Extraction

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Extraction

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Extraction is one of the most common methods of separating an organic product from a reaction mixture or a natural product from a plant.

Three types of extraction:
1. Solid/Liquid extraction

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2. Liquid/Liquid extraction
3. Acid/Base extraction

1. Solid/Liquid extraction
Soxhlet extractor

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Steeping a cup of tea: the hot water dissolves the flavoring and caffeine from the tea bag or tea leaves.

2. Liquid/Liquid extraction
• In liquid-liquid extraction, equilibrium concentrations of a solute are established between two immiscible solvents.
• Extraction is commonly used to separate an organic product from a reaction mixture containing water-soluble impurities.

Distribution Coefficient 32
concentration in solvent2 K= concentration in solvent1 g compound per mL solvent2 g compound per mL solvent1

K=

Properties of extraction solvents
1. It should readily dissolve the substance to be extracted 2. It should have a low boiling point so that it can readily be removed; 28

3. It should not react with the
solute or the other solvent;

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4. It should not be flammable
or toxic; and

5. It should be relatively inexpensive.

Table. Extraction solvents solvent Density (g/mL) Petroleum 40-60 0.64 ether hexane 69 0.66 Ethyl ether 35 0.71 BP

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solvent Toluene Sat. NaCl (aq)

BP 111o

25 Density (g/mL) 0.87

109o

1.20
1.33

Methylene chloride 40

3. Acid/Base extraction

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Acid/Base extraction

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Acid/Base extraction

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Fig Flow diagram for the separation of a strong acid, a weak acid, a neutral compound, and a base-benzoic acid, phenol, naphthalene, and aniline

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Steps in extraction
1. Preparation of separatory funnel

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2. Adding the liquid
3. Mixing the layers

4. Separating the layers
5. Cleaning the separatory funnel

1.Preparation of separatory funnel 19

Set the s. f. in an iron ring

2. Adding the liquids Do not fill the s. f. more than three-quarters full

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3. Mixing the layers

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A “whooshing” sound will be heard as the pressure is released.

4. Separating the layers

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Solvent density

Other techniques used in extraction
1. Multiple extraction 13

2. Washing
3. Drying organic solution

4. Removing solvents
5. emulsion (next week)

K = 7.8 at 22 oC
2.0 g caffeine/200 mL tea water

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100 mL CH2Cl2 (1x)
K = 7.8 =

a/100 (2.0-a)/200

a = 1.59 g (79.5%)
50 mL CH2Cl2 (2X): 88.5 % 33.3 mL CH2Cl2 (3X): 94.5 %

50 mL CH2Cl2 (2x)
K= b/50 (2.0-b)/200

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b = 1.32g
c/50 K= (0.68-c)/200 c = 0.45 g

b + c = 1.77 g (88.5%)

331/3 mL CH2Cl2 (3x)

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d=

(91.8%)

25 mL CH2Cl2 (4x)
e= (93.5%)

20 mL CH2Cl2 (5x)

f=

(94.5%)

1. Multiple extraction

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• If the organic solvent is less dense than water, the organic solvent will be the top layer.
↓Drain the lower aqueous layer into a clean flask.

↓Pour the organic layer out of the top of the separatory funnel into a different clean flask.

↓To do further extractions, return the aqueous layer to the separatory funnel.

↓Add additional solvent and repeat the procedure.
↓ Combine the organic extracts.

• If the organic solvent is more dense than water, the organic solvent will be the bottom layer. ↓Drain the lower organic layer into a clean flask. ↓Add fresh solvent to the aqueous layer remaining in the separatory funnel ↓repeat the extraction procedure. ↓ Combine the organic extracts.

Important Tips Concerning Extraction
1. Never discard any layer until the experiment has been completed!
2. Make certain that the phases are thoroughly mixed by vigorously shaking the container.

3. Using one of these methods to determine which layer is the organic layer and which layer is the aqueous layer:
a. Look up the densities of the solvents in the

Handbook of Chemistry and Physics or the Merck Index.
b. Add 2-3 mL more water to the separatory funnel and see which layer grows. c. Put 1-2 drops from one of the layers onto a watch glass and add several drops of water. If two

layers appear, the layer was organic.

