Experiment # 2

Two- base extraction

• Flow Chart

• Recrystallization

• Distillation

• Chromatography

Extraction

Impure

compound

Isolation

Purification

Establishing

purity

• Melting point

• Boiling point

• Spectroscopy

What is extraction all about !• The technique, extraction is employed for the isolation of the desired

product from the reaction mixture

• The extraction procedure involves partitioning the reaction mixture

between two immiscible liquids , an organic solvent and water.

• The usual organic extracting solvents are dichloromethane ( CH2Cl2 ),

ether ( CH3CH2OCH2CH3 ), ethyl acetate (CH3COOCH2CH3 )

• Except dichlorormethane and chloroform, all other organic solventsocupy top layer

• To test which layer is which add a drop of water to the separatoryfunnel having two layers, if the water drop pass the top layer and goes tothe bottom layer then the bottom layer is aqueous layer.

Solubility rules• This separation technique makes use of three solubility rules

1. Organic compounds are soluble in organic solvents

(exceptions)

2. Ionic compounds (salts) are soluble in water but insoluble

in organic solvents.

3. Organic compounds containing greater than 4 carbons are

insoluble in water

Theory of extraction• The extraction involves partitioning of compounds between two immiscible

phases,Sx , the extracting phase, and So , the original phase

• The partitioning of compounds is due the difference in solubilities of a

substance in two immiscible solvents.

• The ratio of the solute distributed between the two phases will depend on

the relative solubilities of the solute in each phase.

• At a given temperature, the ratio of concentrations of a solute in the two

phases will always be constant, known as the distribution coefficient or the

partition coefficient, K, and is an equilibrium constant.

• The concentrations of solute in each solvent are approximated to the

solubilities of the solute in the pure solvent

K =[A] in So

[A] in Sx

=Solubility of A in So

Solubility of A in Sx

=grams of A in So

grams of A in SxX

ml of Sx

ml of So

Theory of extraction cont’dConsider a compound, A, which dissolves in ether to the extent of 12g/100 ml

and dissolves in water to the extent of 6 g/100ml

If a solution of 6g of A in 100 ml of water is shaken with 100 ml of ether then

From which x = 4.0 g of A in the ether layer

6 – x = 2.0 g left in the water layer

It is, however, more efficient to extract the 100 ml of aqueous solution twice

with 50 ml portions of ether rather than once with a 100 ml portion

From which x = 3.0 g of A in the ether layer

6 – x = 3.0 g left in the water layer

K =6 g/100 ml water

12 g/100 ml ether= 2

K =(6 - x g of A /100 ml water)

( x g of A/100 ml ether)= 2

K =(6 - x g of A /100 ml water)

( x g of A/50 ml ether)= 2

Theory of extraction cont’d

• If this 3.0 g/100ml of water is extracted once more with 50 ml of ether

we can calculate that 1.5 g will be in the ether layer, leaving 1.5 g in

the water layer.

• So two extractions with 50 ml portions of ether will extract total

3.0g + 1.5g = 4.5 g of A, while one extraction with a 100 ml portion

of ether removes only 4.0 g of A.

• Three extractions with 33 1∕3 ml portions of ether would extract

4.7 g.

• In general the fraction of solute A, FA , in original solvent after ‘n’

extractions is given by

Conclusion : Multiple extractions are better than one large one.

n

Types of extraction

Extraction

Simple extraction

Acid-Base extraction

Acid-Base extraction

Mechanism

Two-Base Extraction

Aim : The aim of the experiment is to separate a mixture of three organic compounds, benzoic acid, 2 – naphthol, and naphthalene.

Apparatus: Separatory funnel, ice water bath, apparatus

for vacuum filtration, Erlenmeyer flasks

Dissolution: Dissolve 1.5 g of the mixture by swirling it with 30 ml of diethyl ether in a 125 ml Erlenmeyer flask

Extraction:

1. The ether solution is transferred to a separatory funneland 20 ml of 1.25M (10%) aqueous sodium carbonateis added to it. Now swirl the unstoppered funnel until allfoaming has subsided. Then stopper the funnel and,holding both the stopcock and the stopper of the funneltightly, invert the funnel and immediately vent it byopening the stopcock. Finally, shake the funnel withfrequent venting until gas is no longer evolved.Separate the layers, transferring the aqueous layer to a125 ml Erlenmeyer flask labeled “ Bicarbonate Extract”

Extraction procedure cont’d

Extract the organic solution with a 20 ml of 2.5 M(10%) aq. sodium hydroxide, venting the funnelfrequently during the process. Transfer theaqueous layer to a 125 ml Erlenmeyer flasklabeled “Hydroxide Extract.” Transfer theorganic solution to a 50 ml Erlenmeyer flasklabeled “Neutral Compound” and containingtwo spatula-tips of anhydrous sodium sulfate.Loosely film the flask with paraffin film, and letit stand for at least 15 min with occasionalswirling.

Note : Shake gently to avoid emulsions. Emulsion is a suspension of one liquid as droplets in another

Precipitating and Drying : Cool the “Hydroxide Extract” in an ice-water bath. Carefully acidify this solution with 3M hydrochloric acid, so that the solution is distinctly acidic to pH paper. Upon acidification, a precipitate should form; cool the mixture for 10-15 min to complete the crystallization.

.

Extraction procedure cont’d

• Collect the precipitate by vacuum filtration using a Buchner or Hirsch funnel.

Wash the solid on the filter paper with a small portion of cold water. Transfer

the solid to a labeled watchglass, cover it with a piece of filter paper, and allow

the product to air-dry until the next laboratory period. After drying, transfer the

benzoic acid to a dry, tared vial.

• For the Bicarbonate extract follow the same procedure

• Separate the “Neutral Compound” from the drying agent by decantation into a

beaker. Keep it in the drawer until the next lab period so that the solvent is

evaporated. Scrape the contents of the beaker onto a piece of weighing paper

and then transfer it to a dry, tared vial.

Analysis : Determine the melting point of each crude product.

Safety

• Always point the stem of the separatory funnel away from others during

venting .

• Wear always safety goggles and gloves.

Disposal

• Dispose of the filter papers in solid waste container.

• Flush the acidic filtrates down the drain.

• Lab Report

This should cover

1. Introduction

2. Reaction and mechanisms

3. Table of reagents

4. Table of reactants

5. Procedure

6. Flow chart

7. Observations

8. Results

9. Conclusions and discussions

Due Friday, 02/04/2011.