The idea is that both columns enter the column (or tube) at the same time, but exit the columns at different times, so we can isolate them as they exit. That is, perform column chromatography to separate the two compounds. As long as they have different polarities you can run a flash column. So in this case compound A would be the less polar compound. If so, that means they also have different polarities the higher the R f value, the less polar the compound. The first thing to do would be to run a TLC on the two compounds to see if they have different R f values. Let’s say you had a mixture of compounds A and B. Column chromatography is the method most commonly used to purify your product and remove undesired side products. Usually one of them is what you want, and the other products are, well, garbage. Later this semester, you will be required to make solid derivatives of other compounds.After an organic reaction it’s common to get a mixture of products. This derivative of caffeine has an accurate melting point. A well characterized salt of caffeine is caffeine salicylate formed by using salicylic acid. You will use some of this material for TLC analysis next week.Ĭaffeine is a base which can react with acids to form salts. Save the purified caffeine in a sealed vial. You will not take a mp of the purified caffeine which would require a sealed capillary to prevent sublimation near the melting point. You will use 50 mg of your caffeine to make a salicylate derivative and sublime the remainder (which should be at least 50 mg). The sublimation will be performed as described by your instructor. After air drying, weigh each crop and record your % caffeine recovered from tea. This second crop can also be collected by vacuum filtration but keep it separate from the first crop. A second crop of caffeine may form in the filtrate as the solvent evaporates. Suction filter the caffeine using a small Hirsch funnel and petroleum ether as a transfer/rinse solvent. If you do not get a precipitate, you may have used too much acetone, carefully boil off the excess on a steam bath using a boiling stick for ebullation.

Add a few drops of petroleum ether until you reach the cloud point (caffeine is less soluble in this mixed solvent and is just beginning to precipitate) and then cool the solution. Obtain the weight of crude caffeine by difference.Īdd 5-8 mL of hot acetone to dissolve the crude caffeine and transfer the solution to a 50 mL Erlenmeyer flask for recrystallization. You will be left with a small amount of residue with a greenish tinge. Stripping this solution to dryness will take less than 5 minutes.

Be certain that there is no magnesium sulfate in the solution. Tare weigh a 100-mL rb flask and transfer the dried methylene chloride solution to it. The methylene chloride solution will be stripped on a roto-evaporator. Combine the methylene chloride extracts and, if necessary, dry further with additional anhydrous magnesium sulphate. To break the emulsion formed in the methylene chloride layer, slowly drain the methylene chloride layer through a small amount of anhydrous magnesium sulphate in a powder funnel with a loose cotton plug (a tight plug will prevent drainage).Įxtract the aqueous solution once again with a 35 mL of methylene chloride, repeating the steps above to collect the lower layer. Then shake vigorously for 10 seconds and relieve pressure, repeat the shaking two more times. First, relieve the pressure buildup as soon as you mix the two liquids. In a departure from normal procedure, it will be necessary to vigorously shake the separatory funnel in order to extract the caffeine. Extract with 35 mL of methylene chloride. Rinse again with 50 mL of water.Ĭool the solution to room temperature and pour it into a 500 mL separatory funnel. Carefully press out as much filtrate as possible since the caffeine is in the aqueous layer. Normally, hot solutions are not vacuum filtered. Cool the solution but, while it is still warm, vacuum filter through a Buchner funnel using a fast filter paper, if available. Boil the solution on a hot plate for 20 minutes with occasional stirring. Place 15 g of tea leaves, 5 g of calcium carbonate powder and 200 mL of water into a 600 mL beaker.

Caffeine structure polarity