Vernier Software & Technology

# Separation of Organic Compounds by Acid-Base Extraction Techniques

## Introduction

A commonly used method of separating a mixture of organic compounds is known as liquid-liquid extraction. Most reactions of organic compounds require extraction at some stage of product purification. In this experiment you will use extraction techniques to separate a mixture of an organic acid, a base, and a neutral compound.

Organic acids and bases can be separated from each other and from neutral compounds by extraction using aqueous solutions of different pH values. Most organic carboxylic acids are insoluble or slightly soluble in water, but these compounds are highly soluble in dilute aqueous sodium hydroxide because the acid is deprotonated by the base producing the sodium carboxylate salt.

${\text{RCO}}_{\text{2}}{\text{H(solv)}} + {\text{OH}}{^{\text{-}}}{\text{(aq)}} \to {\text{RCO}}{_{\text{2}}}{^{\text{-}}}{\text{(aq)}} + {\text{H}}{_{\text{2}}}{\text{O(aq)}}$

The carboxylic acid can be selectively isolated by dissolving the mixture in an organic solvent that is immiscible with water, and then extracting the solution with sodium hydroxide. The basic aqueous solution containing the carboxylate salt is acidified, causing the sodium carboxylate salt to convert back to the carboxylic acid, which is not water soluble. The acid will precipitate from the solution, as shown here.

${\text{RCO}}{_{\text{2}}}{^{\text{-}}}{\text{(aq)}} + {\text{H}}{^{\text{+}}}{\text{(aq)}} \to {\text{RCO}}_{\text{2}}{\text{H(s)}}$

Organic bases (e.g., amines) that are insoluble in water can be separated by extraction with hydrochloric acid. Addition of HCl to the amine produces the corresponding ammonium salt, which is soluble in water but not in organic solvents.

${\text{RNH}}_{\text{2}}{\text{(solv)}} + {\text{H}}{^{\text{+}}}{\text{(aq)}} \to {\text{RNH}}_{\text{3}}{^{\text{+}}}{\text{(aq)}}$

The amine can be recovered from the aqueous solution by treatment with a base, converting the ammonium salt back to the amine. The amine is not water-soluble and will precipitate, as shown here.

${\text{RNH}}_{\text{3}}{^{\text{+}}}{\text{(aq)}} + {\text{OH}}{^{\text{-}}}{\text{(aq)}} \to {\text{RNH}}_{\text{2}}{\text{(s)}} + {\text{H}}{_{\text{2}}}{\text{O(aq)}}$

Using your understanding of these properties, separation of a mixture containing a carboxylic acid, an amine, and a neutral compound can be carried out via sequential acid and base extractions. The precipitates will be collected and characterized by melting temperature analysis.

## Objectives

In this experiment, you will

• Separate a mixture containing benzoic acid, 3-nitroaniline, and naphthalene.
• Calculate the percent recovery of each component in the mixture.
• Measure the melting temperature of each isolated compound.

## Sensors and Equipment

This experiment features the following Vernier sensors and equipment.

### Additional Requirements

You may also need an interface and software for data collection. What do I need for data collection?

## Organic Chemistry with Vernier

See other experiments from the lab book.

 1 Determining Melting Temperature 2 Recrystallization 3 Determination of a Boiling Point 4 Identifying an Unknown Analgesic by Three Methods 5 Separation of Organic Compounds by Acid-Base Extraction Techniques 6 Understanding Polarimetry 7 Identification of Organic Unknowns Using Polarimetry 8 Investigating Gas Chromatography 9 Fractional Distillation of Esters 10 Understanding Intermolecular Forces Using a Gas Chromatograph: Enthalpy of Vaporization 11 Investigating Thermodynamic Relationships of Substituted Hydrocarbons 12 Extraction of Spinach Pigments and Analysis by Electronic Absorption Spectroscopy 13 SN1: Synthesis of t-butyl chloride 14 SN2: Synthesis of 1-bromobutane 15 Observing the Reaction Kinetics of Sucrose with Polarimetry 16 The Synthesis and Analysis of Aspirin 17 Isolation of R-(+)-Limonene from Oranges using Steam Distillation 18 Synthesizing Ethyl Acetate by Fisher Esterification 19 Synthesis of Dibenzalacetone by Aldol Condensation 20 The Diels-Alder Reaction of Anthracene with Maleic Anhydride 21 Friedel-Crafts Acylation of Ferrocene 22 Grignard Formation of Crystal Violet 23 Synthesis of Fluorescein 24 Synthesis of Methyl Orange and Its Application to Textiles 25 Analysis of Natural Products 26 Using a Gas Chromatograph: Identifying an Unknown Compound

### Experiment 5 from Organic Chemistry with Vernier Lab Book

#### Included in the Lab Book

Vernier lab books include word-processing files of the student instructions, essential teacher information, suggested answers, sample data and graphs, and more.