Extraction is one of the common operations used in organic chemistry experiments to extract purified organic compounds. Application extraction can extract the required substances from the reaction mixture or animal and plant tissues, and can also be used to wash away small amounts of impurities in the mixture. The former is usually called "extraction" or "helping"; the latter is "washing"
Basic principle: Benzene extraction is an operation that uses the difference in solubility or distribution ratio of substances in two immiscible (or slightly soluble) solvents to achieve the purpose of separation, extraction or purification. This can be illustrated by using an organic solvent that is immiscible (or slightly soluble) with water to extract organic compounds from water. When an aqueous solution containing organic compounds is extracted with an organic solvent, the organic compounds are distributed between the two liquid phases. At a certain temperature, the ratio of the concentration of this organic compound in the organic phase and in the aqueous phase is a constant, which is the so-called "distribution law". If the concentrations of a substance in two liquid phases A and B are cA and cB respectively, then at a certain temperature, cA/cB=K, K is a constant, called the "distribution coefficient", which can be approximately regarded as this The ratio of the solubility of a substance in two solvents.
The solubility of organic substances in organic solvents is generally greater than their solubility in water, so they can be extracted from aqueous solutions. But unless the partition coefficient is extremely large, it is impossible to move all the material into the new organic phase with one extraction. When extracting benzene, if a certain amount of electrolyte (such as sodium chloride) is first added to the aqueous solution and the so-called "salting out effect" is used to reduce the solubility of organic compounds and extraction solvents in the aqueous solution, the extraction effect can be improved.
Another type of extraction principle is to use it to chemically react with the substance being extracted. This kind of extraction is usually used to remove small amounts of impurities or separate mixtures from compounds. The operation method is the same as described above. Commonly used extraction agents such as 5% sodium hydroxide aqueous solution, 5% or 10% sodium carbonate, and hydrogen carbonate Sodium solution, dilute hydrochloric acid, dilute sulfuric acid and concentrated sulfuric acid, etc. Alkaline extractants can remove organic acids from the organic phase, or remove acidic impurities from organic compounds dissolved in organic solvents (making acidic impurities form sodium salts and dissolve in water). Dilute hydrochloric acid and dilute sulfuric acid can extract organic alkaline substances from mixtures or be used to remove alkaline impurities. Concentrated sulfuric acid can be used to remove unsaturated hydrocarbons from saturated hydrocarbons, remove alcohols and ethers from alkyl halides, etc.