Extraction of Caffeine with Solvents

648 Words3 Pages
EXPERIMENT 9: EXTRACTION WITH SOLVENTS PG. 115 – 120, SEC. D Introduction The purpose of this lab is to extract caffeine from tea using the same technique used in the previous lab. More specifically, this lab involved a mixture from which a single chemical needed to be recovered from a mixture whose contents were unknown. Success of this technique was measured by finding the recovered mass of caffeine. Procedure In a 500-mL Erlenmeyer flask, place 30 g of ordinary dry tea, 300 mL of water, and 15 g of powdered calcium carbonate. After boiling the mixture gently for 20 min, occasionally swirling it, add 5 g of Celite or other filter aid, filter the hot mixture in a Buchner funnel, and press the filter cake firmly with a large cork to obtain as much of the liquid as possible. Cool the aqueous extract to 15-20C, transfer it to a separatory funnel, and extract the caffeine with four successive 25-mL portions of dichloromethane. Transfer the extracts to a simple-distillation assembly and distill off all but 10 mLof the solvent on a steam bath. Save the recovered solvent. Evaporate the combined solutions to dryness on a steam bath or hot-water bath in a hood. To purify the crude product, dissolve it in about 5 mL of acetone by warming the mixture on a steam bath; add dropwise just enough mixed “hexanes” to turn the warmed solution faintly cloudy; then allow the solution to cool and allow the product to crystallize. Collect the green-tinged crystals on a small vacuum filter and wash them with a little mixed “hexanes.” The melting point of caffeine reported in the literature is 236°. This is too high to be safely determined in an apparatus using a mineral-oil bath. The green color of the caffeine sample can be removed by sublimation. Table of Chemicals Chemical | Quantity | MW | bp, °C | mp, °C | Density | Caffeine | - | 194 | - | 236 | - |
Open Document