Sciencemadness Discussion Board

Yellow ether?

victornguyen - 10-3-2019 at 00:41

Recently synthesized some ether using ethanol and sulfuric per the article in pre pub. I then dried it over some NaOH for a few days. When I came back to it , it had this yellow cloudiness that I didn't recognize. There was not much water in the ether since none separated out with the hydroxide, but I'm thinking the yellow coloring was produced by the formation of sodium ethoxide from residual ethanol reacting with the lye. Do you think that could be the case, or did something else cause the yellow coloring? I also had a small piece of copper wire in the bottle for prevention peroxide formation, which I didn't not remove before adding the NaOH. I redistilled and it is perfectly clear now.

unionised - 10-3-2019 at 01:11

At a guess, traces of acetaldehyde (from oxidation of the ethanol) which polymerises in alkaline conditions to form a yellow/ brown resin.

fusso - 10-3-2019 at 06:56

Can H2SO4 oxidize EtOH in such conditions?

Felab - 10-3-2019 at 08:41

This happened to me as well. It might be sodium ethyl sulphate, acetaldehyde or maybe something else. And yes acetaldehyde is formed as a side product in this synth by the oxidation of ethanol with sulphuric acid.

I doubt it is sodium ethoxide because the amount that would be generated should be prety minimum and it should also be colourless.

BTW sodium hydroxide destroys peroxides by itself so you don't need to ad the copper as long as you have it over the NaOH

unionised - 10-3-2019 at 13:46

Acetaldehyde can be formed from peroxides I think.
Air will certainly oxidise ethanol, so, unless you carefully distilled that before you did the ether synth, there will be acetaldehyde.
Of course, there could be other stuff too.
The last ethanol I bought had MEK as a denaturant and that would do a fine job of going yellow in strongly alkaline conditions

nimgoldman - 14-5-2019 at 21:27

Yes this happened to me. I store ether over KOH and whiff a bit of argon in the bottle to make an inert pillow. It still yellowed but the peroxide test came out negative. It was likely the ethanol (common impurity in ether) reacted with the hydroxide. Distilling the stuff removed discoloration.

CobaltChloride - 15-5-2019 at 12:05

This happened as well with ether distilled from starter fluid in my case. In order to ensure purity, I just followed the procedure in this video .