Natural Science Forum / Chemistry / Organic Synthesis / May 2005

I am familiar with benzene azeotropic distillation. The trouble is that
it takes a good (=large and expensive) fractional distillation column,
plus lot of time, and the product is not perfectly dry and it contains
benzene. They used this method in industry long time ago but it was not
the nicest way of doing it in the lab.

The traditional drying method was to pre-dry ethanol with CaO, then
dissolve Na, add diethyl phtalate, boil for a while and distil.

Alternative was to dissolve Mg ribbon, (like with MeOH), boil for a
while and distill. The trouble with Mg method is that you need to have
less than 1% of water already - otherwise Mg fails to dissolve. And you
may need to add a soluble mercury salt like HgCl2 to amalgamate Mg to
get the reaction started.

So all and all, I would recommend buying anhydrous EtOH - it is easier
and cheaper.

molecular sieves or anhydrous CuSO4 won't do it?

Drying over 4 angstrom molecular sieves is the way to go.

If I were you, I'd dry the ethanol by refluxing it over magnesium
turnings for a few hours before distilling it.  You'd probably want to
pre-dry it with drierite or MgSO4 first, though.

Cheers,
Darren S. A. George, PhD, LRHSC

I would guess any ternary with those solvents would not be that useful.  The
traditional way (which works!) is to use benzene.  In fact you can go one
step futher and add sodium hydroxide and keep azeodrying and end up with
sodium ethoxide solution.  I used to work where they did exactly that, to
make tonnage quantities of malonic esters.

Actually the benzene/ethanol/water azeotrope is the most commonly used.  But
a much better technique is a to take 1 L of ethanol and add 25 g of
magnesium metal.  Reflux until the metal is consumed (add a few drops of
chloroform if it doesn't start to get cloudy).  It will take a good 24 h to
convert the metal to magnesium ethoxide.

Then just distill the ethanol off.  It will be very dry.

Dave

Peter Jason a ?crit dans le message ...

There should be no problem doing the esterification with
95% EtOH.  The fastest and most simple method to "dry" alcohol or produce
absolute alcohol is to run it through a column of corn meal.  Yes!! Corn
meal.
  However, since you asked the question I would think it is unlikely that
this esterification is something you could do successfully or safely.
    You might want to drop by an University  and ask about this at their
chemistry department.
JOL

Thank you.  The use of NaOH to produce the ethylate might be the way for us
to go because is involves only one equipment setup.

Thank you.  The use of NaOH to produce the ethylate might be the way for us
to go because is involves only one equipment setup.