Some notes on the manufacture of diethyl ether...
Recently I have started making ether again and I have discovered several things that greatly influence the yield, speed, and efficiancy of the
reaction.
The first thing is the reagents themselves. Use only Everclear or other 95% pure grain alcohol. Forget about drain cleaner, use only 98% ACS grade
sulfuric acid. By pre-drying the EtOH with molecular sieves prior to addition, dehydration capacity of the sulfuric acid is somewhat increased.
For a 500ml or so sized batch of ether, set your apparatus up for fractional distillation with the distillation flask in an oil bath, then add 250ml
of EtOH into a 1L RB 3 neck flask and then slowly add 250ml of H2SO4 with magnetic stirring. Then load the addition funnel up with 500ml of EtOH. The
heat generated from the addition will just about darn near put the contents of the flask at reaction temps saving you quite a bit of time waiting for
things to heat up.
A good fractionating column is not only essential, but it allows the use a normal addition funnel to drop the EtOH right on the surface of the liquid
in the reaction flask. Use a 300-400mm Vigreux and put a fan on it. That should keep most of the unreacted EtOH down in the flask where it belongs. As
a bonus, your ether will be purer and your yields will be increased.
Temperature control should be based not on textbook numbers of 130-140C but rather on the efficiancy of the reflux column your using. The real method
to knowing how much heat you should be using is in your sense of touch. The top of the fractionating column should feel a little warm, and the bottom
of the column should feel sorta like a heating pad on high towards the end of the alcohol addition. Funny thing though is when the alcohol has all
been added, the reaction flask is still producing ether and the column temp at the bottom drops. If your brave enough, you can actually touch the top
part of the flask for a few seconds without getting burnt. For my particular setup, running the reaction at around 120-125C seems to work very well.
The addition of the EtOH should be about the same rate at which it distills over. If you add it too quickly you will notice the bottom of your column
temp going up. It should take about 5-6 hours to run 500ml of ether from setup till the time you kill the heat to your hot plate.
Cooling can't be stressed enough... don't even think of using a liebig condenser for this. Use only a double surface or coil type condenser,
preferably at least 300mm long. Use a 1L flask submerged in a cooler filled with an ice/water bath as close the top of the joint as reasonable. Use a
cooler and ice/water for your condenser as well. Expect to go thru about 10-12 kg of ice over the course of a run.
So what about yields? Last run I collected approx 525ml of distillate from 750ml of PGA over the course of about 5 hours. I won't know exactly what
the actual molar conversion rate is until I get it processed further, but I'm hoping it will be over 80%.
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
