Synthesis of Acetanilide
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. Introduction: 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 the solvent because of its solubility. The calculated percent yield was 96%. Procedures: Acetic anhydride (1mL, 10. 8) was added in several small portions along with 6 mL of deionized water to (0. 1 g, 1. 08 mmol) of aniline. The immediate formation of a solid precipitate was observed. After adding 20mL of deionized water to the mixture, it was then heated until all of the material was dissolved. A crystalline solid was obtained while cooling to room temperature, then filtered and washed with 2mL of chilled water. The material was allowed to dry for approximately 15 minutes and (0. 9795 g, 96%) of Acetanilide was recovered.
Moles of Aniline: 0. 7 g C6H5NH2 / X x 93. 3 g C6H5NH2 / 1 mole = 0. 7g / 93. 13 g x X 93. 13 g / 93. 13 g = X = . 0075 mol x 1000 = 7. 5 mmol Moles of acetic anhydride: 1. 08 g C4H6O3 / X x 102. 09 g / 1 mol = 1. 08 g / 102. 09 g x X 102. 09 g / 102. 09 g = X = 0. 0106 mol 1 mL x 1. 08 g / 1 mL = 1. 08 g
0. 7 g C6H5NH2 x 1 mol C6H5NH2/93. 13 g = 1 mol C8H9NO/ 1 mol C6H5NH2 x 135. 17 g C8H9NO/1 mol C8H9NO = 1. 016 g C8H9NO
The limiting reagent is Aniline. Mass of product: .9795 g Acetanilide x 1 mol/135. 17 g Acetanilide = 0. 0073 mol Percent Yield: Percent yield