April 9, 2013
Organic Chemistry Lab 1; Professor J. Hutchison
Recrystallization is a common method of purifying organic substances through the differences in solubility at different temperature. In this experiment, acetanilide was produced by acetylation of aniline with acetic anhydride. The crude acetanilide was dissolved in a solvent in a heated water bath. The solution was cooled slowly in an ice bath as crystals form out. As the compound crystallizes from the solution, the limiting reagent Aniline and the percent yield of 96% was obtained.
This experiment involves four functional groups common in organic chemistry. The substrate (reactants) which are Aniline and Acetic anhydride are both liquids and one of the products is solid (Acetanilide). The reaction of aniline with acetic anhydride is a transformation in which products acetanilide and acetic acid are obtained. A solid product (Acetanilide) is obtained so that it may be recrystallized and a melting point determined. The Reaction:
Aniline (C6H5NH2) + acetic anhydride (C4H6O3) Acetanilide (C8H9NO) + acetic acid (C2H4O2) Results and Discussion:
Amines can be treated (Acylated, adding a Carbonyl and losing a proton) using Acetic Anhydride as a source of an “Acyl” group to form an Amide. The Synthesis of Acetanilide (an Amide) through a Nucleophilic Acyl Substitution (addition / elimination) reaction between Aniline (an Amine) is acting as the Nucleophile and an Acyl group from Acetic Anhydride acting as the Electrophile. The Mechanism:
The desired product is isolated from its impurities by differences in solubility. Soluble impurities remain in the cold solvent after recrystallization. The desired product should be as soluble as possible in hot solvent and as insoluble as possible in cold solvent. The selection of solvent is therefore critical to the successful recrystallization which in this experiment, water was used as...