February 23, 2024

Benzoic acid from benzamide synthesis: Pharmaceutical Chemistry Practical

Benzoic acid from benzamide synthesis: Pharmaceutical Chemistry Practical

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To synthesize Benzoic acid from benzamide and to find out its percentage practical yield and melting point



Round bottom flask (250 ml), Reflux condenser, Beaker (250 ml) Beaker (500 ml), Buchner’s flask and funnel; Vacuum pump, 25 ml measuring cylinder.


Benzamide, Sodium hydroxide (10%) solution Hydrochloric acid



It is a process in which new product with unique structural formula, molecular weight, and melting point is produced with chemical reaction


Purification is the process of removing impurities from the product. Purification of product includes application of recrystallization, washing and drying the product in oven at a definite temperature for a desired period of time. Assembly of Buchner’s funnel and flask:


Recrystallization is the process in which the compound is dissolved in selected solvent with heating and then cooled slowly to a saturated solution from which pure compound is crystallised out.

Yield: It is the quantity of the product obtained in the synthesis. They are: Theoretical yield, Practical yield and Percentage yield.

Theoretical Yield is the weight of the product that one should get based on the stoichiometric quantities of the reagents, assuming100% completion of the reaction.

Practical Yield is the weight of the product actually obtained after purification of the product.

Percentage yield is calculated from the formula given below:

%Yield =practical yield/Theoretical ×100


Hydrolysis is a process of breaking of a bond with addition of water molecule.

Functional derivatives of carboxylic acid like amides or esters can be hydrolysed in acidic oralkaline media to yield the carboxylic acid (in the form of salt) and ammonia/ amine or alcohol/phenol. Hydrolysis of functional derivative of carboxylic acid is an example of nucleophilic substitution reaction.


1. Place 5g of Benzamide and 75ml of sodium hydroxide solution in 250 ml round bottom flask fitted with a reflux condenser.

2. Add few pieces of unglazed porcelain into the reaction mixture.

3. Boilthemixturegentlyfor30minutes.

4. Cool the solution in ice-water mixture and add slowly cone. Hydrochloric acid till the mixture is strongly acidic. A white product separates out immediately.

5. Cool the mixture in ice water for about 10minutes and collect the product at Buchner funnel at pump.

6.Wash with cold water and drain.

Recrystallize by dissolving the product in minimum quantity of boiling water, filter the hot solution if necessary.

7. Allow to cool to room temperature. Practically colourless crystals of benzoic acid are obtained.

8. Collect the product at pump and dry.

9. Weigh accurately the yield obtained and determine melting point of the same.


1. Amount of Benzamide taken for synthesis = 5g

2. Practical yield of there crystallised product =

 3. Melting point of the product =


1. Theoretical Yield of the product. From the reaction, 121g of benzamide gives 122g of benzoic acid

5g of benzamide will give 5.04g of benzoicacid

2. Percentage Practical Yield

%yield= practical yield/Theoretical yield×100


1. Percentage yield of Benzoicacid_________%

2. Melting point of Benzoic acid is__________

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