CHEM 036 Fall 2006

Experiment #4: Acid/Base Extraction

Acid/base is an extremely useful separation technique in organic chemistry. Using simple acid/basereactions, several different classes of organic molecules can be separated from one another. This procedureis most easily visualized using the flow chart for acid/base extraction on the following page.

In this experiment you will be randomly assigned a mixture containing two components; an acid, a base, ora neutral component. The goal will be to separate the mixture by acid/base extraction, recrystallize thesolid compounds and identify them based on solubility and melting point determination. You will be givenapproximately 2 g of the mixture and use the miniscale procedure described in the text.

Objectives:1. Separate the two compounds of your unknown mixture.

2. Purify the unknowns by recrystallization.

3. Analyze and identify the compounds by melting point determination.

Helpful Hints:

1. Do not throw anything away until you have collected all the compounds.

2. Always label your beakers, flasks, test tubes, etc.

3. Be clear which layer is which; water vs. organic.

4. If you create an emulsion, be patient.

5. Drying agents do not need to be weighed out exactly. Add enough drying agent to cover thebottom and swirl the flask. When the drying agent flows freely, the solvent is dry.

6. Do not add drying agent to the water layer!

7. Do not forget to vent your separatory funnel.

CHEM 036 Fall 2006

Acid/Base Extraction Separation Scheme

H2O Layer CH2Cl2 Layer

concd. HCl

RCONa

O

RCOH

O

RHRNH2

RNH3Cl

H2O Layer

RH

CH2Cl2 Layer

RN H2

SOLID ACID

CH2Cl2 5 % NaOH

5 % HCl

SOLID N EUTRAL

SOLID BASE

Unknown Mixture (three components)

+

evaporate

5 % NaOH

acid base neutral

RCOH

O

RNH2 RH

Extraction UnknownsFall 2006

NAME STRUCTURE MP (C)

p-anisic acid 182-185

anthracene216-218

benzoic acid 121-123

biphenyl 69-72

camphor 175-177sublimes

4-chloroaniline69-72

2-chlorobenzoic acid 138-140

trans-cinnamic acid 133-134

1,4 -dimethoxybenzene56-60

ethyl-4-aminobenzoate88-90

COH

O

Cl

CH

CCO

OHH

C OH

O

NH2

Cl

OCH3

CH3O

C OH

O

CH3O

O

H2N

O

O

Extraction UnknownsFall 2006

fluorene 114-116

naphthalene80-82

sublimes

4-nitroaniline 149-151

phthalic acid

205 dv. water soluble

salicylic acid 158-160

trans-stilbene 122-124

o-toluic acid 103-105

m-toluic acid 108-110

p-toluidine 41-46

NH2

O2N

NH2

H3C

OHCO

OH

CH3CO

OH

CO

OHH3C

C C

H

H

O

OH

O

OH