Expt. 1, Part A. Separation of 4-Chloroaniline, Benzoic acid, and 4-Dibromobenzene.

Procedures

Weigh out 2.0 g of the mixture of benzoic acid, 4-chloroaniline and 4-dibromobenzene and transfer the solid to a 125 mL Erlenmeyer flask. Add to the flask 10 - 15 mL of ether and swirl until the solid is dissolved. Transfer the solution to a 60 mL separatory funnel, washing out the Erlenmeyer flask with a small volume (ca. 3-5 mL) of ether (use a Pasteur pipette) to ensure that no solid remains in the flask, and then add carefully to a separatory funnel 15 mL of 2 M HCl. Stopper the funnel and shake it carefully, remembering to release the pressure caused by the heat of the reaction at frequent intervals through the tap. When shaking is complete, remove the stopper and set the funnel on a clamp or a support ring, to allow the two layers to separate.

[Note: Ether has a boiling point (bp) of only 35^oC; during hot weather much of your ether may evaporate during the extraction process. If this occurs (as you will see by your upper layer being very small in volume) simply add 5 -10 mL more ether.]

When separation is complete, carefully run off the lower aqueous layer into a clean 125 mL Erlenmeyer flask, and then add a further 15 mL (approx.) of 2 M HCl to the remaining ether solution in the separatory funnel and repeat the extraction procedure. The second 15 mL of aqueous solution may then be run off and combined with 15 mL obtained from the first extraction. The ether layer should now be washed by adding to it 15 mL of water, shaking as before and then running off the aqueous washings into the combined aqueous extracts. The resulting aqueous solution (total of approx. 45 mL) should then be labelled "4-chloroaniline, hydrochloride salt" and set aside.

Now add carefully to the separatory funnel 15 mL of 5% sodium bicarbonate solution. Stopper the funnel and shake it carefully, remembering to release the pressure caused by carbon dioxide evolution at frequent intervals through the tap. When shaking is complete, remove the stopper and set the funnel on a clamp or a support ring, to allow the two layers to separate.

When separation is complete, run off the lower aqueous layer into a second clean 125 mL Erlenmeyer flask, and then add a further 15 mL of 5% sodium bicarbonate solution to the remaining ether solution in the separatory funnel and repeat the extraction procedure. The second 15 mL of aqueous solution may then be run off and combined with 15 mL obtained from the first extraction. The ether layer should now be washed by adding to it 15 mL of water, shaking as before and then running off the aqueous washings into the combined aqueous extracts. The resulting aqueous solution (total of approx. 45 mL) should then be labelled "benzoic acid, sodium salt" and set aside.

The ether solution which remains in the separatory funnel may now be run off into a clean 125 mL Erlenmeyer flask. Wash the inside of the funnel with 5 mL of ether. Anhydrous sodium sulfate (approx. 2 g) is added to the flask in order to dry the ether solution by removing any traces of water which remain. The mixture should be allowed to stand for several minutes, with frequent agitation, before filtering. This solution is then filtered through a gravity filter (fluted! see Fig. 1.1 in Part B, Intro) into a dry 125 mL Erlenmeyer flask, which has been previously weighed.

[Make sure you wash the Na₂SO₄ with a few mL of ether and wash the filter paper to get all the organic material into the flask.]

The ether is removed then by evaporation on a steam-bath or a beaker of hot water (USE FUME HOOD [CAUTION: NO FLAMES!]) to leave a residue of molten 4-dibromobenzene whose weight should be determined. Do not overheat the 4-dibromobenzene, which is recovered molten but will solidify on cooling. 4-Dibromobenzene has an appreciable vapour pressure at room temperature (even as the solid) and therefore should be stored in a stoppered Erlenmeyer to prevent any loss of material by evaporation. The flask plus sample should be weighed, to allow you to calculate the % of 4-dibromobenzene present.

Save your sample for PART B where you will determine its melting point.

The solution of benzoic acid as the sodium salt must now be treated with dilute acid to recover the benzoic acid. To do this, simply add dilute (6M) hydrochloric acid slowly and carefully to the solution, with constant swirling, until a dense, white precipitate of benzoic acid is apparent and the solution is acidic to Congo Red indicator paper (blue in acid at about pH2). During this addition, carbon dioxide is evolved and care is necessary in order to prevent the solution from frothing out of the flask.

When precipitation of the benzoic acid is complete, it may be separated from the solution by filtering on a Buchner funnel (Part B Intro, Fig. 1.2). The precipitate is then washed with a little ice-cold water, dried on a sheet of filter paper and weighed.

[If you obtained little, or no, precipitate of benzoic acid you probably did not extract the mixture with NaHCO₃ correctly and had too dilute a solution - leave your acidified solution in an Erlenmeyer with a filter paper cover and place in your drawer until your next lab period.]

Save your sample for PART B where you will determine its melting point.

The solution of 4-chloroaniline hydrochloride must now be treated with base to recover the free amine. Add, a bit at a time and with stirring, 10% NaOH solution to your Erlenmeyer containing the 4-chloroaniline hydrochloride; cool your flask in cold water if necessary (you should use ca. 30-35 mL of the 10% NaOH). Check the pH with pH-paper in the latter stages of the addition to ensure that the pH of the solution becomes 11-12. When the precipitation of the 4-chloroaniline is complete, it may be separated from the solution by filtering on a Buchner funnel (Part B Intro, Fig. 1.2).

[Because ether has some solubility in water your crystals may be small and sticky and they will not filter well. To help filtration, swirl your Erlenmeyer while blowing over the surface of the liquid, then when you do the filtration use two pieces of filter paper.]

The precipitate is then washed with a little cold water, dried on a sheet of filter paper and weighed.

[If you do not have time to acidify or basify your solutions or evaporate your ether layer, these may be stoppered and stored until your next Laboratory period]

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