PROCEDURE NOTE IN PREPARTION FOR EXPERIMENT 5, THE SYNTHESIS OF ETHYL-4- AMINOBE

Question

PROCEDURE NOTE IN PREPARTION FOR EXPERIMENT 5, THE SYNTHESIS OF ETHYL-4- AMINOBENZOATE, CLEAN AND DRY A 250 mL RBF. IF THE FLASK IS DIRTY WASH IT WITH SOAP AND WATER AND RINSE WELL WITH ACETONE a) Separation of the components Weigh a sample of the benzoic acid/ biphenyl mixture (use approximately 2 g, but record the actual mass used). Dissolve the mixture of biphenyl and benzoic acid in 30 mL ethyl acetate (IUPAC Name: ethyl ethanoate) in an Erlenmeyer flask then transfer the solution to the separatory funnel (see the figure in apparatus appendix). Rinse the flask with 10 mL ethyl acetate and add it to the contents of the separatory funnel. Add a 20 mL portion of 1.0 mol L sodium hydroxide solution to the separatory funnel. Shake the separatory funnel gently, holding the stopper in place. Periodically invert the funnel and vent any gas pressure by opening the stopcock momentarily. Place the funnel in a ring clamp and allow the layers to separate. Remove the stopper and draw off the lower (aqueous) layer through the stopcock into an Erlenmeyer flask. To the upper (organic) layer in the separatory funnel, add a second 20 mL portion of 1.0 mol L1 sodium hydroxide solution and extract as before. Draw off the lower layer into the Erlenmeyer flask containing the first lower layer and pour the top layer out of the top of the funnel into a dry Erlenmeyer flask. b) Isolation of biphenyl To the organic layer (the top layer in the Erlenmeyer flask), add ½ of a scoop of anhydrous potassium carbonate, swirl gently, cork the flask, and allow it to stand for at least 20 minutes (swirl occasionally for more efficient drying). Check to be sure the drying agent does not become saturated with water. More potassium carbonate may be added if necessary. The dry solution should be clear above the solid drying agent Determine the mass of an appropriately-sized dry round bottom flask (containing boiling stones). During a distillation the distilling flask should be ½ to full of liquid. c) Isolation of benzoic acid To the combined aqueous layers add 9 mL of 6.0 mol L hydrochloric acid. The solution should be acidic to litmus (Test it with litmus paper) and a heavy precipitate should be obtained (If no precipitate forms, consult an instructor). Chl the sample in ice for 5-10 minutes. Collect the precipitate by suction filtration (see techniques). Wash the product several times with small amounts of ice-cold water then transfer the solid to a pre-weighed watch glass and allow it to dry in your locker for a week before weighing.

Explanation / Answer

Diphenylamine is an organic base and naphthalene is an aromatic hydrocarbon. Both are organic, so we add ethyl acetate to the mixture and transfer it to a separatory funnel. Shake well and add dilute HCl. Diphenylamine being a base will react with dilute HCl and move to the aqueous layer. The organic layer will be left with naphthalene. Remove the aqueous layer and then again add dilute HCl to the separatory funnel containing naphthalene and ethyl acetate. Shake well. This will help in removing traces of base to the acid layer. Again remove the aqueous layer. So, now we have aqueous solution containing diphenylamine and organic layer would be having naphthalene.

To the organic layer, add anhydrous potassium carbonate. This will help in removal of water which is there in the organic layer. Filter the lumps you get in the organic layer through filter paper. After it is done, again add some more anhydrous potassium carbonate. If the added anhydrous potassium carbonate is in powder form and not in lumps, then it means that whole of water is removed. Then keep the sample to let ethyl acetate evaporate or use rotary evaporator to remove solvent.

To the aqueous layer, add a base. Add 5.0 M NaOH to the solution. Add it until the litmus paper turns blue indicating the basic solution. The diphenylamine will start precipitating. Cool the solution with precipitates and filter the precipitates out through suction. Dry the precipitates and you will be left diphenylamine.

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