[addle]

I'm new here. I'm trying to make some sense in a rxn I carried out earlier. It was a basic Fischer Esterification, namely p-Aminobenozic acid to benzocaine. We ended up using excess ethanol which had to be 95%. I'm thinking the excess is to drive the overall reaction to the right but I'm not sure why it had to be 95% ethanol. Could it be something about water?

[Mitch]

Probably because 100% ethanol would require a various assortment of permits.

[Yggdrasil]

What base did you use?  If you used NaOH or even KOH, the 95% ethanol dissolves the base better than absolute ethanol, which will make the reaction proceed faster.

[addle]

Thanks for the help I think I've figured it out. I used H2SO4...acid catalyzed esterification. It's cause the water would drive the rxn to the left. Either taking out the product or excess reagents drive it to the right. Excess ETOH was used and 95% was to minimize H2O.

[AWK]

What base did you use?  If you used NaOH or even KOH, the 95% ethanol dissolves the base better than absolute ethanol, which will make the reaction proceed faster.

Fisher esterification use acid catalyst.  Sodium carbonate is used for its neutralization at the end of synthesis.

[Yggdrasil]

My bad.  I read the word basic in the first post and though he was taking about a base-catalyzed esterification.  One reason why chemists should only use the word basic when they mean alkaline and not when they mean simple!

[edit: on second thought, you wouldn't want water around in a base-catalyzed esterification, so I guess you wouldn't want to use 95% EtOH for a base-cat esterification in the first place.  So yeah, I'm just completely wrong.]

[AWK]

For Fisher esterification reaction, water is unnecessary, but it is much easier use 95 % ethanol than absolute one (Mitch pointed out this problem).
Esterification is an equilibrium reaction that stop at about 60 % yield when we use 1 mole of an acid and 1 mole of an alcohol and water is also a product of this reaction.
To obtain a better yield we use an excess of a cheaper reagent, a greater excess when it contains minute amounts of water

[movies]

You can also remove the water from the equilibrium using a Dean-Stark trap.  I've done this many times and you can get quantitative yields with only 1.5 equivalents of alcohol.  It doesn't work so well with low boiling alcohols like MeOH and EtOH, but anything bigger ought to work.