of forming π complex between silver nitrate and double bond. The number, position and three-dimensional configuration of double bond are different, and the degree of complexation is different. The more double bonds there are, the easier it is to complex. The more terminal double bonds, the easier the complexation. The cis form is easier to complex than the trans form. Identification of Volatile Oil by Gas Chromatography (I) Gas chromatography Mobile phase carrier gas: hydrogen, nitrogen or helium is generally used. Stationary phase: non-polar saturated hydrocarbon lubricants (such as silicone, methyl silicone oil, etc.)-components with large boiling point difference. Polar stationary phase type (such as polyester, polyethylene glycol, etc.)-components with small boiling point difference but different polarity. The effect of column temperature on the separation of essential oils: Generally, monoterpenes can be separated at 130 ℃ or lower than 130 ℃; sesquiterpenes can be separated well at 170 ~ 180 ℃ or higher; while the separation of oxygenated derivatives is between 130 ~ 190 ℃. At present, the method of programmed temperature is often used to separate monoterpenes, sesquiterpenes and their oxygen-containing derivatives from volatile oil at one time. Identification: under the same chromatographic condition, the relative retention value of the volatile oil and the reference substance with known components is determined to preliminarily determine the corresponding components in the volatile oil. (2) Gas chromatography-mass spectrometry (GC-MS) Application: Gas chromatography-mass spectrometry (GC-MS) should be used to analyze and identify many unknown components in volatile oil without reference substance. Methods: During the analysis, the sample was injected into the gas chromatograph first, and then the separated components entered the separator in turn, and the concentrated components entered the mass spectrometer in turn. The mass spectrometer detects and analyzes the structure of each component to obtain the mass spectrum of each component, and the possible structure of the compound can be given by comparing the computer with the standard spectrum of the database,cbd centrifugal extractor, and can also be confirmed by referring to relevant literature data, thereby greatly improving the speed and research level of analysis and identification of volatile oil. In addition, the advent of multi-stage mass spectrometry (MSn) provides a new way for the qualitative and quantitative analysis of complex volatile oils. Return to Sohu to see more Responsible Editor:. toptiontech.com
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