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Recrystallization Technology Recrystallization Technology As we all know, recrystallization is a very basic but very important technology in organic synthesis. It has a simple principle and is easy to use. However, it is not so easy to do recrystallization well, especially the selection of solvents and the treatment of emulsification phenomena. There is a lot of knowledge. Here is an article about recrystallization technology. I hope it will be helpful to everyone! 1. Principle: The solubility of solid organic matter in solvents is closely related to temperature. Generally, as the temperature increases, the solubility increases. If a solid is dissolved in a hot solvent to reach saturation, the solution will become supersaturated and crystals will precipitate due to the decrease in solubility when cooled. The purified substance can be precipitated from the supersaturated solution by utilizing the different solubility of the solvent to the purified substance and impurities. Let all or most of the impurities remain in the solution (if the solubility in the solvent is extremely small, it will be made into a saturated solution and then filtered out), thereby achieving the purpose of purification. 2. Discussion on the application of recrystallization method: Suppose a solid mixture consists of 9.5 grams of purified substance A and 0.5 grams of impurity B. A certain solvent is selected for recrystallization. The solubilities of A and B in this solvent at room temperature are SA and SB respectively. There are usually three situations:: (1) Impurities are easier to dissolve at room temperature (SB>SA). Assuming that SB = 2.5 g/100ml and SA = 0.5 g/100ml at room temperature, if the solubility of A in this boiling solvent is 9.5 g/100ml, then using 100ml of solvent can completely dissolve the mixture when boiling. If the filtrate is cooled to room temperature, 9g of A can be precipitated (regardless of operational losses) and B remains in the mother liquor. The loss of A is very small, that is, the recovery rate of the purified product reaches 94%. If the solubility of A in this boiling solvent is 47.5 g/100 ml, then only 20 ml of solvent can be used to completely dissolve the mixture when boiling. At this time, 9.4 g of A can be precipitated from the filtrate, and B can still remain in the mother liquor. The recovery rate of the purified product is as high as 99%. It can be seen that if the solubility of the impurity is large when cold and the solubility of the product is small when cold, or the solubility of the product by the solvent changes greatly with temperature, both aspects are conducive to improving the recovery rate. (2) Impurities are difficult to dissolve (SB