Welcome to the Organic Chemistry I laboratory. My name is Sully Isaeva. I am an instructor of chemistry department and today I would like to introduce you to the first experiment recrystallization of acetanilide.
One of the major tasks in the organic chemistry laboratory is purifying chemicals. Solid organic compounds can be purified successfully by recrystallization. Recrystallization involves several steps. Choosing a good recrystallization solvent, dissolving the sample in the minimum amount of boiling sample, filtering the hot solution to get rid of insoluble impurities, cooling down the solution to induce crystallization.
Separating the solid from the solution by vacuum filtration. Washing the solid on the filter with a small amount of cold solvent to remove traces of the mother liquor. Drying the solid to remove traces of solvent. Before beginning recrystallization, you must select an appropriate solvent. Knowing the structure of the compound may help you choose a good solvent.
There are several criteria for choosing a good solvent. The compound purifier should be very soluble in the hot solvent and have very limited solubility in the cold solvent. Ideally, the impurities should be either be soluble in the cold solvent or very insoluble in the hot solvent. Boiling point of the solvent should be in the range 50-120 degrees Celsius because solvent with lower than 50 degrees Celsius A very quickly evaporated room temperature and solvents with boiling points higher than 120 degrees Celsius are difficult to remove from the recrystallized product.
The boiling point of the solvent should be lower than the melting point of the product. The solvent should not react chemically with the product to be purified. Given several choices, the solvent with the lower toxicity should be chosen.
Very often solid organic chemicals contain small amounts of colored impurities. They can be removed by adding activated charcoal to the hot solution. Because the compound to be purified can be also absorbed on the charcoal particles, the amount of carbon should not be excessive.
In this experiment, we dissolve our sample acetylenolide in the solvent water, and we will use two important filtrations hot filtration and cold filtration. Insoluble impurities present in the hot solution are removed during the hot filtration. A small portion of fresh water is placed in the Lennmeyer flask. One or two boiling chips are added and the funnel and the fluted filter paper are placed on the top.
The boiling chips allow the smooth formation of bubbles during the boiling and prevent boil over and mix the liquid at the same time. Both Ellenmeyer flasks, the one that receives the filtrate and the one that contains the sample, should be kept on the hot plate. When the funnel has been heated by the steam generated of water, quickly discard the remaining water, but keep the boiling chips and begin pouring the acetanilide charcoal suspension into the fluted filter paper with the aid of the glass rod. The hot filtration should be carried out very carefully to avoid crystallization of the solid in the filter paper.
Fill the funnel no more than half full and maintain the temperature of both solutions to prevent premature crystallization in the funnel. After completing the hot filtration, allow the flask to cool to room temperature before placing it in an ice water bath. If system cools down too quickly, Small crystals form and absorb a large amount of impurities from the mother liquor. On the other hand, very slow crystallization results in the formation of big crystals that sometimes may occlude impurities.
An intermediate rate of crystallization is recommended. Once the compound has completely precipitated out of solution, the suspension is vacuum-filtered using a Wagner funnel. A disco filter paper that covers the holes of the funnel without touching the walls is positioned on the funnel.
The vacuum is turned on and the filter paper wetted with a small portion of the cold solvent to adhere it to the funnel and prevent it from moving when the bulk of the solution is added. The crystals are then collected by pouring the cooled suspension through the funnel. The purity of the crystallized solid is usually checked by melting point determination. Experimentally, a melting point range, rather a melting point, is determined. The melting point range is the temperature interval between the beginning and ending of melting process.
Pure organic solids have a very narrow melting point range, usually 0.5-2 °C. For example, a sample of pure cholesterol melts at 148-149 °C. Most impurities have a dual effect on the melting point of organic compounds.
They depress the melting point and extend the melting point range. For example, a contaminated sample of cholesterol may melt between 100 and 125 °C rather than at 148-149 °C. Welcome to Organic Chemistry 1 lab. Always wear lab coat, gloves and safety goggles at all times, no matter what you are doing or where you are in the lab.
Now let's start our lab experiment number one, recrystallization of acetonolide. In this laboratory experiment we will use the following reagents acetonolide, activated charcoal, water and boiling chips. The necessary chemical equipment. Weigh 2 grams of impure acetylene and place it in 125 ml of a mild flask.
Add 2 boiling chips and 30 ml of DIY water. Bring the suspension to a boil by heating it on a hot plate. Stir the system frequently with a glass rod.
As soon as boiling begins, add more water until all the solid dissolves. You may be required up to 10 ml of DI water to completely dissolve as a stunner light. After dissolving all solid, remove the flask from the hot plate. Grind and weigh 0.1 gram of activated charcoal.
Now slowly add this activated charcoal. Never add charcoal to a solution on the verge of boiling, glucose boil over. Place the flask on the hot plate again and bring the system to a second boil.
Now you can see how to make a fluted filter paper. Finally, fold the filter paper like an accordion. It will maximize the filter surface area and result in a faster filtration.
Place two boiling chips, approximately 10 ml of DI water, short stamp funnel with filter paper and copper wire. Place the complete apparatus on the hot plate. After the funnel has been heated, discard the remaining water into the beaker. Now we begin the hot filtration by pouring a stainless charcoal suspension into the fluted filter paper with the aid of the glass rod.
To avoid making the hole in the filter, make sure that the glass rod doesn't touch its center. If substantial crystallization of acetyl-anilide occurs in the filter, add more water to dissolve acetyl-anilide completely and filter again. After completing the hot filtration, allow the flask to cool at room temperature before placing it in an ice water bath.
Wipe the filter paper and make sure that it covers all the holes on the buprenorphanum without touching the walls. Wet the filter paper with 5-10 ml of cold water to prevent it from moving during the cold filtration. Filter your cold acetyl white water mixture by pouring it into the Buckeme panel with the aid of the glass rod.
Gently swirl the contents of the RLMAE flask in order to transfer all solid acetylene. Once you finish filtering the whole solution, remove the boiling chips with tweezers. Press the crystals with a spatula to remove as much water as possible.
Let the solid dry on the filter with the vacuum on for 5-10 minutes. Wear the watch glass. Carefully transfer the solid with the filter paper on a pre-heated watch glass. Dry the solid in the oven at approximately 70 degrees Celsius.
Wear the dry test on a light and calculate the person pick-up. Thrust the crystals into the capillary tube by tapping the open end of the capillary tube against the watch glass or beaker. Invert the capillary tube and tap the closed end against the bench top to make the solid descend.
Drop the capillary tube through the glass tube onto the bench. Repeat this process until 1-2 mm of well-packed solid accumulate at the end of the capillary tube. Place the capillary tube inside the walls of the melting point apparatus.
Thank you. As you can see, the crude and purified acetonolides start to melt at the range between 100 and 1416 degrees Celsius. Thanks for your attention.