In ester preparation, describe the purpose of :reflux, distillation, isolation, and the function of Na2CO3.?

Question

Hey everyone! =)

We did a chemistry prac today, and this reflux-distillation stuff has always blown over my head. i would greatly appreciate it if you'd give just some basic answers to those questions mentioned above.

Cheers again!

Answer 1

The general eq for esterification is:

RCOOH + R'OH <---> RCOOR' + H2O

The reaction is run at reflux temp because the higher the temp, the faster it goes. The refluxing vapors are usually condensed into a Dean-Stark trap where the water formed is continuously removed, while the organics are returned to the reaction vessel...this drives the equilibrium reaction to the right.

When the esterification is complete, Na2CO3 is added to neutralize any unreacted acid and make it water-soluble.  This is then washed several times with water to remove the RCOONa and (hopefully) any unreacted R'OH...the aq layer being drawn off after each wash.

The organic is then dried over eg Drierite. If the R'OH had been removed by being soluble in the water washes, what's left is your ester product. If R'OH remains with the ester, they are separated via fractional distillation

This is the general procedure...but there are many rammifications, selected to deal with specific reaction pairs.

Hope that's clear :-))

Answer 2

It's difficult to answer your question exactly since you didn't give us much information about what the reaction involved, but my guess is that you did a Fischer Esterification. In this reaction a carboxylic acid (RCOOH) is allowed to react with an alcohol, R'OH, in the presence of an acid catalyst, commonly H2SO4. These 3 components are usually refluxed for the reaction to go to completion. The reaction workup may involve an extraction with Na2CO3 solution. This is to neutralize the remaining acid from the reaction as well as to remove any unreacted starting material (RCOOH). Does this sound like what you where looking for?