CHEM 2313 Lecture Notes - Dichloromethane, Paracetamol, Analgesic

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lemonrat895

17 Feb 2014

School

Northeastern University

Department

Chemistry & Chemical Biology

Course

CHEM 2313

Professor

Stenburg

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Document Summary

The objective of this experiment is to separate the components in an excedrin tablet. One excedrin tablet was slightly dissolved in dichloromethane and filtered using vacuum filtration. The liquid was set aside for extraction of caffeine and aspirin. Water was added to the solid and it was heated in a hot water bath. The acetaminophen dissolved into the water and was separated from the tablets binder again using vacuum filtration. The hot solution was then placed in an ice bath until crystals of acetaminophen formed. The crystals were separated again using vacuum filtration. To extract the caffeine and aspirin, sodium hydroxide was added to the dichloromethane filtrate from the beginning of the experiment. This separated it into layers and the aqueous upper layer was extracted from the tube for later use in order to yield caffeine. The liquid left in the tube was dried with calcium chloride pellets, and then dried using vacuum evaporation, leaving caffeine.

Related Questions

Separation of Acidic, Basic, and Neutral Compounds:

This is for an Ochem Lab. 1st-8th is just the steps of the procedure we followed and the question corresponds to the 8th step in the procedure;â In the first portion of the experiment, what is the purpose of washing the dichloromethane (layer C) with two 15 mL portions of water?

Background :

A mixture containing acidic, basic, and neutral compounds can be separated by acidic and basic properties. Commercial headache tablets, such as Excedrine, contain Aspirin (Acidic), Acetaminophen (Neutral), and Caffeine (Basic).

Procedure

1st)Weigh two headache tablets.

2nd)Crush using a mortal and pestle.

3rd)Dissolve the crushed tablets in 25mL of dichloromethane. Some solid binder may not dissolve so filter the dichloromethane using gravity filtration to remove the undissolved binder. This binder can be discarded.

4th)Transfer the dichloromethane solution to a separatory funnel and extract three times with 15 mL portions of 5% aqueous sodium bicarbonate.

5th)Combine the sodium bicarbonate layers in 100 mL beaker Labeled A.

6th)Extract the dichloromethane again but using three successive 15mL portions of 10% aqueous HCl.

7th)Combine the HCl layers in a beaker Labeled B.

8th)Lastly, wash* the dichloromethane with two 15mL portions of distilled water. The water will be the waste. Dry the dichloromethane over anhydrous calcium chloride. Label this C. 1.

Experiment: Extraction to seperate benzoic acid and naphthalene.

Procedure-

Place 2 g of a 1:1 (by weight) mixture of benzoic acid and naphthalene in a small beaker; record the exact mass of the mixture in your notebook. Add 35 mL of dichloromethane to the beaker and stir until the solid mixture has completely dissolved. Carefully pour the solution into a separatory funnel.

Add 20 mL of 3.0 M NaOH to the separatory funnel, stopper it, and shake the mixture with frequent venting. When the layers have separated, drain the bottom portion into a clean flask. Pour the aqueous layer into another clean flask labeled âaqueous layer.â Pour the organic layer back into the separatory funnel and extract with a second portion of 3.0 M NaOH. Drain the bottom layer into a clean flask labeled âorganic layerâ and pour the aqueous layer into the âaqueous layerâ flask.

Put the organic layer back into the separatory funnel and shake with 20 mL of saturated NaCl solution. Drain the organic layer into a clean, dry flask and add a small amount of anhydrous calcium chloride to dry the solution. Allow this solution to stand for at least ten minutes, with occasional swirling, then remove the drying agent by gravity filtration; place the filtrate in a round-bottom flask and remove the solvent by simple distillation or by using the rotovap. Once the dichloromethane has been removed, scrape the crystals out of the round-bottom flask into a clean, labeled, tared vial, and determine the weight and melting point of the naphthalene crystals.

Acidify the combined aqueous layers with 6.0 M HCl until the solution tests acidic to litmus paper. A white precipitate of benzoic acid should develop as the solution is neutralized. Chill the solution in an ice bath for at least ten minutes to finish precipitating the solids, then collect the benzoic acid by vacuum filtration. Wash the crystals with a small amount of cold water; then scrape the crystals into a clean, labeled, tared vial and allow to dry. Once the crystals are dry, determine their weight and melting point.

Post-Lab Question:

Write a balanced equation (using structures) for the reaction that takes place when the aqueous layer is acidified with HCl. Why does the precipitate form when the solution is neutralized? (HINT: benzoic acid (slightly soluble in water) and sodium benzoate (soluble in water)

CHEM 2313 Lecture Notes - Dichloromethane, Paracetamol, Analgesic

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