Question

I need to know the procedures of the experiment below :

Separation of a Three-Component Mixture by Extraction ​

benzoic acid     ethyl 4-hydroxybenzoate diphenyl sulfone

A 1.5-gram sample of a 1:1:1 (by weight) mixture of benzoic acid, ethyl 4-hydroxybenzoate and diphenyl sulfone was added to a 125 mL separatory funnel. Isopropyl acetate (20 mL) was added to the separatory funnel and the mixture swirled until all solids had dissolved. The solution was sequentially extracted with saturated aqueous NaHCO3 solution (4 X 5 mL), then with water (1 X 5 mL); with the aqueous extracts from each extraction being added to a 50 mL beaker (beaker 1). [The separatory funnel should be shaken for at least 1 minute during each of the four NaHCO3 extractions. Venting of the funnel should be done every 20-25 seconds during each extraction. When draining off the aqueous layer in these and all subsequent extractions leave a two mm tall layer of aqueous solution in the separatory funnel. This greatly reduces the amount of organic layer that contaminates the aqueous extracts.] Next the organic layer was extracted sequentially with 5% aqueous NaOH solution (3 X 5 mL) then with water (1 X 5 mL). Each aqueous extract was collected in a 50 mL beaker (beaker 2). [The separatory funnel should be shaken for at least 1.0 minute during each NaOH extraction..] The remaining organic layer is extracted with saturated aqueous NaCl solution (5 mL) and the aqueous layer is discarded [Do not leave any water in the funnel after this extraction]. The organic layer is transferred to a 50 mL erlenmeyer flask (flask 3). The separatory funnel is washed with isopropyl acetate (2 X 2 mL) with each washing being added to flask 3. The organic solution in flask 3 is dried (Na2SO4) then decanted into a tared 50 mL Erlenmeyer flask (flask 4). The drying agent is washed with isopropyl acetate (2 X 1 mL) with each rinse being added to flask 4. The solvent in flask 4 is evaporated to give crude diphenyl sulfone as a white solid: .416 g, 83.2%, M. pt.=121-127oC. [Evaporate the solvent using a hot plate sat on a moderate (4) setting. You must be very careful not to overheat the product when all the solvent has boiled away. The only way to actually know when all of the solvent has been removed is to weight the flask at the point of “ presumed dryness”, then reheat for a few seconds and re-weigh the flask. If the weight does not change, the product is solvent free. An alternative, and probably better, procedure is to evaporate the isopropyl acetate until only 3-5 mL of solution remains, cool, add hexane (10 mL), chill in an ice bath then filter. Both procedures work well. If insufficient time remains to isolate this material on day 1, then store the dried isopropyl acetate solution in your drawer until the next lab period. The solvent will have evaporated by then. Optional: tlc (alumina,

70/30 hexane/ethyl acetate) showed a single spot, Rf = .58. The crude product is recrystallized from toluene to give the crude product; M. pt.= 125-127 C.]

The aqueous solution in beaker 1 was acidified (acid to litmus paper) by the addition of 6 M HCl solution to give a white precipitate. [Caution! Foaming will occur due to liberation of CO2] After cooling the resulting mixture in an ice bath for 10 minutes, the solid was isolated by vacuum filtration, washed with ice water (3 X 1ml), and air dried to give crude benzoic acid as a white solid: .358 g, 71.6%, M. pt.= 115-120oC. [OPTIONAL: tlc (alumina, 70/30 hexane/ethyl acetate) showed a single spot (Rf = .03). This material was recrystallized from water to give pure benzoic acid; M. pt. = 118- 120C.]

