acetaldehyde from bleach?

[10fingers]

I've seen a couple of references to using bleach, (sodium hypochlorite) to oxidise ethanol to acetaldehyde. As yet I have not been able to find an exact process for this. This may also work for converting methanol to formaldehyde.
I know the usual method is to use sodium or potassium dichromate. Potassium permanganate will also work but I think it would need a different procedure than the one given on Mega's page. I made a big mess when I tried to substitute the permanganate for the dichromate. The permanganate spontaneously reacts when mixed with ethanol.
If bleach would work it make this route a lot cheaper.

[CodeMason]

Bleach might work, I'm not sure, however it may just chlorinate the alcohol leaving you with ethyl dichloride (CH₃CH₂Cl₂).

True, permanganates are awfully messy when it comes to controlled oxidizations. Not only that, yields are intolerably low. Chromates are far more suited for the job.

------------------
Visit my website (in development): http://codemason.cjb.net

[rikkitikkitavi]

How will you oxidize alcohol over copper without oxygen ? Chlorine, fluorine, ozone..

Ethanol will react with hypoclorite (ClO-)
but it will form chloroform due to the "haloform" reaction. Some acetaldehyde might be formed but main product is CCl3H.

Other oxidants (Cr2O7, S2O8) will give
acetaldehyde , witch can be distilled of from the reaction vessel thanks to the low boiling point of aldehyde (21 C) compared to
ethanol (78C) but some acetic acid will also be formed.

[CodeMason]

That reaction needs a proton donor, madscientist, one weaker than HOCl however, such as acetic.

------------------
Live free or die! | http://codemason.cjb.net

[CodeMason]

Also, organic hypochlorites are extremely unstable and can be broken down by small amounts of light or heat. It is almost certain that they can explode (albeit much weaker than say an organic nitrate or perchlorate). Organic bases cannot be that strong either.

------------------
Live free or die! | http://codemason.cjb.net

[CodeMason]

Oh nevermind about the base thing, didn't see the NaOH.

------------------
Live free or die! | http://codemason.cjb.net

[10fingers]

I think the reaction of converting ethanol to acetaldehyde is also termed a dehydrogenation. Two atoms of hydrogen are split off but there needs to be an oxygen source present for them to combine with to form a molecule of water.
I wonder if it would work to just bubble oxygen into an acidified solution of ethanol?
The problem with using potassium dichromate or potassium permanganate is the cost. Both of these chemicals cost from $5.00 to $7.00 per pound and you are only going to get around 200 milliters of acetaldehyde from a pound. Pretty slim pickens.
Vapor phase oxidation of ethanol with a copper catalyst @ 300 C is a possibility. I have done some experimenting with it and have had a little success but it is easier in theory than practice. The ratio of ethanol to oxygen, temperature and pressure all need to be controlled to get a decent output.
I have found a very cheap source of ethanol. Gas stations in my area have started selling it for around $1.10 per gallon. It is 85% ethanol and 15% gasoline. The gasoline can easily be separated by adding an equal amount of water to it. The ethanol will mix with the water but the gasoline rises to the top. Supposedly there are stations selling %95 ethanol, which would be usable as is, but I have not found one yet.
Methanol can also be purchased for around the same price. Some gas line anti-freeze is pure methanol and windshield wash is mostly methanol with a little water.

[rikkitikkitavi]

Madscientist, I see what you mean with your reaction. But isopropylalcohol is a secondary alcohol , reacting very different than ethanol , a primary alcohol.
If you pass ethanol vapour over copper @300 C you will dehydrate it to ethylene and water
http://theforum.virtualave.net/ubb/smilies/frown.gif .

To get acetaldehyde you need oxygen, since it is a oxidation-reduction reaction.

/rickard

[CodeMason]

madscientist: If you'll scroll up you'll see I never said it was wrong, just that you needed an acid weaker than HOCl for the reaction to work. That and isolating organic hypochlorites without very careful conditions (no light or excess heat or physical agitation) is not going to happen.

------------------
Live free or die! | http://codemason.cjb.net

[10fingers]

Madscientist, using sodium dichromate is the standard laboratory method for converting ethanol to acetaldehyde. It does work.
Go to Megas controversial chem lab and look up the procedure for making acetaldehyde.