Mixture of benzoic acid, anthracene, and p-nitroaniline

Extractions

COH

O

NH2

NO2

Mixture

Density of CH2Cl2 is 1.33 g/mL

CH2Cl2

H2O

Methylene Chloride and Water

If we dissolve NaCl in this mixture which phase has the highest salt concentration?

Salts concentrate in the water layer

Add Salt

If we dissolve benzoic acid in this mixture in which phase would it concentrate?

Neutral organic compounds concentrate in the organic phase

Salts

Add Benzoic Acid

Salts in water phase

Neutral organic compounds in the organic phase

Water

CH2Cl2

Phases

COOH + Na OH COO Na

Benzoic Acid Sodium Benzoate

Treatment of benzoic acid with sodium hydroxide converts it into the salt, sodium benzoate.

Sodium Benzoate

COOH + Na OH COO Na

Salts in Water Phase

NH3 + HCl NH4+ Cl-

Base Acid Salt

Ammonia and Acid

NH2O2N + HCl NH3O2N Cl

Aniline and Acid

Use separatory funnel for separating liquid phases.

Separatory Funnel

Hold stopper and stopcock

Shake to be sure phases equilibrate

Vent frequentlyVent frequently

benzoic Acid

p-nitroaniline

anthracene

HCl CH2Cl2

NH3O2N ClBenzoic acid

Anthracene

Extract with HCl

benzoic Acid

anthracene

NaOH CH2Cl2

COO Na anthracene

Extract with NaOH

NH3O2N Cl COO Na

NH2O2N

NaOH

COOH

Filter wash dry weigh

HCl

Filter wash dry weigh

Dry filter evaporate weigh

Extraction Summary

Addition of acid to the sodium benzoate solution causes benzoic acid to precipitate.

Precipitate Benzoic Acid

The benzoic acid is filtered, washed, and dried.

Purify Benzoic Acid

Weigh the benzoic acid and measure its melting point.

Weight, m.p.

NH2O2NNH3O2N ClNaOH

Cool to complete precipitation

Precipitate p-Nitroaniline

Dry the methylene chloride solution of anthracene with a small amount of sodium sulfate.

Dry Methylene Chloride

Remove the drying agent by filtration through a fluted filter paper.

Filter

Evaporate the methylene chloride on a steam bath.

Use an inverted funnel connected to the vacuum line to collect the vapor.

Remove Methylene Chloride

Put your samples in labeled vials and give them to your TA.

Weigh your products and measure their melting points.

10 g t-butyl alcohol100 mL ether100 mL water

Partition Coefficients

2.2 = x g / 200 mL

( 10 - x)g /100 mL

x = 8.1 grams

10 grams t-butyl alcohol

Extract once with 200 mL or twice with 100 mL?

Which is better?

Extract once with 200 mL yields 6.7 grams

Extract once with 100 mL yields 5.0 grams

Second extraction with 100 mL yields 2.5 grams

Total 2 extractions with 100 mL = 7.5 grams

If K = 1.0, a = 10 grams, S2 = 100 mL

Grams extracted vs. number of extractions