Sciencemadness Discussion Board

drying ether

soma - 31-7-2010 at 05:51

Having done some searching I haven't found anything about drying (ethyl) ether by distilling from concentrated sulfuric acid.

Would there be a problem doing this?

If not, I was wondering how much sulfuric would be used? Also, would it remove peroxides?


entropy51 - 31-7-2010 at 06:55

Soma, there are multiple threads on drying ether. The subject has been beaten practically to death and many good methods have been suggested. Sulfuric is not one of them as best I can remember.

Check out the existing threads if you haven't already.

soma - 31-7-2010 at 12:28

I have checked out the threads and sulfuric wasn't a method I saw mentioned - but I don't know why not - it would seem to be a simple method. I was wondering if it would also remove peroxides.

smuv - 1-8-2010 at 10:15

Sulfuric acid cannot be used for drying ether because it reacts with it.

Sulfuric acid, not only has a high enough pKa to protonate ether, making the etherate (HCl can do this too) and the bisulfate ion, but it is also a strong enough nucleophile to attack the etherate causing cleavage to ethyl hydrogen sulfate and ethanol (-Cl is not a strong enough nucleophile to do this under normal conditions). The ethyl hydrogen sulfate and ethanol can go on to form various products in the presence of H2SO4 (water being one of them).

This is why ether is stable to some strong acids which are poor nucleophiles (actually HCl is the only one that comes to mind) but not stable to others which are good nucleophiles.

If you were to take a mixture of ether and H2SO4 and distill it, I would expect the formation of a lot of ethylene with very little ether distilling over, whatever did carry over would probably contain quite some ethanol and maybe water. Also, H2SO4 cannot simply be shaken with either and then separated from it in a sep funnel, as Ether is miscible with conc. H2SO4 (due to formation of the etherate).

transformer - 1-8-2010 at 16:40

Passibg the ether to a column with alumina will removed the peroxides and if your ether is not soaking wet mol sieves are a most excellent way to dry it.

rrkss - 2-8-2010 at 03:57

I've dried ether to grignard grade by first treating it with acidified FeSO4 to destroy peroxides and then, doing an initial dry on anhydrous CaCl2. I distill it from the CaCl2 and dry it over either type 3A or 4A molecular sieves overnight and distill from that using oven dried glassware.

I've run grignards with ether using this method multiple times with no problem.

Ozone - 2-8-2010 at 07:07

Distill from continuous reflux over Na-ketyl (benzophenone). Good for THF, too.

rrkss - 2-8-2010 at 08:36

Quote: Originally posted by Ozone  
Distill from continuous reflux over Na-ketyl (benzophenone). Good for THF, too.

I think if he is asking this he won't have the equipment to setup an O2/Moisture free still to do this though that is standard procedure in my university's graduate labs.

Methyl.Magic - 2-8-2010 at 14:33

Et2O can be checked by adding a KI crystal and few AcOH drops. If the Et2O is still colorless it's peroxide-free.

Wet Et2O can be dried over Na2SO4 (cheap),then distilled from CaO to get anhydrous Et2O. Then conserv it over molecular sieve. Works well for Grignard , BuLi and LiAlH4 but it can still fizzes with this latter when you add the first portion.

Melgar - 5-8-2010 at 18:23

If the goal is drying ether for a Grignard reaction, best to use sodium hydroxide as your drying agent. If you're getting it from starter fluid, which I'm assuming you are because that's the easiest source, then not only do you have to remove water, but CO2 as well. CO2 is usually used as the propellant in starter fluid, so this is quite important. Calcium oxide should work theoretically, but I think sodium hydroxide is easier to get. Drying ether for about a week using sodium hydroxide will make it suitable for a Grignard reaction.

mario840 - 6-8-2010 at 00:16

this is simple .... you take 1 l ether and add 120 CaCl2 and shake , leave for couple days , shake every day , filter and add thin sodium metal , if evolution of hydrogen will stop you got anhydrous ether good for grignards reaction but you may destill if above sodium and protect with drying tube CaCl2 ...that's all

Oxydro - 6-8-2010 at 17:11

Mario840, to consider anything with metallic sodium 'simple' disregards the resources (or rather, lack of) that most of us have. Sodium is definitely not OTC, courtesy of both litigation and Birch.

mario840 - 6-8-2010 at 23:07

sorry for me is OTC cheap like a beer and on this site is illustrated how to make sodium metal ... plutonium-239 is OTC

mario840 - 6-8-2010 at 23:08

it should be: is NOT OTC :) for plutonium

ether peroxides

soma - 8-8-2010 at 01:38

I'm trying to understand the mechanism of peroxide formation with ether. I assume that the ethyl groups donate electrons and make the oxygen basic? Therefore, acids might prevent peroxide formation?

Thanks to all who replied to my other question about ether drying.

Lambda-Eyde - 8-8-2010 at 01:51

chemrox - 8-8-2010 at 21:47

Contrary to common undergraduate beliefs fairly wet ether will still work in the Grignard. The main precaution I've found important is making a good blanket of ether vapor over the Mg turnings before starting the reaction. In other words I start the reflux and then run in the first, more concentrated aliquot of halocarbon. Br-C's seem the easiest. Any oxide on the Mg is problem. If the turnings have got any grey edges use them for something else like fireworks or making MgCl2.