Sooo... why does water matter with ethyl esters so much?

!!!!?

I too have been wondering this. Since I have been interested in the Master Formula from OCH and it keeps everything in suspension anyway, why can that formula be used (with KOH), whether or not it is 99%+ proof/pure or whether it has 5% water in it already?

Girl mark, on a side note. I had pm'd you about this as well as some other questions. Did you get my email/pm or not?

Cheers, Pete'

I'm guessing that it might have to do with methonal's propensity to attach to water which then doesn't allow it to react the oil. I speculate that becasue when it is washed, the methonal is pulled from the mixture. This is all speculation because i don't understand all of the chemistry invovled.

Kind of an old thread, but in case anybody's still interested....

OH- + CH3OH <-> H2O + CH3O-

ie, hydroxide ion (from NaOH or KOH) plus methanol is in equilibrium with a bit of water and a bit of methoxide ion. There's actually very little of the right side in what we call "methoxide". If you add water to the mix, you push the equilibrium even further to the left -- less methoxide ion. How much methoxide ion you get in solution is the result of the "competition" between water and methanol as to which behaves like the stronger acid.

Ethanol is less acidic than methanol (ie, less "willing" to give up a hydrogen ion to become an ethoxide ion), which is why you have to use so much more KOH for ethanol than for methanol. And it also means that any added water in the mix pushes the equilibrium even MORE strongly to the left than would be the case with methanol, and you end up with not enough ethoxide to run the transesterification.

I wonder how water-absorbent molecular sieve would stand up to the ethanol/ethoxide/hydroxide environment. Potentially, with a little extra care and some initial up-front expense, you could probably quite nicely produce a sort of "concentrated ethoxide" equilibrium by removing a great deal of the competition acid H2O.

Also, do you think this might be why I seemed to have a success when I "overloaded" my water-containing ethanol with quite a bit of excess NaOH?

I'm not sure if the sieve would like the alkalinity -- I'll give it a try. You could always reflux vapors up through a column of sieve if neccesary -- lotta work!

Another way to get anhydrous ethoxide is to start with sodium metal rather than NaOH

Excess alkali will compensate for a bit of water, but not much. How wet was your ethanol? You know KOH goes into solution much quicker than NaOH.....