Clamp a filtration flask to a ring stand and connect the flask to a vacuum line. Pour the mixture of solution and crystals into the funnel and begin vacuum filtration. Rinse any crystals remaining in the flask into the funnel with cold solvent. Wash the crystals on the funnel with cold solvent to remove soluble impurities. Continue drawing air through the funnel to dry the crystals and then turn off the vacuum pump. If necessary, the crystals may be allowed to stand at room temperature to air dry or placed in a desiccator before storing the crystallized solid.
The yellow impurities present in the crude compound have been removed, yielding an off-white solid. Based on the identity of the compound and the impurities, the purity of the crystals can be verified by NMR spectroscopy, melting point measurements, or visual inspection. X-ray crystallography is a powerful characterization technique that identifies the three-dimensional atomic structure of a molecule.
This requires a pure single crystal, which is obtained by recrystallization. Some classes of molecules such as proteins are difficult to crystallize, but their structures are extremely important for understanding their chemical functions.
With careful selection of recrystallization conditions, even these classes of molecules can be analyzed by X-ray crystallography. To learn more about this process, see this collection's video on growing crystals for crystallography. Impure reactants can cause unwanted side reactions. Purifying reactants by recrystallization improves product purity and yield.
Once a solid product has been isolated and washed, reaction yield can also be increased by removing volatiles from the filtrate and recrystallizing the product from the resulting solid. Antifreeze proteins, or AFPs, are expressed in many organisms that live in icy environments. AFPs hinder internal ice growth by binding to ice planes, inhibiting recrystallization into larger ice crystals.
Different AFPs bind to different types of ice crystal planes. Investigating AFP binding mechanisms involves adsorbing them onto single ice crystals. Proper growth of a single ice crystal is essential for clear and informative results. These proteins have applications from the engineering of cold-resistant crops to cryosurgery. You've just watched JoVE's introduction to purifying compounds by recrystallization.
You should now be familiar with the principles of the technique, a purification procedure, and some applications of recrystallization in chemistry. An example of the results of recrystallization is shown in Figure 2. The yellow impurities present in the crude compound have been removed, and the pure product is left as an off-white solid.
The purity of the recrystallized compound can now be verified by nuclear magnetic resonance NMR spectroscopy or, if it is a compound with a published melting point, by how similar its melting point is to the literature melting point.
If necessary, multiple recrystallizations can be performed until the purity is acceptably high. Figure 2. Recrystallization is a method of purifying a compound by removing any impurities that might be mixed with it.
It works best when the compound is very soluble in a hot solvent, but very insoluble in the cold version of the same solvent.
The compound must be a solid at room temperature. Recrystallization is often used as a final clean-up step, after other methods such as extraction or column chromatography that are effective at removing larger amounts of impurities, but that do not raise the purity of the final compound to a sufficiently high level.
Recrystallization is the only technique that can produce absolutely pure, perfect single crystals of a compound. These crystals can be used for X-ray analysis, which is the ultimate authority in determining the structure and three-dimensional shape of a molecule. In these cases, the recrystallization is allowed to proceed very slowly, over the course of weeks to months, to allow the crystal lattice to form without the inclusion of any impurities.
Special glassware is needed to allow the solvent to evaporate as slowly as possible during this time, or to allow the solvent to very slowly mix with another solvent in which the compound is insoluble called antisolvent addition. The pharmaceutical industry also makes heavy use of recrystallization, since it is a means of purification more easily scaled up than column chromatography. These different crystal forms might have different biological properties or be absorbed into the body at different rates.
A more common use of recrystallization is in making rock candy. Rock candy is made by dissolving sugar in hot water to the point of saturation. Wooden sticks are placed into the solution and the solution is allowed to cool and evaporate slowly.
After several days, large crystals of sugar have grown all over the wooden sticks. Mayo, D. Armarego, W. Ray, P. Google Patents: Hightower, T. Journal of Chemical Education 83 11 , Rohani, S. Organic Chemistry. Purifying Compounds by Recrystallization. To learn more about our GDPR policies click here. If you want more info regarding data storage, please contact gdpr jove. Your access has now expired.