The aqueous solution in beaker 2 was acidified (acid to litmus paper) by the addition of 6 M HCl to give a white precipitate. The resulting aqueous mixture was cooled in an ice bath for 10 minutes. The resulting white solid was isolated by vacuum filtration, washed with ice water (3 X 1 mL), and air dried to give the crude ethyl 4-hydroxybenzoae: .353 g, 70.6%, M.pt.= 113-117oC. [Optional: tlc (alumina, 70/30 hexane/ethyl acetate) showed a single spot (Rf = .42). The crude material was recrystallized from 1/1 toluene/hexane to give the pure ethyl 4-hydroxybenzoate as a white solid; M. pt.= 115- 117C.]

Answer 1

Step1=1.5-gram sample of the mixture of benzoic acid, ethyl 4-hydroxybenzoate and diphenyl sulfone is to be taken in equal amounts. say 1.5/3g=0.5g (each) and then added to a 125 mL separatory funnel.

2) Add 20ml of Isopropyl acetate to the funnel and swirl it to dissolve the mixture

3)Now add aqueous NaHCO3 solution (4 - 5 mL) to it and agitate the mixture. As Isopropyl acetate and NaHCO3 solution are immiscible in each other ,they will form two distinct layer in the funnel.NaHCO3 solution forms the bottom aqueous layer and Isopropyl acetate forms the top organic layer.

Benzoic acid will dissolve into the NaHCO3 solution layer while ethyl 4-hydroxybenzoate and diphenyl sulfone will go into organic layer .Drain the bottom layer first from the funnel by opening the stop cork of the funnel in a 50 ml beaker marked 1. Add (4 - 5 mL) of water next to the funnel now and shake for 1 minute and drain again.Do it atleast four time to make sure all benzoic acid has been extracted by the aqueous solution While draining leave 2mm of aqueous layer in the funnel,else the top layer would come out along with it.

4) Now benzoic acid is already separated but we have ethyl 4-hydroxybenzoate and diphenyl sulfone mixture in Isopropyl acetate.To separate these two we will add 5% aqueous NaOH solution (3-5 mL) and repeat the process of extraction.We drain the NaoH solution(bottom layer ) in another 50 ml beaker marked 2.

Now ethyl 4-hydroxybenzoate goes into the NaOH solution and diphenyl sulfone stays in the ethyl acetate solution.

5)Extract the organic layer now by adding (2 -2 mL) isopropyl acetate .Repeat 4 times and empty the contents of the funnel in beaker marked 3.

6) We will dry the water in beaker 3 by adding Na2SO4 for any excess water and then evaporate the entire organic solvent by heating in an Erlenmeyer flask (flask 4).We will get crude diphenyl sulfone as white solid after complete evaporation of the solvent.

7)Check the weight of the erlenmeyer flask until you find it constant even after reheating the contents.you can be sure that all solvent is evaporated now.

An alternative procedure is to evaporate the isopropyl acetate until only 3-5 mL of solution remains, cool, add hexane (10 mL), chill in an ice bath then filter. Store the dried isopropyl acetate solution in your drawer until the next lab period.

Next day,the crude product is recrystallized from toluene to give the pure dimethyl sulfone and its melting point is determined.

8) now move to beaker 1 .It has benzoic acid dissolved in NaHCO3 solution.Add 6 M HCl solution to it untill you get a white precipitate.

The solution foams as CO2 gas is evolved.

Cool the mixture now in an ice bath for 10 minutes. And separate the white precipitate ,which is benzoic acid , by vacuum filtration.

Keep washing with ice water (3 - 1ml) while vacumm filtering.Air dry it to give crude benzoic acid as a white solid:This material is then recrystallized from water to give pure benzoic acid

9) Move to beaker 2 now. It has ethyl 4-hydroxybenzoate dissolved in NaOH solution.To separate it ,add 6 M HCl to it until it gives a white precipitate (it is ethyl 4-hydroxybenzoate).

Cool the contents in an ice bath for 10 minutes. The resulting white solid was isolated by vacuum filtration, washed with ice water (3 X 1 mL), and air dried to give the crude ethyl 4-hydroxybenzoate.

It can be recrystallized from 1/1 toluene/hexane to give the pure ethyl 4-hydroxybenzoate as a white solid;