What is the experimental purpose and principle of recrystallization, and what is the principle of re

Recrystallization is the process of dissolving crystals in a solvent or melting, and then recrystallizing them from a solution or melt. Recrystallization allows impurities to be purified or salts that are mixed together separate from each other.

1. Principle: The solubility of solid organic matter in the solvent is closely related to the temperature. Generally, the temperature increases, and the solubility increases.

If the solid is dissolved in a hot solvent to reach saturation, the solubility decreases and the solution becomes supersaturated and crystals are precipitated when cooling. The solubility of the solvent to the purified substance and impurities is different, and the purified substance can be precipitated from the supersaturated solution. And let all or most of the impurities remain in the solution (if the solubility in the solvent is very small, it will be prepared into a saturated solution and then filtered out), so as to achieve the purpose of purification.

Taking advantage of the difference in the solubility of different substances in the same solvent, compounds containing impurities can be purified. The so-called impurities refer to some substances with small contents, which include insoluble mechanical impurities and soluble impurities. In actual operation, the purified substance is first dissolved in a certain amount of water under the condition of heating, a saturated solution is formed, and the insoluble mechanical impurities are removed while it is hot, and then the filtrate is cooled, and the purified substance is already supersaturated and crystallized and precipitated from the solution; For soluble impurities, they are far from saturation and remain in the mother liquor.

Filtration separates the crystals from the mother liquor to obtain a purer crystalline substance. This process is called recrystallization. If one crystallization does not achieve the purpose of purification, a second recrystallization can be performed, and sometimes multiple crystallization operations are required to obtain a pure compound.

The method of recrystallization of purified substances is only suitable for compounds whose solubility increases with increasing temperature. This is not suitable for compounds whose solubility is less affected by temperature.

A method of using different solubility under different conditions to achieve the purpose of purification.

RecrystallizationThe principle is to use the components of the mixture in a certain solventSolubilityor different solubility at different temperatures in the same solvent to separate them from each other. The solubility of solid organic compounds in solvents changes easily with the change of temperature, and the solubility usually increases with the increase of temperature. Conversely, the solubility decreases.

Recrystallization conditions:

1. Do not react chemically with the purified substance.

2. At higher temperatures, it can dissolve a large amount of pure substances that are lifted vertically; At room temperature or lower, only a small amount of the substance can be dissolved.

3. The dissolution of impurities is very large or very small (in the former case, the impurities should be left in the mother liquor and not precipitated with the crystals of the purified substance; In the latter case, impurities are filtered out during thermal filtration.

4. It is easy to volatilize (the boiling point of the solvent is low), and it is easy to be separated from crystallization.

5. It can produce better crystals.

Generally, it includes selecting a suitable solvent, making a hot saturated solution, thermal filtration, removing insoluble impurities (including decolorization), cooling crystallization, suction filtration, removing the mother liquor, washing and drying, and removing the attached mother liquor and solvent.

The choice of solvent should be based on the general principle of similar miscibility. Solutes tend to be soluble in solvents that are structurally similar to them. Literature and manuals can also be consulted to understand the solubility of a compound at different temperatures in various solvents.

The solubility of the compound can also be determined experimentally. A small amount of recrystallized substances can be taken in the test tube, and different kinds of solvents can be added for pre-testing.

(1) Select the appropriate solvent;

2) the crude product is heated and dissolved with the selected solvent to make a saturated or near-saturated solution;

3) Add activated carbon for decolorization;

4) Filter while hot to remove insoluble impurities and activated carbon;

5) cooling, precipitation crystals;

6) Suction filtration, washing crystals;

7) Dry crystals.

The solvent is selected, the extract to be heated to boiling solvent is added to dissolve, impurities are removed (adsorption, reaction), filtered, evaporated solvent, and cooled and crystallized.

The experimental content of recrystallization is that there is a significant difference with the change of temperature, the solubility is large at higher temperature, and the solubility is small at lower temperature, so that separation and purification can be realized.

Recrystallization is the use of different solubility of target components in a solid mixture in a certain solvent, or different solubility at different temperatures in the same solvent, so that they are separated from each other. That is, there is a significant difference with the change of temperature, the solubility is large at a higher temperature, and the solubility is small when the temperature is reduced, so that separation and purification can be realized.

Recrystallization is the most common procedure used by pharmaceutical companies for the purification of solid products. A good recrystallization process can provide high-yield qualified products, and try to avoid the manpower and material resources consumed by secondary recrystallization, and reduce the production cost as much as possible.

Commonly used solvents in recrystallization experiments:

Commonly used solvents for crystallization and recrystallization are: water, methanol, ethanol, isopropanol, acetone, ethyl acetate, chloroform, glacial acetic acid, dioxane, carbon tetrachloride, benzene, petroleum ether, etc. In addition, toluene, nitromethane, ether, dimethylformamide, dimethyl sulfoxide, etc. are also commonly used.

Dimethylformamide and dimethyl sulfoxide have a large solubility and can be tried when no other suitable solvent can be found. However, it is often difficult to precipitate crystals from the solvent, and the boiling point is high, and the solvent adsorbed on the crystal is not easy to remove, which is its disadvantage. Although ether is a commonly used solvent, it is best not to use ether if there are other suitable solvents.