Provide feedback to your librarian. If you have any questions, please do not hesitate to reach out to our customer success team. Login processing Previous Video Next Video. Overview Source: Laboratory of Dr. Jimmy Franco - Merrimack College Recrystallization is a technique used to purify solid compounds. Perform all steps in a fume hood to prevent exposure to solvent fumes. Selecting a Solvent Place 50 mg of the sample N-bromosuccinimide in an Erlenmeyer flask.
If the sample dissolves completely, the solubility in the cold solvent is too high to be a good recrystallization solvent. If the sample does not dissolve in the cold solvent, heat the test tube until the solvent boils. If the sample has not completely dissolved at this point, add more boiling solvent drop-wise, until all of the solid dissolves.
If it takes more than 3 mL to dissolve the sample in the hot solvent, the solubility in this solvent is probably too low to make it a good recrystallization solvent. If the first choice of solvent is not a good recrystallization solvent, try others. If a single solvent that works cannot be found, try a two solvent system. If you cannot find a suitable single solvent system, then a solvent pair may be necessary. When identifying a solvent pair, there are several key considerations 1 The first solvent should readily dissolve the solid.
As a general rule "likes dissolve likes" meaning that polar compounds tend to be soluble in polar solvents and non-polar compounds are often more soluble non-polar compounds. Also make sure the boiling point of the solvent is lower than the melting point of the compound, so the compound forms as solid crystals rather than as an insoluble oil.
Confirm that the impurities are either insoluble in the hot solvent so they can be hot-filtered out, once the compound is dissolved or soluble in the cold solvent so they stay dissolved during the entire process. This is a better choice than a beaker, since the sloping sides help trap solvent vapors and slow the rate of evaporation. Place the solvent water in a separate Erlenmeyer flask, and add boiling chips or a stir bar to keep it boiling smoothly. Heat it to boiling on a hotplate.
Add hot solvent to a flask at room temperature containing the compound in small portions, swirling after each addition, until the compound is completely dissolved. During the dissolution process, keep the solution hot at all times by resting it on the hotplate, too. Do not add more hot solvent than necessary - just enough to dissolve the sample.
If a portion of the solid does not seem to dissolve, even after more hot solvent has been added, it is likely due to the presence of very insoluble impurities. If this happens, stop adding solvent and do a hot filtration before proceeding.
To perform a hot filtration, fold a piece of filter paper into a fluted cone shape and place it into a glass stemless funnel. Pour the solution through the paper. If crystals begin to form at any time during the process, add a small portion of warm solvent to dissolve them. Cooling the Solution Set the flask containing the dissolved compound on a surface that does not conduct the heat away too quickly, such as a paper towel set on a benchtop.
Lightly cover the flask as it cools to prevent evaporation and to prevent dust from falling into the solution. Leave the flask undisturbed until it cools to room temperature. Once the crystals have formed, place the solution in an ice bath to ensure that the maximum amount of crystals is obtained.
The solutions should be left undisturbed in the ice bath for 30 min to 1 h, or till the compound appears to have completely crystalized out of solution. If no crystal formation is evident, it can be induced by scratching the inside walls of the flask with a glass rod or by adding a small seed crystal of the same compound. If this still fails to work, then too much solvent was probably used. Reheat the solution, allow some of the solvent to boil off, then cool it. Isolating and Drying the Crystals Set the cold flask containing the newly formed crystals on a benchtop.
Lightly cover the flask to prevent evaporation and to prevent dust from falling into the solution. To dry the crystals, leave them in the filter funnel and draw air through them for several minutes.
Crystals can also be air-dried by allowing them to stand uncovered for several hours or days. Students were to select a method to synthesize aspirin to test. After performing the synthesis, they were to write a formal lab report explaining their process and findings. For one, she had a very well-researched and detailed introduction and background that went well beyond the scope of the assignment.
It really helped put the synthesis into context. Additionally, despite the fact that there were struggles during the synthesis, she was meticulous about giving detail. In the scientific world, this detail would help other scientists look at her work and overcome the challenges.
For centuries, willow and myrtle trees have been a known source of salicin. Ancient medicine recognized the herbal origins of salicin as a successful way to treat pain, inflammation, and fever. Babylonian and Assyrian civilizations were among the first to use willow bark to relieve pain.
