Title

Extraction with Acid and Alkaline

Objective

1. To investigate the separation of organic compounds by using acid or alkaline2. To determine the product extracted of its purity.

Introduction

Acid-base extraction is a type of procedure that uses sequential liquid-liquid extractions to purify acids and bases from mixtures based on their chemical properties.Acid-base extraction is routinely performed during the work-up after chemical syntheses and for the isolation of compounds and natural products like alkaloids from crude extracts. This product is free of neutral and acidic or basic impurities. It is not possible to separate chemically similar acids or bases using this simple method.

Most reactions of organic compounds require extraction at some stage of product purification. Extraction was classified as one of the oldest chemical operations, and it is a widely employed method of separating organic compounds from mixtures. Normally the purest separations of organic compounds can be effected by the use of acid and alkaline solutions which convert the compound to be extracted to a water soluble, ether insoluble salt. With this, one or more extractions are performed during the isolation of the products from practically every organic chemical reaction. In its simplest form, extraction results from the unequal distribution of a solute between two immiscible solvents.

Thus,a widely employed method of separation of organic compounds from mixture is through the use of a solvent-solvent extraction.In its simplest form, the extraction results from unequal distribution of a solute between two immiscible solvents.When choosing a solvent system,some general rules must be adhered to.This includes:

1. Solvent must be immiscible

2. The solvent must have favorable distribution coefficient for components to be separated

3. The solvent must not react chemically with components of the mixture

4. Solvents must be readily removed from solute following extraction

Most of the organic acids and bases can be separated from each other or from neutral compound by extraction using aqueous solutions of differing pH.Most organic acids are

insoluble or only slightly soluble in water,but this compounds are highly soluble in dilute aqueous sodium hydroxide because organic acid reacts with the base according to this equation

RCO2H + NaOH RCO2 - Na+ (water soluble salt) + H2O

Therefore, the acid can be selectively removed from a mixture by means of dissolving the mixture in an organic solvent like dichloromethane and then extracting the solution using dilute NaOH. The recovered organic acid can then be extracted from the aqueous solution by acidification which causes the mixture to precipitate,and the mixture is filtered.

RCO2- Na+ + HCl RCO2H (s) + NaCl

Organic bases that are insoluble in water can be separated by extraction by using hydrochloric acid. Dilute hydrochloric acid is often employed in the extraction of basic substances from a mixture and also in the removal of basic impurities. For example, most amines are insoluble in water, but are soluble in organic solvents like ether. Amines can be separated from non-amine compounds by converting them to their conjugate acids by the addition of HCl.

Procedure