Separation of a Two-Component Mixture Using Extraction Techniques

Aim To separate a two-component mixture using extraction techniques and then to identify the isolated components by determining their melting points.

Theory Extraction is a method of separating organic compounds. If one compound in the mixture can be chemically converted to an ionic form. The ionic form is soluble in an aqueous layer and can be extracted into it. Other, non-ionic organic compounds in the mixture will remain dissolved in the organic solvent layer. Separation of the two layers results in the separation of the two compounds. Consider, the reactions of a carboxylic acid and a phenol with bicarbonate ion. The carboxylic acid has a lower pKa than the conjugate acid of bicarbonate ion (carbonic acid). The reaction, therefore, proceeds to products. The reaction of a phenol, however, favours the reactants since the pKa of phenol is larger than that of the carbonic acid. Acid-base reactions favour the side with the weaker acid (that is, they favour the side with the larger pKa). So, extracting a mixture of these two compounds with bicarbonate results in the ionization and extraction of a carboxylic acid in the presence of phenol thus separating the two compounds from one another. Consider, the reactions of a carboxylic acid and a phenol with hydroxide ion. In both cases, the reactions favour the formation of products. Extracting with hydroxide ion would result in the ionization and extraction of both compounds at the same time. Hence, separating a mixture of a carboxylic acid and a phenol would be done using bicarbonate ion since only the carboxylic acid is converted into its conjugate base by bicarbonate. The conjugate base of the carboxylic acid, being an ionic species, is soluble in the aqueous layer while the phenol (left unionized) would remain dissolved in the organic layer. However, if we were to extract with hydroxide ion, both the carboxylic acid and the phenol would be converted into their conjugate bases. The conjugate bases, again are both ionic species and therefore soluble in the aqueous layer. This means that both compounds would be extracted at the same time, resulting in no separation. The amine functional group can be protonated by dilute hydrochloric acid (2 N) to form a charged species which is then extracted from organic layer into water. After separation of the aqueous and organic layer, the amine may be recovered by basification of the aqueous layer. A neutral compound will not react with either bicarbonate ion or hydroxide ion hydrochloric acid. Since a neutral compound does not have protons acidic enough to be removed by these bases and basic enough to accept protons from strong acid. Therefore, such a compound will remain dissolved in the organic layer, no matter which base/acid is added.

Apparatus and chemicals required 1. Beaker (100 mL, 250 mL and 500 mL), separatory funnel (250 mL) and dropper

2. NaHCO3, NaOH, HCl, diethylether, anhydrous Na2SO4 and litmus paper or pH paper.

Procedure Approximately 3.0 g of unknown mixture was dissolved in 50 mL of diethylether and the solution was poured the solution into a clean separatory funnel.

1. Sodium bicarbonate separation 1. Added 10 mL of 10% aqueous sodium bicarbonate to the separatory funnel. 2. Stoppered the funnel and inverted it. Opened the stopcock slowly to release any built-up pressure, then closed the stopcock. 3. Gently, shaked the separatory funnel to allow intimate mixing of the solutions and effect extraction of the compound from the organic mixture. (Caution: When shaken, the mixture developed the pressure and it was vented periodically). 4. Clamped the separatory funnel to a retort stand and allowed the mixture to separate into two layers. 5. Removed the stopper and collected the aqueous layer (the lower layer) in the 100 mL clean

beaker flask labelled "Aq. NaHCO3". 6. Repeated the steps 1-4 two more times draining each portion successively into the same flask. At the end of this sequence you will have extracted the organic solution with three 10 mL portions of 10% aqueous sodium bicarbonate. 7. 100 mL beaker labelled "bicarbonate" kept aside in a safe place. Later, the compound that was extracted by the hydroxide will be isolated.

2. Sodium hydroxide separation 1. Added 10 mL of 10% aqueous sodiumhydroxide to the separatory funnel with the remaining diethylether. 2. Stoppered the funnel and inverted it. Opened the stopcock slowly to release any built-up pressure, then closed the stopcock. 3. Gently, shaked the separatory funnel to allow intimate mixing of the solutions and effect extraction of the compound from the organic mixture. (Caution: When shaken, the mixture developed the pressure and it was vented periodically). 4. Clamped the separatory funnel to a retort stand and allowed the mixture to separate into two layers. 5. Removed the stopper and collected the aqueous layer (the lower layer) in the 100 mL clean beaker flask labelled "Aq. NaOH". 6. Repeated the steps 1-4, two more times draining each portion successively into the same beaker. 7. 100 mL beaker labelled "hydroxide" kept aside in a safe place. Later, the compound that was extracted by the hydroxide will be isolated.

