Hippuric Acid Synthesis Lab Report

Introduction: This preparation illustatrates the benzoylation of amino acid by Schotten Baumann reaction, the hippuric acid is precipitated upon acidifying the reaction mixture.

Reaction:

Procedure: Dissolve 2.5g of glycine in 25 ml of 10 % NaOH contained in a conical flask. Add 5.4g (4.5 ml) of benzoyl chloride in two proportions to the solutions. Stopper the flask and shake vigorously after each addition until all the chlorine has reacted. Transfer the solution to a 100 ml beaker and rinse the conical flask with a little water. Place a few grams of crushed ice in the solution and add conc. HCl slowly with stirring until the mixture is acidic to congo red paper. Collect the resulting crystalline precipitate of hippuric acid or benzoyl

Then add nitrobenzene to it in installments of about 1 mL from the top of the condenser and shake the flask for mixing the reaction products. Due to exothermic nature of reaction the mixture becomes hot and acquires a deep brown colour.After the addition of all the nitrobenzene ,place the flask in a water bath and heat for about 15 minutes. At this stage a few drops of reaction mixture is cooled and poured in cold water and if the hard pale yellow solid separates then the heating is discontinued. The reaction mixture is cooled and the contents poured with vigorous stirring for about 300 mL water containing a few pieces of ice when m-Dinitrobenzene separates as a hard yellow solid. Filter it on a Buchner funnel with suction ,wash with water and dry by pressing between filter papers. Recrystallize it from rectified spirit when pale yellow crystals of m-Dinitrobenene are obtained.

Mechanism:

Reaction

In the second step is reduction of p-nitroacetanilide to p-nitroaniline .

Step I: Preparation of p-nitroacetanilide from acetanilide (Nitration)

Reaction:

Procedure: Place 8 g acetanilide in a 250 mL round bottom flask and add to it 8 mL glacial acetic acid and 16 mL conc.H2SO4.Cool the flask in an ice bath. Meanwhile mix 4 mL each of conc.HNO3 and Conc.H2SO4 in a test tube and cool the mixture. Add this nitrating mixture to the solution of acetanilide drop wise with stirring and keep the temperature below 10 0C. After the addition of nitrating mixture remove the flask from ice bath and allow to stand for 1 hour. Then transfer the reaction mixture in to 200 mL water containing a piece of crushed ice to get crude p-nitroacetanilide. Allow it to stand for 15 minutes ,filter on a Buchner funnel with suction ,wash with cold water and dry in an oven at 100 0C.o-nitroacetanilide is also formed together with p-isomer but being more soluble in water remains in the filtrate. Recrystallize a portion of crude product from rectified spirit when pale yellow crystals of pure p-nitroacetanilide are obtained.

Mechanism:

Reaction