The steps are as follows:

1. Prepare the crystals and choose the appropriate solvent.

2. To choose experimental equipment, the first must have a stirring rod, the second is to choose a suitable Ronghe chopstick, and the third is to choose a heater to serve the defense equipment.

3. Put the crystals into the container and then add the slow solution, and stop when the crystals are about to dissolve.

4. Start to heat up the solvent and evaporate part of the solvent. When the solvent evaporates moderately, remove the old and missing crystals of the cooling junction, and the heavy crystals can be obtained.

Recrystallization is a common form of thermodynamic phenomenon in solid matter, which refers to the precipitation of solutes from the original crystals at a certain temperature and recrystallization into new crystals. Recrystallization is widely used in the fields of material preparation, metal physics, chemical reactions, and geochemistry. The principle of recrystallization is briefly described below.

1.The process of recrystallization is essentially a phase transition that occurs within a system. The process of recrystallization begins when the free energy (g) of the system is reduced to a minimum, i.e., when g reaches the equilibrium state.

The process of recrystallization can be described as two main steps: nucleation and crystal growth.

2.First, new crystalline nuclei are formed in the original material. The formation of crystal nuclei is affected by factors such as solubility, degree of supersaturation, and perturbation.

When the solute in the solution exceeds the saturation, the excess solute begins to nucleate, and the rot hall will select the better crystal nucleus according to the thermodynamic law. The new nuclei formed in the original crystals are unstable, and their development depends on factors such as the reference crystal (also known as the seed crystal), temperature, pressure, cleanliness of the solution, and so on.

3.Second, new crystals are formed around the new crystal nuclei. This growth is the process of disconnecting and recombining the original crystals, which involves the atomic movement of the material.

Since the rate of growth is usually slower than that of nucleation, new crystals will continue to grow and expand, and eventually be able to selectively occupy space, produce crystal volumes with better scalability, standardization and organizational uniformity, and achieve reasonable separation of substances.

4.In short, recrystallization is an important technology in the world's major industries involving the purity and morphology of ingredients, and its main principle is to re-form pure crystals by maintaining the chemical equilibrium in the system, setting appropriate temperature, pressure and other conditions. Recrystallization has a wide range of applications in the fields of new material design, mineral identification, and chemical separation.

Recrystallization is the process of dissolving crystals in a solvent or melting, and then recrystallizing them from a solution or melt. Recrystallization allows impure substances to be purified or substances that are mixed together separate from each other.

Principle: The solubility of a solid mixture in a solvent is closely related to temperature. Generally, the temperature increases, and the solubility increases.

If the solvent dissolved in heat is saturated, the solubility decreases and the solution becomes oversaturated and crystals are precipitated when cooling. Because different substances often form different lattice structures, the probability of crystallization of substances with the same lattice structure and substances with different lattice structures is very low. Substances with the same lattice structure are more likely to crystallize together with similar radii. The solubility of the solvent to the purified substance and impurities is different, and the purified substance can be precipitated from it.

And let all or most of the impurities remain in the solution (if the dissolution in the solvent is very small, it will be prepared into a saturated solution and then filtered out), so as to achieve the purpose of purification. This method can also be used to separate optical isomers.

An asymmetrical environment is created by adding a pure photoactive isomer to a hot saturated or supersaturated racemic solution. When cooled to a certain temperature, a slightly excess of isomers identical to the seed will preferentially crystallize. After the crystallization is filtered, a saturated solution of heat excitation fiber made of water and racemate is added to the remaining mother liquor, and then cooled to a certain temperature of the remaining sail, at which point another slightly excess isomer will crystallize.

Theoretically, if the feedstock can form racemates of aggregates, then repeating the above process can convert all enantiomers into pure optical isomers. In the absence of pure enantiomer seeds, sometimes chiral compounds with similar structures, or even with achiral compounds, can be successfully resolved. <>

The principle of recrystallization is to use the different solubility of each component in the mixture in a certain solvent, or the solubility of different temperatures in the same solvent to separate them from each other. The solubility of solid organic matter in the lysable agent is easy to change with the change of temperature, and the solubility increases with the increase of temperature. Conversely, the solubility decreases.

For the former common case, heating dissolves the solute in the solvent, and when the temperature decreases, its solubility decreases, and the solution becomes supersaturated, thus precipitating crystallization. Due to the difference in the solubility of the purified compounds and impurities, the substances required for purification can be separated.

Scope of application: It is suitable for systems where the properties of products and impurities are quite different, and the impurity content in products is less than 5%.

When performing recrystallization, the selection of the ideal solvent is key, and the ideal solvent must meet the following conditions:

1. Do not react chemically with the purified substance.

2) At higher temperatures, it can dissolve a large amount of purified substances; At room temperature or lower, only a small amount of the substance can be dissolved.

3) The dissolution of impurities is very large or very small (in the former case, the impurities should be left in the mother liquor and not precipitated with the crystals of the purified substance; One of the cases is that impurities are filtered out during thermal filtration).

4. It is easy to volatilize (the boiling point of the solvent is low), and it is easy to be separated from crystallization.

5. It can produce better crystals.