Question

Why is absolute ethanol rather than 95% ethanol used in an experiment for the preparation of Benzocaine?

Answer 1

Benzocaine is not very soluble in water.

Explanation:

Benzocaine is soluble in Ethanol, Methanol and Diethyl Ether. But it is not very soluble in water. Having water in the solution would decrease the solubility and would create a lot of hassle later.

Answer 2

Using 95 % ethanol would reduce the yield of benzocaine.

Explanation:

Benzocaine is prepared by the Fischer esterification of 4-aminobenzoic acid with ethanol.

`underbrace("H"_2"NC"_6"H"_4"COOH")_color(red)("4-aminobenzoic acid") + underbrace("HOCH"_2"CH"_3)_color(red)("ethanol") stackrelcolor(blue)("H"_2"SO"_4)(color(white)(l)⇌) color(white)(l)underbrace("H"_2"NC"_6"H"_4"COOCH"_2"CH"_3)_color(red)("benzocaine") + "H"_2"O"`

The reaction is a chemical equilibrium.

Per Le Châtelier's Principle, any water in the mixture will shift the position of equilibrium to the left.

Using 95 % ethanol-5 % water will decrease the yield of benzocaine.