Synthesis of Benzocaine

 

Aim: To prepare  and submit Benzocaine from p-amino benzoic acid.

Chemicals Required: 

• PABA
• Ethanol
• Conc H₂SO₄
• Dry Na₂CO₃ solution.

Principle: Aromatic esters are prepared by esterification of aromatic acids with alcohol in the presence of an Conc H₂SO₄ or dry HCl which fastens the reaction. Benzocaine is an ester which was prepared by esterification of PABA with ethanol in presence of HCl.

 

Procedure: Place 80ml of absolute ethanol in a 250-ml two-necked flask equipped with double surface reflux condenser and a gas inlet tube. Pass dry hydrogen chloride through the alcohol until saturated. the increase in weight is about 20gm, remove the gas inlet tube, introduce 12gm of p-aminobenzoic acid and heat the mixture under reflux for 2 hours. upon cooling, the reaction mixture sets to a solid mass of the hydrochloride of ethyl p-aminobenzoate. It is better, however, to pour the hot solution into 30ml of water (no hydrochloride separates) and add solid sodium carbonate carefully to the clear solution until it is neutral to litmus. Filter off the precipitated ester at the pump and dry in the air.

Calculation: 

Molecular Weight of  p-amino benzoic acid =137g/mole

molecular weight of Benzocaine =165g/mole

137gm of p-amino benzoic acid=165gm of benzocaine 

3.4gm of p-amino benzoic acid =X gm of benzocaine.

% yield = (Practical yield /Theoritical yield)X100

 

Report: Benzocaine was prepared and submitted in the laboratory and its percentage yields was found to be ___%