Making acetaldehyde or formaldehyde

[Sonny Jim]

I was thinking, that if you set up some distillation kit, and where the condenser is normally a piece of copper pipe could be hooked up. This pipe could be heated to around 300*C over an area, and then cooled towards the other end.

You would evaporate your alcohol and then the vapor would pass over the hot copper, and I was just reading that it is possible to oxidise alcohols to aldehydes this way. Im concerned that this oxidation could go too far though, perhaps to methanoic or ethanoic acid.

What do you think? Could the oxidaton of the aldehyde be prevented, or wouldn't it even happen? Sorry if this sounds daft but I have it stuck in my head and am interested to see if it could work.

[megalomania]

Sure it can work, and we have talked about this before... check out:

http://roguesci.org/theforum/showthread.php?s=&threadid=1857&highlight=copper+formaldehyde
http://roguesci.org/theforum/showthread.php?s=&threadid=2089&highlight=copper+formaldehyde

[Mumble]

Its not an really an oxidation per say I don't believe. The method you are speaking of is called dehydrogenation. This method only goes as far as the aldehyde. The only to make another product different that the aldehyde or hydrogen, is to heat past the decomposition point. I don't believe that only heating one end of the copper would do it. I think the heat would transfer too much.

Besides condensing there are basically 2 ways to get the most amount saved from evaporation. Bubble into a few ice water, wash bottles if you will. Then distill off the acetaldehyde. It is also possilble to bubble into ice cold ether wash bottles and make the ammonia complex from there. That is how it is done on Mega's site at least. I've never tried it, but i see no reason for it not to work.

[Sonny Jim]

Heh, and there was me thinking I'd just happened upon a new idea! Oh well, that thread was very interesting, thanks for the links.

I'm right in thinking that methylated spirits is about 95% ethanol arent I? I might try this with that and see how it goes.

[xyz]

Yes, methylated spirits is about 96% ethanol with the rest being water and methanol.

[Dave Angel]

I was just flicking through one of my organic textbooks and came across a seemingly simple reaction to make acetaldehyde.

Apparantly, ethylene glycol (anti freeze) heated to 900C at low pressure will lose a molecule of water and form vinyl alcohol (the enol form of acetaldehyde). This will then slowly turn into the acetaldehyde by itself.

I have read about processes suggesting the use of an acid catalyst, however this seems to favor the formation of dioxane, a useful chemical in itself, but not what we want here.

The temperatures involved certainly give rise to some flammability issues, but I believe this could be a suitable route if metaldehyde is not available for the depolymerisation route.

[Skean Dhu]

I've been trying to find a way to make formaldehyde for use in a Hexamine sysnthesis, and I see that dichromates seem to be the easier rout to making aldehydes as opposed to potassium permangate. Now I was wondering will ammonium dichromate work for making acetaldehyde and formaldehyde. since being able to make your own Pentaerythritol wounldn't be so bad either

I posted something like this last night and now I don't see my post so if my computer/ISP is retarded I apologize for the wasted space/bandwidth

[megalomania]

I don't know, you might want to check out the other thread on methyl alcohol oxidation using copper. There are two detailed laboratory procedures taken from professionally published literature sources.

[Skean Dhu]

I sucessfully made acetaldehyde today. I'd give you the measurements and equations but I didnt't do any, I threw the chemicals together kinda haphazzardly to see if it would work. Anyways What I did was even proportions of 26% H2O2 and Denatured alcohol(which coincidentally has some ethyl aldehyde in it as a denaturant,the fruity smell) into my trusty pyrex Wal*Mart Knock-off measuring cup and then added a splash of H2SO4.
General observations:
When I first added the H2O2 the mixture got cloudy and over a period of 10-25 seconds(how ever long it took me to walk back to the house to find my H2SO4) it got luke warm, then whenthe sulfuric acid was added the mixture got a bit warmer and the fruity smell of denatured alcohol got stronger. Then about 45 min later I started getting a headache and its been hounding me since ~5pm my time, sensative to light and all, similar to a sinus/light migraine headache.

took me 3-4 tries to post this, I kept getting interrupted

[Marvin]

With a liquid or liquid/solid phase reaction you are unlikley to get a good yeild of aldehyde without distillation, its too good a reducing agent itself. Unless you use an exotic chromate that is. Distilling a mixture with hydrogenperoxide in it would not be a good idea though.

Useful yeilds from manganese dioxide/distillation should be possible. You can make this from pot permanganate by its reaction with manganese salts. Most of the methods I have tend to go the whole hog with purification by forming an aldehyde compound with ammonia, preciptating with ether and regenerating the aldehyde. This might be related to the degree of contamination you get using oxidising agents other than pot/sodium dichromate.