Preparation of Benzocaine
Benzocaine is the ethyl ester of p-aminobenzoic acid (PABA). It can be prepared from PABA and ethanol by Fischer esterification or via the reduction of ethyl p-nitrobenzoate. Benzocaine is sparingly soluble in water; it is more soluble in dilute acids and very soluble in ethanol, chloroform, and ethyl ether. The melting point of benzocaine is 88–
90 °C and the boiling point is about 310 °C. The density of benzocaine is 1.17 g/cm3.
Structure:
Synthesis: Benzocaine can be prepared by esterification using 4-aminobenzoic acid and ethanol. It can also be prepared by reduction of ethyl 4-nitrobenzoate to the amine. In industrial practice, the reducing agent is usually iron and water in the presence of a little acid.
Guide Questions:
1. What is Fischer Esterification Mechanism?
2. Observed that a solid precipitate is formed upon addition sulphuric acid. What would this solid be?
3. Write an equation which accounts for the solubility of benzoic acid in aqueous base.
4. Write out the structures of the following:
A. Carboxylic acid
B. Acyl halide
C. Acid anhydride
D. Ester
E. Amide
5. What is the mechanism of action of Benzocaine? Give its side effects.