3. Dilute hydrochloric acid separation 1. Added 10 mL of 10% aqueous 2 N hydrochloric acid to the separatory funnel with the remaining diethylether. 2. Stoppered the funnel and inverted it. Opened the stopcock slowly to release any built-up pressure, then closed the stopcock. 3. Gently, shaked the separatory funnel to allow intimate mixing of the solutions and effect extraction of the compound from the organic mixture. (Caution: When shaken, the mixture developed the pressure and it was vented periodically). 4. Clamped the separatory funnel to a retort stand and allowed the mixture to separate into two layers. 5. Removed the stopper and collected the aqueous layer (the lower layer) in the 100 mL clean beaker flask labelled "Aq. HCl". 6. Repeated the steps 1-4, two more times draining each portion successively into the same beaker. 7. 100 mL beaker labelled " Aq. HCl " kept aside in a safe place. Later, the compound that was extracted by the hydroxide will be isolated.

4. Neutral compound separation

1. To the remaining diethylether, added 5 mL of saturated aqueous NaCl and 5 mL of distilled

H2O in the separatory funnel. 2. Gently, shaked the separatory funnel to allow intimate mixing of the solutions and effect extraction of the compound from the organic mixture. (Caution: When shaken, the mixture developed the pressure and it was vented periodically). 3. Clamped the separatory funnel to a retort stand and allowed the mixture to separate into two layers. 4. Removed the stopper, expelled the aqueous layer and collected the organic layer (the top layer) in the 100 mL clean dry beaker labelled "Neutral".

5. Treated the organic layer with anhydrous Na2SO4. Filtered the dried organic solution into a dry pre-weighed 100 mL round bottom flask and evaporated the ether layer on a rotary evaporator. A solid/liquid remains after evaporation of the diethylether.

5. Isolation of the carboxylic acid or phenol from aqueous NAHCO3 or NaOH layer

1. Taken the100 mL beaker labelled " Aq. NaHCO3" or " Aq. NaOH" and acidified the aqueous solution by the dropwise addition of 2 N HCl. (Caution: The bicarbonate solution vigorously liberated the carbon dioxide when neutralized with HCl) 2. Added the acid solution until the solution changes the blue litmus to red paper. 3. The solution was poured into a clean separatory funnel. 4. Added 30 mL of diethylether to the separatory funnel. 5. Stoppered the funnel and inverted it. Opened the stopcock slowly to release any built-up pressure, then closed the stopcock. 6. Gently, shaked the separatory funnel to allow intimate mixing of the solutions and effect extraction of the compound from the organic mixture. (Caution: When shaken, the mixture developed the pressure and it was vented periodically). 7. Clamped the separatory funnel to a retort stand and allowed the mixture to separate into two layers. 8. Removed the stopper, expelled the aqueous layer.

9. Added 5 mL of saturated aqueous NaCl and 5 mL of distilled H2O to the ether layer in the separatory funnel. 10. Gently, shaked the separatory funnel to allow intimate mixing of the solutions. 11. Clamped the separatory funnel to a retort stand and allowed the mixture to separate into two layers. 12. Removed the stopper, expelled the aqueous layer and collected the organic layer (the top layer) in the 100 mL clean dry beaker.

13. Treated the organic layer with anhydrous Na2SO4. 14. Filtered the dried organic solution into a dry pre-weighed 100 mL round bottom flask and evaporated the ether layer on a rotary evaporator. A solid/liquid remains after evaporation of the diethylether.

6. Isolation of the amine from aqueous HCl layer 1. Taken the100 mL beaker labelled " Aq. HCl" and basified the aqueous solution by the dropwise addition of 10 % NaOH. 2. Added the hydroxide solution until the solution changes the red litmus to blue paper. 3. The solution was poured into a clean separatory funnel. 4. Added 30 mL of diethylether to the separatory funnel. 5. Stoppered the funnel and inverted it. Opened the stopcock slowly to release any built-up pressure, then closed the stopcock. 6. Gently, shaked the separatory funnel to allow intimate mixing of the solutions and effect extraction of the compound from the organic mixture. (Caution: When shaken, the mixture developed the pressure and it was vented periodically). 7. Clamped the separatory funnel to a retort stand and allowed the mixture to separate into two layers. 8. Removed the stopper, expelled the aqueous layer.

Report The given mixture was separated by sodium bicarbonate or sodium hydroxide or dilute hydrochloric acid separation.