4. Vent frequently, especially with very volatile solvents such diethyl ether or methylene chloride (CH2Cl2). 5. If the liquid is not draining evenly from the separatory funnel, check to make certain that the stopper has been removed 6. A Teflon stopcock should not be greased. Glass stoppers should not be greases.

7. If there is only one layer in the separatory funnel and there should be two, perhaps the wrong layer was used. Find the correct layer and repeat the extraction. 8. An emulsion is a suspension that prevents a sharp interface between the layers.

2. Washing

•The term “extraction” and “washing” imply slightly different process, although the mechanics are the same. •Extraction is the process of removing a compound of interest from a solution or a solid mixture. •Washing, usually means removing impurities from the substance of interest.

2. Washing
Wash (extract with fresh water) to remove any water-soluble impurities. • volume: 10 % of organic layer • 5 % NaHCO3 or NaCl (Brine, saturated NaCl) • Washing is accomplished by placing the organic soln in the S. F. along with the wash solution, then shaking and separating in the usual manner

3. Drying organic solution
• During extraction, the organic layer becomes saturated with water. A drying agent must be used to remove water from the organic solvent. • Drying agents are anhydrous salts that are used to remove water from “wet” organic liquids. • The salts bond to water molecules to form hydrated salts that can easily be removed by gravity filtration.

procedure
↓Place the solution to be dried in an Erlenmeyer flask. ↓Add a spatula-tip full of the drying agent to the solution. ↓Swirl to suspend the particles.
In the presence of water, the small particles of the drying agent clump together. Continue adding small portions of the drying agent until the solution is completely clear or when additional drying agent is free flowing.

↓let the solution stand for 10-15 min
↓prepare a gravity filtration apparatus ↓pour the dried soln carefully through the filter paper ↓Rinse the flask and filter paper with additional portions of solvent ↓combine the solvent washing

3. Drying organic solution

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Table. Common drying agents Drying Acidity Hydrated agent products Molecular neutral sieves MgSO4 neutral MgSO4·H2O MgSO4·7H2O

Drying agent Na2SO4 CaCl2

Acidity neutral neutral

9 Hydrated products Na2SO4·7H2O Na2SO4·10H2O CaCl2·H2O CaCl2·2H2O CaCl2·6H2O

Drying agent CaSO4
K2CO3

Acidity neutral
basic

Hydrated products CaSO4·½H2O CaSO4·2H2O K2CO3 ·1½H2 O K2CO3 ·2H2O

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Drying agent M.S MgSO4 Na2SO4

Efficiency Rate very high medium to high low fast fast slow

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Drying agent CaCl2 CaSO4 K2CO3

Efficiency medium high medium

Rate

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medium fast medium

Important Tips Concerning Drying agents
1. A solvent that has been in contact with water is not considered to be dry unless it has been dried with a drying agent.

2. Exact amounts of drying agent are usually not specified in a procedure. The only way to know for sure how much drying agent to add is by careful addition and observation.
3. Do not add more drying agent than is necessary. The drying agent can adsorb the organic product as well as water.

4. Swirling the drying agent and the solution enhances the speed of the drying. 5. If a liquid dissolves the drying agent, that liquid is probably water. Check to see if the correct layer has been chosen following an extraction. 6. Be aware that different organic solvents absorb differing amounts of eater, so they will require different amounts of drying agent.

4. Removing solvents a. Distillation b. Rotary Evaporator

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Reagents: Benzoic acid
O OH

4 Acetanilide
H N O

mp:122-123;

mp:111-115

Ethyl Acetate; 10% NaHCO3(aq); anhydrous MgSO4; conc. HCl

Procedure:

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↓Place 1.6 g of mixture in a E.
flask

↓Dissolves with 20 mL EA
↓Transfer into s. f.

↓ Extract with 10 mL
10% NaHCO3 (3X)

↓ EA layer transfer into a clean and dry E. flask ↓ Add anhydrous MgSO4

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↓ Shake until clear and stand
for 5 min

↓ Gravity filtration (received by
a tared R.B flask)

1 ↓ Remove solvent by Rotary Evaporator ↓ weigh the RB flask (contain acetanilide) ↓ Aq. Soln’ cooled with ice bath ↓ Acidify with conc. HCl (pH < 3) ↓ Suction filtration (wash with cold water)

↓ Collect the solid and dry

Home work: Search for the method now commonly used to extract caffeine from coffee to manufacture decaffeinated coffee.

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