Separating Acids and Neutral Compounds by

Solvent Extraction

Definition

Extraction Washing

ExtractionExtraction::a process that selectively dissolves one or more compounds into an appropriate solvent. The resulting solution is called an extract.refers to the transfer of these compounds from one liquid solvent to another one.can be used to separate unwanted impurities or to separate mixtures of compounds.

The two solvents used for extraction must be immiscible.Washing is the removal of impurities from a solvent containing your compound by a second immiscible solvent.

Choosing the solvents:

Two immiscible solvents: water vs organic solvent.

Nonpolar hydrocarbons and ethers (polar) are less dense than water, so the water tends to move to the bottom.

Most chlorinated solvents are more dense than water, so the water will be on top.

Like dissolves like (nonpolar compounds are more soluble in nonpolar solvents).

To confirm the identities of the layers, add one or two drops of water to the funnel:

If water mixes with the top layer, then the top layer is water.

If water falls through the top layer, the bottom layer is water.

cyclohexanecyclohexanepetroleum etherpetroleum etherhexanehexanetoluenetoluenediethyl etherdiethyl etherdichloromethanedichloromethaneethanolethanolacetoneacetonemethanolmethanol

leastleast polarpolar

most polarmost polar

Hydrocarbons/EthersWater

Chemistry of Extraction

WaterChlorinated solvents

O

OH

O

O+ H+

Ka

O

OH

O

O+ H2CO3+ HCO3

-

OH + HCO3- O + H2CO3

pKa 4.2 pKa 6.4

pKa 6.4pKa 10.2

Acid-Base Extractions Analyzing ReactivityppKKaa = - log Ka

Ka [HA] = [A-] [H+]Lower Lower pKapKa = Stronger acid= Stronger acid

O

NH

acetanilidepKa 24

p-toluic acidpKa 4.2

OH

p-tert-butylphenolpKa 10.2

O

OH

XOrganic-solvent soluble Water soluble

The Extraction Setup

Make sure the stopcock of the separatory funnel is closed!

1. Prepare your solution in a beaker. Weigh mixture and mix with TBME.

Transfer the solution into a separatory funnel.

2. Pour a measured amount of extraction liquid.

3. Place stopper securely in the funnel.

Experimental Procedure

4. Using your fingers to secure the cover, shake the mixture several times.

5. Vent the pressure by inverting and opening the stopcock. (Vent often!)

NOTENOTE:: The cover is always The cover is always securedsecured

during the whole operationduring the whole operation

Experimental Procedure

6. Place the separatory funnel in the iron ring.

7. Remove the cover and allow the layers to separate.

8. Identify the layers (solvents). (Don't throw anything away until sure.)

9. Remove bottom solvent by draining through the stopcock. Pour the

upper solvent through the top of the funnel.

Experimental Procedure

O

O

O

NH

OH

O

NH

O

- rotary evaporator distillation – use house vacuum to remove any residual solvent.

- transfer to E. flask- dry with anhydrous Na2SO4- decant to a pre-weighed rbf

- heat <60° C in the hood- then cool in an ice-bath- acidify w/ HCl dropwise- vacuum filter

- dissolve in TBME-wash with NaHCO3 solution (Weak base only deprotonates the

strong acid)

- wash with NaOH solution (Strong base deprotonatesthe weaker acid)

- acidify w/ HCl solution to pH ≤ 3- filter precipitate

Filtrate

Residue

Filtrate

Distillate

(discard)

(discard)

(discard)

(discard)

O

NH

acetanilidepKa 24

p-toluic acidpKa 4.2

OH

p-tert-butylphenolpKa 10.2

O

OH

O

OH

OH

Decantate

O

NH

MacroscaleMacroscale (p.139)(p.139) 1.3 g of mixture(TA will give you the breakdown of the components!!)

AQ

ORG

ORG

ORGAQ

ORG

Miscellaneous Notes

Waste Organic Solvents: a waste bottle will be in the hood that will be used for all of the organic solvents.

Waste Aqueous Solutions: a waste bottle will be in the hood for the acid/base solutions from your extractions.

Grading: approximately 2/3 of your grade will be based upon the written lab report (prelab and postlab questions, experimental procedures, conclusions, etc.).

Use the Microscale Flow Chart on page 135 as a guide (see the handout), but

use the MacroscaleMacroscale procedureprocedure on page 139.

Step 1. The mixture of the three compounds is already prepared for you. (TA will give you the breakdown of the components!!)

Step 2. Weak base (NaHCO3) only deprotonates the strong acid, which means your

compounds are in both phases.

Step 3. Strong base (NaOH) deprotonates the weaker acid, which means you will again

have compounds in both phases.

Step 4. Isolated p-toluic acid will need to dry in your drawer. Don't forget to pre-weigh

your filter paper.

Step 5. When heating, don't allow the temperature to exceed 60 ºC. Before adding HCl, cool the solution in an ice bath. Allow the isolated p-tert-butylphenol to dry in

your drawer. (Pre-weigh paper!!) (Heating is done in the hood.)

Step 6. Pre-weigh a round bottomed flask (not a beaker). Perform distillation by rotary evaporation instead of the evaporation procedure in the lab manual. See 2nd

handout for instructions. Use the house vacuum to remove any residual solvent.

Make Note of the Following: