Subject: Re: dehydration of ethanol to ether
From: Frank Harrison <firstname.lastname@example.org>
Date: Jan 16 1997
email@example.com (Anonymous) wrote:
> The Kirk-Othmer Encyclopedia says (under ethyl ether):
> "concentrated sulfuric acid and 95% ethyl alcohol are
> charged...in the ratio of three parts acid to one part
> alcohol...A supply of alcohol vapor is continuously fed into the
> acid-alcohol mixture at a rate to maintain ca 127 degrees C."
> But Morrison and Boyd say: "ethyl ether is prepared by heating a
> mixture of ethyl alcohol and concentrated sulfuric acid to 140
> degrees, alcohol being continuously added to keep it in excess."
> 1. It would seem like Kirk-Othmer is saying that the sulfuric
> should be in excess but Morrison and Boyd say the ethanol should
> be. Anyone know which is correct and what proportions are best?
> 2. What concentrations of sulfuric would be best? Is 95% ok?
> Would 98% be better? What is the least % that would be effective?
> 3. Anyone know a reference for this preparation? (Like an Org Syn
> method, or some lab manual that might give a simple laboratory
> prep?) (I couldn't find it listed in Org Syn).
I don't know of a reference right off hand, but there isn't anything
complicated or mysterious about making ether this way, just tedious.
Rig a flask with heat, stirring, an efficient condensor, and a way
of introducing the ethanol below the surface of the acid. I used a
500 ml flask about 1/3 full with concentrated sulfuric which I
obtained by cooking the water out of battery acid. 190 proof grain
alcohol is suitable for the ethanol. Start the stirring, bring the
acid up to 140 C, and let the alcohol start running into the acid
very slowly. What distills out is a mixture of water, ethanol, and
ethyl ether in about equal proportions by volume. This mixture is
then separated by distillation. If you heat the acid to 180 C you get
a lot of ethylene gas along with everything else. When you are ready
to shut the process down, stop the alcohol flow and keep the temperature
at 140 C until no more liquid distills over. You can use the same batch
of sulfuric for a long time. Eventually it will gum up with tar, but
this takes several weeks of continuous operation. After separation,
and before drying, the ether is shaken with a 10% volume of 5%
ferrous sulfate solution to remove peroxides. Anhydrous copper
sulfate can be used for drying. Ferrous sulfate and copper sulfate are
available at the feed and seed or hardware store as "copperas" and
the usual disclaimers apply,
Store the ether in a dark bottle with a piece of clean copper wire to
prevent the formation of peroxids.