# Why do esters have to be distilled during purification?

I am currently designing a lab experiment for a school project in which I am to determine the effect of catalyst concentration ($\ce{H2SO4}$) on the rate of reaction between methanoic (formic) acid and ethanol to create ethyl methanoate. I plan to do this by varying the concentration of sulfuric acid at the beginning, and comparing the end yield of ester. $$\ce{HCOOH +C2H5OH <=>[varied concentrations of H2SO4] HCOOC2H5 + H2O}$$

I am aware that distillation is a crucial step following reflux in pretty much every esterification for purification, but why? Can't one simply wash the crude ester with deionised water to catch all remaining ethanol, use CaCO$_3$ to neutralise the acids, and filter off via a separatory funnel?

I am asking this because my school project has a set timeframe for all experiments of officially 8 hours over two weeks, in which it is recommended that I conduct at least '5 measurements at 5 intervals'. I know I won't reach this, even if I reflux each of my esters for 10 minutes because of the distillation.

• Hello and welcome to Chemistry.SE. If you have any questions about the site you can visit the help center. Also, best of luck with your project; it looks like you've been provided with a good challenge! – airhuff Mar 15 '17 at 0:40
• Thanks :) The esterification with these specific reagents I decided on myself, as I thought the typical acetic acid + ethanol one was quite an overdone one. The advantage of my one is that if I were to distill the crude ester, there is a ~24C difference in boiling points between ester and alcohol, whereas the aforementioned 'typical' one only has a 1-2C difference. – tim9800 Mar 15 '17 at 1:40
• For future reference I like to add the section Laboratory Experiment in the Journal of Chemical Education as a quite instructive reference. The coverage of reactions is wide, already tested in classes, with protocols (details in the SI) including statements like if the experiment is completed in 4h or more. (One recent example of esterification, but deviating from your aim, is pubs.acs.org/doi/abs/10.1021/ed400721p) – Buttonwood Mar 15 '17 at 15:13
• Isn't it more expedient to measure the rate of reaction to the equilibrium position at, say, three acid concentrations? Then you don't have to distil. – Beerhunter Mar 16 '17 at 7:29
• I talked to my chemistry teacher today, and apparently the school doesn't have any formic acid, so I have to switch to the ol' ethanol + acetic acid <-> ethyl acetate, which is a shame... :(. – tim9800 Mar 17 '17 at 11:03