Question

What is the role of abs. ethanol in Fischer Esterification to produce Benzocaine?

Answer 1

The absolute ethanol has three functions in the Fischer esterification to produce benzocaine.

Explanation:

The equation for the reaction is:

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

1. The ethanol serves as a reactant to form the ethyl ester.

2. The ethanol is probably an excess reactant, so it also serves as a solvent.

The most important reason for using absolute ethanol is that the Fischer esterification is an equilibrium reaction with a `K_"eq" ≈ 4`.

If you use ordinary 95 % ethanol as a reactant, the 5 % water will push the position of equilibrium somewhat to the left and decrease your yield.

The absolute alcohol contains no water, so the reaction will be able to go further to the right.

You won't have to use as large an excess of ethanol to get a good yield.