1

Collect:

• Filter paper

(2017/04/24)

Prepare: • Separatory funnel

• Ring support

• Funnel

• Erlenmeyer flasks (50 mL, 2)

• Round bottom flask (100 mL)

• Hirsch funnel

• Filtering tube

• Rubber stopper

• Sample vial

• Water aspirator

C25 Extraction

C25 Extraction Objective: use acid-base reaction to extract and

separate the organic compounds

Techniques

– Electric balance

– Extraction

– Suction filtration

– Gravity filtration

– Rotary evaporator

Flowchart

Part I: extraction by acid-base reaction

Part II: separation of benzoic acid

Part III: separation of acetanilide 2

3

RCO2H (acid)

RNH2 (base)

R-H (neutral)

Water layer

Organic soln

Organic

layer

RNH3+Cl-

RCO2H

R-H

Water layer

Organic

layer

RNH2

NaOH(aq)

R-H

RCO2Na HCl(aq)

RCO2H

Principle

Extraction Transfer of a solute from one solvent to another by means

of the distribution process

Extraction by acid-base reaction

HCl(aq)

NaOH(aq)

Check the stopper and

stopcock to avoid leaking

Support on an iron ring

Close the stopcock

Add soln. through funnel

Rinse the sample flask

twice

Pour the extraction solvent,

close with the stopper, and

identify the layers

Open

Close

Extraction-Preparation

4

Stopcock

Stopper

Hold the stopper securely in place

with one hand, then invert the funnel

Open the stopcock slowly with the

other hand to relieve the pressure

Close the stopcock and shake the

funnel vigorously to mix two solvents

Repeat venting and shaking until the

“whoosh” is no longer audible

Notice

– Put the nitrile gloves on

– Operate in fume hood

– Do not point the opening to the others

– Repeat venting as many times as possible

5

Extraction-Shaking and Venting

Extraction－Separation

Replace the funnel on ring

support

Remove the stopper immediately

Allow the two layers of liquid to

separate

Drain the lower layer through the

stopcock

Close the stopcock until the

interface between the upper and

lower phases just begins to enter

the bore of the stopcock

The remaining upper layer is

removed by pouring it from the

top opening 6

Emulsions

Emulsion is a colloidal suspension of one liquid in another

liquid

Minute droplets of an organic solvent often are held in

suspension in an aqueous solution when the two are mixed

vigorously

Break up emulsion

• Add a saturated aqueous NaCl soln

• Gravity filtration

• Gently swirling

• Allow the emulsion to stand for a time

• Place emulsion in a freezer

7

8

Weigh 0.5 g benzoic acid

and acetanilide

Transfer to a 50 mL

Erlenmeyer flask

Add 10 mL EA to dissolve

Pour the soln to separatory

funnel

Wash the flask with 2 mL

EA twice A

1st extraction: with 5 mL 5%NaOH

Drain the lower layer to flask A

2nd extraction: with 5 mL D.I. water

Combine the lower layer to flask A

Pour the upper layer from top to another flask B

Place flask A in ice-

water bath

Add 6 M HCl drop by

drop till no more white

ppt form and pH < 3

Part I: Extraction by Acid-Base Reaction

6 M HCl(aq)

Flask A

Sample soln

9

Collect benzoic acid

by suction filtration

Suction dry for 10 min

Collect product on a

filter paper

Press dry with filter

paper; then air dry for

10 min

Part II: Separation of Benzoic Acid

• Label and weigh the

mass of an empty vial

• Store the crystals in the

vial

• Weigh it again to

calculate the percent

yield

Use a piece of

aluminum foil to

seal the vial

Poke small

holes to allow

further drying

Keep for the

next experiment

10

Manipulation of Suction Filtration

Fix water-trap bottle and filtering

tube with extension clamp

Place a rubber stopper between

suction tube and Hirsch funnel

Cut the filter paper to cover all of

the holes in the bottom of the

Hirsch funnel but it must not extend

up the sides

Moisten the filter paper with small

portions of solvent

Close the two-way valve, then start

and test the suction

Start filtering when the filter paper is

tightly stuck on the funnel

Release the pressure before turn off

the water aspirator

Fill water in water aspirator;

that water comes in from

bottom and flows out from

top

11

Part III: Separation of Acetanilide

Add proper

amount of MgSO4

(ca. 2 g) to flask B

and swirl until the

solution is clear

Filter the soln in flask B to

remove MgSO4 by gravity

filtration to a weighed

round bottom flask

Rinse the flask B with ca.

2 mL EA, then filter and

combine the filtrate into

round bottom flask

Evaporate EA and

obtain acetanilide in

round bottom flask by

rotary evaporator

Weigh and calculate

the percent yield

Transfer the product

to a sample vial

B

Rotary Evaporator (Rotavap) To begin an operation

1. Turn on circular cooling system

2. Turn on and set the water bath to suitable temp (E)

3. Place the flask on the rotavap (A) and secure the

flask with a Keck clip

4. Balance the system with atmosphere (B)

5. Turn on the water aspirator

6. The flask is lowered into the water bath (C)

7. Turn on the rotation to appropriate speed (D)

8. Turn the stopcock at the top of the condenser (B) to

adjust the vacuum and avoid bumping

9. Start collecting solvent on the condenser and drip

into the receiving flask. (F)

End of the operation

1. Release vacuum (B) and discontinue spinning (D)

2. Raise the flask out of the water bath (C) and

disconnect the flask (A)

3. Turn off water bath, water aspirator, and circular

cooling system Keck clip

A

B

C

D

12

E

F

13

Notice

Check the stopper and stopcock of separatory funnel to

avoid leaking

Operate the extraction in fume hood

Repeat venting from time to time

Place the separatory funnel on ring support to avoid

breaking it

Drain the lower layer from the bottom of funnel

Pour out the upper layer from the top of funnel

Keep both layers to the end of the class

Keep the products to determine the m.p. next week

Recycle the organic waste to designated waste bins