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

2 Answers
May 19, 2016

Benzocaine is not very soluble in water.


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.

Dec 24, 2016

Using 95 % ethanol would reduce the yield of benzocaine.


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.