In BC, the Egyptians treated inflammation with willow leaves. Following in the footsteps of the Egyptians, the Chinese treated rheumatic fever, colds, hemorrhages, and goiter with extracts from willow and poplar tree bark. The Greek philosopher Hippocrates recommended women to drink a concoction containing willow leaves to reduce the pain of childbirth. A Greek physician named Dioscorides prescribed willow bark to patients to relieve the symptoms of inflammation in AD. The healing effects of willow extracts were first introduced into the modern era in the mids by Reverend Edward Stone.
Stone composed a letter to the Royal Society of London that described how powdered willow bark reduced fever. This letter was inspired by the Doctrine of Signatures, a document stating that the environment of plants offers clues to the types of illnesses the plants might remedy.
For example, willow trees grow in moist soil, and moist soil is associated with fever. The results of his study indicate that willow powder will completely reduce both fever and joint inflammation. The substance in willow bark that is responsible for relieving pain and fever is salicin. The French pharmacist Henri Leroux crystallized a pure form of this yellow substance in Salicin was oxidized to form salicylic acid in early by the German chemist Lowig.
After partnership with Friedrich von Heyden, Kolbe established a factory to produce large quantities of salicylic acid using this method. Kolbe also discovered that salicylic acid could be used as both a food preservative and an antiseptic. However, Joseph Lister had already popularized a more potent as well as less expensive antiseptic known as carbolic acid.
Although salicylic acid was not the most widely used antiseptic of the time, it did become an important intermediate in the production of other pharmaceuticals, dye, and perfumes.
It was not until after the death of Hermann Kolbe that salicylic acid was used in the manufacturing process of aspirin. Felix Hoffmann was credited with the first synthesis of aspirin during his employment at Bayer Company. Hoffmann hypothesized that salicylic acid would be tolerable if it were more soluble in stomach acid.
To achieve this more soluble form, Hoffmann replaced the hydrogen from the hydroxy group on the benzene ring of salicylic acid with an acetyl group. This resulted in acetylsalicylic acid. The director of pharmacologic research at Bayer renamed the compound to aspirin in because it was difficult to pronounce under the chemical name.
Bayer and Company in October Under his direction, Felix Hoffmann synthesized acetylsalicylic acid on August 10, Eichengrun never received full credit for his work in the discovery of aspirin because a footnote in an encyclopedia published in Nazi Germany in only gave credit to Hoffmann. Eichengrun was Jewish, and he could not speak out to refute the footnote. Eichengrun sent a letter from the Theriesentadt concentration camp to the management of the incorporated F. Bayer and Company.
Despite this letter, most authorities still did not recognize Eichengrun as a partner in the discovery of the drug. Sir John Vane discovered how aspirin works in the body while researching at the Royal College of Surgeons of England in Healthy tissues have a certain normal concentration level of these hormones.
When a tissue becomes damaged, it synthesizes more prostaglandins. A higher concentration of prostaglandins in the damaged tissue results in a sensation of pain. Aspirin inactivates enzymes that are essential in prostaglandin synthesis; therefore, it decreases pain by reducing the sensitivity of the damaged tissue to pain stimuli.
The role of aspirin in reducing inflammation is not known with certainty. Prostaglandins synthesized by bacterial toxins in the hypothalamus increase body temperature. Aspirin is an antipyretic because it reduces the amount of prostaglandins that result from bacterial toxins in the hypothalamus.
The synthetic scheme for aspirin is indicated above. We began by weighing out 0. Using a 2. I added two drops of phosphoric acid catalyst to the reaction flask with a plastic pipette. I carefully swirled the flask to completely mix the contents.
We heated the flask over a mL beaker of hot water for about ten minutes to approximately degrees Celsius. We added four drops of de-ionized water from the plastic bottle in the lab.
I measured 3 mL of de-ionized water in a 4. We placed the Erlenmeyer flask into a mL beaker filled with ice. The flask cooled in the ice bath for 16 minutes and crystals formed.
We connected the Hirsch funnel to the water aspirator located in the hood and crystals were collected via filtration. Kelsey added a small amount of de-ionized water to wash the crystals out of the flask. The crystals were allowed to dry on the Hirsch funnel for an additional 15 minutes. We placed a small amount of the crude product into a pre-weighed vial 2.
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